HomeMy WebLinkAboutENCLAVE AT REDWOOD - PDP210004 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT
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February 11 , 2021
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Enclave at Redwood
Preliminary Drainage Report
HKS Project No. 201013
Dear Staff:
This preliminary drainage report for Enclave at Redwood (“Site”) is to summarize the
proposed updated storm sewer, water quality system and detention for the development of
the Site. The Site is in designed to follow Fort Collins Stormwater Criteria Manual (“FCSCM”).
The proposed Site is proposed to include 230 for-rent dwelling units within 161 buildings, ten
garage buildings and private amenities such as a clubhouse, pool, and on-site park like spaces.
Water quality treatment and Low Impact Design (“LID”), including the “Four Step Process,” will
be incorporated into the proposed drainage of the Site and be discussed in more detail in the
second submittal of this preliminary drainage report. For this preliminary drainage report a
detention pond has been initial sized for review by City of Ft. Collins staff. The development of
the Site is not anticipated to adversely impact downstream properties or infrastructure.
Please contact me if you have any questions or require additional information.
Sincerely,
HARRIS KOCHER SMITH
Michael Moore, PE
Associate Principal
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PRELIMINARY DRAINAGE REPORT
FOR
ENCLAVE AT REDWOOD
February 11, 2021
Prepared for:
9555 S Kingston Court
Englewood, CO 80112
Prepared by:
Michael Moore, P.E.
1120 Lincoln Street, Suite 1000
Denver, CO 80203
Ph.: 303-623-6300, Fax: 303-623-6311
Harris Kocher Smith Project No.: 201013
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Table of Contents
General Location & Existing Site Information ..............................................................................4
I. Location ........................................................................................................................4
II. City Master Report ........................................................................................................4
III. Existing Sub-Basins ......................................................................................................4
IV. Existing Site Information ...............................................................................................4
Master Drainage Basin Information .............................................................................................5
I. History ..........................................................................................................................5
II. Improvements ...............................................................................................................5
Floodplain Information .................................................................................................................5
Project Description ......................................................................................................................5
I. Existing Conditions .......................................................................................................5
II. Proposed Conditions .....................................................................................................5
Proposed Drainage Facilities ......................................................................................................5
I. General Concept ...........................................................................................................5
II. Proposed Drainage Basins ...........................................................................................6
III. Detention Pond ...........................................................................................................11
IV. Hydrological Criteria ....................................................................................................11
V. Hydraulic Computations ..............................................................................................11
VI. LID ..............................................................................................................................11
Variance Requests ....................................................................................................................12
Erosion Control .........................................................................................................................12
Conclusion ................................................................................................................................12
I. Compliance with standard ...........................................................................................12
References ...............................................................................................................................12
Appendix A – Vicinity Map & Firmette .......................................................................................14
Appendix B – Soil Information ...................................................................................................15
Appendix C – Hydrologic Computations ....................................................................................16
Appendix D – Hydraulic Computations ......................................................................................17
Appendix E – Supplemental Information ...................................................................................18
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General Location & Existing Site Information
I. Location
The Enclave at Redwood multi-family project (“Site”) to be developed is bounded by private
property to the north, Redwood Drive and private property to the west, and Lake Canal (“Canal”)
to the south and east of the Site. The private properties to the west are a part of The Meadows
at Redwood residential subdivision (“Meadows”).
The Site is situated in the Southeast 1/4 of Section 1, Township 7 North, Range 69 West of the
6th P.M, City of Fort Collins (“City”), County of Larimer, State of Colorado. See Appendix A for
vicinity map.
II. City Master Report
The Site is located within the City’s Dry Creek Master Drainage Basin. The Site generally drains
from northwest to the southeast to the Canal. The area is also subject to restrictions as
delineated in the Draft Final North East College Corridor Outfall (NECCO) Design Report,
prepared by Ayres Associates, dated August 2009 (“Master Report”). A copy of the Master
Report can be seen in Appendix E.
III. Existing Sub-Basins
The Site historically drains to the southeast and is collected in the Canal via sheet flow
conditions. West of the Site is the Meadows and also the Redwood Pond as discussed in the
Master Report. The Redwood Pond collects the drainage from Redwood Village and off-site
drainage basins to the north of the Site and discharges runoff into the Site. The Site is designed
to incorporate the discharge from Redwood Pond and route it through the Site to the existing
NECCO storm sewer main within Suniga Drive. Additional information can be seen within the
Retreat at Fort Collins Preliminary Drainage Report, prepared by Northern Engineering, dated
July 25, 2018, in Appendix E. Within the Master Report, the Site is identified at sub-basins 113
and 313, with the Redwood Pond and the Meadows being sub-basins 812 and 213,
respectively. The Master Report also indicates that the development of the Site sub-basins
requires on-site detention at 0.2 cfs/acre release rate and water quality. These design
requirements are address in more detail below.
IV. Existing Site Information
The Site is currently zoned R-L-P (Low Density Planned Residential District). The Site is
currently covered in natural shrubs and vegetation, there are currently no existing structures on
Site. According to the National Resources and Conservation Service online soils information
mapper (“Soils Report”), there are four (4) existing soil types are found within the limits of the
Site; Caruso Clay Loam makes up 0.5% of the Site, Loveland Clay Loam makes up 30.0% of
the Site, Nunn Clay loam makes up 41.8% of the Site and Nunn Clay Loam Wet makes up
27.7% of the Site. The Soil Report for the Site can be seen in Appendix B.
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Master Drainage Basin Information
I. History
Dry Creek, which is a tributary to the Poudre River, extends from near the Wyoming border to
where it joins the Poudre River near Mulberry and Timberline. The Dry Creek Basin is
app roximately twenty-three miles long, six miles wide, and encompasses approximately sixty-
two square miles. The land use in the upper, and middle portions, of the basin are primarily
rangeland and irrigated hay meadows and pastures. The majority of the lower basin is
developed and includes commercial, industrial, and residential uses. The natural channel has
disappeared in some areas of the lower basin because of urbanization with the area.
II. Improvements
No additional improvements to the Dry Creek Basin are proposed with the development of the
Site.
Floodplain Information
According to FEMA maps and subsequent revisions, amendments and revalidations, the Site is
located outside the 100-year floodplain in Zone X. Zone X is an area determined to be outside
of the 0.2% annual chance floodplain. The FEMA maps, printed on February 11, 2021, are
included in Appendix A of this report.
Project Description
I. Existing Conditions
The Site is 27 .83 acres of vacant undeveloped land. Existing grades on Site generally slope
from northwest to southwest at slopes between 0.5% and 2%, with approximately seven feet of
drop across the Site.
II. Proposed Conditions
The development of the Site is proposed to include 230 for-rent dwelling units within 161
buildings, ten garage buildings and private amenities such as a clubhouse, pool, and on-site
park like spaces. The Site will also include private drives, utilities, surface parking, curb and
gutter, hardscaping, and landscaping.
Proposed Drainage Facilities
I. General Concept
The Site has been divided into twenty six drainage basins. Runoff from the majority of the
basins will be routed through the proposed curb and gutter, on-site private storm sewer and
public off-site storm sewers to proposed on-site Detention Basin. LID water quality elements
will also be considered and incorporated with subsequent submittals of this report.
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II. Proposed Drainage Basins
Basin A (1.22 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 1. Any carry overflow will bypass the inlet and surface flow
downstream to the detention pond in Basin C. Peak runoff rates from Basin A are calculated to
be 1.56 CFS for the minor storm and 6.78 CFS for the major storm event. Stormwater from the
detention pond will ultimately drain through the private property to the regional detention pond
off site.
Basin B (1.22 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 1. Any carry overflow will bypass the inlet and surface flow downstream to the detention
pond in Basin C. Peak runoff rates from Basin B are calculated to be 1.42 CFS for the minor
storm and 6.20 CFS for the major storm event. Stormwater from the detention pond will
ultimately drain through the private property to the regional detention pond off site.
Basin C (1.23 acre) consists of portions of landscaping and the detention pond. Runoff from this
basin will surface-drain to the Deten tion Pond in the center of the of the basin. Any carry
overflow will bypass the Detention Ponds and surface flow downstream to the NECCO storm
line to the south. Peak runoff rates from Basin C are calculated to be 0.66 CFS for the minor
storm and 2.89 CFS for the major storm event. Stormwater from the detention pond will
ultimately drain through the private property to the regional detention pond off site.
Basin D (0.75 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 3. Any carry overflow will bypass the inlet and surface flow
downstream to Design Point 2. Peak runoff rates from Basin D are calculated to be 0.91 CFS
for the minor storm and 3.96 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin E (1.25 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 2. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 1. Peak runoff rates from Basin E are calculated to be 1.16 CFS for the minor storm and
5.78 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
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Basin F (0.63 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 4. Any carry overflow will bypass the inlet and surface flow
downstream to the Design Point 3. Peak runoff rates from Basin F are calculated to be 0.78
CFS for the minor storm and 3.42 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin G (1.01 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 4. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 3. Peak runoff rates from Basin G are calculated to be 1.3 3 CFS for the minor storm and
5.78 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin H (1.4 5 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 4. Any carry overflow will bypass the inlet and surface flow
downstream to the Design Point 3. Peak runoff rates from Basin H are calculated to be 1.58
CFS for the minor storm and 6.88 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin I (0.94 acre) consist of portions of buildings, garages, drives, sidewalks, and landscaping.
Runoff from this basin will either be captured by roof drains and landscape drains, or surface-
drain to an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at
Design Point 4. Any carry overflow will bypass the inlet and surface flow downstream to the
Design Point 3. Peak runoff rates from Basin I are calculated to be 1.06 CFS for the minor
storm and 4.63 CFS for the major storm event. Stormwater from the detention pond will
ultimately drain through the private property to the regional detention pond off site.
Basin J (0.56 acre) consist of portions of buildings, garages, drives, sidewalks, and landscaping.
Runoff from this basin will either be captured by roof drains and landscape drains, or surface-
drain to an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at
Design Point 4. Any carry overflow will bypass the inlet and surface flow downstream to the
Design Point 3. Peak runoff rates from Basin J are calculated to be 0.77 CFS for the minor
storm and 3.36 CFS for the major storm event. Stormwater from the detention pond will
ultimately drain through the private property to the regional detention pond off site.
Basin K (0.55 acre) consist of portions of buildings, drives, sidewalks, and landscaping. Runoff
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from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 8. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 7. Peak runoff rates from Basin K are calculated to be 0.78 CFS for the minor storm and
3.41 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin L (0.89 acre) consist of portions of drives, sidewalks, and landscaping. Runoff from this
basin will either be captured by landscape drains, or surface-drain to an inlet along the
proposed storm sewer and conveyed to the proposed storm sewer at Design Point 5. Any carry
overflow will bypass the inlet and surface flow downstream to the Design Point 4. Peak runoff
rates from Basin L are calculated to be 0.47 CFS for the minor storm and 2.06 CFS for the
major storm event. Stormwater from the detention pond will ultimately drain through the private
property to the regional detention pond off site.
Basin M (0.72 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 5. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 4. Peak runoff rates from Basin M are calculated to be 0.97 CFS for the minor storm and
4.22 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin N (1.49 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 5. Any carry overflow will bypass the inlet and surface flow
downstream to the Design Point 4. Peak runoff rates from Basin N are calculated to be 1.46
CFS for the minor storm and 6.37 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin O (1.22 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 8. Any carry overflow will bypass the inlet and surface flow
downstream to the Design Point 7. Peak runoff rates from Basin O are calculated to be 1.40
CFS for the minor storm and 6.12 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin P (1.53 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
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an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 8. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 7. Peak runoff rates from Basin P are calculated to be 2.2 8 CFS for the minor storm and
9.93 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin Q (1.06 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 7. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 6. Peak runoff rates from Basin Q are calculated to be 1.4 6 CFS for the minor storm and
6.38 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin R (0.66 acre) consists of portions of drives, sidewalks, and landscaping. Runoff from this
basin will either be captured by landscape drains, or surface-drain to an inlet along the
proposed storm sewer and conveyed to the proposed storm sewer at Design Point 6. Any carry
overflow will bypass the inlet and surface flow downstream to the Design Point 5. Peak runoff
rates from Basin R are calculated to be 0.92 CFS for the minor storm and 4.02 CFS for the
major storm event. Stormwater from the detention pond will ultimately drain through the private
property to the regional detention pond off site.
Basin S (1.24 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 6. Any carry overflow will bypass the inlet and surface flow
downstream to the Design Point 5. Peak runoff rates from Basin S are calculated to be 1.27
CFS for the minor storm and 5.55 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin T (1.30 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 15. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 14. Peak runoff rates from Basin T are calculated to be 1.41 CFS for the minor storm and
6.15 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin U (1.77 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
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Point 13. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 11 . Peak runoff rates from Basin U are calculated to be 2.26 CFS for the minor storm and
9.85 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin V (1.06 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 9. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 6. Peak runoff rates from Basin V are calculated to be 1.3 6 CFS for the minor storm and
5.93 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin W (1.0 9 acre) consists of portions of buildings, drives, sidewalks, and landscaping. Runoff
from this basin will either be captured by roof drains and landscape drains, or surface-drain to
an inlet along the proposed storm sewer and conveyed to the proposed storm sewer at Design
Point 10. Any carry overflow will bypass the inlet and surface flow downstream to the Design
Point 9. Peak runoff rates from Basin W are calculated to be 1.1 5 CFS for the minor storm and
5.02 CFS for the major storm event. Stormwater from the detention pond will ultimately drain
through the private property to the regional detention pond off site.
Basin X (1.47 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 11. Any carry overflow will bypass the inlet and surface flow
downstream to the Design Point 10. Peak runoff rates from Basin X are calculated to be 1.86
CFS for the minor storm and 8.11 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin Y (0.83 acre) consists of portions of buildings, garages, drives, sidewalks, and
landscaping. Runoff from this basin will either be captured by roof drains and landscape drains,
or surface-drain to an inlet along the proposed storm sewer and conveyed to the proposed
storm sewer at Design Point 12. Any carry overflow will bypass the inlet and surface flow
downstream to the Design Point 11. Peak runoff rates from Basin Y are calculated to be 1.03
CFS for the minor storm and 4.50 CFS for the major storm event. Stormwater from the detention
pond will ultimately drain through the private property to the regional detention pond off site.
Basin Z (0.68 acre) consists of portions of sidewalks and landscaping. Runoff from this basin
will either be captured by landscape drains, or surface-drain to an inlet along the proposed
storm sewer and conveyed to the proposed storm sewer at Design Point 12. Any carry overflow
will bypass the inlet and surface flow downstream to the Design Point 11. Peak runoff rates
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from Basin Z are calculated to be 0.50 CFS for the minor storm and 2.16 CFS for the major
storm event. Stormwater from the detention pond will ultimately drain through the private
property to the regional detention pond off site.
Both Off site basins OS-1 and OS-2 flow on to the Site through Redwood Pond located in OS-2.
According to the Retreat Final Drainage report the Site will have an additional Off-Site flow of
5.63 CFS for the minor storm and 25.68 CFS for the Major Storm. This additional flow is routed
through the Site and under the proposed Detention Pond to the existing off site detention pond.
Preliminary Drainage Plan showing the different Basin locations can be found in Appendix E.
III. Detention Pond
As mentioned above, the Master Report requires water quality and detention for the
development of the Site. Required Water Quality Capture Volume (“WQCV) was calculated
using Mile High Flood District Urban Drainage Detention Worksheet. The Site requires 0.761 ac-
ft for WQCV. The proposed detention pond on site has been designed to hold 1.061 ac-ft.
The Master Report requires a 0.2 cfs/acres release from the developed Site. For the 27.8-acre
development this yields an allowable release of 5.6 cfs. The Site detention pond is modeled
with a 100-year volume of 5.6 acre-feet. SWMM results indicate that this detention pond
releases at a rate of 5.1 cfs, which is below the allowable rate. The preliminary design for the
water quality pond has a 40-hour drain time to allow for sedimentation to occur. Flow from the
outlet structure of the detention pond will connect to the existing NECCO line in Suniga .
IV. Hydrological Criteria
The City Rainfall Intensity-Duration-Frequency Curves, as depicted in the FCSCM, are utilized
as the source for all hydrologic computations associated with the development of the Site.
The Rational Method has been utilized to calculate stormwater runoff for the proposed condition
sub-basins within the Site. The coefficients tables from the FCSCM have been utilized in
support of these calculations.
A hydrologic stormwater routing analysis for the project was completed using the US
Environmental Protection Agency Storm Water Management Model (SWMM) v. 5.1. SWMM
model inputs include three onsite basins, the storm sewer main network, and the water quality
and detention ponds. These Site elements are shown in the SWMM schematic and rain gauge,
pond stage-storage and stage-discharge information is included in Appendix C.
V. Hydraulic Computations
Hydraulic computations will be provided in subsequent submittals.
VI. LID
Once the on-site layout of units and roads have been approved by the City planning staff, the
applicant will work to address the City’s LID requirements and the “Four Step Process.”
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Permanent BMP’s will be evaluated and incorporated in the grading and stormwater design in
subsequent submittals. Given the medium to high-density nature of the development of the
Site, we are anticipating that we will review potential locations where the allowable BMPS,
including permeable pavement, bioretention, bioswales, sand filters, rain gardens, underground
infiltration, and tree filters. Given the available area with the currently proposed plan for the Site,
it is not anticipated that vegetative buffers, constructed wetland channels or constructed wetland
pond are feasible options for this Site.
Variance Requests
As of the date of this report there are no variances being requested.
Erosion Control
Erosion control report and plans will be provided in a later submittal. Drainage report and plan
are within compliance of future erosion control report and plan.
Conclusion
I. Compliance with standard
The drainage design was prepared in compliance with the FCSCM and the Master Report.
II. Summary
The Site is currently all pervious and flows undetained and untreated. The proposed
development will include storm sewer which will convey the untreated water to an on-site water
quality treatment pond and detention pond. All flows on Site will be captured, treated, detained
and eventually direct to the NECCO storm sewer main within Suniga. The development of the
Site is not anticipated to adversely impact downstream properties or infrastructure.
References
Fort Colins Stormwater Criteria Manual, City of Fort Collins, Revised December 2018
Urban Storm Drainage Criteria Manual, Volumes 1 and 2, Urban Drainage and Flood Control
District, Revised January 2016.
Urban Storm Drainage Criteria Manual, Volume 3, Urban Drainage and Flood Control District,
Revised October 2019.
Final Drainage Report for the Retreat @ Fort Collins, Northern Engineering, Revised July 25,
2018.
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Northeast College Corridor Outfall (NECCO) Design Report, Ayres Associates, Revised August
2009.
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Appendix A – Vicinity Map & Firmette
SHEET NUMBER
PROJECT #:
1120 Lincoln Street, Suite 1000
Denver, Colorado 80203
P: 303.623.6300 F: 303.623.6311
HarrisKocherSmith.comPlotted: TUE 02/02/21 5:10:46P By: Jeffrey Nye Filepath: k:\201013\engineering\xref\vic map.dwg Layout: layout1201013
ENCLAVE AT REDWOOD - VICINTY MAP
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DHI COMMUNITIES
NO CHANGES ARE TO BE MADE TO THIS DRAWING WITHOUT WRITTEN PERMISSION OF HARRIS KOCHER SMITH.
0
SCALE: 1" =
800 800 1600
800'
National Flood Hazard Layer FIRMette
0 500 1,000 1,500 2,000250
Feet
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SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or DepthZone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mileZone X
Future Conditions 1% Annual
Chance Flood HazardZone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood HazardZone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 2/11/2021 at 10:16 AM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
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B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
105°4'32"W 40°36'11"N
105°3'55"W 40°35'44"N
Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020
National Flood Hazard Layer FIRMette
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Feet
Ü
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or DepthZone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mileZone X
Future Conditions 1% Annual
Chance Flood HazardZone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood HazardZone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 2/11/2021 at 9:54 AM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
8
B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
105°3'55"W 40°36'27"N
105°3'18"W 40°36'N
Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020
Page | 15
Appendix B – Soil Information
United States
Department of
Agriculture
A product of the National
Cooperative Soil Survey,
a joint effort of the United
States Department of
Agriculture and other
Federal agencies, State
agencies including the
Agricultural Experiment
Stations, and local
participants
Custom Soil Resource
Report for
Larimer County
Area, ColoradoNatural
Resources
Conservation
Service
January 25, 2021
Preface
Soil surveys contain information that affects land use planning in survey areas.
They highlight soil limitations that affect various land uses and provide information
about the properties of the soils in the survey areas. Soil surveys are designed for
many different users, including farmers, ranchers, foresters, agronomists, urban
planners, community officials, engineers, developers, builders, and home buyers.
Also, conservationists, teachers, students, and specialists in recreation, waste
disposal, and pollution control can use the surveys to help them understand,
protect, or enhance the environment.
Various land use regulations of Federal, State, and local governments may impose
special restrictions on land use or land treatment. Soil surveys identify soil
properties that are used in making various land use or land treatment decisions.
The information is intended to help the land users identify and reduce the effects of
soil limitations on various land uses. The landowner or user is responsible for
identifying and complying with existing laws and regulations.
Although soil survey information can be used for general farm, local, and wider area
planning, onsite investigation is needed to supplement this information in some
cases. Examples include soil quality assessments (http://www.nrcs.usda.gov/wps/
portal/nrcs/main/soils/health/) and certain conservation and engineering
applications. For more detailed information, contact your local USDA Service Center
(https://offices.sc.egov.usda.gov/locator/app?agency=nrcs) or your NRCS State Soil
Scientist (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?
cid=nrcs142p2_053951).
Great differences in soil properties can occur within short distances. Some soils are
seasonally wet or subject to flooding. Some are too unstable to be used as a
foundation for buildings or roads. Clayey or wet soils are poorly suited to use as
septic tank absorption fields. A high water table makes a soil poorly suited to
basements or underground installations.
The National Cooperative Soil Survey is a joint effort of the United States
Department of Agriculture and other Federal agencies, State agencies including the
Agricultural Experiment Stations, and local agencies. The Natural Resources
Conservation Service (NRCS) has leadership for the Federal part of the National
Cooperative Soil Survey.
Information about soils is updated periodically. Updated information is available
through the NRCS Web Soil Survey, the site for official soil survey information.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its
programs and activities on the basis of race, color, national origin, age, disability,
and where applicable, sex, marital status, familial status, parental status, religion,
sexual orientation, genetic information, political beliefs, reprisal, or because all or a
part of an individual's income is derived from any public assistance program. (Not
all prohibited bases apply to all programs.) Persons with disabilities who require
2
alternative means for communication of program information (Braille, large print,
audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice
and TDD). To file a complaint of discrimination, write to USDA, Director, Office of
Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or
call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity
provider and employer.
3
Contents
Preface....................................................................................................................2
How Soil Surveys Are Made..................................................................................5
Soil Map..................................................................................................................8
Soil Map................................................................................................................9
Legend................................................................................................................10
Map Unit Legend................................................................................................11
Map Unit Descriptions.........................................................................................11
Larimer County Area, Colorado......................................................................13
22—Caruso clay loam, 0 to 1 percent slope...............................................13
64—Loveland clay loam, 0 to 1 percent slopes...........................................14
73—Nunn clay loam, 0 to 1 percent slopes.................................................15
76—Nunn clay loam, wet, 1 to 3 percent slopes.........................................17
References............................................................................................................19
4
How Soil Surveys Are Made
Soil surveys are made to provide information about the soils and miscellaneous
areas in a specific area. They include a description of the soils and miscellaneous
areas and their location on the landscape and tables that show soil properties and
limitations affecting various uses. Soil scientists observed the steepness, length,
and shape of the slopes; the general pattern of drainage; the kinds of crops and
native plants; and the kinds of bedrock. They observed and described many soil
profiles. A soil profile is the sequence of natural layers, or horizons, in a soil. The
profile extends from the surface down into the unconsolidated material in which the
soil formed or from the surface down to bedrock. The unconsolidated material is
devoid of roots and other living organisms and has not been changed by other
biological activity.
Currently, soils are mapped according to the boundaries of major land resource
areas (MLRAs). MLRAs are geographically associated land resource units that
share common characteristics related to physiography, geology, climate, water
resources, soils, biological resources, and land uses (USDA, 2006). Soil survey
areas typically consist of parts of one or more MLRA.
The soils and miscellaneous areas in a survey area occur in an orderly pattern that
is related to the geology, landforms, relief, climate, and natural vegetation of the
area. Each kind of soil and miscellaneous area is associated with a particular kind
of landform or with a segment of the landform. By observing the soils and
miscellaneous areas in the survey area and relating their position to specific
segments of the landform, a soil scientist develops a concept, or model, of how they
were formed. Thus, during mapping, this model enables the soil scientist to predict
with a considerable degree of accuracy the kind of soil or miscellaneous area at a
specific location on the landscape.
Commonly, individual soils on the landscape merge into one another as their
characteristics gradually change. To construct an accurate soil map, however, soil
scientists must determine the boundaries between the soils. They can observe only
a limited number of soil profiles. Nevertheless, these observations, supplemented
by an understanding of the soil-vegetation-landscape relationship, are sufficient to
verify predictions of the kinds of soil in an area and to determine the boundaries.
Soil scientists recorded the characteristics of the soil profiles that they studied. They
noted soil color, texture, size and shape of soil aggregates, kind and amount of rock
fragments, distribution of plant roots, reaction, and other features that enable them
to identify soils. After describing the soils in the survey area and determining their
properties, the soil scientists assigned the soils to taxonomic classes (units).
Taxonomic classes are concepts. Each taxonomic class has a set of soil
characteristics with precisely defined limits. The classes are used as a basis for
comparison to classify soils systematically. Soil taxonomy, the system of taxonomic
classification used in the United States, is based mainly on the kind and character
of soil properties and the arrangement of horizons within the profile. After the soil
5
scientists classified and named the soils in the survey area, they compared the
individual soils with similar soils in the same taxonomic class in other areas so that
they could confirm data and assemble additional data based on experience and
research.
The objective of soil mapping is not to delineate pure map unit components; the
objective is to separate the landscape into landforms or landform segments that
have similar use and management requirements. Each map unit is defined by a
unique combination of soil components and/or miscellaneous areas in predictable
proportions. Some components may be highly contrasting to the other components
of the map unit. The presence of minor components in a map unit in no way
diminishes the usefulness or accuracy of the data. The delineation of such
landforms and landform segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned, onsite
investigation is needed to define and locate the soils and miscellaneous areas.
Soil scientists make many field observations in the process of producing a soil map.
The frequency of observation is dependent upon several factors, including scale of
mapping, intensity of mapping, design of map units, complexity of the landscape,
and experience of the soil scientist. Observations are made to test and refine the
soil-landscape model and predictions and to verify the classification of the soils at
specific locations. Once the soil-landscape model is refined, a significantly smaller
number of measurements of individual soil properties are made and recorded.
These measurements may include field measurements, such as those for color,
depth to bedrock, and texture, and laboratory measurements, such as those for
content of sand, silt, clay, salt, and other components. Properties of each soil
typically vary from one point to another across the landscape.
Observations for map unit components are aggregated to develop ranges of
characteristics for the components. The aggregated values are presented. Direct
measurements do not exist for every property presented for every map unit
component. Values for some properties are estimated from combinations of other
properties.
While a soil survey is in progress, samples of some of the soils in the area generally
are collected for laboratory analyses and for engineering tests. Soil scientists
interpret the data from these analyses and tests as well as the field-observed
characteristics and the soil properties to determine the expected behavior of the
soils under different uses. Interpretations for all of the soils are field tested through
observation of the soils in different uses and under different levels of management.
Some interpretations are modified to fit local conditions, and some new
interpretations are developed to meet local needs. Data are assembled from other
sources, such as research information, production records, and field experience of
specialists. For example, data on crop yields under defined levels of management
are assembled from farm records and from field or plot experiments on the same
kinds of soil.
Predictions about soil behavior are based not only on soil properties but also on
such variables as climate and biological activity. Soil conditions are predictable over
long periods of time, but they are not predictable from year to year. For example,
soil scientists can predict with a fairly high degree of accuracy that a given soil will
have a high water table within certain depths in most years, but they cannot predict
that a high water table will always be at a specific level in the soil on a specific date.
After soil scientists located and identified the significant natural bodies of soil in the
survey area, they drew the boundaries of these bodies on aerial photographs and
Custom Soil Resource Report
6
identified each as a specific map unit. Aerial photographs show trees, buildings,
fields, roads, and rivers, all of which help in locating boundaries accurately.
Custom Soil Resource Report
7
Soil Map
The soil map section includes the soil map for the defined area of interest, a list of
soil map units on the map and extent of each map unit, and cartographic symbols
displayed on the map. Also presented are various metadata about data used to
produce the map, and a description of each soil map unit.
8
9
Custom Soil Resource Report
Soil Map
44942504494330449441044944904494570449465044947304494250449433044944104494490449457044946504494730494260 494340 494420 494500 494580 494660 494740 494820 494900 494980
494260 494340 494420 494500 494580 494660 494740 494820 494900 494980
40° 36' 12'' N 105° 4' 5'' W40° 36' 12'' N105° 3' 32'' W40° 35' 56'' N
105° 4' 5'' W40° 35' 56'' N
105° 3' 32'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 150 300 600 900
Feet
0 50 100 200 300
Meters
Map Scale: 1:3,580 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 15, Jun 9, 2020
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Aug 11, 2018—Aug
12, 2018
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
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10
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
22 Caruso clay loam, 0 to 1
percent slope
0.1 0.5%
64 Loveland clay loam, 0 to 1
percent slopes
7.7 30.0%
73 Nunn clay loam, 0 to 1 percent
slopes
10.8 41.8%
76 Nunn clay loam, wet, 1 to 3
percent slopes
7.1 27.7%
Totals for Area of Interest 25.8 100.0%
Map Unit Descriptions
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions, along
with the maps, can be used to determine the composition and properties of a unit.
A map unit delineation on a soil map represents an area dominated by one or more
major kinds of soil or miscellaneous areas. A map unit is identified and named
according to the taxonomic classification of the dominant soils. Within a taxonomic
class there are precisely defined limits for the properties of the soils. On the
landscape, however, the soils are natural phenomena, and they have the
characteristic variability of all natural phenomena. Thus, the range of some
observed properties may extend beyond the limits defined for a taxonomic class.
Areas of soils of a single taxonomic class rarely, if ever, can be mapped without
including areas of other taxonomic classes. Consequently, every map unit is made
up of the soils or miscellaneous areas for which it is named and some minor
components that belong to taxonomic classes other than those of the major soils.
Most minor soils have properties similar to those of the dominant soil or soils in the
map unit, and thus they do not affect use and management. These are called
noncontrasting, or similar, components. They may or may not be mentioned in a
particular map unit description. Other minor components, however, have properties
and behavioral characteristics divergent enough to affect use or to require different
management. These are called contrasting, or dissimilar, components. They
generally are in small areas and could not be mapped separately because of the
scale used. Some small areas of strongly contrasting soils or miscellaneous areas
are identified by a special symbol on the maps. If included in the database for a
given area, the contrasting minor components are identified in the map unit
descriptions along with some characteristics of each. A few areas of minor
components may not have been observed, and consequently they are not
mentioned in the descriptions, especially where the pattern was so complex that it
was impractical to make enough observations to identify all the soils and
miscellaneous areas on the landscape.
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The presence of minor components in a map unit in no way diminishes the
usefulness or accuracy of the data. The objective of mapping is not to delineate
pure taxonomic classes but rather to separate the landscape into landforms or
landform segments that have similar use and management requirements. The
delineation of such segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned, however,
onsite investigation is needed to define and locate the soils and miscellaneous
areas.
An identifying symbol precedes the map unit name in the map unit descriptions.
Each description includes general facts about the unit and gives important soil
properties and qualities.
Soils that have profiles that are almost alike make up a soil series. Except for
differences in texture of the surface layer, all the soils of a series have major
horizons that are similar in composition, thickness, and arrangement.
Soils of one series can differ in texture of the surface layer, slope, stoniness,
salinity, degree of erosion, and other characteristics that affect their use. On the
basis of such differences, a soil series is divided into soil phases. Most of the areas
shown on the detailed soil maps are phases of soil series. The name of a soil phase
commonly indicates a feature that affects use or management. For example, Alpha
silt loam, 0 to 2 percent slopes, is a phase of the Alpha series.
Some map units are made up of two or more major soils or miscellaneous areas.
These map units are complexes, associations, or undifferentiated groups.
A complex consists of two or more soils or miscellaneous areas in such an intricate
pattern or in such small areas that they cannot be shown separately on the maps.
The pattern and proportion of the soils or miscellaneous areas are somewhat similar
in all areas. Alpha-Beta complex, 0 to 6 percent slopes, is an example.
An association is made up of two or more geographically associated soils or
miscellaneous areas that are shown as one unit on the maps. Because of present
or anticipated uses of the map units in the survey area, it was not considered
practical or necessary to map the soils or miscellaneous areas separately. The
pattern and relative proportion of the soils or miscellaneous areas are somewhat
similar. Alpha-Beta association, 0 to 2 percent slopes, is an example.
An undifferentiated group is made up of two or more soils or miscellaneous areas
that could be mapped individually but are mapped as one unit because similar
interpretations can be made for use and management. The pattern and proportion
of the soils or miscellaneous areas in a mapped area are not uniform. An area can
be made up of only one of the major soils or miscellaneous areas, or it can be made
up of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is an example.
Some surveys include miscellaneous areas. Such areas have little or no soil
material and support little or no vegetation. Rock outcrop is an example.
Custom Soil Resource Report
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Larimer County Area, Colorado
22—Caruso clay loam, 0 to 1 percent slope
Map Unit Setting
National map unit symbol: jpvt
Elevation: 4,800 to 5,500 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature: 48 to 50 degrees F
Frost-free period: 135 to 150 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Caruso and similar soils:85 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Caruso
Setting
Landform:Stream terraces, flood-plain steps
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Mixed alluvium
Typical profile
H1 - 0 to 35 inches: clay loam
H2 - 35 to 44 inches: fine sandy loam, sandy loam
H2 - 35 to 44 inches: sand, gravelly sand
H3 - 44 to 60 inches:
H3 - 44 to 60 inches:
Properties and qualities
Slope:0 to 1 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Somewhat poorly drained
Runoff class: High
Capacity of the most limiting layer to transmit water (Ksat):Moderately low to
moderately high (0.06 to 0.20 in/hr)
Depth to water table:About 24 to 48 inches
Frequency of flooding:OccasionalNone
Frequency of ponding:None
Calcium carbonate, maximum content:5 percent
Maximum salinity:Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm)
Available water capacity:High (about 9.8 inches)
Interpretive groups
Land capability classification (irrigated): 3w
Land capability classification (nonirrigated): 5w
Hydrologic Soil Group: D
Hydric soil rating: No
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Minor Components
Loveland
Percent of map unit:9 percent
Landform:Terraces
Hydric soil rating: Yes
Fluvaquents
Percent of map unit:6 percent
Landform:Terraces
Hydric soil rating: Yes
64—Loveland clay loam, 0 to 1 percent slopes
Map Unit Setting
National map unit symbol: jpx9
Elevation: 4,800 to 5,500 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature: 48 to 50 degrees F
Frost-free period: 135 to 150 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Loveland and similar soils:90 percent
Minor components:10 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Loveland
Setting
Landform:Flood plains, stream terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Alluvium
Typical profile
H1 - 0 to 15 inches: clay loam
H2 - 15 to 32 inches: clay loam, silty clay loam, loam
H2 - 15 to 32 inches: very gravelly sand, gravelly sand, gravelly coarse sand
H2 - 15 to 32 inches:
H3 - 32 to 60 inches:
H3 - 32 to 60 inches:
H3 - 32 to 60 inches:
Properties and qualities
Slope:0 to 1 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Poorly drained
Runoff class: Medium
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Capacity of the most limiting layer to transmit water (Ksat):Moderately high (0.20
to 0.60 in/hr)
Depth to water table:About 18 to 36 inches
Frequency of flooding:OccasionalNone
Frequency of ponding:None
Calcium carbonate, maximum content:15 percent
Maximum salinity:Very slightly saline to slightly saline (2.0 to 4.0 mmhos/cm)
Available water capacity:Very high (about 16.7 inches)
Interpretive groups
Land capability classification (irrigated): 3w
Land capability classification (nonirrigated): 3w
Hydrologic Soil Group: C
Hydric soil rating: No
Minor Components
Aquolls
Percent of map unit:5 percent
Landform:Swales
Hydric soil rating: Yes
Poudre
Percent of map unit:5 percent
Hydric soil rating: No
73—Nunn clay loam, 0 to 1 percent slopes
Map Unit Setting
National map unit symbol: 2tlng
Elevation: 4,100 to 5,700 feet
Mean annual precipitation: 14 to 15 inches
Mean annual air temperature: 48 to 52 degrees F
Frost-free period: 135 to 152 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Nunn and similar soils:85 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Nunn
Setting
Landform:Terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Pleistocene aged alluvium and/or eolian deposits
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Typical profile
Ap - 0 to 6 inches: clay loam
Bt1 - 6 to 10 inches: clay loam
Bt2 - 10 to 26 inches: clay loam
Btk - 26 to 31 inches: clay loam
Bk1 - 31 to 47 inches: loam
Bk2 - 47 to 80 inches: loam
Properties and qualities
Slope:0 to 1 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Well drained
Runoff class: Medium
Capacity of the most limiting layer to transmit water (Ksat):Moderately low to
moderately high (0.06 to 0.20 in/hr)
Depth to water table:More than 80 inches
Frequency of flooding:None
Frequency of ponding:None
Calcium carbonate, maximum content:7 percent
Maximum salinity:Nonsaline (0.1 to 1.0 mmhos/cm)
Sodium adsorption ratio, maximum:0.5
Available water capacity:High (about 9.1 inches)
Interpretive groups
Land capability classification (irrigated): 3e
Land capability classification (nonirrigated): 4e
Hydrologic Soil Group: C
Ecological site: R067BY042CO - Clayey Plains
Hydric soil rating: No
Minor Components
Heldt
Percent of map unit:10 percent
Landform:Terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R067BY042CO - Clayey Plains
Hydric soil rating: No
Wages
Percent of map unit:5 percent
Landform:Terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R067BY002CO - Loamy Plains
Hydric soil rating: No
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76—Nunn clay loam, wet, 1 to 3 percent slopes
Map Unit Setting
National map unit symbol: jpxq
Elevation: 4,800 to 5,600 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature: 48 to 50 degrees F
Frost-free period: 135 to 150 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Nunn, wet, and similar soils:90 percent
Minor components:10 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Nunn, Wet
Setting
Landform:Alluvial fans, stream terraces
Landform position (three-dimensional):Base slope, tread
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Alluvium
Typical profile
H1 - 0 to 10 inches: clay loam
H2 - 10 to 47 inches: clay loam, clay
H2 - 10 to 47 inches: clay loam, loam, gravelly sandy loam
H3 - 47 to 60 inches:
H3 - 47 to 60 inches:
H3 - 47 to 60 inches:
Properties and qualities
Slope:1 to 3 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Somewhat poorly drained
Runoff class: Medium
Capacity of the most limiting layer to transmit water (Ksat):Moderately low to
moderately high (0.06 to 0.60 in/hr)
Depth to water table:About 24 to 36 inches
Frequency of flooding:RareNone
Frequency of ponding:None
Calcium carbonate, maximum content:10 percent
Maximum salinity:Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm)
Available water capacity:Very high (about 19.8 inches)
Interpretive groups
Land capability classification (irrigated): 2w
Land capability classification (nonirrigated): 3s
Hydrologic Soil Group: C
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Hydric soil rating: No
Minor Components
Heldt
Percent of map unit:6 percent
Hydric soil rating: No
Dacono
Percent of map unit:3 percent
Hydric soil rating: No
Mollic halaquepts
Percent of map unit:1 percent
Landform:Swales
Hydric soil rating: Yes
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18
References
American Association of State Highway and Transportation Officials (AASHTO).
2004. Standard specifications for transportation materials and methods of sampling
and testing. 24th edition.
American Society for Testing and Materials (ASTM). 2005. Standard classification of
soils for engineering purposes. ASTM Standard D2487-00.
Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of
wetlands and deep-water habitats of the United States. U.S. Fish and Wildlife
Service FWS/OBS-79/31.
Federal Register. July 13, 1994. Changes in hydric soils of the United States.
Federal Register. September 18, 2002. Hydric soils of the United States.
Hurt, G.W., and L.M. Vasilas, editors. Version 6.0, 2006. Field indicators of hydric
soils in the United States.
National Research Council. 1995. Wetlands: Characteristics and boundaries.
Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service.
U.S. Department of Agriculture Handbook 18. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/national/soils/?cid=nrcs142p2_054262
Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for
making and interpreting soil surveys. 2nd edition. Natural Resources Conservation
Service, U.S. Department of Agriculture Handbook 436. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053577
Soil Survey Staff. 2010. Keys to soil taxonomy. 11th edition. U.S. Department of
Agriculture, Natural Resources Conservation Service. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053580
Tiner, R.W., Jr. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service and
Delaware Department of Natural Resources and Environmental Control, Wetlands
Section.
United States Army Corps of Engineers, Environmental Laboratory. 1987. Corps of
Engineers wetlands delineation manual. Waterways Experiment Station Technical
Report Y-87-1.
United States Department of Agriculture, Natural Resources Conservation Service.
National forestry manual. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/
home/?cid=nrcs142p2_053374
United States Department of Agriculture, Natural Resources Conservation Service.
National range and pasture handbook. http://www.nrcs.usda.gov/wps/portal/nrcs/
detail/national/landuse/rangepasture/?cid=stelprdb1043084
19
United States Department of Agriculture, Natural Resources Conservation Service.
National soil survey handbook, title 430-VI. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/soils/scientists/?cid=nrcs142p2_054242
United States Department of Agriculture, Natural Resources Conservation Service.
2006. Land resource regions and major land resource areas of the United States,
the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook
296. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?
cid=nrcs142p2_053624
United States Department of Agriculture, Soil Conservation Service. 1961. Land
capability classification. U.S. Department of Agriculture Handbook 210. http://
www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052290.pdf
Custom Soil Resource Report
20
Page | 16
Appendix C – Hydrologic Computations
Project Name:Enclave at Westwood
Composite C-Value Computations
Post-Development
Project No:201013
Date:02/03/21
Revised:
Design by:JMN
Checked by:MSM
BASIN TOTAL AREA
(ACRES)ROOFS (95%) DRIVES &
WALKS (95%)
GARAGE &
STREETS
(95%)
LANDSCAPE
AREA (25%)
PERCENT
IMPERVIOUS C2=C5=C10=C100=
A 1.22 0.15 0.49 0.01 0.57 62.34%0.62 0.62 0.62 0.78
B 1.22 0.26 0.31 0.00 0.65 57.82%0.58 0.58 0.58 0.72
C 1.23 0.00 0.02 0.00 1.21 26.14%0.26 0.26 0.26 0.33
D 0.75 0.09 0.25 0.01 0.40 57.73%0.58 0.58 0.58 0.72
E 1.25 0.26 0.09 0.00 0.90 44.60%0.45 0.45 0.45 0.56
F 0.63 0.18 0.12 0.01 0.32 59.52%0.59 0.59 0.59 0.74
G 1.01 0.10 0.48 0.00 0.43 65.20%0.65 0.65 0.65 0.81
H 1.45 0.24 0.35 0.01 0.85 54.00%0.54 0.54 0.54 0.67
I 0.94 0.31 0.10 0.00 0.53 55.53%0.56 0.56 0.56 0.69
J 0.56 0.16 0.17 0.00 0.23 66.25%0.66 0.66 0.66 0.83
K 0.55 0.17 0.17 0.00 0.21 68.27%0.68 0.68 0.68 0.85
L 0.89 0.00 0.00 0.00 0.89 25.00%0.25 0.25 0.25 0.31
M 0.72 0.24 0.17 0.00 0.31 64.86%0.65 0.65 0.65 0.81
N 1.49 0.31 0.18 0.01 0.99 48.57%0.49 0.49 0.49 0.61
O 1.22 0.16 0.40 0.03 0.63 58.98%0.59 0.59 0.59 0.74
P 1.53 0.38 0.65 0.00 0.50 72.12%0.72 0.72 0.72 0.90
Q 1.06 0.39 0.24 0.00 0.43 66.60%0.67 0.67 0.67 0.83
R 0.66 0.03 0.35 0.00 0.28 65.73%0.66 0.66 0.66 0.82
S 1.24 0.21 0.24 0.00 0.79 50.40%0.50 0.50 0.50 0.63
T 1.30 0.29 0.22 0.01 0.78 53.04%0.53 0.53 0.53 0.66
U 1.77 0.46 0.45 0.03 0.83 62.26%0.62 0.62 0.62 0.78
V 1.06 0.31 0.29 0.00 0.46 64.62%0.65 0.65 0.65 0.81
W 1.09 0.22 0.18 0.01 0.68 51.38%0.51 0.51 0.51 0.64
X 1.48 0.32 0.44 0.01 0.71 61.45%0.61 0.61 0.61 0.77
Y 0.83 0.20 0.21 0.00 0.42 59.58%0.60 0.60 0.60 0.74
Z 0.68 0.00 0.10 0.00 0.58 35.29%0.35 0.35 0.35 0.44
OS1 8.20 8.20 25.00%0.25 0.25 0.25 0.31
OS2 3.50 0.00 0.00 0.00 3.50 25.00%0.25 0.25 0.25 0.31
Total On-Site 27.83 5.44 6.68 0.14 15.57 39.69%0.56 0.56 0.56 0.70
Total Detained 27.83 5.44 6.68 0.14 15.57 39.69%0.56 0.56 0.56 0.70
Total 39.53 5.44 6.68 0.14 27.27 27.94%0.47 0.47 0.47 0.58
TYPE C/D HYDRAULIC SOIL
2 YR - KCD =0 < Table RO-4 USDCM
5 YR - KCD =-0.10i+0.11 < Table RO-4 USDCM
100 YR - KCD =-0.39i+0.46 < Table RO-4 USDCM 0.95
0.95 Flat < 2%Flat 0.10
CCD =KCD+(0.858i3-0.786i2+0.774i+0.04)< RO-7 from USDCM 0.95 2% to 7%Average 0.15
0.8 > 7%Steep 0.20
0.5
Concrete
Surface Coefficients
Hardscape Landscape
Asphalt Sandy soil
Rooftop
Recycled Asphalt
Gravel Clayey Soil
Preliminary Enclave - Rational Method-Routin1.xlsx
Project Name:Designed By:JMN
Project No: Checked By:MSM
Date:
Revised:
FINAL REMARKS
BASIN AREA C5 LENGTH SLOPE Ti LENGTH SLOPE Cv VELOCITY Tt COMPOS.TOTAL Tc = (L/180) + 10 Tc
(AC)(FT)%(MIN)(FT)%(FPS)(MIN)Tc (MIN)LENGTH (MIN)(MIN)
A 1.22 0.62 45.71 2.00 22.22 341 2.00 20.00 2.83 2.01 24.23 387 12.15 12.15
B 1.22 0.58 199 2.00 50.71 269 2.00 20.00 2.83 1.59 52.30 468 12.60 12.60
C 1.23 0.26 180 2.00 77.51 180 2.00 7.00 0.99 3.03 80.54 360 12.00 12.00
D 0.75 0.58 69 2.00 29.95 185 2.00 20.00 2.83 1.09 31.04 254 11.41 11.41
E 1.25 0.45 122 2.00 49.76 187 2.00 20.00 2.83 1.10 50.87 309 11.72 11.72
F 0.63 0.59 121 2.00 38.31 155 2.00 20.00 2.83 0.91 39.22 276 11.53 11.53
G 1.01 0.65 110 2.00 32.37 365 2.00 20.00 2.83 2.15 34.52 475 12.64 12.64
H 1.45 0.54 125 2.00 43.16 337 2.00 20.00 2.83 1.99 45.15 462 12.57 12.57
I 0.94 0.56 150 2.00 45.96 267 2.00 20.00 2.83 1.57 47.53 417 12.32 12.32
J 0.56 0.66 175 2.00 39.87 137 2.00 20.00 2.83 0.81 40.68 312 11.73 11.73
K 0.55 0.68 135 2.00 33.40 160 2.00 20.00 2.83 0.94 34.34 295 11.64 11.64
L 0.89 0.25 49 2.00 40.99 168 2.00 7.00 0.99 2.83 43.82 217 11.21 11.21
M 0.72 0.65 143 2.00 37.19 182 2.00 20.00 2.83 1.07 38.26 325 11.81 11.81
N 1.49 0.49 164 2.00 54.23 287 2.00 20.00 2.83 1.69 55.92 451 12.51 12.51
O 1.22 0.59 369 2.00 67.69 256 2.00 20.00 2.83 1.51 69.20 625 13.47 13.47
P 1.53 0.72 149 2.00 31.85 198 2.00 20.00 2.83 1.17 33.02 347 11.93 11.93
Q 1.06 0.67 138 2.00 35.12 184 2.00 20.00 2.83 1.08 36.20 322 11.79 11.79
R 0.66 0.66 120 2.00 33.41 81 2.00 20.00 2.83 0.48 33.89 201 11.12 11.12
S 1.24 0.50 125 2.00 45.90 291 2.00 20.00 2.83 1.71 47.62 416 12.31 12.31
T 1.30 0.53 262 2.00 63.56 123 2.00 20.00 2.83 0.72 64.29 385 12.14 12.14
U 1.77 0.62 158 2.00 41.41 215 2.00 20.00 2.83 1.27 42.68 373 12.07 12.07
V 1.06 0.65 264 2.00 50.79 282 2.00 20.00 2.83 1.66 52.45 546 13.03 13.03
W 1.09 0.51 125 2.00 45.19 232 2.00 20.00 2.83 1.37 46.56 357 11.98 11.98
X 1.48 0.61 175 2.00 44.27 212 2.00 20.00 2.83 1.25 45.52 387 12.15 12.15
Y 0.83 0.60 118 2.00 37.73 168 2.00 20.00 2.83 0.99 38.72 286 11.59 11.59
Z 0.68 0.35 299 2.00 88.99 49 2.00 7.00 0.99 0.82 89.82 348 11.93 11.93
OS2 3.50 0.25 155 2.00 15.40 0 2.00 20.00 2.83 0.00 15.40 155 10.86 10.86
(URBANIZED BASINS)
Tc CHECKTRAVEL TIME
(Tt)
44230
STANDARD FORM SF-2
TIME OF CONCENTRATION
SUB-BASIN INITIAL/OVERLAND
DATA TIME (Ti)
201013
Enclave at Westwood
Preliminary Enclave - Rational Method-Routin1.xlsx
Return 1-hour
Interval (YR)Rainfall
WQ 0.6
2 0.82
5 1.1
10 1.4
100 2.86
tc WQ 2yr 5yr 10yr 100yr
5 1.220 2.850 3.731 4.870 9.950
6 0.550 2.670 3.546 4.560 9.310
7 1.770 2.520 3.381 4.310 8.800
8 1.763 2.400 3.233 4.100 8.380
9 1.690 2.300 3.098 3.930 8.030
10 1.623 2.210 2.976 3.780 7.720
11 1.562 2.130 2.864 3.630 7.420
12 1.506 2.050 2.761 3.500 7.160
13 1.454 1.980 2.666 3.390 6.920
14 1.407 1.920 2.579 3.290 6.710
15 1.362 1.870 2.497 3.190 6.520
16 1.321 1.810 2.421 3.080 6.300
17 1.282 1.750 2.351 2.990 6.100
18 1.246 1.700 2.284 2.900 5.920
19 1.212 1.650 2.222 2.820 5.750
20 1.180 1.610 2.164 2.740 5.600
.
1-HR Rainfall
Preliminary Enclave - Rational Method-Routin1.xlsx
Project Name:Designed By:
Project No:Checked By:
Date:Design Storm:2 YR
Revised:
BASIN (s)DESIGN POINTAREA (AC)RUNOFF COEFFTc (min)C x A (AC)I (IN/HR)DIRECT RUNOFF, Q (CFS)Tc (MAX)S(C x A) (AC)I (IN/HR)TOTAL RUNOFF, Q (CFS)SLOPE (%)STREET FLOW (CFS)INLET DESIGN FLOW (CFS)STREET OR INLET INTERCEPTION (CFS)CARRYOVER (CFS)DESIGN FLOW (CFS)PIPE SLOPE (%)PIPE SIZE (IN) QFULL (CFS) LENGTH (FT)VELOCITY (FPS)Tt (min)BYPASS RUNOFF, Q (CFS)LENGTH (FT)SLOPE (%)VELOCITY (FPS)Tt (min)REMARKS
A 1.22 0.62 12.15 0.76 2.05 1.56 12.15 0.76 2.05 1.56
B 1.22 0.58 12.60 0.71 2.02 1.42 12.60 0.71 2.02 1.42
C 1.23 0.26 12.00 0.32 2.06 0.66 12.00 0.32 2.06 0.66
D 0.75 0.58 11.41 0.43 2.10 0.91 11.41 0.43 2.10 0.91
E 1.25 0.45 11.72 0.56 2.08 1.16 11.72 0.56 2.08 1.16
F 0.63 0.59 11.53 0.37 2.09 0.78 11.53 0.37 2.09 0.78
G 1.01 0.65 12.64 0.66 2.01 1.33 12.64 0.66 2.01 1.33
H 1.45 0.54 12.57 0.78 2.02 1.58 12.57 0.78 2.02 1.58
I 0.94 0.56 12.32 0.52 2.04 1.06 12.32 0.52 2.04 1.06
J 0.56 0.66 11.73 0.37 2.08 0.77 11.73 0.37 2.08 0.77
K 0.55 0.68 11.64 0.38 2.09 0.78 11.64 0.38 2.09 0.78
L 0.89 0.25 11.21 0.22 2.12 0.47 11.21 0.22 2.12 0.47
M 0.72 0.65 11.81 0.47 2.07 0.97 11.81 0.47 2.07 0.97
N 1.49 0.49 12.51 0.72 2.02 1.46 12.51 0.72 2.02 1.46
O 1.22 0.59 13.47 0.72 1.96 1.40 13.47 0.72 1.96 1.40
P 1.53 0.72 11.93 1.10 2.06 2.28 11.93 1.10 2.06 2.28
Q 1.06 0.67 11.79 0.71 2.07 1.46 11.79 0.71 2.07 1.46
R 0.66 0.66 11.12 0.43 2.13 0.92 11.12 0.43 2.13 0.92
S 1.24 0.50 12.31 0.63 2.04 1.27 12.31 0.63 2.04 1.27
T 1.30 0.53 12.14 0.69 2.05 1.41 12.14 0.69 2.05 1.41
U 1.77 0.62 12.07 1.10 2.05 2.26 12.07 1.10 2.05 2.26
V 1.06 0.65 13.03 0.69 1.99 1.36 13.03 0.69 1.99 1.36
W 1.09 0.51 11.98 0.56 2.06 1.15 11.98 0.56 2.06 1.15
X 1.48 0.61 12.15 0.91 2.05 1.86 12.15 0.91 2.05 1.86
Y 0.83 0.60 11.59 0.49 2.09 1.03 11.59 0.49 2.09 1.03
Z 0.68 0.35 11.93 0.24 2.06 0.50 11.93 0.24 2.06 0.50
OS2 5.63
1 37.46
0.68
Allowed Detained Release 1.58 cfs
Undetained Release cfs
Total Release 1.58 cfs
STORM SEWER PIPE TRAVEL TIME CARRYOVER FLOWS
02/03/21 Rational Method Procedure
01/00/00
DIRECT RUNOFF TOTAL RUNOFF STREET/INLET
Enclave at Westwood STANDARD FORM SF-2 JMN
201013 Post-Development MSM
Preliminary Enclave - Rational Method-Routin1.xlsx
Project Name:Designed By:
Project No:Checked By:
Date:Design Storm:100 YR
Revised:
BASIN (s)DESIGN POINTAREA (AC)RUNOFF COEFFTc (min)C x A (AC)I (IN/HR)DIRECT RUNOFF, Q (CFS)Tc (MAX)S(C x A) (AC)I (IN/HR)TOTAL RUNOFF, Q (CFS)SLOPE (%)STREET FLOW (CFS)INLET DESIGN FLOW (CFS)STREET OR INLET INTERCEPTION (CFS)CARRYOVER (CFS)DESIGN FLOW (CFS)PIPE SLOPE (%)PIPE SIZE (IN) QFULL (CFS) LENGTH (FT)VELOCITY (FPS)Tt (min)BYPASS RUNOFF, Q (CFS)LENGTH (FT)SLOPE (%)VELOCITY (FPS)Tt (min)REMARKS
A 1.22 0.78 12.15 0.95 7.14 6.78 12.15 0.95 7.14 6.78
B 1.22 0.72 12.60 0.88 7.03 6.20 12.60 0.88 7.03 6.20
C 1.23 0.33 12.00 0.40 7.18 2.89 12.00 0.40 7.18 2.89
D 0.75 0.72 11.41 0.54 7.33 3.96 11.41 0.54 7.33 3.96
E 1.25 0.56 11.72 0.70 7.25 5.05 11.72 0.70 7.25 5.05
F 0.63 0.74 11.53 0.47 7.30 3.42 11.53 0.47 7.30 3.42
G 1.01 0.81 12.64 0.82 7.02 5.78 12.64 0.82 7.02 5.78
H 1.45 0.67 12.57 0.98 7.04 6.88 12.57 0.98 7.04 6.88
I 0.94 0.69 12.32 0.65 7.10 4.63 12.32 0.65 7.10 4.63
J 0.56 0.83 11.73 0.46 7.25 3.36 11.73 0.46 7.25 3.36
K 0.55 0.85 11.64 0.47 7.27 3.41 11.64 0.47 7.27 3.41
L 0.89 0.31 11.21 0.28 7.39 2.06 11.21 0.28 7.39 2.06
M 0.72 0.81 11.81 0.58 7.23 4.22 11.81 0.58 7.23 4.22
N 1.49 0.61 12.51 0.90 7.05 6.37 12.51 0.90 7.05 6.37
O 1.22 0.74 13.47 0.90 6.82 6.12 13.47 0.90 6.82 6.12
P 1.53 0.90 11.93 1.38 7.20 9.93 11.93 1.38 7.20 9.93
Q 1.06 0.83 11.79 0.88 7.23 6.38 11.79 0.88 7.23 6.38
R 0.66 0.82 11.12 0.54 7.41 4.02 11.12 0.54 7.41 4.02
S 1.24 0.63 12.31 0.78 7.10 5.55 12.31 0.78 7.10 5.55
T 1.30 0.66 12.14 0.86 7.14 6.15 12.14 0.86 7.14 6.15
U 1.77 0.78 12.07 1.38 7.16 9.85 12.07 1.38 7.16 9.85
V 1.06 0.81 13.03 0.86 6.92 5.93 13.03 0.86 6.92 5.93
W 1.09 0.64 11.98 0.70 7.18 5.02 11.98 0.70 7.18 5.02
X 1.48 0.77 12.15 1.14 7.14 8.11 12.15 1.14 7.14 8.11
Y 0.83 0.74 11.59 0.62 7.29 4.50 11.59 0.62 7.29 4.50
Z 0.68 0.44 11.93 0.30 7.20 2.16 11.93 0.30 7.20 2.16
OS2 25.68
1 164.44
0.68
Allowed Detained Release 39.53 cfs
Undetained Release cfs
Total Release 39.53 cfs
STORM SEWER PIPE TRAVEL TIME CARRYOVER FLOWS
02/03/21 Rational Method Procedure
01/00/00
DIRECT RUNOFF TOTAL RUNOFF STREET/INLET
Enclave at Westwood STANDARD FORM SF-2 JMN
201013 Post-Development MSM
Preliminary Enclave - Rational Method-Routin1.xlsx
SWMM Schematic
Water Quality PondFormulas:orifice formula: Q = CoAo(2gH)0.5, with Co = 0.60 weir formula: Q = CdLH1.5 with Cd = 2.8low-flow outletlow-flow outletlow-flow outletmajor-flow outletoverflow spillwaydiameter / length (ft):0.080.080.081650invert elevation:49544955495649594960w.s. elevOutlet Orifice flowOutlet Weir flowOverflow Weir flowTotal Discharge QArea Area incrementalaccumulated Vol.(cfs)(cfs)(cfs)(cfs)(sf)(acre)volume (ac-ft)(ac-ft)04954.0- - - - - - - - - 14955.00.03 - - - - 0.03 1,385 0.030.011 0.011 24956.00.04 0.03 - - - 0.06 1,942 0.040.03 0.04 34957.00.05 0.04 0.03 - - 0.11 2,560 0.060.05 0.09 44958.00.05 0.05 0.04 - - 0.14 3,242 0.070.07 0.16 54959.00.06 0.05 0.05 - - 0.16 3,987 0.090.08 0.24 64960.00.06 0.06 0.05 45 - 45 4,806 0.110.10 0.34 74961.00.07 0.06 0.06 127 140 267 4,807 0.110.11 0.45 Detention Pondlow-flow outletlow-flow outletlow-flow outletmajor-flow outletoverflow spillwaydiameter / length (ft):0.70020200invert elevation:49544957495949634963.5w.s. elevOutlet Orifice flowOutlet Weir flowOverflow Weir flowTotal Discharge QArea Area incrementalaccumulated Vol.(cfs)(cfs)(cfs)(cfs)(sf)(acre)volume (ac-ft)(ac-ft)04954.0- - - - - - - 0.00- - 14955.01.85 - - - - 1.85 217860.500.17 0.167 24956.02.62 - - - - 2.62 254670.580.54 0.71 34957.03.21 - - - - 3.21 292830.670.63 1.34 44958.03.70 - - - - 3.70 332330.760.72 2.05 54959.04.14 - - - - 4.14 373180.860.81 2.86 64960.04.54 - - - - 4.54 415400.950.90 3.77 74961.04.90 - - - - 4.90 458951.051.00 4.77 84962.05.24 - - - - 5.24 486491.121.09 5.86 94963.05.56 - - - - 5.56 515681.181.15 7.01 104964.05.86 - - 56 198 260 546621.251.22 8.23
Table 4.1-4. IDF Table for SWMM
H:M Duration (min)Intensity 2-year (in/hr)Intensity 100-year (in/hr)
0:05 5 0.29 1
0:10 10 0.33 1.14
0:15 15 0.38 1.33
0:20 20 0.64 2.23
0:25 25 0.81 2.84
0:30 30 1.57 5.49
0:35 35 2.85 9.95
0:40 40 1.18 4.12
0:45 45 0.71 2.48
0:50 50 0.42 1.46
0:55 55 0.35 1.22
1:00 60 0.3 1.06
1:05 65 0.2 1
1:10 70 0.19 0.95
1:15 75 0.18 0.91
1:20 80 0.17 0.87
1:25 85 0.17 0.84
1:30 90 0.16 0.84
1:35 95 0.15 0.78
1:40 100 0.15 0.75
1:45 105 0.14 0.73
1:50 110 0.14 0.71
1:55 115 0.13 0.69
2:00 120 0.13 0.67
2-year Event EPA STORM WATER MANAGEMENT MODEL - VERSION 5.1 (Build 5.1.013) -------------------------------------------------------------- WARNING 04: minimum elevation drop used for Conduit 5 ********************************************************* NOTE: The summary statistics displayed in this report are based on results found at every computational time step, not just on results from each reporting time step. ********************************************************* **************** Analysis Options **************** Flow Units ............... CFS Process Models: Rainfall/Runoff ........ YES RDII ................... NO Snowmelt ............... NO Groundwater ............ NO Flow Routing ........... YES Ponding Allowed ........ NO Water Quality .......... NO Infiltration Method ...... HORTON Flow Routing Method ...... KINWAVE Starting Date ............ 02/08/2021 00:00:00 Ending Date .............. 02/13/2021 00:00:00 Antecedent Dry Days ...... 0.0 Report Time Step ......... 00:05:00 Wet Time Step ............ 00:05:00 Dry Time Step ............ 01:00:00 Routing Time Step ........ 30.00 sec ************************** Volume Depth Runoff Quantity Continuity acre-feet inches
************************** --------- ------- Total Precipitation ...... 2.269 0.978 Evaporation Loss ......... 0.000 0.000 Infiltration Loss ........ 0.993 0.428 Surface Runoff ........... 1.189 0.513 Final Storage ............ 0.097 0.042 Continuity Error (%) ..... -0.441 ************************** Volume Volume Flow Routing Continuity acre-feet 10^6 gal ************************** --------- --------- Dry Weather Inflow ....... 0.000 0.000 Wet Weather Inflow ....... 1.189 0.388 Groundwater Inflow ....... 0.000 0.000 RDII Inflow .............. 0.000 0.000 External Inflow .......... 0.000 0.000 External Outflow ......... 1.174 0.383 Flooding Loss ............ 0.000 0.000 Evaporation Loss ......... 0.000 0.000 Exfiltration Loss ........ 0.000 0.000 Initial Stored Volume .... 0.000 0.000 Final Stored Volume ...... 0.000 0.000 Continuity Error (%) ..... 1.260 ******************************** Highest Flow Instability Indexes ******************************** Link 5 (13) Link 4 (13) ************************* Routing Time Step Summary ************************* Minimum Time Step : 30.00 sec Average Time Step : 30.00 sec
Maximum Time Step : 30.00 sec Percent in Steady State : 0.00 Average Iterations per Step : 1.01 Percent Not Converging : 0.00 *************************** Subcatchment Runoff Summary *************************** ------------------------------------------------------------------------------------------------------------------------------ Total Total Total Total Imperv Perv Total Total Peak Runoff Precip Runon Evap Infil Runoff Runoff Runoff Runoff Runoff Coeff Subcatchment in in in in in in in 10^6 gal CFS ------------------------------------------------------------------------------------------------------------------------------ East 0.98 0.00 0.00 0.40 0.54 0.00 0.54 0.20 15.70 0.552 Midd 0.98 0.00 0.00 0.45 0.49 0.00 0.50 0.14 11.90 0.507 West 0.98 0.00 0.00 0.49 0.45 0.01 0.46 0.05 4.83 0.467 ****************** Node Depth Summary ****************** --------------------------------------------------------------------------------- Average Maximum Maximum Time of Max Reported Depth Depth HGL Occurrence Max Depth Node Type Feet Feet Feet days hr:min Feet --------------------------------------------------------------------------------- 1 JUNCTION 0.01 1.09 4960.09 0 00:40 1.06 2 JUNCTION 0.01 1.14 4956.34 0 00:42 1.08
6 JUNCTION 0.00 0.00 4946.54 0 00:00 0.00 7 OUTFALL 0.00 0.00 4946.54 0 00:00 0.00 4 STORAGE 0.92 5.55 4959.55 0 00:46 5.55 5 STORAGE 0.05 1.63 4955.63 0 02:03 1.63 ******************* Node Inflow Summary ******************* ------------------------------------------------------------------------------------------------- Maximum Maximum Lateral Total Flow Lateral Total Time of Max Inflow Inflow Balance Inflow Inflow Occurrence Volume Volume Error Node Type CFS CFS days hr:min 10^6 gal 10^6 gal Percent ------------------------------------------------------------------------------------------------- 1 JUNCTION 15.70 15.70 0 00:40 0.204 0.204 0.000 2 JUNCTION 11.90 25.58 0 00:42 0.138 0.341 0.000 6 JUNCTION 0.00 2.33 0 02:03 0 0.383 0.000 7 OUTFALL 0.00 2.33 0 02:03 0 0.383 0.000 4 STORAGE 4.83 29.79 0 00:42 0.0455 0.386 0.368 5 STORAGE 0.00 24.89 0 00:46 0 0.385 0.502 ********************* Node Flooding Summary ********************* No nodes were flooded. ********************** Storage Volume Summary ********************** -------------------------------------------------------------------------------------------------- Average Avg Evap Exfil Maximum Max Time of Max Maximum Volume Pcnt Pcnt Pcnt Volume Pcnt Occurrence Outflow
Storage Unit 1000 ft3 Full Loss Loss 1000 ft3 Full days hr:min CFS -------------------------------------------------------------------------------------------------- 4 1.557 4 0 0 13.457 39 0 00:45 24.89 5 0.693 0 0 0 25.267 7 0 02:03 2.33 *********************** Outfall Loading Summary *********************** ----------------------------------------------------------- Flow Avg Max Total Freq Flow Flow Volume Outfall Node Pcnt CFS CFS 10^6 gal ----------------------------------------------------------- 7 30.97 0.38 2.33 0.383 ----------------------------------------------------------- System 30.97 0.38 2.33 0.383 ******************** Link Flow Summary ******************** ----------------------------------------------------------------------------- Maximum Time of Max Maximum Max/ Max/ |Flow| Occurrence |Veloc| Full Full Link Type CFS days hr:min ft/sec Flow Depth ----------------------------------------------------------------------------- 1 CONDUIT 14.71 0 00:42 5.63 0.15 0.26 2 CONDUIT 25.63 0 00:42 8.64 0.18 0.29 5 DUMMY 2.33 0 02:03 3 DUMMY 24.89 0 00:46 4 DUMMY 2.33 0 02:03 ************************* Conduit Surcharge Summary
************************* No conduits were surcharged. Analysis begun on: Wed Feb 10 11:02:02 2021 Analysis ended on: Wed Feb 10 11:02:02 2021 Total elapsed time: < 1 sec
100-Year Event EPA STORM WATER MANAGEMENT MODEL - VERSION 5.1 (Build 5.1.013) -------------------------------------------------------------- WARNING 04: minimum elevation drop used for Conduit 5 ********************************************************* NOTE: The summary statistics displayed in this report are based on results found at every computational time step, not just on results from each reporting time step. ********************************************************* **************** Analysis Options **************** Flow Units ............... CFS Process Models: Rainfall/Runoff ........ YES RDII ................... NO Snowmelt ............... NO Groundwater ............ NO Flow Routing ........... YES Ponding Allowed ........ NO Water Quality .......... NO Infiltration Method ...... HORTON Flow Routing Method ...... KINWAVE Starting Date ............ 02/08/2021 00:00:00 Ending Date .............. 02/13/2021 00:00:00 Antecedent Dry Days ...... 0.0 Report Time Step ......... 00:05:00 Wet Time Step ............ 00:05:00 Dry Time Step ............ 01:00:00 Routing Time Step ........ 30.00 sec ************************** Volume Depth Runoff Quantity Continuity acre-feet inches
************************** --------- ------- Total Precipitation ...... 8.515 3.672 Evaporation Loss ......... 0.000 0.000 Infiltration Loss ........ 1.729 0.746 Surface Runoff ........... 6.733 2.903 Final Storage ............ 0.097 0.042 Continuity Error (%) ..... -0.517 ************************** Volume Volume Flow Routing Continuity acre-feet 10^6 gal ************************** --------- --------- Dry Weather Inflow ....... 0.000 0.000 Wet Weather Inflow ....... 6.733 2.194 Groundwater Inflow ....... 0.000 0.000 RDII Inflow .............. 0.000 0.000 External Inflow .......... 0.000 0.000 External Outflow ......... 6.712 2.187 Flooding Loss ............ 0.000 0.000 Evaporation Loss ......... 0.000 0.000 Exfiltration Loss ........ 0.000 0.000 Initial Stored Volume .... 0.000 0.000 Final Stored Volume ...... 0.000 0.000 Continuity Error (%) ..... 0.301 ******************************** Highest Flow Instability Indexes ******************************** Link 5 (7) Link 4 (7) ************************* Routing Time Step Summary ************************* Minimum Time Step : 30.00 sec Average Time Step : 30.00 sec
Maximum Time Step : 30.00 sec Percent in Steady State : 0.00 Average Iterations per Step : 1.01 Percent Not Converging : 0.00 *************************** Subcatchment Runoff Summary *************************** ------------------------------------------------------------------------------------------------------------------------------ Total Total Total Total Imperv Perv Total Total Peak Runoff Precip Runon Evap Infil Runoff Runoff Runoff Runoff Runoff Coeff Subcatchment in in in in in in in 10^6 gal CFS ------------------------------------------------------------------------------------------------------------------------------ East 3.67 0.00 0.00 0.71 2.14 0.80 2.93 1.11 82.30 0.799 Midd 3.67 0.00 0.00 0.78 1.96 0.91 2.87 0.80 60.43 0.781 West 3.67 0.00 0.00 0.77 1.77 1.11 2.89 0.29 25.27 0.786 ****************** Node Depth Summary ****************** --------------------------------------------------------------------------------- Average Maximum Maximum Time of Max Reported Depth Depth HGL Occurrence Max Depth Node Type Feet Feet Feet days hr:min Feet --------------------------------------------------------------------------------- 1 JUNCTION 0.03 2.85 4961.85 0 00:40 2.73 2 JUNCTION 0.03 3.08 4958.28 0 00:41 2.86
6 JUNCTION 0.00 0.00 4946.54 0 00:00 0.00 7 OUTFALL 0.00 0.00 4946.54 0 00:00 0.00 4 STORAGE 0.95 6.51 4960.51 0 00:41 6.43 5 STORAGE 0.77 7.72 4961.72 0 02:23 7.71 ******************* Node Inflow Summary ******************* ------------------------------------------------------------------------------------------------- Maximum Maximum Lateral Total Flow Lateral Total Time of Max Inflow Inflow Balance Inflow Inflow Occurrence Volume Volume Error Node Type CFS CFS days hr:min 10^6 gal 10^6 gal Percent ------------------------------------------------------------------------------------------------- 1 JUNCTION 82.30 82.30 0 00:40 1.11 1.11 0.000 2 JUNCTION 60.43 134.90 0 00:41 0.797 1.9 0.000 6 JUNCTION 0.00 5.14 0 02:23 0 2.19 0.000 7 OUTFALL 0.00 5.14 0 02:23 0 2.19 0.000 4 STORAGE 25.27 158.44 0 00:41 0.288 2.19 0.158 5 STORAGE 0.00 158.00 0 00:41 0 2.19 0.017 ********************* Node Flooding Summary ********************* No nodes were flooded. ********************** Storage Volume Summary ********************** -------------------------------------------------------------------------------------------------- Average Avg Evap Exfil Maximum Max Time of Max Maximum Volume Pcnt Pcnt Pcnt Volume Pcnt Occurrence Outflow
Storage Unit 1000 ft3 Full Loss Loss 1000 ft3 Full days hr:min CFS -------------------------------------------------------------------------------------------------- 4 1.645 5 0 0 17.968 52 0 00:41 158.00 5 20.115 6 0 0 245.117 68 0 02:23 5.14 *********************** Outfall Loading Summary *********************** ----------------------------------------------------------- Flow Avg Max Total Freq Flow Flow Volume Outfall Node Pcnt CFS CFS 10^6 gal ----------------------------------------------------------- 7 33.11 2.04 5.14 2.187 ----------------------------------------------------------- System 33.11 2.04 5.14 2.187 ******************** Link Flow Summary ******************** ----------------------------------------------------------------------------- Maximum Time of Max Maximum Max/ Max/ |Flow| Occurrence |Veloc| Full Full Link Type CFS days hr:min ft/sec Flow Depth ----------------------------------------------------------------------------- 1 CONDUIT 78.53 0 00:41 8.77 0.82 0.68 2 CONDUIT 135.04 0 00:41 13.00 0.94 0.77 5 DUMMY 5.14 0 02:23 3 DUMMY 158.00 0 00:41 4 DUMMY 5.14 0 02:23 ************************* Conduit Surcharge Summary
************************* No conduits were surcharged. Analysis begun on: Wed Feb 10 10:49:07 2021 Analysis ended on: Wed Feb 10 10:49:07 2021 Total elapsed time: < 1 sec
Page | 17
Appendix D – Hydraulic Computations
Page | 18
Appendix E – Supplemental Information
PRELIMINARY DRAINAGE REPORT
The Retreat at Fort Collins
Fort Collins, Colorado
July 25, 2018
Prepared for:
Landmark Properties
4455 Epps Bridge Parkway, Suite 20
Athens, GA 30606
Prepared by:
301 North Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 1290-002
This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
July 25, 2018
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
The Retreat @ Fort Collins
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies the Preliminary Development Review submittal for the
proposed The Retreat @ Fort Collins.
This report has been prepared in accordance to the Fort Collins Stormwater Criteria Manual
(FCSCM), and serves to document the stormwater impacts associated with the proposed The
Retreat @ Fort Collins project. We understand that review by the City is to assure general
compliance with standardized criteria contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Stephanie Thomas, PE
Project Engineer
The Retreat @ Fort Collins
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ....................................................................................................................................... 1
B. Description of Property ................................................................................................................ 2
C. Floodplain .................................................................................................................................... 3
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 4
A. Major Basin Description ............................................................................................................... 4
B. Sub-Basin Description .................................................................................................................. 4
III. DRAINAGE DESIGN CRITERIA ................................................................................... 4
A. Regulations .................................................................................................................................. 4
B. Four Step Process ........................................................................................................................ 5
C. Development Criteria Reference and Constraints ......................................................................... 5
D. Hydrological Criteria .................................................................................................................... 6
E. Hydraulic Criteria ......................................................................................................................... 6
F. Floodplain Regulations Compliance .............................................................................................. 6
G. Modifications of Criteria .............................................................................................................. 6
IV. DRAINAGE FACILITY DESIGN .................................................................................... 7
A. General Concept .......................................................................................................................... 7
B. Detention Ponds and Water Quality/Low Impact Development ................................................. 10
C. Release Rate Compliance ........................................................................................................... 12
D. Low Impact Development (LID) Compliance ............................................................................... 14
V. CONCLUSIONS ...................................................................................................... 15
A. Compliance with Standards ........................................................................................................ 15
B. Drainage Concept ...................................................................................................................... 15
References ....................................................................................................................... 16
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers (For Future Use)
B.2 – Inlets (For Future Use)
B.3 – Detention Facilities (For Future Use)
APPENDIX C – Water Quality Design Computations
APPENDIX D – SWMM Analysis / Model
APPENDIX E – FEMA Firmette
APPENDIX F – Erosion Control Report
The Retreat @ Fort Collins
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2– Proposed Site Plan ................................................................................................ 3
Figure 3 – Existing FEMA Floodplains .................................................................................... 4
Table 1 - Drainage Summary Table .................................................................................... 10
Table 2 – Detention Summary ............................................................................................ 12
Table 3 – Underground Chamber Summary .......................................................................... 12
Table 4 – Allowable Release Rate ....................................................................................... 13
Table 5 – Proposed Release Rate ........................................................................................ 14
MAP POCKET:
C6.00 - Drainage Exhibit
The Retreat @ Fort Collins
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The Retreat @ Fort Collins project is located in the southeast quarter of Section 1,
Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins,
County of Larimer, State of Colorado.
3. The project site is located east of Redwood Village PUD I and Redwood Street and
south of Evergreen Parkway, Third Filing. The project site encompasses Redwood
Village PUD Phase II.
4. The project is currently bordered to the south by Dry Creek, west by Redwood Village
PUD, Phase II and Redwood Street, north by Evergreen and Park, Third Filing and to
the east by Lake Canal Irrigation Ditch.
The Retreat @ Fort Collins
Preliminary Drainage Report 2
B. Description of Property
1. The Retreat @ Fort Collins is approximately 31.49 net acres. Approximately 1.17
acres of the site consists of the proposed extension of Suniga Road and 2.32 acres of
the site consists of area proposed to remain undeveloped with this project.
Figure 1 – Aerial Photograph
2. The Retreat @ Fort Collins consists of a mix of fee-simple townhomes, multi-family
apartments, duplexes, clubhouse, parking garage, parking lots, private and public
roadways, sidewalks and trails.
3. The existing site consists of undeveloped grasslands.
4. Historically, off-site drainage entering from the Redwood Village neighbor enters the
site along the western boundary. All runoff generated from the project historically
drains to the southeast and is collected in the Lake Canal Irrigation Ditch.
5. In the northwestern corner of the site is an existing detention pond. This detention
pond detains a portion of the Redwood Village and the upstream developments.
6. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey, the vast majority of the site consists of
variations of clay loam, which falls into Hydrologic Soil Groups C. This soil type has a
slow rate of infiltration.
7. The proposed development will include a mix of above ground extended detention
basins and underground detention and water quality chambers. The underground
detention and water quality chambers will provide LID treatment for the site in
accordance with the City of Fort Collins guidance for LID treatment.
The Retreat @ Fort Collins
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
8. No existing irrigation facilities or major drainageways are located within the property
limits. A regional conveyance, associated with the NECCO project, has been planned
on the property and will be included as a part of this project.
9. The project site is within the Low Density Mixed-Use Neighborhood District (L-M-N)
Zoning District. The proposed use is permitted within the zone district.
C. Floodplain
1. The subject property is located in the FEMA regulatory Dry Creek 100-year floodplain.
A FEMA high-risk floodway and floodplain is located on the very southern tip of the
property. This area is not proposed to be developed at this time.
2. The FEMA Panel 08069C0977G illustrates the proximity of the project site to the
nearest FEMA delineated regulatory floodplain. These Firmette for this FEMA panel is
provided in the Appendix.
The Retreat @ Fort Collins
Preliminary Drainage Report 4
Figure 3 – Existing FEMA Floodplains
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The Retreat @ Fort Collins is located within the Dry Creek Basin, which is generally
located in north Fort Collins. This area is also subject to the restrictions as delineated
in the North East College Corridor Outfall (NECCO) Design Report.
B. Sub-Basin Description
1. The property historically drains to the southeast and is collected in the Lake Canal
Irrigation Ditch.
2. Off-site drainage from the Redwood Village neighborhood is routed onto the property
and entering from the western boundary.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
The Retreat @ Fort Collins will be subject to the regulations set forth in the FCSCM, as
well as regulations associated with the Dry Creek Drainage Basin and the NECCO project.
The Retreat @ Fort Collins
Preliminary Drainage Report 5
B. Four Step Process
The overall stormwater management strategy employed with The Retreat @ Fort Collins
project utilizes the “Four Step Process” to minimize adverse impacts of urbanization on
receiving waters. The following is a description of how the proposed development has
incorporated each step.
Step 1 – Employ Runoff Reduction Practices
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use by implementing multiple Low-Impact Development (LID) strategies including:
Providing vegetated open areas throughout the site to reduce the overall impervious
area and to minimize directly connected impervious areas (MDCIA).
Routing flows, to the extent feasible, through drain rock within the underground
detention section to increase time of concentration, promote infiltration and provide
initial water quality.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release
The efforts taken in Step 1 will facilitate the reduction of runoff; however, this
development will still generate stormwater runoff that will require additional BMPs and
water quality. The majority of stormwater runoff from the site will ultimately be
intercepted and treated in proposed underground Stormtech water quality chambers.
Water quality for areas not routed through the Stormtech chambers will be provided within
the detention pond volume.
Step 3 – Stabilize Drainageways
As stated in Section I.B.5, above, there are no major drainageways in or near the subject
site. While this step may not seem applicable to The Retreat @ Fort Collins, the proposed
project indirectly helps achieve stabilized drainageways nonetheless. Furthermore, this
project will pay one-time stormwater development fees, as well as ongoing monthly
stormwater utility fees, both of which help achieve Citywide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs.
This step typically applies to industrial and commercial developments and is not
applicable for this project.
C. Development Criteria Reference and Constraints
1. The Retreat @ Fort Collins will be subject to the regulations set forth in the FCSCM,
as well as regulations associated with the Dry Creek Drainage Basin and the NECCO
project.
2. This property was included in the NECCO Design Report. As this project is expected
to release into the NECCO drainage system, this project will be subject to the
requirements set forth with the NECCO Design Report.
3. Though this site was not included in the Redwood Village PUD Drainage design. The
Redwood Village neighborhood does discharge to the project site. As such, the
Redwood Village report was referenced for this project.
4. Several constraints have been identified during the course of this analysis that will
impact the proposed drainage system including:
The Retreat @ Fort Collins
Preliminary Drainage Report 6
Tie in elevation into the NECCO Drainage system.
NECCO storm drainage planned to traverse this property. This storm drain will be
designed with this project.
The NECCO design requires a 0.2 cfs/acres release from the developed site. This
minimal release rate does not provide substantial leeway for any undetained flows.
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations
associated with this development. Tabulated data contained in Table RA-7 has been
utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. The EPA Storm Water Management Model (SWMM) software has been utilized for
detention storage calculations.
4. Three separate design storms have been utilized to address distinct drainage
scenarios. The first event analyzed is the “Minor,” or “Initial” Storm, which has a 2 -
year recurrence interval. The second event considered is the “Major Storm,” which
has a 100-year recurrence interval. The third storm computed, for comparison
purposes only, is the 10-year event.
5. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
E. Hydraulic Criteria
1. As previously noted, the subject property historically drains into the Lake Canal
Irrigation Ditch. This site will be rerouted to drain to the existing NECCO storm
improvements.
2. All drainage facilities proposed with The Retreat @ Fort Collins project are designed in
accordance with criteria outlined in the FCSCM and/or the Urban Drainage and Flood
Control District’s (UDFCD) Urban Storm Drainage Criteria Manual.
3. As stated in Section I.C.1, above, the subject property is located within a FEMA
regulatory floodplain. As such, this project is subject to the development restrictions
as provided by FEMA and the City of Fort Collins.
4. No structures are proposed within the floodplain or floodway.
5. The Retreat @ Fort Collins project does not propose to modify any natural
drainageways.
F. Floodplain Regulations Compliance
1. As previously mentioned, all structures are located outside of any FEMA 100-year or
City floodplain, and thus are not subject to any floodplain regulations .
G. Modifications of Criteria
1. The proposed The Retreat @ Fort Collins development is not requesting any
modification at this time.
The Retreat @ Fort Collins
Preliminary Drainage Report 7
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of The Retreat @ Fort Collins drainage design collect and treat all
developed runoff from the site, direct all stormwater release from the site to the
NECCO stormwater improvements adjacent to the site and minimize the amount of
undetained drainage and/or provide additional detention and treatment of off-site
areas to balance any undetained basins.
2. As previously mentioned, off-site flows from the Redwood Village neighborhood drain
onto the existing property.
3. A list of tables and figures used within this report can be found in the Table of
Contents at the front of the document. The tables and figures are located within the
sections to which the content best applies.
4. The Retreat @ Fort Collins project is composed of eight major drainage basins,
designated as Basins A, B, C, D, E, F, UD, and RW. The drainage patterns for each
major basin are further described below.
Basin A
Basin A is located in the northern half of the site. This basin is subdivided into 8 sub-
basins. These basins consist of buildings, parking lots, roadways and landscaping.
Runoff from these basins drains via curb and gutter to curb inlets. These basins are
detained and treated for LID in underground Chambers A7, and water quality is
provided in Detention Pond 1. This pond releases directly to a proposed outfall pipe
that connects outfalls into the proposed Detention Pond 2. 100-year detention of this
basin is provided in Detention Pond 1.
Basin B
Basin B is located in the center and southern area of the site. This basin is subdivided
into 11 sub-basins. These basins consist of buildings, parking lots, roadways and
landscaping. Runoff from these basins drains via curb and gutter to curb inlets.
These basins are detained and treated for LID in underground Chambers B2, B6 and
B9. Water quality is also provided in Detention Pond 2. This pond releases directly
to a proposed outfall pipe that connects to the NECCO stormwater improvements.
This pond receives the detained release from Detention Pond 1. 100-year detention
of this basin is provided in Detention Pond 2.
Basin C
Basin C is located along the northern boundary of the site adjacent the southern
boundary of the Redwood Village. This basin consists of one sub-basin. This basin
consists of buildings, parking lots, roadways and landscaping. Runoff from these
basins drains via curb and gutter to curb inlets and curb cuts. These basins are
detained and treated for water quality in Detention Pond 3. 100-year detention of this
basin is provided by Detention Pond 3.
The Retreat @ Fort Collins
Preliminary Drainage Report 8
Basin D
Basin D is located along the western boundary of the site adjacent the eastern
boundary of the Redwood Village. This basin is subdivided into 2 sub-basins. This
basin consists of buildings, parking lots, roadways and landscaping. Runoff from
these basins drains via curb and gutter to curb cuts and swale. Water quality for this
basin is provided in Detention Pond 4. 100-year detention of this basin is provided by
a combination of Detention Pond 4 and Detention Pond 3. Once Detention Pond 4 is
full it will spill to the adjacent parking lot that will convey additional flow to Detention
Pond 3.
Basin E
Basin E is located along the southern boundary of the site. This basin consist of
buildings, parking lots, roadways and landscaping. Runoff from this basin drains via
curb and gutter to curb inlets. These basins are detained and treated for water
quality/LID in underground Chambers E1 and Detention Pond 5. Detention Pond 5
consists of underground detention chambers. These ponds release directly to a
proposed outfall pipe that connects to the NECCO stormwater improvements.
Basin F
Basin F is located in the northern corner of the site. This basin consists of a roadway
connection to Conifer Street. Due to grading constraints this area will drain to the
existing inlets at the intersection of Conifer Street and Redwood Street. These inlets
discharge to Redwood Detention Pond. Based on the proposed plans to the Redwood
Pond that were delineated in the NECCO report. This basin can easily be detained in
the Redwood Pond without much consequence. Further discussion is provided in the
Detention Pond section of this report
Basin UD1
Basin UD1 is located along the western boundary of the site, adjacent Redwood
Street. This basin consists of buildings, parking lots, roadways and landscaping. The
runoff from this basin drains undetained via curb and gutter to existing curb inlets on
Redwood Street. These inlets are connected to the NECCO stormwater improvements.
Basin UD2
Basin UD2 is located along the southern boundary of the site. This basin consists of
Suniga Street. The runoff from this basin drains undetained via curb and gutter to
inlets designed with the NECCO stormwater improvements. Per the NECCO plan, this
basin was not required to be detained by this project. This area is listed as Basin 950
and 951 in the NECCO plan.
Basin UD3
Basin UD3 is located south of Suniga Street. This basin is not planned for
development and will remain as its existing condition . Per the NECCO plan, this basin
was not required to be detained by this project. This area is listed as Basin 413 in
the NECCO plan.
The Retreat @ Fort Collins
Preliminary Drainage Report 9
Basin RW
Basin RW consists of the existing Redwood Village neighborhood. This basin was
further divided into 5 sub-basins. Basin RW1 drains via curb and gutter to the north
and will be collected in proposed inlets. The runoff from Basin RW1 will bypass the
Retreat site. Basin RW2 currently drains via a concrete pan and discharges onto The
Retreat site. This basin’s runoff will be detained in Detention Pond 4. Basin RW3
currently drains via overland flow onto The Retreat site. This basin’s runoff will be
detained in Detention Pond 4 and 3. Basin RW4 currently drains via grass swale onto
The Retreat site. This basin’s runoff will be collected in an inlet and conveyed to the
NECCO system by the planned NECCO extension. The runoff from Basin RW4 will
bypass the Retreat site. Basin RW5 currently drains via overland flow onto The
Retreat site. This basin’s runoff will be detained in Detention Pond 3.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
The Retreat @ Fort Collins
Preliminary Drainage Report 10
Table 1 - Drainage Summary Table
DRAINAGE SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-
yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
A1 A1 0.66 0.62 0.78 5.0 5.0 1.17 5.11
A2 A2 1.61 0.69 0.86 13.8 11.4 2.16 10.25
A3 A3 1.33 0.76 0.95 9.0 7.6 2.37 10.83
A4 A4 1.42 0.67 0.84 7.2 5.2 2.39 11.81
A5 A5 0.71 0.76 0.95 6.7 5.0 1.38 6.63
A6 A6 2.11 0.70 0.87 10.5 9.3 3.19 14.74
A7 A7 0.20 0.84 1.00 5.0 5.0 0.49 2.04
A8 A8 3.54 0.38 0.47 10.4 9.5 2.96 13.20
B1 B1 1.59 0.70 0.88 11.8 10.4 2.33 10.76
B2 B2 1.26 0.45 0.56 9.1 7.6 1.31 6.11
B3 B3 1.23 0.85 1.00 8.3 5.0 2.51 12.25
B4 B4 2.07 0.68 0.85 6.7 5.4 3.66 17.55
B5 B5 0.52 0.74 0.93 5.9 5.0 1.07 4.84
B6 B6 0.67 0.49 0.62 6.4 5.2 0.89 4.14
B7 B7 1.30 0.77 0.96 6.8 5.0 2.60 12.48
B8 B8 0.27 0.77 0.97 5.3 5.0 0.60 2.62
B9 B9 0.14 0.80 1.00 5.0 5.0 0.31 1.36
B10 B10 0.81 0.77 0.96 5.1 5.0 1.77 7.70
B11 B11 1.43 0.34 0.42 9.9 9.0 1.09 4.83
C1 C1 1.16 0.54 0.68 7.6 6.3 1.56 7.36
D1 D1 0.83 0.64 0.80 7.0 5.2 1.34 6.61
D2 D2 0.83 0.51 0.63 5.0 5.0 1.20 5.24
E1 E1 0.79 0.62 0.77 8.3 6.6 1.17 5.53
F1 F1 0.72 0.38 0.47 14.2 13.3 0.52 2.36
UD1 UD1 0.79 0.52 0.65 8.0 6.6 0.99 4.66
UD2 UD2 1.17 0.80 1.00 5.0 5.0 2.68 11.66
UD3 UD3 2.32 0.30 0.37 32.0 29.0 0.86 3.96
RW1 RW1 3.42 0.45 0.56 15.9 14.7 2.83 12.71
RW2 RW2 1.08 0.45 0.56 9.6 8.4 1.09 5.08
RW3 RW3 0.10 0.45 0.56 6.8 5.6 0.12 0.55
RW4 RW4 1.20 0.45 0.56 9.6 8.4 1.22 5.65
RW5 RW5 0.31 0.45 0.56 6.8 5.6 0.37 1.69
B. Detention Ponds and Water Quality/Low Impact Development
Due to the complication of designing the underground chambers for both LID treatment
and 100-year detention, the detention ponds and the LID treatments are labeled
differently. The labeling of the detention ponds designed for 100 -year detention are
denoted by a number (ie. Pond 1, Pond 2, Pond 3). The labeling for the underground
chambers designed for LID Treatment ONLY are labeled with the basin for which they are
located (ie. Chamber A7, Chamber B2). Some chamber areas are labeled with both a
Detention Pond label and a LID label. These chamber areas have both LID and detention
components, and these components are calculated separately.
The Retreat @ Fort Collins
Preliminary Drainage Report 11
Detention Pond 1 and Chambers A7
Detention Pond 1 was designed to detain the stormwater runoff during a 100 -year event
from the entire Basin A. Water Quality is provided for Basin A8 as extended detention
within Detention Pond 1. Detention Pond 1 releases to Detention Pond 2.
Chambers A7 provides LID and water quality treatment for Basin A1-A7.
Detention Pond 2 and Chambers B2 and B3
Detention Pond 2 was designed to detain the stormwater runoff during a 100-year event
from Basin B. Water Quality is provided for Basin B11 as extended detention within
Detention Pond 2. Detention Pond 2 also takes the release from Detention Pond 1.
Chambers B2 provides LID and water quality treatment for Basins B1 and B2. Chambers
B6 provides LID and water quality treatment for Basins B3-B6. Chambers B9 provides
LID and water quality treatment for Basins B7 and B9-B10.
Detention Pond 3
Detention Pond 3 was designed to detain the stormwater runoff during a 100-year event
from Basin C and Basin RW5. Water Quality is provided for Basin C1 as extended
detention within Detention Pond 3. During a 100-year event Detention Pond 3 will spill
to the adjacent parking lot, and be detained within the parking lot.
Detention Pond 4
Detention Pond 4 was designed to detain a portion of the stormwater runoff during a
100-year event from Basin D, Basin RW2 and Basin RW3. Water Quality is provided for
Basin D as extended detention within Detention Pond 4. During a 100-year event
Detention Pond 4 will spill to the adjacent parking lot. This additional flow will be
detained in Detention Pond 3.
Detention Pond 5 and Chambers E1
Detention Pond 5 was designed to detain the stormwater runoff during a 100-year event
from Basin E within underground chambers.
Chambers E1 provides LID and water quality treatment for Basin E1 and Basin B8.
Redwood Detention Pond
As Basin F drains to the existing Redwood Pond, the Redwood Pond can be considered to
detain runoff from Basin F. Basin F is a 0.72 acre basin with a 25% imperviousness.
The total existing tributary area that drains to the Redwood Pond from the existing
neighborhoods is 49.8 acres of 70% imperviousness. Therefore, this small additional
basin area is minimal in comparison to the full tributary.
The Redwood Pond is planned to be updated by the City with the NECCO project. The
reconstruction of the pond will have a total 100 -year volume of 9.86 ac-ft (2.12 ac-ft of
that volume is water quality) and an updated outfall pipe (built by The Retreat). The
100-year depth shown in the NECCO report was shown at 4.65 feet deep.
The Redwood Pond was included in the SWMM model in order to see the effect this
additional area from Basin F will have on the proposed Redwood Pond. The addition of
Basin F was shown to raise the 100-year water level by about 0.04 ft and the total
volume by 0.13 ac-ft. This change is negligible.
A summary of the detention volumes and water quality volumes for each pond are found
below:
The Retreat @ Fort Collins
Preliminary Drainage Report 12
Table 2 – Detention Summary
Open Detention Pond Summary | Proposed Condition
Pond Pond Description
100-yr
Volume
(cf)
100-yr
Volume
(ac-ft)
100-yr WSEL WQCV
(cf) WQCV WSEL
Max
Release
(cfs)
1 Open Detention 116,789 2.68 4956.93 1,319 4956.93 0.70
2 Open Detention 112,201 2.58 4949.65 377 4956.52 1.60
3 Open Detention 9,363 0.21 4955.03 746 4857.14 3.80
4 Open Detention 17,091 0.39 4959.04 1,131 4956.80 2.25
Table 3 – Underground Chamber Summary
Underground Chamber Summary | Proposed Condition
Chamber Description
100-yr
Volume
(cf)
100-yr
Volume
(ac-ft)
100-yr WSEL WQCV
(cf) WQCV WSEL
Max
Release
(cfs)
A7 Underground LID n/a n/a n/a 5,507 to be provided at
final n/a
B2 Underground LID n/a n/a n/a 1,619 to be provided at
final n/a
B6 Underground LID n/a n/a n/a 3,124 to be provided at
final n/a
B9 Underground LID n/a n/a n/a 1,827 to be provided at
final n/a
E1/Pond
5
Underground LID and
Detention 7,683 0.18 to be provided at
final 676 to be provided at
final 0.20
C. Release Rate Compliance
The Retreat @ Fort Collins has a total combined area of 27.99 acres that are subject to
the 0.2 cfs/acre release rate as denoted per the NECCO design. As such, the total release
allowed from The Retreat @ Fort Collins site is 5.60 cfs. By adding the release from the
Redwood Pond (12 cfs), the total release allowable from all Ponds is 17.60 cfs.
Ponds 2, 3, 4, 5 and the Redwood Pond release directly into the proposed outfall pipe
connected to the NECCO Stormwater improvements. These ponds combined have a total
release of 19.85 cfs. This is 2.25 cfs more than the allowable from the site.
The undetained basin UD1 100-year runoff rate of 4.66 cfs combined with the additional
2.25 cfs release from the ponds shows an increase of release of 6.91 cfs. In order to
balance this undetained flow, off-site basins RW2, RW3, and RW5 were detained. These
off-site basins have a 100-year runoff rate of 5.08 cfs, 0.55 cfs, and 1.69 cfs (total 7.32
cfs).
By subtracting the existing undetained flow of 7.32 cfs from the proposed additional
developed flow of 6.91 cfs, it is shown that the development will decrease the stormwater
release from the site by 0.41 cfs.
The table on the next page illustrates these calculations:
The Retreat @ Fort Collins
Preliminary Drainage Report 13
Table 4 – Allowable Release Rate
Allowable Stormwater Release from Combined Redwood and Retreat Site
Basin Area
(acres)
100-yr Release
Rate (cfs)
Basin A 11.57 2.31
Basin B 11.3 2.26
Basin C 1.16 0.23
Basin D 1.66 0.33
Basin E 0.79 0.16
Basin F 0.72 0.14
UD1 0.79 0.16
Total On-site Release 27.99 5.60
Off-site Basins
RW1 3.42 12.71
RW2 1.08 5.08
RW3 0.1 0.55
RW4 1.2 5.65
RW5 0.31 1.69
Redwood Pond 49.8 12.00
Total Off-site Release 55.91 37.68
Total Release from Combined
Redwood and Retreat Basins 83.9 43.28
The Retreat @ Fort Collins
Preliminary Drainage Report 14
Table 5 – Proposed Release Rate
Proposed Stormwater Release from Combined Redwood and Retreat
Site
Pond/ Basin 100-yr Release
Rate (cfs)
Pond 2 1.60
Pond 3 3.80
Pond 4 2.25
Pond 5 0.20
Redwood Pond 12.00
Total Detention Release 19.85
Undetained Basins
RW1 12.71
RW4 5.65
UD1 4.66
Total Undetained Release 23.02
Total Release from Combined
Redwood and Retreat Basins 42.87
Based on this, the release from the site is well within the allowable release rate for the
site.
D. Low Impact Development (LID) Compliance
This site provides 73.5% treatment of new impervious area through a Low Impact
Development treatment facility. The LID treatment is provided through underground
detention and water quality chambers. These chambers will be designed as Stormtech
chambers at the time of final design.
The Retreat @ Fort Collins
Preliminary Drainage Report 15
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with The Retreat @ Fort Collins project complies with
the City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with The Retreat @ Fort Collins project complies with
the City of Fort Collins’ Master Drainage Plan for the Old Town Basin.
3. There are no regulatory floodplains associated with The Retreat @ Fort Collins
development.
4. The drainage plan and stormwater management measures proposed with The Retreat
@ Fort Collins development are compliant with all applicable State and Federal
regulations governing stormwater discharge.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit potential damage
associated with its stormwater runoff. The Retreat @ Fort Collins will detain for
proposed impervious area and release at a rate in conformance with the Dry Creek
major drainage basin of 0.2 cfs/acre.
2. The proposed The Retreat @ Fort Collins development will not impact the Master
Drainage Plan recommendations for the North East College Corridor Outfall (NECCO)
within Dry Creek major drainage basin.
The Retreat @ Fort Collins
Preliminary Drainage Report 16
References
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities ,
November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007 .
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
DRAFT FINAL
NORTH EAST COLLEGE CORRIDOR OUTFALL
(NECCO)
DESIGN REPORT
Prepared for
City of Fort Collins Utilities
700 Wood Street
Fort Collins, Colorado 80521
DRAFT FINAL
NORTH EAST COLLEGE CORRIDOR OUTFALL
(NECCO)
DESIGN REPORT
Prepared for
City of Fort Collins Utilities
700 Wood Street
Fort Collins, Colorado 80521
P.O. Box 270460
Fort Collins, Colorado 80527
(970) 223-5556, FAX (970) 223-5578
Ayres Project No. 32-0950.11
NECCO8TX.DOC
August 2009
i Ayres Associates
TABLE OF CONTENTS
1. Introduction ................................................................................................................1.1
1.1 Project Description..............................................................................................1.1
1.2 Purpose and Scope of Project.............................................................................1.1
1.3 Background.........................................................................................................1.3
1.4 Previous Studies .................................................................................................1.4
2. Project History............................................................................................................2.1
2.1 Alternative Analysis.............................................................................................2.1
3. Hydrology...................................................................................................................3.1
4. final storm sewer design and hydraulic analysis.........................................................4.1
4.1 Intersection of Blue Spruce and Bristlecone Drives.............................................4.6
4.1.1 Option 1: Storm Lines E1 and E2................................................................4.6
4.1.2 Option 2: Re-grade the Intersection ............................................................4.7
4.2 Evergreen West Pond.........................................................................................4.7
4.2.1 Evergreen West Swale.................................................................................4.8
4.3 Regional Pond.....................................................................................................4.8
4.3.1 Storm Line B1 ..............................................................................................4.9
4.3.2 Storm Line B2 ............................................................................................4.10
4.3.3 Storm Line B3 ............................................................................................4.11
4.3.4 Storm Line C1 and C2................................................................................4.12
4.4 Redwood Pond..................................................................................................4.13
4.5 East Vine Diversion Channel / Regional Detention Pond Outfall .......................4.15
4.5.1 Storm Line A1 ............................................................................................4.15
4.5.2 Storm Line A2 ............................................................................................4.17
4.5.3 Storm Line A3 ............................................................................................4.18
4.5.4 Storm Line A4 ............................................................................................4.18
4.6 EPA SWMM Hydraulic Summary ......................................................................4.18
5. Cost Estimate.............................................................................................................5.1
6. Water Quality and Erosion Control.............................................................................6.1
6.1 Temporary Sediment/Erosion Control Methods...................................................6.1
6.2 Permanent Sediment/Erosion Control Methods...................................................6.2
6.3 Materials Handling and Spill Prevention..............................................................6.3
6.4 Inspection and Maintenance................................................................................6.4
APPENDIX A – Modified Existing Condition ModSWMM Model...........................................--
APPENDIX B – ModSWMM Input/Output.............................................................................--
APPENDIX C – EPA SWMM Analysis Output......................................................................--
APPENDIX D – Inlet Calculations.........................................................................................--
APPENDIX E – Headwall and Wingwall Calculations...........................................................--
APPENDIX F – Regional and Redwood Pond Calculations..................................................--
APPENDIX G – Annotated 75% Review Comments ............................................................--
APPENDIX H – Meeting Minutes..........................................................................................--
ii Ayres Associates
LIST OF FIGURES
Figure 1.1. Vicinity map....................................................................................................1.2
Figure 1.2. North East College Corridor Outfall – limits of project. ...................................1.3
Figure 4.1. Proposed storm infrastructure........................................................................4.4
Figure 4.2. Future detention and water quality requirements............................................4.5
LIST OF TABLES
Table 4.1. Evergreen West Pond. ....................................................................................4.7
Table 4.2. Regional Pond.................................................................................................4.9
Table 4.3. Storm Line B2 Inlet Summary........................................................................4.11
Table 4.4. Storm Line B3 Inlet Summary........................................................................4.12
Table 4.5. Storm Line C1 and C2, 10- and 100-Year Inlet Summary..............................4.13
Table 4.6. Redwood Pond..............................................................................................4.14
Table 4.7. Dry Creek Tailwater Rating Curve. ................................................................4.15
Table 4.8. Storm Line A1, 10- and 100-Year Inlet Summary. .........................................4.16
Table 4.9. 100-Year EPA SWMM Hydraulic Summary...................................................4.19
1.1 Ayres Associates
1. INTRODUCTION
1.1 Project Description
In January 2007, the City of Fort Collins (City) awarded Ayres Associates a contract for the
final design of the North East College stormwater improvements. The project entails the
final design of a storm sewer system to mitigate local flooding (during a 100-year storm) in
the area generally north of East Vine Drive, west of Lemay Avenue, south of the Larimer and
Weld Canal, and east of College Avenue. The design incorporates a combination of storm
sewer and increased detention to convey local storm runoff to the future East Vine Diversion
Channel. The storm drainage design coordinates with the design efforts of the East Vine
Drive realignment, which is being done concurrently by Ayres Associates. A Vicinity map for
the project area is included on the following page (Figure 1.1).
1.2 Purpose and Scope of Project
The following work items were performed:
Task 1 – Meetings, Coordination, and Data Collection
• Project team kick-off meeting
• Progress meetings
• Utility coordination
• Supplemental surveys, Property ownership, and Legal Descriptions
• Geotechnical Data Collection
• Potholing
• Public Outreach
Task 2 – Analysis and Design
• Field investigation
• Hydrologic Analysis
• Hydraulic Analysis and Design
• Water Quality Pond Design
Task 3 – Preparation of Construction Plans
• Storm Sewer improvements design
• Estimate of Construction Cost
• Final design analysis report
1.2 Ayres Associates
Figure 1.1. Vicinity map.
1.3 Ayres Associates
1.3 Background
The North East College Corridor Outfall Drainage Improvements are located within the
Lower Dry Creek Basin. Generally, the Dry Creek Basin has been divided into the Upper,
Middle, and Lower Basins when studied. The Dry Creek Basin encompasses approximately
62 square miles and extends south from near the Wyoming border to where it discharges
into the Cache la Poudre River (Poudre River), near the intersection of Timberline Road and
Mulberry Street. The Upper Dry Creek Basin extends from the top of the watershed to
Douglas Reservoir. The Middle Basin extends from Douglas Reservoir to the point where it
discharges into the Larimer and Weld Canal. The Lower Basin includes the area south of
the Larimer and Weld Canal to the Poudre River. The specific limits of this project are from
the Larimer and Weld Canal downstream to where Dry Creek crosses East Vine Drive, just
east of Lemay Avenue, as shown in Figure 1.2.
Figure 1.2. North East College Corridor Outfall – limits of project.
The Lower Basin is mostly developed with commercial, residential, and industrial types of
development. There were several major flood control improvements in the upper and middle
basins that effectively reduced the floodplain for the lower basin. However, even with the
improvements in the Upper and Middle Basin, there is still significant flooding risk to the
study area from local drainage, primarily due to inadequately sized storm sewer lines, inlets,
and culverts.
1.4 Ayres Associates
1.4 Previous Studies
Several previous studies exist that investigated storm drainage in the project area. They
include:
• Dry Creek Master Plan (URS 2002)
• North College Drainage Improvements Design (NCDID) Alternative Analysis Report
(Ayres 2006)
The Dry Creek Master Plan prepared by URS in 2002 studied the area and identified several
drainage improvements in the area of the Lower Basin to eliminate overtopping at all of the
major street crossings within the project reach. The North College Drainage Improvements
Design Alternative Analysis Report by Ayres Associates in 2006 expanded on the URS
Master Plan in an attempt to further evaluate the flooding issues and provide a number of
cost effective and feasible alternatives to mitigate these concerns. This study and its
suggested alternate were used as the starting point for this design.
2.1 Ayres Associates
2. PROJECT HISTORY
2.1 Alternative Analysis
In 2006, Ayres Associates was contracted to prepare an alternative analysis of the North
College/Lemay channel drainage improvements. The goal of the project was to develop a
number of alternatives that would address the local flooding issues that occur in the Lower
Basin. The objective was to evaluate events not exceeding a 100-year storm, in the area
generally north of East Vine Drive, west of Lemay south of the Larimer and Weld Canal and
east of the UPRR. Due to the natural division of drainage areas, difficulty in crossing
College Avenue, and flow routing on the west side of College, the design team concluded
that the project area should be divided into two areas with College Avenue being the dividing
line. Five conceptual alternatives were identified and evaluated in order to find a cost
effective and constructible alternative that provided the most benefit to the North College
Corridor. Three alternatives (Alternative 1 thru 3) were developed for the west side of
College and two (Alternative 4 and 5) for the east side of College. The alternatives were as
follows:
1. Constructing a new storm sewer system along the west side of College within the
existing street configuration of Willox Lane, Hibdon, Hickory, and Mason Streets and to
provide two regional detention ponds to solve local flooding issues.
2. Constructing a new storm sewer system along the west side of College within the
proposed Mason Street Corridor and provide two regional detention ponds.
3. Constructing a new storm sewer system along the west side of College within the
proposed Mason Street Corridor without regional detention.
4. Construct a new storm sewer system along the east side of College within Red Cedar
Circle and provide regional detention south of Conifer Street. The outfall to the regional
detention pond would follow the future Vine Drive alignment.
5. Construct a new storm sewer system on the east side of College within Red Cedar Circle
and incorporating a drainage channel downstream of Lake Canal which will follow the
future Vine Drive alignment.
A conceptual design was prepared for each alternative that included the investigation of
potential utility conflicts. The designs included horizontal layouts, vertical profiles, and
construction cost estimates. Alternative 4, which incorporates a new storm sewer system
along Red Cedar Circle and providing regional detention south of Conifer Street, was the
recommended alternative due to groundwater and maintenance issues with constructing a
channel.
3.1 Ayres Associates
3. HYDROLOGY
The North College Drainage Improvements are located within the Lower Dry Creek Basin.
The Lower Basin is mostly developed with commercial, residential, and industrial types of
development. There are a number of flood mitigation projects in the Upper and Middle
Basins that will eliminate spills into the North College area out of the Larimer and Weld
Canal, from the upper and middle basins, for storms up to the 100-year recurrence interval.
For the North East College Corridor Drainage Improvements, Ayres started with the
developed conditions with existing facilities ModSWMM model from The Dry Creek Master
Plan, prepared by URS in 2002. Due to the flood mitigation projects, Ayres modified this
model to eliminate the spills from the Larimer and Weld Canal into the lower basin from the
upper and middle basin. This modified model was the starting point for the North East
College Corridor Outfall (NECCO) hydrologic model (see Appendix A for the model output
and the project CD for the electronic model).
The black and white aerial photography that was obtained for the North College Drainage
Improvements Project (NCDID) was used to update and add basins that were previously
delineated for the NCDID project. Each design point, where flow enters the system, was
added to the NCDID model. These basins were added to quantify the stormwater runoff
during the 100-year event to proposed inlets and conveyance elements along the system.
For the inlets proposed along the re-aligned Vine Drive, a 10-year model was run to quantify
flow at each location. The ModSWMM hydrologic parameters were re-evaluated and
adjusted as necessary. Those parameters that were adjusted include:
• Basin Area –revised to obtain a more detailed model
• Basin Slope – revised based on new basin areas
• Basin Width – determined based on the equation: A/Ltr = Basin Width
Where: Ltr = average length of overland flow path (300 ft maximum)
A = area of revised sub-basin
• Percent Impervious – based on the new aerial photography, five to six representative
areas were measured for percent impervious values, and then those values were applied
to the larger sub-basins. For undeveloped areas in the developed condition model, the
percent impervious values were determined from zoning maps and the associated
percent impervious given in the City's Drainage Criteria Manual
The infiltration parameters were reviewed and left unchanged from the Dry Creek Master
Plan ModSWMM model. Included in table format in Appendix B are the updated
ModSWMM basin parameters for NECCO and the 100-year hydrographs (refer to the project
CD for the 10- and 100-year ModSWMM model). Routing for the NECCO project area was
done using EPA SWMM 5.0.013. The inflow hydrographs developed in ModSWMM were
imported into the EPA SWMM model with updated conveyance element routing. The
physical parameters of length and average slope were measured from the updated 1-foot
contour mapping developed for the NCDID. The routing information for the existing storm
sewer diameters and slopes was updated from field investigation, field survey, and from data
provided in the City of Fort Collins Storm Water Inventory Notebooks from the utility
department. Some of the slopes were determined from outfall inverts and field measured
depths to the storm sewer (refer to the project CD for the updated EPA SWMM 5.0.013
model of the project area).
3.2 Ayres Associates
From the previous NCDID study, the results showed that the existing storm sewer within the
NECCO project area is undersized for the 2-year storm event.
During the final design process the following assumptions were made for each of the
basins:
• Basin 102 will discharges into the Blue Spruce Channel once developed via storm
sewer. This storm sewer was not design with the NECCO project. The ModSWMM
model accounts for the east half of the intersection of Willox and College to drain east
towards Blue Spruce, to be intercepted by the proposed inlets in Bristlecone Drive and
then discharge into the Blue Spruce channel that outfall into the Evergreen West Pond.
The west side of the intersection is assumed to drain west along Willox as it currently
drains today. The potential for an improved intersection at College and Willox is not
accounted for in this design.
• Basin 103 consists of the existing Albertson shopping center. The shopping center
drains to a detention pond at the south end of the basin. This detention pond ultimately
drains to the Evergreen West Pond.
• Basin 104 is a large developed basin that ultimately drains into the Evergreen West
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 108 ultimately drains to the Evergreen East Pond via overland flow, curb and
gutter or an existing storm sewer system. This Evergreen East Pond was modeled as
ultimately draining into the proposed storm sewer Line A4. If redeveloped, the existing
drainage patterns are to remain, or be improved, and the basin will ultimately drain into
the proposed system.
• Basin 109 was modeled as ultimately draining into proposed storm sewer Line A4. If
redeveloped, the existing drainage patterns are to remain, or be improved, and the basin
will ultimately drain into the proposed system.
• Basin 111 was modeled as ultimately draining into proposed storm sewer Line A4. If
redeveloped, the existing drainage patterns are to remain, or be improved, and the basin
will ultimately drain into the proposed system.
• Basin 112 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. A overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 113 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole A4.
• Basin 114 is currently an undeveloped basin. It will drain into the future east Vine
Diversion Channel.
3.3 Ayres Associates
• Basin 115 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole A1.
• Basin 116 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole Riser A6.
• Basin 117 is currently an undeveloped basin. It was modeled as a developed basin that
drains into the proposed storm sewer downstream of Manhole Riser A5.
• Basin 118 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. A overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 119 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 120 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 122 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 123 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 124 drains via curb and gutter to the intersection of Conifer and Red Cedar Circle
to proposed Inlet B4B. If redeveloped, the basin will continue to drain to this inlet.
• Basin 124 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 126 is currently an undeveloped basin. It was modeled as a developed basin that
drains to proposed Manhole B.
3.4 Ayres Associates
• Basin 127 is currently an undeveloped basin. It was modeled as a developed basin that
drains to proposed Manhole C.
• Basin 128 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. A overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 203 discharges into the Albertson shopping center detention pond and ultimately
to the Evergreen West pond. If the Albertson detention pond is removed, the
development will need to account for drainage from basins 103 as well as 203.
• Basin 204 drains to the existing inlets at the intersection of Bristlecone Drive and Blue
Spruce Drive and ultimately into the Evergreen West Pond. This intersection will need to
be improved with either grading or new storm sewer. If redeveloped, the existing basin
drainage patterns need to remain or be improved.
• Basin 205 discharges to an existing storm sewer system along the east side of the
Albertson Shopping center. This storm sewer ultimately discharges into Evergreen West
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 206 drains to proposed Inlet B7A, If redeveloped, the basin will continue to drain
to this inlet.
• Basin 207 drains to the existing inlets at the intersection of Bristlecone Drive and Blue
Spruce Drive and ultimately into the Evergreen West Pond. This intersection will need to
be improved with either grading or new storm sewer. If redeveloped, the existing basin
drainage patterns need to remain or be improved.
• Basin 209 drains to proposed Inlet B8A. If redeveloped, the basin will continue to drain
to this inlet.
• Basin 213 drains overland to an existing drainage swale to the east of the basin and
ultimately to proposed Inlet A6. If redeveloped, the basin will continue to drain to this
inlet. The drainage swale on the east side of the basin can be removed as long as the
basin ultimately drains to the proposed storm sewer system.
• Basin 214 drains to the existing inlets at the intersection of Bristlecone Drive and Blue
Spruce Drive and ultimately into the Evergreen West Pond. This intersection will need to
be improved with either grading or new storm sewer.
• Basin 221 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
3.5 Ayres Associates
• Basin 224 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole B6.
• Basin 225 drains via curb and gutter to proposed Inlet B10A and to the intersection of
Conifer and Blue Spruce (proposed Inlets B9A and B9B). If redeveloped, the basin will
continue to drain to these inlets.
• Basin 226 drains overland to proposed Inlet B5A. If redeveloped, the basin will continue
to drain to the inlet. This basin drains through basins 326 and 426 and will need to
accounted for in the drainage of these basins.
• Basin 227 drains overland to the intersection of Conifer and Red Cedar Circle to
proposed Inlets B4A and B4B. If redeveloped, this basin will continue to drain to these
inlets. This basin drains through basins 228, 328 and 229 and will need to accounted for
in the drainage of these basins.
• Basin 228 drains overland to the intersection of Conifer and Red Cedar Circle to
proposed Inlets B4A and B4B. If redeveloped, this basin will continue to drain to these
inlets. Basin 227 drains through this basins and will need to be accounted for in the
redevelopment of basin 228.
• Basin 229 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole B5.
• Basin 230 drains overland to the Evergreen West pond outlet swale to the east of the
basin. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 304 discharges to an existing storm sewer system along the east side of the
Albertson Shopping center. This storm sewer ultimately discharges into Evergreen West
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 305 is an undeveloped basin that discharges to an existing storm sewer system
along the east side of the Albertson Shopping center. This storm sewer ultimately
discharges into Evergreen West Pond. When developed, the existing basin drainage
patterns need to remain or be improved.
• Basin 306 drains to the existing inlets at the intersection of Bristlecone Drive and Blue
Spruce Drive and ultimately into the Evergreen West Pond. This intersection will need to
be improved with either grading or new storm sewer. If redeveloped, the existing basin
drainage patterns need to remain or be improved.
• Basin 313 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole Riser A8.
• Basin 315 drains overland and through existing storm sewer to proposed Inlet C3. If
redeveloped, the basin will continue to drain to this inlet.
3.6 Ayres Associates
• Basin 316 currently drains to an onsite detention ponds. This pond will be removed with
the construction of the re-aligned Vine Drive. The basin will flow overland to proposed
Inlet C4B. If redeveloped, the basin will continue to drain to this inlet.
• Basin 317 was modeled as discharging into proposed Manhole C7. The proposed storm
sewer required to connect the basin to the proposed manhole was not designed with the
NECCO project.
• Basin 318 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet C4A.
• Basin 320 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole A1. The storm sewer that would be required to connect
this basin with the proposed manhole was not designed with the NECCO project.
• Basin 321 was modeled as discharging into proposed Manhole A1. The storm sewer
that would be required to connect this basin with the proposed manhole was not
designed with the NECCO project.
• Basin 324 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole B6. Basin 424 drains through this basin and will need to
be accounted for in the development of basin 324 and 326.
• Basin 326 drains overland to proposed Inlet B6A. If redeveloped, the basin will continue
to drain to the inlet. Basin 424 and part of Basin 226 drain through this basin and will
need to be accounted for in the redevelopment of basins 326 and 324.
• Basin 327 is currently an undeveloped basin. This basin contains the proposed regional
Detention Pond.
• Basin 328 drains to an existing onsite detention pond. This pond will connect into the
proposed storm sewer at Manhole B5. If redeveloped, the existing basin drainage
patterns need to remain or be improved and ultimately connect into the proposed
manhole.
• Basin 330 is currently an undeveloped basin. It was modeled as a developed basin that
drains into the Evergreen West Pond outlet swale just east of the basin.
• Basin 407 drains to an existing onsite detention pond. This pond will connect into the
proposed storm sewer at Manhole Riser C2. If redeveloped, the basin can discharge
directly into the proposed storm sewer and the detention pond can be removed.
• Basin 408 is currently an undeveloped basin. It was modeled as a developed basin that
drains to proposed Manhole C1.
• Basin 410 is the Old Town North development. This basin currently discharges into an
existing detention pond with ultimately discharges into Lake Canal. With the NECCO
project, this basin will continue to discharge into the existing detention pond. However, a
storm sewer (A3) was designed to pick up the flow from the detention pond and re-route
them from the Lake Canal and into the proposed storm sewer (Line A).
3.7 Ayres Associates
• Basin 412 is currently an undeveloped basin consisting of the Raptor Center. It was
modeled as a developed basin that drains into proposed Manhole A1. The storm sewer
that would be required to connect this basin with the proposed manhole was not
designed with the NECCO project.
• Basin 413 is currently an undeveloped basin. It was modeled as a developed basin that
drains into the proposed Regional Detention Pond. The storm sewer that would drain
this basin to the proposed detention facility was not designed with the NECCO project.
The future pipe will cross the re-aligned Vine Drive. This pipe crossing must take into
account the GWET and NEWT waterline clearances. These clearances are very critical.
• Basin 414 consists of the Alta Vista development. If redeveloped, the basin was
modeled as discharging into proposed Manhole Riser A4 (or downstream of transition
A1). The storm sewer that would be required to connect this basin with the proposed
manhole was not designed with the NECCO project.
• Basin 417 is currently an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole Riser A3.
• Basin 417 is currently an undeveloped basin. It will drain into the future east Vine
Diversion Channel.
• Basin 418 is currently an undeveloped basin. It was modeled as a developed basin that
drains downstream of the proposed Manhole Riser A2.
• Basin 419 is currently an undeveloped basin. It will drain into the future east Vine
Diversion Channel.
• Basin 420 is currently an undeveloped basin. It will drain into the future east Vine
Diversion Channel.
• Basin 421 is currently an undeveloped basin. It will drain into the future east Vine
Diversion Channel.
• Basin 422 is currently an undeveloped basin. It will drain into the future east Vine
Diversion Channel.
• Basin 424 drains overland to proposed Inlet B6A. If redeveloped, the basin will continue
to drain to the inlet. This basin drains through basins 324 and 326 and will need to
accounted for in the drainage of these basins.
• Basin 426 is currently an undeveloped basin. It was modeled as a developed basin that
drains to proposed Manhole B5. Basin 226 drains through this basin and will need to be
accounted for in the redevelopment of basin 426.
• Basin 427 drains overland to proposed Inlet B6A.
• Basin 510 currently drains into the Lake Canal. This basin was not further analyzed with
the NECCO project.
3.8 Ayres Associates
• Basin 512 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 513 ultimately drains to the Evergreen East Pond via overland flow, curb and
gutter or an existing storm sewer system. This Evergreen East Pond was modeled as
ultimately draining into the proposed storm sewer Line A4. If redeveloped, the existing
drainage patterns are to remain, or be improved, and the basin will ultimately drain into
the proposed system.
• Basin 517 was modeled as discharging into proposed Manhole C7. The proposed storm
sewer required to connect the basin to the proposed manhole was not designed with the
NECCO project.
• Basin 524 drains via curb and gutter to proposed Inlet B10A. If redeveloped, the
development will tie into proposed Manhole B9.
• Basin 526 is currently an undeveloped basin. It was modeled as a developed basin that
drains to the proposed Regional Detention Pond.
• Basin 604 is currently a undeveloped basin. It was modeled as a developed basin that
drains to the intersection of Blue Spruce Drive and Bristlecone Drive and ultimately to the
Evergreen West Pond via storm sewer. This storm sewer was not designed with the
NECCO project.
• Basin 612 is currently an undeveloped basin which ultimately drains to the Redwood
Pond via overland flow, curb and gutter or an existing storm sewer system. An overflow
weir at Redwood Pond will ultimately need to be constructed in order to insure the
conveyance of the storm flows into the Redwood Pond. If redeveloped, the existing
basin drainage patterns need to remain or be improved.
• Basin 624 is mainly an undeveloped basin. It was modeled as a developed basin that
drains into proposed Manhole B2. It can also drain into proposed Manhole B1.
• Basin 625 is mainly an undeveloped basin. It currently drains via curb and gutter to the
intersection of Conifer and Blue Spruce to proposed Inlet B9A. It was modeled as a
developed basin that connected into proposed Inlet B9A.
• Basin 626 drains via curb and gutter to proposed Inlet B10B. If redeveloped, the basin
will continue to drain to these inlets.
• Basin 627 drains via curb and gutter to the intersection of Conifer and Blue Spruce to
proposed Inlet B9B. If redeveloped, the basin will continue to drain to this inlet.
• Basin 628 drains via curb and gutter to the intersection of Conifer and Blue Spruce to
proposed Inlet B9A.
3.9 Ayres Associates
• Basin 704 drains to the existing inlets at the intersection of Bristlecone Drive and Blue
Spruce Drive and ultimately into the Evergreen West Pond. This intersection will need to
be improved with either grading or new storm sewer. If redeveloped, the existing basin
drainage patterns need to remain or be improved.
• Basin 712 ultimately drains to the Redwood Pond via overland flow, curb and gutter or
an existing storm sewer system. An overflow weir at Redwood Pond will ultimately need
to be constructed in order to insure the conveyance of the storm flows into the Redwood
Pond. If redeveloped, the existing basin drainage patterns need to remain or be
improved.
• Basin 726 drains to the Evergreen West Pond outlet swale through a proposed curb-cut
on the south side of Conifer.
• Basin 810 is currently an undeveloped portion of the Old Town North Development. It
was modeled as a developed basin that drains into the proposed Regional Detention
Pond. The storm sewer that is required to connect this basin to the proposed detention
facility was not designed with the NECCO project. The future pipe will cross the re-
aligned Vine Drive. This pipe crossing must take into account the GWET and NEWT
waterline clearances. These clearances are very critical.
• Basin 812 was modeled as Redwood Pond. It will discharge into Storm Line A2.
• Basin 912 is currently an undeveloped basin. It was modeled as a developed basin that
drains into the Evergreen West Pond outlet swale just west of the basin.
• Basin 930 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet C6B.
• Basin 931 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet C6A.
• Basin 950 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A5B.
• Basin 951 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A5A.
• Basin 960 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A7B.
• Basin 961 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A7A.
• Basin 970 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A8B.
• Basin 971 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A8A.
3.10 Ayres Associates
• Basin 980 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A9B.
• Basin 981 is currently an undeveloped basin. It was modeled as a developed basin
consisting of the re-aligned Vine Drive and to proposed Inlet A9A.
Refer to Exhibit 1 in Appendix B for the updated 100-year ModSWMM Basin Map.
4.1 Ayres Associates
4. FINAL STORM SEWER DESIGN AND HYDRAULIC ANALYSIS
ModSWMM was used to develop the basin hydrographs only, while EPA SWMM 5.0.013
was used for the hydraulic routing of the basins in the developed condition with proposed
facilities model. EPA SWMM was used to model the inflows and outflows of the existing
Evergreen West and Redwood Ponds as well as model the proposed storm sewer lines A, B,
C, and E.
The input requirements for the EPA SWMM 5.0.013 model include the following:
• Pipe lengths, diameters, inverts and material
• Reservoir stage vs. area information for each pond
• Inflow hydrographs – These were developed from the ModSWMM analysis described
previously
• Geometry of outlet structures, i.e., weirs, orifices etc.
UD Inlet version 2.14a was used to size inlets for each system. The City of Fort Collins
Storm Drainage Criteria was followed to determine the street carrying capacity and
encroachment for the 100-year storm event. The same criterion was followed to size the
inlets along re-aligned Vine Drive for the 10-year storm event. Snout oil-water debris
separators are incorporated into the design of the inlets along realigned Vine Drive (refer to
Appendix D for the inlet calculations).
Following is a list summarizing the detention and water quality assumption made for
each basin during the final design process:
• Undeveloped properties east of Redwood require future on-site detention and water
quality. These basins were modeled assuming a proposed detention facility 100-year
release rate of 0.2 cfs/acre.
- Basins: 113, 114*, 115, 116, 117, 313, 320, 412, 417, 418, 419*, 420*, 421*, 422*
*These basins do not discharge into the proposed NECCO Storm Sewer.
• The undeveloped area south of Conifer Street, west of Redwood and north of the
proposed re-aligned Vine Drive would discharge into the regional pond without on-site
detention or water quality.
- Basins: 126, 127, 327*, 408, 526, 726
*Proposed Regional Detention Pond
• Dry Creek, behind Autozone and south to the Proposed East Vine Drive, will be filled in.
Currently basins 407, 316 and 315 drain into Dry Creek.
Currently Basin 407 drains into an existing detention pond. This pond will be connected
into the proposed storm sewer. This pond can be removed as long as basin 407
ultimately discharges into the proposed NECCO storm sewer system.
Currently Basin 316 drains into an existing detention pond. This pond will be removed
with the construction of the re-aligned Vine Drive. The flow that currently travels to the
southern pond will be conveyed overland to Vine Drive where it will be collected in the
proposed storm sewer.
4.2 Ayres Associates
Basin 316 currently discharges into Dry Creek via overland flow and an existing storm
sewer. With the removal of Dry Creek, the basin will discharge into the proposed
NECCO storm sewer.
Conveyance, detention, and water quality will be provided for these basins in the regional
detention pond. If these basins are re-developed, the current percent impervious value
(as modeled) as well as the total runoff for the basin will need to be maintained. If these
values are increased then detention will be required so the total runoff matches current
conditions. Water quality does not need to be provided.
- Basins and current I% (percent impervious):
315 (85%), 407 (49.2), 316 (44.4%)
• The undeveloped area north of Conifer Street would provide on-site detention when
development occurs. Water Quality will not need to be provided. These basins were
modeled assuming a proposed detention facility 100-year release rate of 0.2 cfs/acre.
- Basins: 102, 224, 229, 305, 324, 330, 426, 604, 624, 625
• Re-developing land north of Conifer Street would be required to provide the same
amount of detention that they currently provide. The re-developing land will need to
maintain the current percent impervious value (as modeled) as well as the total runoff for
the basin. If these values are increased then detention will be required so the total runoff
matches current conditions during a 100-year event. Water quality does not need to be
provided.
- Basins and current I% (percent impervious): 104 (49.6%), 124 (85%), 203 (85%),
204 (85%), 205 (86.7%), 206 (85%), 207 (85%), 209 (85%), 214 (85%), 225 (85%),
226 (85%), 227 (85%), 228 (85%), 230 (85%), 304 (85%), 306 (85%), 326 (85%),
328 (85%), 424 (85%), 427 (85%), 524 (85%), 626 (89.4%), 627 (85%), 628 (85%),
704 (85%)
• The Albertson Shopping Center detention pond, located southwest of Albertsons on
basin 103, currently discharges into a storm sewer that runs east along Bristlecone Drive
and outfalls into a swale that enters the Evergreen West Pond. The analysis assumed
that the existing Albertsons pond would be removed once the downstream improvements
are built. Albertsons will be required to collect their undetained storm runoff and convey
it to the Evergreen West Pond. The Evergreen West swale has the capacity to convey
undetained flows from Albertsons. However, the developer will need to analyze the
proposed outfall with the NECCO improvements as well as with existing conditions prior
to removal of the pond. Basin 203 currently drains into the Albertson Center Detention
Pond. With the removal of the detention pond, the flows from basin 203 will need to be
accounted for in the design of the new storm sewer.
- Basins: 103
• Re-developed properties east of Redwood will need to maintain the current percent
impervious value (as modeled) as well as the total runoff for the basin during a 100-year
event. If these values are increased then detention will be required so the total runoff
matches current conditions during a 100-year event. The developments have to provide
onsite water quality.
- Basins and current I% (percent impervious):
213 (55%), 414 (66.5), 321 (67.4%)
4.3 Ayres Associates
• Inlets located along re-aligned Vine Drive would be constructed with the roadway project
and will be adjusted as needed per final design of the re-aligned Vine Drive. These
basins do not require detention and water quality will be provided through the use of
BMP Snouts.
- Basins: 318, 930, 931, 950, 951, 960, 961, 970, 971, 980, 981
• Existing storm sewer in Redwood Street, combined with the street capacity, meets the
City of Fort Collins street criteria for the 100-year event, therefore it is considered
adequate. Re-developed properties will need to maintain the current percent impervious
value (as modeled) as well as the total runoff for the basin during a 100-year event. If
these values are increased then detention will be required so the total runoff matches
current conditions during a 100-year event. The developments do not have to provide
onsite water quality, it will be provided in the Redwood Pond.
- Basins and current I% (percent impervious): 112 (64.5%), 118 (55%), 119 (60.2%),
120 (65.4%), 121 (30.7%), 122 (5%), 123 (55%), 128 (5%), 221 (85%), 512 (55%),
612 (5%), 712 (70.8%), 812 (----)*
*Redwood Pond
• Due to the location of the following basins, water quality and detention does not need to
be provided if the basins ultimately discharge into the Regional Detention Pond. It will be
provided in the proposed Regional Detention Pond.
- Basins: 912, 810, 413
• Re-developed properties south of the re-aligned Vine Drive will need to maintain the
current percent impervious value (as modeled) as well as the total runoff for the basin
during a 100-year event. If these values are increased then detention will be required so
the total runoff matches current conditions during a 100-year event. The developments
do not have to provide onsite water quality, it will be provided in the Redwood Pond.
- Basins and current I% (percent impervious):
317 (37.6%), 517 (49.1%)
• The Old Town North Basin provides its own detention and water quality. The proposed
storm Line A3 will connect into the outlet of the existing detention pond for the
development. Water quality and detention is not provided in the proposed Regional
Detention Pond.
- Basin: 410
• Rating Curves for the ponds which currently contain water, i.e., The Evergreen West
Pond and the Redwing Marsh Pond, start at the "normal pool" water surface elevation.
The "normal pool" water surface elevation is the normal/constant water surface elevation
in the pond based on the elevation of the pond outlet. The rating curve therefore, does
not take into account the full volume in the pond, just the volume available for storage
above the elevation of the outlet. This was done because the pond volume below the
pond outlet is typically full of water prior to a storm event and therefore not available for
storage.
The 100-year EPA SWMM model results are included in Appendix C.
Figure 4.1 represents the backbone structure of the proposed storm infrastructure as
described in the following sections. Figure 4.2 depicts the future detention and water quality
requirements as mentioned above.
4.4 Ayres Associates
Figure 4.1. Proposed storm infrastructure.
LEGENDDRAINAGE BASINBASIN NUMBERBASIN AREA (ACRES)EXHIBIT 4.2FUTURE DETENTION AND WATER QUALITY REQUIREMENTSRESTRICT AMOUNT OF RUNOFFTO EXISTING CONDITIONS IFRE-DEVELOPED. WATER QUALITYPROVIDED IN REDWOOD PONDREQUIRE FUTURE ON-SITEDETENTION & WATERQUALITY. RELEASE RATE @ 0.20 cfs/acreREQUIRE FUTURE ON-SITEDETENTION.WATER QUALITY PROVIDEDIN REGIONAL POND.FUTURE RE-ALIGNED VINEDRIVE. WATER QUALITYPROVIDED WITH SNOUTS.DISCHARGE INTOREGIONAL POND WITHOUTFUTURE DETENTION ORWATER QUALITY.RESTRICT AMOUNT OF RUNOFFTO EXISTING CONDITIONS IFRE-DEVELOPED. FUTURE WATERQUALITY REQUIRED.RESTRICT AMOUNT OF RUNOFFTO EXISTING CONDITIONS IFRE-DEVELOPED. WATER QUALITYPROVIDED IN REGINAL POND.BASIN 103: NO DETENTION ORWATER QUALITY REQURED IFDISCHARGING INTOEVERGREEN WEST PONDCOLLEGE AVENUERED CEDAR CIRCLELEMAY AVENUE
DRY CREEK BRISTLECONE DRIVECONIFER STREETNOKOMIS COURTBLUE SPRUCE DRIVE
CONIFER STREETLUPINE DRIVEREDWOODPONDREGIONALPONDREDWOOD STREETCOLLEGE AVENUEJEROME STREETBONDELL STREET OSIANDER STREETEAST VINE DRIVE70.0 ac68.2 ac13.2 ac18.5 ac8.7 ac29.3 ac11.4 ac9.8 ac11.4 ac4.8 ac16.4 ac3.3 ac1.3 ac31.6 ac52.7 ac21.3 ac7.4 ac18.1 ac17.0 ac2.5 ac2.7 ac2.0 ac4.6 ac2.5 ac13.1 ac3.9 ac13.7 ac1.8 ac0.2 ac7.2 ac6.0 ac3.8 ac0.6 ac2.4 ac5.2 ac1.6 ac2.6 ac35.7 ac2.6 ac1.8 ac1.8 ac1.6 ac1.2 ac0.7 ac4.2 ac2.6 ac13.6 ac13.0 ac8.6 ac7.1 ac5.1 ac4.5 ac4.2 ac10.9 ac8.2 ac19.2 ac16.0 ac32.4 ac17.5 ac9.8 ac16.6 ac29.3 ac6.0 ac10.3 ac5.9 ac1.5 ac1.3 ac21.2 ac1.2 ac1.5 ac1.1 ac1.1 ac8.2 ac1.0 ac8.6 ac5.2 ac14.8 ac2.0 ac1.6 ac3.3 ac1.4 ac5.3 ac1.2 ac1.0 ac2.7 ac2.2 ac3.9 ac3.3 ac3.4 ac4.4 ac7.9 ac0.2 ac4.2 ac1.1 ac1.7 ac2.4 ac2.0 ac1.0 ac36.2 ac5.5 ac49.1 ac
4.6 Ayres Associates
4.1 Intersection of Blue Spruce and Bristlecone Drives
The intersection of Blue Spruce and Bristlecone Drives contains an undersized storm sewer
system. During minor events, less than a 2-year, the existing storm sewer system collects
storm runoff and conveys it into the Evergreen West Pond. During larger events, the storm
sewer system reaches capacity and storm runoff overtops the highpoint in Blue Spruce and
travels south to an existing storm sewer system that has also reached its capacity. To
ensure that storm water at this intersection is being conveyed to the Evergreen West Pond,
this system requires improvements. There are two options for this intersection:
1. Upgrade the existing storm sewer to convey the majority of the 100-year underground to
the Evergreen West Pond,
2. Re-grade the Blue Spruce and Bristlecone Drives intersection so the storm runoff drains
overland to the Evergreen West Pond.
The storm sewer option, along with the intersection grading option, will need to be analyzed
in further detail prior to final design. An estimated cost comparison can be found in section
5.0.
4.1.1 Option 1: Storm Lines E1 and E2
In order to convey the 100-year underground at the intersection of Blue Spruce and
Bristlecone Drives, the existing storm sewer system will be replaced with Storm Lines E1 and
E2. This option is shown in the drawing set for the NECCO project.
Storm Line E1 runs east to west just north of the Blue Spruce and Bristlecone intersection.
This system is comprised of 6-Type 13 combination inlets (Inlet E1A ) and dual 30-inch RCP
storm sewer. This system will replace the existing undersized system. Inlet E1A is located
in a sump and will capture 67 cfs before overtopping the centerline at 4971.29. The
remaining 12 cfs will carry-over to Inlet E2B. The 67 cfs captured at Inlet E1A accounts for
the overflow from Inlet B7A (approximately 4 cfs). An existing 18-inch storm sewer from the
west will also connect into Inlet E1. A new 8-foot diameter manhole will replace an existing
manhole located within the intersection and connect the existing 24-inch system from the
north.
Storm Line E2 runs east to west just south of the Blue Spruce and Bristlecone intersection.
This system is comprised of 6-Type 13 combination inlets (Inlet E2A and Inlet E2B), 30-inch
RCP storm sewer, and dual 30-inch RCP storm sewer. This storm sewer will replace an
existing undersized system. Inlet E2A is located in a sump and will capture the 12 cfs of
carryover flow from Inlet-E1A and an additional 18 cfs with 100% capture. Inlet E2B is also
located in a sump and will capture 100% of the 20 cfs flowing to it.
The existing headwall will be replaced with a new headwall incorporating the dual 30-inch
pipes from Storm Line E1 and E2.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of Storm Sewer Lines E1 and E2.
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4.1.2 Option 2: Re-grade the Intersection
In order to convey the 100-year above ground and into the Evergreen West Pond, the
intersection will need to be regarded. Along with regrading the intersection, a sidewalk
chase will be need to be constructed totaling an approximate length of 75 ft. This will allow
the storm water to flow under the sidewalk on a regular basis. Erosion control protection will
need to be provided downstream of the weir and the existing headwall will need to be
modified to allow the storm flows to flow overtop. Appendix G contains an exhibit that was
created to demonstrate the general idea for this option.
Hydraulic Modeling
No Hydraulic modeling was performed for this option.
4.2 Evergreen West Pond
W ith the construction of either option 1 or 2, flows will be added into the Evergreen West
Pond. Due to this added inflows into the Evergreen West Pond, the outlet structure and the
southeast end of the pond need improvement. The outlet will be increased to a 34- by 53-
inch HERCP pipe. The upstream and downstream headwalls will be replaced to
accommodate the improved outlet. Currently a swale, at the southeast corner of the pond,
runs east just north of Nokomis Court. This swale overtops at an elevation of approximately
4964.5. To prevent overtopping, this swale needs to be bermed up to an elevation of
4965.5. This is shown to more detail in the plan set for the NECCO project (sheet C-236).
Table 4.1 shows the major characteristics of the Evergreen West Pond.
Table 4.1. Evergreen West Pond.
Description
Elevation
(ft)
Pond
Volume
(ac-ft)
Normal Pool 4962.07 ---
Top of Pond 4965.50 11.39
100-year WSEL 4965.04 9.41
WSEL = Water Surface Elevation
EPA SWMM Hydraulic Modeling
The Evergreen West Pond was modeled with EPA SWMM. The rating curve for the
Evergreen West Pond was determined from a combination of the 1-foot aerial topography
flown in December 2004 and information provided in the Evergreen West drainage report.
The aerial photo and topography indicated a constant depth of water (or normal pool) in the
Evergreen West Pond which does not "see" past the water surface elevation. The constant
depth of water cannot be used as storage; as a result the pond rating curve starts at the
"normal pool" water surface elevation. The rating curve therefore, does not take into
account the full volume in the pond, just the volume available for storage.
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4.2.1 Evergreen West Swale
The Evergreen West Pond currently outlets at the south end of the pond and into a swale.
The swale runs south to three existing 42-inch culverts under Conifer Street. These culverts
run under Conifer and continue south to Dry Creek. With this project, the 42-inch culverts
were analyzed and found to have adequate capacity to convey the 100-year design storm.
The swale just south of the culvert will be redirected into the proposed Regional Detention
Pond. The swale will convey approximately 133 cfs to the existing culverts at Conifer Street
and ultimately to the proposed Regional Detention Facility. Scour stop will be installed at the
outlet of this channel into the regional detention pond. Scour stop was sized by the
manufactured.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of the triple 42-inch pipes under Conifer Street
and the Evergreen West drainage swale. The proposed design shows that both conveyance
elements have the capacity to carry the additional flow from the Evergreen West Pond and
local drainage during a 100-year event.
4.3 Regional Pond
The proposed location of the regional detention/water quality pond is south and east of the
intersection of Conifer Street and Blue Spruce Drive, along the west side of Redwood Street
and north of the Old Town North Development. This location was selected in the NCDID
study to utilize the un-developable land beneath the existing power lines as much as
possible. The detention portion of the regional pond requires a total volume of 30.02 ac-ft
(including water quality), a surface area of 8.5 acres and an approximate depth of 11 ft. The
water quality portion of the pond requires an additional 10.44 ac-ft of storage which would be
placed below the detention storage. A 20-foot wide, 3-foot deep low flow channel with a 4-
foot concrete pan will be incorporated into the design of the pond. An additional 4-foot
concrete pan will be incorporated to convey nuisance flows from Storm Line C2. Undulating
slopes varying from 3:1 to 5:1 are graded along the perimeter of the pond to create less of a
"bathtub" looking pond.
During final design of the NECCO storm sewer, the following assessments of the Regional
Detention Pond need to be completed:
• Public outreach will need to be completed in order to determine the final nature and
aesthetics of the Regional Detention Pond.
• Geotechnical borings will need to be taken in order to perform a detailed groundwater
investigation. The groundwater investigation will used to determine the following:
- An appropriate groundwater system to lower the groundwater surrounding the
detention pond. This system could include, but is not limited to, an under drain
network, a slurry wall or perimeter drains.
- An appropriate groundwater dewatering system during construction and possible
dewatering discharge locations.
- The stability of the pond slopes due to the high groundwater in the area.
4.9 Ayres Associates
Table 4.2 shows the major characteristics of the proposed Regional Pond.
Table 4.2. Regional Pond.
Description
Elevation
(ft)
Pond
Volume
(ac-ft)
Pond
Depth
(ft)
Pond Invert 4947.00 --- ---
Water Quality
WSEL 4953.36 10.44 6.36
100-year WSEL 4957.93 40.46 10.94
Spillway Elevation 4958.00 40.96 11.00
WSEL = Water Surface Elevation
Four storm sewer systems outfall into the proposed regional detention pond. The pond
outfall will discharge into a proposed storm sewer and ultimately tie into the future East Vine
Diversion Channel. This storm system will collect additional flow from Old Town North, the
Redwood Pond, and the Green briar Outfall before discharging into the future channel.
These proposed systems are discussed further in the sections below.
The outlet structure for the regional pond is a combination of two Type D inlets in series.
The inlets will be separated by a steel plate with an orifice opening sized to provide a 40-
hour drain time for the water quality portion of the pond. One of the frequent maintenance
issues associated with water quality structures is the clogging of the orifice plates. For this
reason we are proposing to install an 18F snout oil-water debris separator inside the first
Type D inlet over the water quality plate. The snout should prevent the orifice plate from
clogging. The second Type D inlet will be set at the water quality elevation. This Type D
inlet controls the release rate from the pond (see Appendix F for the Regional Pond
calculations).
EPA SWMM Hydraulic Modeling
The detention pond was given an initial depth of 6.36 ft to account for water quality storage.
The pond outlet structure was modeled using a combination of a low flow orifice and
overflow weir. A side calculation was performed to check the accuracy of the generated
EPA SWMM rating curve out of the pond. Based on the calculations the discharge from the
pond is being controlled by the weir flow into the inlet. The overflow weir length in the model
was adjusted to match the results of the calculations.
4.3.1 Storm Line B1
Storm Line B1 is a major storm drain system conveying flow from College Avenue,
continuing east along Conifer Street, then south at the drainage swale west of the Redwood
Pond, and outfalling into the Proposed Regional Pond. This system consists of circular
storm sewer ranging from 30- to 66-inch, as well as 3 ft x 8 ft and 2 ft x 8 ft RCBC.
A 5-foot diameter manhole at College Avenue was placed for future storm sewer
connections. This connection would occur with the improvements of College Avenue and
the addition of curb and gutter. Once improved, street flows will be conveyed via curb and
gutter and ultimately discharged into Storm Line B1. This manhole and sewer are designed
at a depth of approximately 13 ft to avoid utility conflicts for the future connection and to
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avoid two 8-inch sanitary sewer and waterline conflicts along Conifer Street. The east half of
College Avenue has been included in the size of the proposed Regional Detention Pond.
The East half of College is included in basin 226.
A 10-foot box base manhole is proposed at the intersections of Red Cedar Circle and
Conifer, as well as Blue Spruce Drive and Conifer. These manholes will connect to Storm
Line B2 and B3 (discussed below). A box culvert is located where Storm Line B1 turns and
heads south towards the regional pond. The 24-inch ELCO line, 8-inch sanitary line, and
minimum clearance requirements controlled the pipe design for this section.
A 6-foot wide curb cut is located on the south side of Conifer Street. This curb cut will
convey flow from the south side of Conifer Street into the Evergreen West outfall drainage
swale and into the regional pond. This curb cut is sized to prevent additional carryover to the
existing undersized system north of the Redwood Pond.
The existing storm sewer located at the intersection of College Avenue and Conifer Street
will remain in place. The storm sewer within Conifer shall be abandoned in-place or
removed as necessary. All storm manholes and inlets shall be removed as indicated on the
construction plans.
A headwall with wing walls and scour stop are incorporated into the outlet of Storm Line B1.
Scour stop was sized by the manufactured. The storm sewer contributes approximately 270
cfs to the regional pond.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of Storm Sewer Lines B1. The proposed
design shows the energy grade line of the system to be below the flowline of the inlets,
therefore the inlets will function properly during a 100-year event.
4.3.2 Storm Line B2
Storm Line B2 extends north along Red Cedar Circle from Storm Line B1 to Bristlecone
Drive, then west along Bristlecone Drive to College Avenue. This system consists of circular
storm sewer ranging from 24- to 54-inch RCP, contains 5 storm laterals and a total of 31-
Type 13 combination inlets.
A 36-inch Anheuser Busch water line runs east to west across Red Cedar Circle and crosses
Storm Line B2. Due to the depth of the waterlines a 36-inch RCP is placed 9 inches above
the 36-inch waterline. Avoiding a conflict with this utility causes several minor utilities to be
adjusted along Red Cedar Circle and Bristlecone Drive as indicated on the construction
drawings.
Another conflict is an 8-inch sanitary sewer running north and south across Bristlecone
Drive. At the location where the proposed storm sewer crosses the existing sanitary sewer,
a notched will be created out of the wall of the proposed storm sewer in order to "cradle" the
existing 8-inch sanitary sewer.
Lateral B8 is located on the north east corner of the intersection of College Avenue and
Bristlecone Drive. Inlet B8A picks up flows being conveyed to Bristlecone Drive from
College Avenue. Lateral B7 is located on the north side of Bristlecone Drive just south of the
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Albertson’s Pond. Lateral B6 and B5 are located along Red Cedar Circle. This group of
inlets and lateral are required due to the limited street capacity of Red Cedar Circle and
Bristlecone Drive. Lateral B4 replaces an existing undersized storm sewer located at the
intersection of Conifer Street and Red Cedar Circle.
Table 4.3 shows Storm Line B2 Inlet Summary.
Table 4.3. Storm Line B2 Inlet Summary.
ID Number
and Type Condition Flow to
Inlet (cfs) Capture % Carry-Over
(cfs)
Carry-Over
Location
Inlet
B8A
4-Type 13
Combination On-Grade 12 87 2 B7A
Inlet
B7A
5-Type 13
Combination
On-Grade(large events)
Sump (minor events) 27 87 4 E1A
Inlet
B6A
4-Type 13
Combination On-Grade 20 84 3 B5A
Inlet
B5A
7-Type 13
Combination On-Grade 43 82 8 B4A
Inlet
B4A
6-Type 13
Combination Sump 43 --
Overtops 9 B4B
Inlet
B4B
5-Type 13
Combination On-Grade 43 79 9 B11A
There is an existing detention pond located just west of proposed lateral B5, in basin 328.
After further investigation, this pond does not have a gravity fed outlet. The invert of the
pond was constructed at an elevation lower than the storm sewer it discharges into. As part
of this project, this storm sewer will be abandoned in-place and a new outfall will run from the
invert of the pond to proposed Manhole B5.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of Storm Sewer Line B2. The model results
show the energy grade line of the system to be below the flowline of the inlets, therefore the
inlets will function properly during a 100-year event.
4.3.3 Storm Line B3
Storm Line B3 extends north along Blue Spruce Drive from Storm Line B1 in Conifer Street.
This system consists of a 54-inch RCP storm sewer, contains 2 storm laterals and a total of
22-Type 13 combination inlets.
Storm Lateral B9 and associated inlets are replacing existing storm sewer inlets located on
either side of Blue Spruce at the intersection with Conifer. An existing fire hydrant conflicts
with the inlet location therefore; it is being relocated further south and to the other side of the
street. The west curb return will be re-graded at the intersection of Blue Spruce and Conifer
to convey flow from Conifer to Inlet B9A.
Storm Lateral B10 and its associated inlets are being added approximately 500 ft north of
the Conifer Street and Blue Spruce Drive Intersection. This grouping of inlets and laterals
are required due to limited street capacity on Blue Spruce Drive. Approximately 95 cfs is
flowing to inlet B10A and due to the inadequate street capacity and costs associated with
additional inlets to achieve 80% efficiency, 4 inlets were placed at this location with 52.7 cfs
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of carryover to inlet B9A. Due to the large amount of flow to the inlet and the large amount
of carryover flow, the EPA SWMM model was adjusted to reflect the inlet capacities and
carryover flow for these two inlets. The hydrograph into "INLET_B10A" caps off at 44 cfs.
The remaining 52 cfs was added downstream as node "Carryover_TO_B9A."
Table 4.4 shows Storm Line B3 Inlet Summary.
Table 4.4. Storm Line B3 Inlet Summary.
ID Number and
Type Condition Flow to
Inlet (cfs)
Capture
%
Carry-Over
(cfs)
Carry-Over
Location
Inlet
B10A
4-Type 13
Combination On-Grade 95 52 46 B9A
Inlet
B10B
4-Type 13
Combination On-Grade 26 80 5 B9B
Inlet
B9A
8-Type 13
Combination Sump 69 100 - -
Inlet
B9B
6-Type 13
Combination On-Grade 24 97 2
Existing
Redwood Pond
Inlets
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of Storm Sewer Lines B3. The model results
show the energy grade line of the system to be below the flowline of the inlets, therefore the
inlets will function properly during a 100-year event.
4.3.4 Storm Line C1 and C2
Storm Lines C1 and C2 are a parallel system on the north and south sides of re-aligned Vine
Drive, starting at the detention pond and traveling west to Jerome Street. Storm Line C1
continues north along existing Dry Creek to a pond just south of JAX. The combined system
consists of a storm sewer ranging in diameter from 36- to 66-inch RCP, contains 5 storm
laterals, a total of 12-Type 13 combination inlets, 3-Type 3 Inlets and two snout oil-water
debris separators (54R and 96F).
Initial design of Storm Lines C1 and C2 consisted of a large, single sewer along the
alignment of Storm Line C1. This system conflicted with the 60-inch GWET and 42-inch
NEWT waterlines being constructed within the proposed East Vine ROW by The City of
Greeley. Due to utility constraints, ground water issues and discussions between the City of
Fort Collins and the City of Greeley, the decision was made to construct the parallel storm
sewer system along this stretch of re-aligned Vine Drive.
Storm Line C1 and the regional pond have been designed to provide conveyance, detention,
and water quality for the properties between College Avenue and existing Dry Creek (Basins
315, 407, and 316) that currently discharge into Dry Creek. The south most pond, near the
re-aligned Vine Drive, will be removed and Dry Creek will be filled in. Proposed Inlet C4B
located in the re-aligned Vine Drive, will capture overland flow from Basin 316. The existing
pond just south of JAX will connect into the proposed storm sewer. This pond can be
removed if re-development occurs as long as the development discharges into Storm Line
C1. The 3-Type C inlets (C3) located in the old Dry Creek will capture overland flow from
Basins 315 and 407 once the pond just south of JAX is removed.
4.13 Ayres Associates
The Regional Detention Pond has been sized for additional flows generated from the un-
developed portion of the Old Town North development. A storm sewer was not designed to
convey the flows north to the proposed Regional Detention Pond. When this storm sewer is
designed, special considerations must be given to the GWET and NEWT waterline
crossings. These clearances are very critical.
Laterals C6A and C6B are located just west of the regional detention pond along re-aligned
Vine Drive. Lateral C5A is at the intersection of Blondel and Future Vine Drive. This inlet
will reduce flows from Blondel Street. Laterals C4A and C4B are placed just east of College
Avenue and the future re-aligned Vine Drive.
The inlets located within the re-aligned Vine Drive were designed for the 10-year minor storm
event and the 100-year major storm event being handled within the road, based on current
COFC criteria.
Table 4.5 shows Storm Line C1 and C2, 10- and 100-Year Inlet Summary.
Table 4.5. Storm Line C1 and C2, 10- and 100-Year Inlet Summary.
ID Number
and Type Condition
10- / 100-Year
Flow to Inlet
(cfs)
10- / 100-Year
Capture %
10- / 100-Year
Carry-Over (cfs)
Carry-Over
Location
Inlet
C6A
3-Type 13
Combination On-Grade 5 / 11 90 / 83 1/ 2 A5A
Inlet
C6B
3-Type 13
Combination On-Grade 5 / 11 87/ 77 1 / 3 A5B
Inlet
C5A
1-Type 13
Combination On-Grade 5 / 5 100 - -
Inlet
C4A
2-Type 13
Combination Sump 4.5 / 10 100 - -
Inlet
C4B
3-Type 13
Combination Sump 10 / 27 100 - -
Inlet
C3A 3-Type C Orifice/Weir 24 / 60 - - -
A headwall with wing walls and scour stop are incorporated into the outlet of Storm Line C1
and C2. Scour stop was sized by the manufactured. Storm Line C1 will discharge
approximately 202 cfs to the regional pond during a 100-year storm. Storm Line C2 will
discharge approximately 50 cfs into the regional pond during a 100-year storm.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of the parallel Storm Sewer Lines C1 and C2.
The model results show the energy grade line of the system to be below the flowline of the
inlets, therefore the inlets will function properly during a 10- and 100-year event.
4.4 Redwood Pond
The existing Redwood Pond currently outfalls into existing drainage swale that conveys the
storm water to the Evergreen East Pond. The swale and downstream system does not meet
City of Fort Collins drainage criteria for the 100-year event. The improvements to the pond
included re-grading the pond to outlet at the southeast corner of the site. This outlet will
ultimately discharge into the proposed storm sewer in re-aligned Vine Drive. The re-graded
pond has the same footprint and top of berm elevation as the existing pond. A water quality
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outlet structure is proposed prior to discharging into the proposed storm sewer system. A 4-
foot concrete trickle pan is incorporated into the pond bottom to direct low flows due to
minimal slope across the pond. The overall footprint encompasses approximately 3.5 acres
at an approximate depth of 6 ft. The required 100-year detention volume is 7.70 ac-ft with
an additional 2.16 ac-ft of storage below the detention storage for water quality. Table 4.6
shows the major characteristics of Redwood Pond.
Table 4.6. Redwood Pond.
Description
Elevation
(ft)
Pond Volume
(ac-ft)
Pond Depth
(ft)
Pond Invert 4953.10 --- ---
Outlet Structure
Elevation 4955.12 2.16 2.02
100-year WSEL 4957.75 9.86 4.65
Spillway into
Pond 4958.39 11.94 5.29
Top of Pond 4959 14.00 5.90
WSEL = Water Surface Elevation
The outlet structure for the redwood pond is a combination of two Type C inlets in series.
The inlets will be separated by a steel plate with an orifice opening sized to provide a 40-
hour drain time for the water quality portion of the pond. One of the frequent maintenance
issues associated with water quality structures is the clogging of the orifice plates. For this
reason we are proposing to install an 18F snout oil-water debris separator inside the first
Type C inlet over the water quality plate. The snout should prevent the orifice plate from
clogging. The second Type C inlet will be set at the water quality elevation and the outlet
pipe from the inlet controls the release rate from the pond.
Currently an undersized storm sewer system conveys flow from inlets along Redwood Street
into Redwood Pond. The series of existing inlets surcharge during the minor events creating
localized flooding at the intersection of Redwood Street and Conifer Street. The existing
inlets and storm sewer do not have the capacity for the 100-year runoff from the surrounding
basins. An adequate storm system would require large diameter storm pipe and deep inlets
to prevent surcharging. Due to existing water and sanitary conflicts in the area, and a
controlled invert into Redwood Pond, the only storm sewer system that could fit within the
existing constraints would be multiple shallow 12-inch diameter storm sewer culverts. These
storm sewer culverts would still not alleviate the minor and major storm flooding problem.
To mitigate the flooding, the design incorporates a 90-foot overflow weir graded into the
pond embankment. The 100-year storm event (approximately 85 cfs) will overtop the curb at
an elevation of approximately 4958.39 and be conveyed to the pond through the weir. Minor
event flows will continue to be captured by the existing inlets located north of the pond. This
design can be looked at in more detail during the final design process.
EPA SWMM Hydraulic Modeling
The proposed weir into Redwood Pond was modeled using a weir in EPA SWMM. The
transverse weir option was chosen with a discharge coefficient of 3.0. During a 100-year
event the 90 foot weir will convey approximately 80 cfs at a max depth of 0.45 ft.
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The detention pond was given an initial depth of 2.02 ft to account for water quality storage.
The pond outlet structure was modeled using a combination of a low flow orifice and
overflow weir. A side calculation was performed to verify the accuracy of the generated EPA
SWMM rating curve out of the pond. Based on the calculations the discharge from the pond
is being controlled by the outflow pipe. The model results matched the side calculations (see
Appendix F for Redwood Pond Calculations).
4.5 East Vine Diversion Channel / Regional Detention Pond Outfall
The future East Vine Diversion Channel will serve as the outfall to the North East College
Corridor Outfall drainage system.
Table 4.7 represents the tailwater rating curve that was used in the EPA SWMM model for
the downstream boundary condition (Storm Line A1) at the future East Vine Diversion
Channel. This rating curve is based on a conceptual design of the future channel and was
taken from the preliminary HEC-RAS model of the East Vine Diversion Channel from the
DC3 project (Dry Creek Connection Channel).
Table 4.7. Dry Creek Tailwater Rating Curve.
Time (hr) Tailwater (ft)
100-year Storm Event
0.0 4934.24
0.3 4939.31
1 4937.88
1.19 4938.29
2 4937.31
3 4936.94
4 4936.86
5 4936.79
6 4936.42
4.5.1 Storm Line A1
Storm Line A1 is a major component of the proposed storm drainage system east of
Redwood Street. Storm Line A1 starts at the outlet of the regional pond and continues east
along re-aligned Vine Drive. This system will outfall into the future East Vine Diversion
Channel. Storm Line A1 will collect flow from the Redwood Pond outlet (Storm Line A2), the
Old Town North detention pond (Storm Line A3), and the Green briar Outfall (Storm Line
A4). The storm line consists of a storm sewer ranging in diameter from 48- to 54-inch RCP,
4 ft x 7 ft and 4 ft x 12 ft RCBC, contains 4 storm laterals, a total of 25-Type 13 combination
inlets, snout oil-water debris separators for water quality, and a crossing at Lake Canal.
Box culverts are required at the downstream end of the Storm Line A1 due to cover
constraints. The box culvert is mainly located so the outside edge of the box coincides with
the outside edge of the 6-foot sidewalk of the future re-aligned Vine Drive.
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Lateral A5 is located in a sump on the east side of Redwood Street and realigned Vine Drive.
Lateral A7 and associated inlets are placed in re-aligned Vine Drive just west of the Alta
Vista development to accommodate the street capacity and encroachment requirements
from Alta Vista. Lateral A8 is located directly north of the Alta Vista development in a sump.
Lateral A9 is also located in a sump just east of the future re-aligned Lemay Avenue.
Preliminary designs included a lateral with on-grade inlets located just west of Redwood
Street along realigned Vine Drive to prevent flows from crossing the street. The large PRPA
poles and necessary easements that run north and south along the west side of Redwood
Street created a conflict for placement of this lateral; therefore these inlets and lateral were
removed from the design and flows will be conveyed across Redwood Street and intercepted
by Lateral A5. The inlets were removed, but the remaining inlets were not renumbered.
The inlets located along the re-aligned limits of Vine Drive were designed for the 10-year
minor storm event.
Table 4.8 shows Storm Line A1 10- and 100-Year Inlet Summary.
Table 4.8. Storm Line A1, 10- and 100-Year Inlet Summary.
ID
Number
and Type
Condition
10- / 100-Year
Flow to Inlet
(cfs)
10- / 100-Year
Capture %
10- / 100-Year
Carry-Over
(cfs)
Carry-
Over
Location
Snout Size
Inlet
A5A
4-Type 13
Combination Sump 12 / 24 100 - - -
Inlet
A5B
4-Type 13
Combination Sump 10 / 21 100 - - 72 FTBB
Inlet
A7A
3-Type 13
Combination
On-
Grade 7 / 12.56 88 / 81 1 / 2 A8A 30 F
Inlet
A7B
3-Type 13
Combination
On-
Grade 6.8 / 14.67 88/ 77 1 / 3 A8B 30 F
Inlet
A8A
2-Type 13
Combination Sump 6.88 / 15.23 100 - - 36 FTB
Inlet
A8B
3-Type 13
Combination Sump 6.58 / 15.32 100 - - -
Inlet
A9A
3-Type 13
Combination Sump 12.7 / 26.77 100 - - 72 FTBB
Inlet
A9B
3-Type 13
Combination Sump 10.7 / 23.73 100 - - -
Storm Line A1 will ultimately discharge approximately 380 cfs during a 100-year event into
the future East Vine diversion channel.
An existing 24-inch ELCO and 24-inch COFC waterline run north and south in Lemay
Avenue. These waterlines create a conflict with the proposed Storm Line A1. The profile of
Storm Line A1 is controlled by the downstream invert into the proposed East Vine Diversion
Channel and the upstream connection to the regional pond. The waterlines will need to be
lowered under the box culverts to avoid this conflict.
An existing 15-inch sanitary sewer also runs north and south in Lemay Avenue. The sanitary
sewer line is 4 inches below the top of the proposed box culvert. During initial designs,
conflict manholes were considered to avoid this conflict. However after discussions the City
of Fort Collins; the current design incorporates a cast in place concrete box top which will
"cradle" the sanitary sewer.
4.17 Ayres Associates
The 60-inch GWET and 42-inch NEWT water lines were also in conflict with the proposed
storm sewer in several locations along Storm Line A1, primarily at the storm lateral locations.
As mentioned previously, Storm Line A1 system is constrained by the upstream and
downstream inverts. The laterals are constrained by the hydraulics of the system.
Discussions between the City of Fort Collins and the City of Greeley occurred during the
initial design stages. The engineers from both sides offered alternatives and made
accommodations where possible. An agreement was made to allow the Greeley waterlines
to be within 6 inches (outside diameter) of the proposed storm sewer. Manhole risers were
incorporated into the storm sewer design where the hydraulics permitted to allow shallow
storm laterals. The construction drawings reflect GWET and NEWT waterline elevations as
Boyle Engineering submitted to the City of Fort Collins in May 2008.
The potential for future development of the land north of the re-aligned Vine Drive required
Ayres to look at the feasibility of future utilities. After investigating potential sanitary sewer
access locations, it was determined that any development in this area would not be able to
have basements. The sanitary sewer on the east side of Redwood Street posed the
greatest concern. The proposed storm sewer and Greeley waterlines create a utility barrier
along re-aligned Vine Drive. Existing sanitary sewer is currently located in Alta Vista, Lemay
Avenue, and Redwood Street. The sewers located in Lemay Avenue and Redwood Street
do not pose a connection problem, however, the sewer located on the west side of Alta Vista
would required to run at minimum grade and drop manholes would be needed to tie into this
system. Other areas west and east of Redwood should not have issues connecting to
existing utilities.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of the Storm Sewer Lines A1. The proposed
design shows the energy grade line of the system to be underground at the inlets, therefore
the inlets will function properly during a 10- and 100-year event.
4.5.2 Storm Line A2
Storm Line A2 outlets Redwood Pond, continues south and connects into Storm Line A1.
This system consists of storm sewer ranging in diameter from 15- to 48-inch RCP, contains
1 storm lateral and a total of 3-Type C inlets and one snout oil-water debris separator for
water quality.
Storm lateral A6 is placed near the cul-de sac just south of Lupine Drive. Inlet A6 will
replace an existing 12-inch pipe that currently conveys flows north to the existing channel
where Redwood Pond outfalls. Runoff (approximately 73 cfs) from the development will be
re-directed into the proposed system.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of Storm Sewer Lines A2. The analysis shows
the energy grade line of the system to be below the flowline of the inlets, therefore the inlets
will function properly during a 10- and 100-year event.
4.18 Ayres Associates
4.5.3 Storm Line A3
Storm Line A3 extends south from Storm Line A1 to the existing outfall of the Old Town
North (OTN) system. Storm Line A3 will parallel the Lake Canal and connect into the
existing manhole just upstream of the outlet structure for the OTN pond. This system
consists of a 30-inch RCP storm sewer.
The profile for Storm Line A3 is placed relatively shallow compared to Storm Line A1 that it
discharges into. Initial design efforts called for a deeper profile, matching crowns of both
storm sewers. This design created conflicts with the GWET and NEWT waterlines. To
avoid this conflict, Storm Line A3 was raised to an elevation that provides 12-inch of
clearance between the utilities and incorporated a vertical bend to make the connection to
Storm Line A1.
It is believe that there is an existing 12-inch sub-surface tile drain crossing the proposed
Storm Line A3 and outfalling into the Lake Canal. Record drawings have been obtained
from the City of Fort Collins, however, the location of this line could never be field verified.
The drain shall remain in its current location however, a conflict may occur between the tile
drain and the storm sewer during construction. In the event that this occurs, the tile drain will
be siphoned under the proposed Storm Line A3.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of the Storm Sewer Lines A3. The analysis
shows the energy grade line of the system to be below the manhole lids, therefore the
system will function properly during a 100-year event.
4.5.4 Storm Line A4
Storm Line A4 extends north along the east side of Lemay Avenue from Storm Line A1. This
system consists of storm sewer ranging from 48-inch to dual 36-inch RCP. The location of
this system was chosen for ease of construction and future maintenance; however,
additional ROW shall be acquired prior to construction of Storm Line A4. This system will
replace the current Green briar Outfall. Currently, dual 36-inch pipes convey flow under the
Lake Canal into a siphon where the system outfalls into a channel just east of Lemay. The
proposed system will replace the existing 36-inch pipes and place a new junction box where
the existing headwall is located. The system will continue just east of Lemay Avenue and
south to connect to Storm Line A1.
EPA SWMM Hydraulic Modeling
EPA SWMM was used to model the capacity of the Storm Sewer Lines A4. The model
results show the energy grade line of the system to be below the manhole lids, therefore the
system will function properly during a 100-year event.
4.6 EPA SWMM Hydraulic Summary
Table 4.9 presents a summary of the hydraulic grade line (HGL) and energy grade line
(EGL) at each of the structures throughout the proposed storm sewer. Appendix C contains
the complete EPA SWMM output.
4.19 Ayres Associates
Table 4.9. 100-Year EPA SWMM Hydraulic Summary.
Inlet
Pipe
Diameter
(ft)
Discharge
(cfs)
Invert Out
Elevation
(ft)
Ground or
Flowline
Elevation
(ft)
Hydraulic
Grade Line
(ft)
Energy
Grade Line
(ft)
E1A 2--30 60 4966.92 4970.5 4969.43 4969.96
E2A 30 18 4966.78 4970.87 4969.31 4969.59
E2B 2--30 36 4966.4 4970.5 4969.25 4969.36
B6A 24 19 4967.4 4971.78 4968.98 4969.85
B5A 30 38 4964.6 4968.72 4967.57 4968.68
B4A 30 44 4957.98 4967.91 4964.20 4965.49
B4B 30 35 4957.98 4967.82 4964.96 4965.80
B10A 42 48 4955.81 4966.97 4964.91 4965.53
B10B 42 31 4955.92 4966.82 4964.67 4964.82
B9A 48 32 4953.11 4964.8 4963.66 4964.04
B9B 48 23 4953.11 4964.95 4963.55 4963.62
B8A 24 12 4971.98 4977 4973.16 4974.02
B7A 24 26 4969.5 4974 4972.25 4973.56
C3A 48 60 4957.96 4965 4963.68 4964.17
C4A 30 12 4959.11 4965.77 4963.41 4963.89
C4B 30 30 4959.48 4965.77 4963.58 4964.59
C5A 24 5 4955.61 4964.63 4961.01 4961.50
C6A 30 14 4953.85 4963.09 4960.36 4960.58
C6B 30 11 4955.21 4963.12 4959.25 4959.76
A5A 30 21 4949.3 4955.65 4955.42 4955.76
A5B 42 43 4945.84 4955.65 4955.42 4955.58
A6A 48 72 4948.5 4955.99 4954.79 4955.39
A7A 24 15 4944.36 4950.68 4947.20 4947.59
A7B 18 15 4944.98 4950.68 4948.01 4949.40
A8A 30 24 4941.72 4947.93 4946.51 4946.88
A8B 30 12 4941.9 4947.93 4947.07 4947.16
A9A 42 50 4936.51 4943.39 4941.53 4941.95
A9B 30 23 4937.45 4943.12 4941.78 4942.13
Based on the analysis, no surcharging will occur in this system during a 100-year storm
event. The storm sewer will operate under pressure flow conditions but within specified
levels for Class III RCP and R-4 joints. The energy grade line is above the flowline of the
inlet for Inlet A5A, while the hydraulic grade line remains below ground. The peak from this
inlet travels through this system prior to the peak of the proposed NECCO system. The
peak energy grade line in the model represents the peak of the proposed NECCO system,
not the peak of the inlet. At the peak of the inlet the energy grade line is below the flowline
of the inlet, therefore the inlet shall function properly during a 100-year event.
5.1 Ayres Associates
5. COST ESTIMATE
A cost estimate was created for the Utility Plans for Northeast College Corridor Outfall
Drainage Improvements Project, 99% submittal plan set. Below summarizes the cost of the
project:
Description Total
Storm Line A1 $ 3,078,099
Storm Line A2 $ 342,277
Storm Line A3 $ 106,910
Storm Line A4 $ 487,134
Storm Line B1 $ 1,440,154
Storm Line B2 $ 1,088,724
Storm Line B3 $ 490,868
Storm Line C1 $ 678,824
Storm Line C2 $ 465,779
Evergreen West Pond $ 28,578
Blue Spruce and Bristlecone $ 321,624
Redwood Pond $ 217,250
Regional Pond $ 986,265
Total Estimated Price $ 9,732,686
A cost estimate was also put together for the option to re-grade the intersection of Blue
Spruce and Bristlecone. The grading alternative would be approximately $ 150,145. A
detailed break down of the cost estimates by Garney Construction can be found in
Appendix H. Also in Appendix H is a grading analysis from Schmidt Earth Builders, Inc.
The following qualifications, assumptions, and concerns were used for the cost estimate:
Qualifications:
• No allowance has been made for repair or replacement of potential underdrain tiles
• No allowance for removal of existing redwood outlet
• Strip and replace 6-inch topsoil is included and broken out
• "Roll Back" topsoil method because it is the cheapest, and there is nowhere to stockpile
it
• After draw down, trench backfill and sump pits may be required to accommodate trickle
pan installation
• All pump power is by generators 30 days @ Redwood / 60 days @ Regional
• No street repair after trucking has been taken into account
5.2 Ayres Associates
Assumptions:
• Late spring, summer, early fall (good) weather for pond construction
• Traffic Control by City of Fort Collins Streets Department
• 5 miles one-way, 10-mile round trip haul for excess material generated from pipe and
pond construction
• Assume close by discharge points for groundwater (filter bags etc.)
• Excavation and haul-off to be performed by excavator and highway trucks
• Does not include right of way acquisition costs
• Off Road Diesel Fuel = $3/US Gallon
• 4,000 psi Concrete = $98/cy
• Flowfill = $65/ton
• Class 67 Pipe Bedding = $17.7/ton
• Erosion Control = $5/LF of storm sewer
• Dewatering = $35/LF of storm sewer
Concerns:
• Ability to keep ponds dry with pitrun soil and high water
• Ability to keep topsoil slopes/slope stability of pitrun soil and high water
• Five miles one-way, 10 miles round trip for haul for excess material generated from pipe
and pond construction
• Settling ponds for dewatering with limited and narrow easement
• Underdrains may be required to maintain dry ponds and stable slopes
6.1 Ayres Associates
6. WATER QUALITY AND EROSION CONTROL
The phasing for construction of the North East College Corridor Outfall is unknown at the
time of this report; therefore, the erosion control measures discussed below and shown on
the construction drawings are preliminary and shall be re-evaluated at a later date.
Construction of the storm sewer improvements will require implementation of erosion control
BMPs to minimize the amount of sediment carried off-site by wind and water. A SWMP shall
be completed, approved, and implemented at the time of construction.
6.1 Temporary Sediment/Erosion Control Methods
The erosion control methods to be implemented during the construction of the proposed
storm sewer can be seen on the Erosion Control Sheets in the construction plans. Erosion
control BMPs for construction of the North East College Corridor Outfall will include wattle
dikes and straw bale dikes set across all flow paths determined by the general grading plan.
The wattle dikes are placed in the flow paths for each 2 ft of vertical drop to slow the
conveyance of water and prevent significant erosion before vegetation is installed. Wattles
are to be placed at a 45 degree angle toward flow in the street flowline, anywhere that the
stormwater runoff and sediment may exit the site via curb and gutter. The straw bale dikes
will be used in the existing channel outfalling into the regional pond. Silt fencing will be
installed around the construction site as necessary to prevent sediment from leaving the site
during construction. Drop inlet protection will be installed around each existing and
proposed inlet, grated manhole lid, and pond outlet structure to prevent sediment from
leaving the project site and entering the East Vine Diversion Channel or downstream
stormwater facilities. Straw mulch will be applied after seeding to prevent erosion from
runoff and help establish plant cover. A vehicle-tracking pad is to be installed at all existing
pavement locations to prevent mud from being carried off site on vehicle tires. Vehicle
tracking pads must also be provided at any other access locations to the worksite.
Existing vegetation shall be preserved where possible. All disturbed areas not in the
roadway or greenbelt shall have temporary vegetation seed applied within 30 days of initial
disturbance. After seeding, hay or straw mulch shall be applied over the seed at a rate of
1.5 ton/ac minimum, and the mulch shall be adequately anchored, tacked, or crimped into
the soil. Those roads that are to be paved as part of the project must have a 1-inch layer of
gravel mulch applied at a rate of at least 135 ton/ac immediately after grading is completed.
The placement structure shall be applied within 30 days after the utilities have been installed.
If the disturbed areas will not be constructed upon within one growing season, a permanent
seed shall be applied. After seeding, a hay or straw mulch shall be applied over the seed at
a minimum rate of 1.5 ton/ac, and the mulch shall be adequately anchored, tacked or
crimped into the soil.
The above structural practices are temporary and must be installed prior to any grading or
construction on the project site. Temporary sediment control measures shall be checked
regularly and after storms for silt buildup. Silt fence shall be properly installed and
maintained including checking for undermining. Curb inlet protection shall be checked for
openings and silt buildup, if necessary clean or replace gravel to maintain a protective barrier
around all inlets which may receive stormwater. Erosion and sediment control measures
must be replaced or repaired as needed during regular inspections. The temporary
6.2 Ayres Associates
structures must be maintained until the site has uniform cover equivalent to 70% of existing
site conditions. Cover may include vegetation in the interim condition.
6.2 Permanent Sediment/Erosion Control Methods
Structural Practices
Sediment and Stormwater Quality Controls – the following methods will be used to
prevent/reduce sediment from stormwater runoff after construction:
1. Snout Oil-Water Debris Separator – 18F snouts shall be installed in the outlet structure
of the regional pond and one 18F snout shall be installed in the outlet structure of
Redwood Pond. The Snouts will minimize the amount of oil and floating debris entering
the storm sewer system.
2. Snout Oil-Water Debris Separator – Snouts shall be installed in outfall inlets into Storm
Line A1 along re-aligned Vine Drive. The snouts will minimize the amount of oil and
floating debris entering the storm sewer system.
Erosion Controls – the following practices will be used to prevent the erosion of soil after
construction:
1. Scour Stop – shall be installed at the downstream ends of the storm sewer entering the
regional and Redwood Detention Ponds. Scour stop shall also be placed at the outfall
into the East Vine Diversion Channel. Scour stop was sized by the manufactured.
2. Paving – All existing streets shall be repaved prior to the completion of the project. The
post-construction condition for approximately 20% of the project site will be re-surfaced
with concrete walkways, concrete curbs, gutters and asphalt pavement.
Non-Structural Practices
Erosion Controls – the following practices will be used to prevent the erosion of soil after
construction:
1. Permanent seeding – All un-paved disturbed areas shall be reseeded to match native
ground cover as soon after construction or grading as weather permits. This will provide
the opportunity for pollutants to settle out of the stormwater runoff.
2. Cleaning of Construction Site - Drainage ditches, pans, and culverts must be cleaned of
debris and sediment.
Following site construction, the goal is to achieve a stabilized cover condition to provide long-
term stormwater protection. Stabilization is quantified by achieving uniform cover equal to
70% of the pre-disturbance condition. Final stabilization shall be achieved by installation of
permanent erosion control methods. Immediately after the storm sewer improvements have
been constructed, permanent erosion control practices are to be installed and maintained.
Temporary erosion and sediment control measures can be removed after establishment of
permanent stable vegetation to the satisfaction of the City of Fort Collins inspector.
6.3 Ayres Associates
6.3 Materials Handling and Spill Prevention
A project staging area shall be located in the temporary construction easement. The exact
location of the staging area will be determined by the contractor.
Measures should be undertaken to control building materials, waste and disposal of excess
asphalt and concrete to ensure these materials do not leave the site and enter the detention
ponds or The East Vine Diversion Channel. Asphalt, concrete, building materials, waste and
cleanup by-products should not be discharged into the on-site curb inlets and storm sewer
systems nor should they be allowed to enter the detention ponds or The East Vine Diversion
Channel. Measures should be undertaken to remove excess waste products from the site
and dispose of these waste materials off-site in an appropriate manner.
A temporary concrete washout area as well as a separate designated loading/unloading area
shall be located in the project staging area. The exact location of the washout area will be
determined by the contractor. It is the contractor’s responsibility to ensure that the concrete
is handled in the appropriate manner so as not to contaminate the detention ponds, The
East Vine Diversion Channel, or surrounding areas. Upon completion of the project the
concrete in the concrete washout area shall be disposed of in an acceptable waste site. The
concrete wash-out area and designated loading/unloading areas shall be re-vegetated to
existing or better conditions.
The heavy equipment contractor shall be responsible for protecting the soil from
contamination due to any hydrocarbon or other hazardous spills associated with his
contractual obligations. All chemicals used in maintenance (oil, antifreeze, hydraulic fluid,
etc.) are to be stored offsite.
Fertilizers are to be stored in the contractor staging area. The contractor shall be
responsible for preventing contamination in the detention ponds, The East Vine Diversion
Channel and surrounding areas.
Any periodic refueling of earthmoving equipment on site shall be carefully controlled to
ensure these materials are not spilled on the site and will not enter any detention ponds or
The East Vine Diversion Channel. It shall be the responsibility of the heavy equipment
contractor to designate a fueling area and take appropriate actions to ensure pollution of
stormwater does not occur. The fueling area shall be located within the contractor staging
area. The fueling area shall be at least 100 ft from drainage channels and/or storm sewer
systems and be enclosed by a minimum 12-inch high compacted berm capable of retaining
potential spills.
In the event of a spill from the site into an on-site curb inlet or storm sewer system
appropriate measures should be undertaken immediately to contain spilled pollutants and
properly remove the spilled materials along with all contaminated soils and prevent future
spills from occurring. In addition, measures should be undertaken to limit off-site soil
tracking of mud and debris spillage from vehicles leaving the site. Mud and debris should
not be tracked along roadways and allowed to enter any non-protected drainage path.
6.4 Ayres Associates
Several measures are suggested to protect stormwater quality and prevent contaminates
from migrating off-site.
• Washing of vehicles or equipment into the storm drainage system is prohibited.
• Refueling operations should be done in the designated fueling area during dry weather
conditions and on level ground.
• Potential flow paths for spills should be assessed prior to any fuel or hazardous
substance transfer.
• Ample absorbent material and containment should be available to contain a spill.
• Any storm drain conveyance within a containment area should be protected with berms
or plugs.
• Hazardous materials such as fuel, solvent or fertilizer used on site should be in a secure
covered area.
• No dedicated concrete or asphalt batch plants shall exist on the site.
In the event of a spill, spill prevention procedures should be implemented and posted on site.
One person should be designated as the construction site operator who is responsible as the
SWMP Administrator to update the SWMP, coordinate the installation and maintenance of
sediment/erosion BMPs, and serve as contact for reporting spills. The spill is to be reported
to the SWMP Administrator who will determine whether the City and/or the Colorado
Department of Public Health and Environment or downstream users need to be contacted.
Training for cleanup procedures and use of materials should be provided.
6.4 Inspection and Maintenance
The erosion control measures will be inspected daily during construction. The inspection
must include observation of the construction site perimeter and discharge points (including
into a storm sewer system), all disturbed areas, any areas used for material storage that are
exposed to precipitation, any area used for washing of machinery, the vehicle tracking
control pads, and any other erosion and sediment control measures. Silt fence and other
barriers will be checked for undermining and bypass and repaired or expanded as needed.
The temporary vegetation of bare soils will be checked regularly and areas where it is lost or
damaged will be reseeded. Hazardous materials such as fuel, solvent or fertilizer used on
site should be in a secure covered area.
At a minimum the inspections shall occur for all BMPs every 14 days and after significant
precipitation events (i.e., rainfall, snowmelt, etc.). Installations and modifications as required
by the City of Fort Collins or authorized personnel will be implemented immediately or within
48 hours of notification. Mitigation measures shall be inspected for at least the following.
• Accumulation of excess sediment and determination of whether or not the effectiveness
of each structure is significantly reduced. Removal of accumulated sediment shall occur
once a 50% reduction of the design storage capacity becomes evident.
• Damage to structures that need repairing to ensure their effectiveness. Addition or
elimination of sediment and/or erosion control measures that are designed to control the
movement of soil particles in a practical and effective manner.
• Immediate repair and/or replacement of necessary mitigation measures when total
failures are found.
6.5 Ayres Associates
A site log should be kept up to date to record inspections, repairs and maintenance.
Additionally any spills should be fully documented. Include what the spill material was,
reason for spill, date, time of start and finish of spill, quantity, location, weather conditions,
who was contacted, how the spill was cleaned, impact to environment, and method of
disposal of cleanup materials.
All construction activities must also comply with the State of Colorado permitting process for
Stormwater Discharges Associated with Construction Activity. A Colorado Department of
Public Health and Environment CDPHE Construction Permit will be required before any
construction or grading activity can begin.
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AC
BASIN
AREA C MINOR
MAJOR
A
1.22
0.78
0.62
AC
BASIN
AREA C MINOR
MAJOR
B
1.22
0.72
0.58
AC
BASIN
AREA C MINOR
MAJOR
C
1.23
0.33
0.26
AC
BASIN
AREA C MINOR
MAJOR
E
1.25
0.56
0.45
AC
BASIN
AREA C MINOR
MAJOR
D
0.75
0.72
0.58
AC
BASIN
AREA C MINOR
MAJOR
OS-1
8.20
0.75
0.60
AC
BASIN
AREA C MINOR
MAJOR
G
1.01
0.81
0.65
AC
BASIN
AREA C MINOR
MAJOR
H
1.45
0.67
0.54
AC
BASIN
AREA C MINOR
MAJOR
J
0.56
0.83
0.66
AC
BASIN
AREA C MINOR
MAJOR
K
0.55
0.85
0.68
AC
BASIN
AREA C MINOR
MAJOR
O
1.22
0.74
0.59
AC
BASIN
AREA C MINOR
MAJOR
I
0.94
0.69
0.56
AC
BASIN
AREA C MINOR
MAJOR
F
0.63
0.74
0.59
AC
BASIN
AREA C MINOR
MAJOR
P
1.53
0.90
0.72
AC
BASIN
AREA C MINOR
MAJOR
Q
1.06
0.83
0.67
AC
BASIN
AREA C MINOR
MAJOR
L
0.89
0.31
0.25
AC
BASIN
AREA C MINOR
MAJOR
M
0.72
0.81
0.65
AC
BASIN
AREA C MINOR
MAJOR
R
0.66
0.82
0.66
AC
BASIN
AREA C MINOR
MAJOR
T
1.30
0.66
0.53
AC
BASIN
AREA C MINOR
MAJOR
U
1.77
0.78
0.62
AC
BASIN
AREA C MINOR
MAJOR
X
1.48
0.77
0.61
AC
BASIN
AREA C MINOR
MAJOR
Y
0.83
0.74
0.60AC
BASIN
AREA C MINOR
MAJOR
W
1.09
0.64
0.51
AC
BASIN
AREA C MINOR
MAJOR
V
1.06
0.81
0.65
AC
BASIN
AREA C MINOR
MAJOR
S
1.24
0.63
0.50AC
BASIN
AREA C MINOR
MAJOR
N
1.49
0.61
0.49
AC
BASIN
AREA C MINOR
MAJOR
Z
0.68
0.44
0.35
1
3
4
137
6
14
AC
BASIN
AREA C MINOR
MAJOR
OS-2
3.50
0.75
0.60
2 5
9
11
15
8
10
12
BASIN
DESIGNATION
BASIN SIZE
IN ACRES
C COEFFICIENT
C COEFFICIENT
OS 1
0.45
0.67
1.23
AC
BASIN
AREA CMINOR
MAJOR
1 BASIN DESIGN POINT
2-YR RATIONAL
100-YR RATIONAL
Filepath: K:\201013\ENGINEERING\DRAINAGE\PRELIMINARY DRAINAGE PLAN.DWG Layout: LAYOUT16 XREFs: e-base, e-legal, e-util, p-base, p-legal, p-utilPlotted: TUE 02/02/21 4:18:34P By: Jeffrey NyeNO CHANGES ARE TO BE MADE TO THIS DRAWING WITHOUT WRITTEN PERMISSION OF HARRIS KOCHER SMITH.1120 Lincoln Street, Suite 1000
Denver, Colorado 80203
P: 303.623.6300 F: 303.623.6311
HarrisKocherSmith.com
0
SCALE: 1" =
70 70 140
70'
ENCLAVE AT REDWOOD - PRELIMINARY DRAINAGE PLAN
SCALE: 1" = 70'
DIRECT RUNOFF SUMMARY TABLE
BASIN AREA (AC) Q2 (CFS) Q100 (CFS)
A 1.22 1.56 6.78
B 1.22 1.42 6.20
C 1.23 0.66 2.89
D 0.75 0.91 3.96
E 1.25 1.16 5.05
F 0.63 0.78 3.42
G 1.01 1.33 5.78
H 1.45 1.58 6.88
I 0.94 1.06 4.63
J 0.56 0.77 3.36
K 0.55 0.78 3.41
L 0.89 0.47 2.06
M 0.72 0.97 4.22
N 1.49 1.46 6.37
O 1.22 1.40 6.12
P 1.53 2.28 9.93
Q 1.06 1.46 6.38
R 0.66 0.92 4.02
S 1.24 1.27 5.55
T 1.30 1.41 6.15
U 1.77 2.26 9.85
V 1.06 1.36 5.93
W 1.09 1.15 5.02
X 1.48 1.86 8.11
Y 0.83 1.03 4.50
Z 0.68 0.50 2.16
OS-1 8.20 0 0
OS-2 3.50 5.63 25.68