HomeMy WebLinkAboutTHE STANDARD AT FORT COLLINS - PDP - PDP160035 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT
The Standard at Fort Collins
Fort Collins, Colorado
October 18, 2016
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: 1290-001
P This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
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October 18, 2016
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
The Standard @ 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 Standard @ Fort Collins. Comments from the Preliminary Development Review
Letter dated September 1, 2016 have been addressed. Written responses thereto can be found in
the comprehensive response to comments letter on file with Current Planning.
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
Standard @ 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.
Nicholas W. Haws, PE Cody Snowdon
Project Manager Project Engineer
The Standard @ Fort Collins
Final 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 ....................................................................... 5
A. Major Basin Description ............................................................................................................... 5
B. Sub-Basin Description .................................................................................................................. 5
III. DRAINAGE DESIGN CRITERIA ................................................................................... 5
A. Regulations .................................................................................................................................. 5
B. Four Step Process ........................................................................................................................ 5
C. Development Criteria Reference and Constraints ......................................................................... 6
D. Hydrological Criteria .................................................................................................................... 7
E. Hydraulic Criteria ......................................................................................................................... 7
F. Floodplain Regulations Compliance .............................................................................................. 7
G. Modifications of Criteria .............................................................................................................. 7
IV. DRAINAGE FACILITY DESIGN .................................................................................... 8
A. General Concept .......................................................................................................................... 8
B. Specific Details ............................................................................................................................. 9
V. CONCLUSIONS ...................................................................................................... 13
A. Compliance with Standards ........................................................................................................ 13
B. Drainage Concept ...................................................................................................................... 13
References ....................................................................................................................... 14
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 – Erosion Control Report
The Standard @ Fort Collins
Final Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2 – Proposed Site Plan ............................................................................................... 3
Figure 3 – Existing FEMA Floodplains .................................................................................... 4
Figure 4 – Existing City Floodplains ....................................................................................... 4
MAP POCKET:
C8.00 - Drainage Exhibit
C8.01 – Historic Drainage Exhibit
The Standard @ Fort Collins
Final Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The Standard @ Fort Collins project is located in the southwest quarter of Section 14,
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 south of Lake Street and expands all the way to West
Prospect Road. It encompasses Blue Ridge Apartments (775 West Lake Street) and
four single family residences (900, 836 832, and 820 West Prospect Road).
4. Currently the existing lots do not have any stormwater or water quality facilities. The
northern property consists of Blue Ridge Apartments, which includes an existing
building, two parking lots and associated sidewalks. The southern properties consist
of single family residences, which includes, multiple buildings, gravel drives, and
associated sidewalks. The northern project site is composed of 81 percent
imperviousness, while the southern portion of the project is composed of only 20
percent imperviousness, resulting in an overall imperviousness of 49 percent. The
existing site all drains to both West Lake Street and West Prospect Road.
5. The project is currently bordered to the south by West Prospect Road, west by
The Standard @ Fort Collins
Final Drainage Report 2
Plymouth Congregational Church, north by West Lake Street and east by Farmhouse
Fraternity.
B. Description of Property
1. The Standard @ Fort Collins is approximately 4.23 net acres.
Figure 1 – Aerial Photograph
2. The Standard @ Fort Collins consists of five properties with five existing structures
and multiple out buildings. The northern lot consist of Blue Ridge Apartments with
two parking lots and associated sidewalks. The southern lot consists of four single
family residences with associated gravel driveways, multiple accessory buildings and
associated sidewalks. There is no off-site drainage entering the existing properties.
All runoff generated from the project drains either south to West Prospect Road or
north to West Lake Street.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey, 100 percent of the site consists of Altvan-
Satanta loam, which falls into Hydrologic Soil Groups B.
4. The proposed development will include the demolition of the existing structures,
parking lots, gravel drives and associated sidewalks. The proposed project will include
two large multi-family buildings, an internal parking structure and a central drive aisle
acting as a pedestrian spine between West Prospect Road and West Lake Street. The
central drive aisle and courtyards are planned to be composed of StormTech
chambers underneath the surface. These areas will act as a portion of the project’s
water quality and detention facility. Internal to Building B, a concrete vault is
proposed to treat stormwater through the use of a sand filter, as well as detaining the
major storm event. The surrounding green space will act as the remaining water
quality.
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Final Drainage Report 3
Figure 2– Proposed Site Plan
5. No irrigation facilities or major drainageways are within the property limits.
6. The project site is within the High Density Mixed-Use Neighborhood District (H-M-N)
Zoning District. The proposed use is permitted within the zone district.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
2. The FEMA Panel 0801010979H illustrates the proximity of the project site to the
nearest FEMA delineated regulatory floodplain. It is noted that the vertical datum
utilized for site survey work is the City of Fort Collins Benchmark #29-92
Elevation = 5025.67 (NAVD 88)
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Final Drainage Report 4
Figure 3 – Existing FEMA Floodplains
Figure 4 – Existing City Floodplains
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Final Drainage Report 5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The Standard @ Fort Collins is located within the Old Town Basin, which is located
primarily in Old Town Fort Collins.
B. Sub-Basin Description
1. The property historically drains from the southeast corner of the southern lots and to
the northeast corner of the northern lot. Stormwater is routed via overland flow across
the existing lots. The project only consists of two basins; Basin HN1 and HS1
representing the historic basin draining to the north and the historic basin draining to
the south, respectively. The stormwater within Historic Basin HN1, historically
discharges directly into West Lake Street at a rate of 4.11 cfs and 20.03 cfs for the
2-year and 100-year storm event, respectively. The stormwater within Historic Basin
HS1, historically discharges directly into West Prospect Road at a rate of 1.36 cfs and
6.21 cfs for the 2-year and 100-year storm event, respectively. See Section IV.A.4.
below, for a more detailed description of the projects proposed drainage patterns.
2. No drainage is routed onto the property from the surrounding properties.
A full-size copy of the Historic and Proposed Drainage Exhibit can be found in the
Map Pocket at the end of this report.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with The Standard @
Fort Collins project.
B. Four Step Process
The overall stormwater management strategy employed with The Standard @ 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:
Selecting a site that has been previously developed and currently consist of Blue
Ridged Apartments and single family residences, two asphalt parking lots, multiple
gravel access drives and associated sidewalks.
Providing vegetated open areas along the north, south, east and west portion of 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 both within the underground
detention section to increase time of concentration, promote infiltration and provide
initial water quality.
The Standard @ Fort Collins
Final Drainage Report 6
Routing runoff through the drain rock within the underground detention area to
increase time of concentration, promote infiltration and provide 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 stormwater generated from Building B will be routed internally and
discharge into a pond/sand filter located in the garage. The water quality event will be
filtered through the sand layer and discharge into West Lake Street. Stormwater generated
from the northern portion of the central drive will be either treated through the use of
StormTech Chambers or permeable pavers. Stormwater generated from the southern
portion of the central drive will be treated through the use of pavers. Stormwater
generated from Building A will be routed internal and discharge into StormTech Chambers
located around the building where it will be treated through the drain rock section. The
areas running off-site to the west and the east only consist of landscape area and will be
routed across landscape before leaving the site.
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 Standard @ Fort Collins, the
proposed project indirectly helps achieve stabilized drainageways nonetheless. Once again,
site selection has a positive effect on stream stabilization. By repurposing an already
developed, under-utilized site with existing stormwater infrastructure, combined with LID,
the likelihood of bed and bank erosion is greatly reduced. 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. There are no known drainage studies for the existing properties.
2. There are drainage studies for both the Stadium Apartments to the north and The Slab
Project east, but those projects will not have any effect on The Standard @ Fort
Collins project.
3. The subject property is essentially an "in-fill" development project as the property is
surrounded by currently developed properties. As such, several constraints have been
identified during the course of this analysis that will impact the proposed drainage
system including:
Existing elevations along the north property lines adjacent to West Lake Street will
be maintained. Existing elevations along the south property lines adjacent to the
West Prospect Road will be maintained. Existing elevations along the west will
also be maintained. Areas along the southern property line of Building B and east
of the southern half of the alley will be raised through use of a landscape wall.
As previously mentioned, overall drainage patterns within the Master Drainage
Basin will be maintained. To alleviate the current drainage problem within West
Lake Street, the majority of the drainage will be routed to West Prospect Road.
The Standard @ Fort Collins
Final Drainage Report 7
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 Rational Formula-based Modified Federal Aviation Administration (FAA)
procedure has been utilized for detention storage calculations.
4. Three separate design storms have been utilized to address distinct drainage
scenarios. A fourth design storm has also been computed for comparison purposes.
The first design storm considered is the 80th percentile rain event, which has been
employed to design the project’s water quality features. The second event analyzed is
the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third
event considered is the “Major Storm,” which has a 100-year recurrence interval.
The fourth 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 both West Lake Street
and West Prospect Road. The majority of the site drains stormwater via overland
flow.
2. All drainage facilities proposed with The Standard @ 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 not located within any
regulatory floodplain.
4. The Standard @ 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 Standard @ Fort Collins development is not requesting any
modification at this time.
The Standard @ Fort Collins
Final Drainage Report 8
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of The Standard @ Fort Collins drainage design are to maintain
existing drainage patterns, minimize the amount of drainage routed to West Lake
Street and ensure no adverse impacts to any adjacent properties.
2. As previously mentioned, there are no off-site flows draining 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 Standard @ Fort Collins project is composed of four major drainage basins,
designated as Basins N, S, ON, and OS. The drainage patterns for each major basin
are further described below.
Basin N
Basin N is further subdivided into three (3) sub-basins, designated as Basins N1, N2,
and N3. Sub-basin N1 is composed primarily of the drive located west of Building B
and the fire turnaround located north of Building A. It consists of some landscape
surfacing, but predominantly hardscape. Stormwater generated from this sub-basin is
routed via overland and gutter flow and discharges into underground StormTech
Chambers during the water quality event, while bypassing this system during the
major event and discharging undetained into Sub-basin A2. Sub-basin A2 is
composed primarily of the drive located west of Building B and consists of some
landscape surfacing, but predominantly hardscape. Stormwater generated from this
sub-basin is routed via overland flow and gutter flow and is treated through use of a
paver section. During the major storm event, runoff from both Basin A1 and A2 will
be discharged undetained into West Lake Street. Sub-basin N3 is composed entirely
of Building B. Stormwater generated from this sub-basin is routed internal to the
building and discharges into a detention structure within the parking garage. The
structure has two components incorporated within the design. The lower section of
the structure will include a sand bed and treat the stormwater before releasing the
Water Quality event into West Lake Street. The upper section will be open and used
for detention of storm events larger than the Water Quality event. The stormwater
within this section will be routed to West Prospect Road by use of a siphoned storm
drain.
Basin S
Basin S is further subdivided into six (6) sub-basins, designated as Basins S1-S6.
Sub-basin S1 is composed of the area to the west and north Building A, as well as a
portion of the roof from Building A. Stormwater generated from this sub-basin will be
routed both internal and external to the building and discharges directly into Detention
Pond S1. Pond S1 was designed with isolator rows to treat the Water Quality Event
and sized to detain the 100-year event. Sub-basin S2 is composed of the western
courtyard, as well as a portion of the roof from Building A. Stormwater generated from
this sub-basin will be routed both internal and external to the building and discharges
directly into Detention Pond S2. Pond S2 was designed with isolator rows to treat the
Water Quality Event and sized to detain the 100-year event. Sub-basin S3 is
The Standard @ Fort Collins
Final Drainage Report 9
composed of the central courtyard, as well as a portion of the roof from Building A.
Stormwater generated from this sub-basin will be routed both internal and external to
the building and discharges directly into Detention Pond S3. Pond S3 was designed
with isolator rows to treat the Water Quality Event and sized to detain the 100-year
event. Sub-basin S4 is composed of the eastern courtyard, as well as a portion of the
roof from Building A. Stormwater generated from this sub-basin will be routed both
internal and external to the building and discharges directly into Detention Pond S4.
Pond S4 was designed with isolator rows to treat the Water Quality Event and sized to
detain the 100-year event. Sub-basin S4 is composed of a portion of the roof from
Building A. Stormwater generated from this sub-basin will be routed internal to the
building and discharges directly into Detention Pond S5. Pond S5 was designed with
isolator rows to treat the Water Quality Event and sized to detain the 100-year event.
Basin ON
Basin ON is further subdivided into two (2) sub-basins, designated as Basins ON1 and
ON2. Sub-basin ON1 is composed primarily of the area located north of the Building
B, and consists of landscape sand public sidewalk. Stormwater generated from this
sub-basin is routed via overland flow and discharges undetained into West Lake
Street. Sub-basin ON2 is composed of a small area located east and south of Building
B and consists entirely of landscaping. Stormwater generated from this sub-basin is
routed via overland flow and discharges undetained to the east and south.
Basin OS
Basin OS is further subdivided into two (2) sub-basins, designated as Basins OS1 and
OS2. Sub-basin OS1 is composed primarily of the area located south of the Building
A, and consists of landscape sand public sidewalk. Stormwater generated from this
sub-basin is routed via overland flow and discharges undetained into West Prospect
Road. Sub-basin OS2 is composed of a small area located north of Building A and
consists entirely of landscaping. Stormwater generated from this sub-basin is routed
via overland flow and discharges undetained to the north.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
B. Specific Details
1. The main drainage problem associated with this project site is the deficiency of water
quality present within the existing site. The northern portion of the site (Blue Ridge
Apartments) drains overland and discharges directly into the West Lake Street without
water quality. The southern portion of the site (single family residences) drains
overland flow and discharges directly into the West Prospect Road without water
quality. The proposed site will mitigate this issue by instituting the following water
quality devices:
All of the runoff generated from the proposed roof of Building A (Sub-basin N3)
will be routed through a sand filter before discharging into West Lake Street.
All of the runoff generated from the proposed roof of Building A (Sub-basins S1-
S6) will be routed to StormTech Chambers and filter through the drain rock
surrounding the chambers before discharging in to West Prospect Road.
All of the runoff generated to the west of Building A (Sub-basin S1) will be treated
by a paver section, as well as the StormTech Chambers within the drive aisle.
The Standard @ Fort Collins
Final Drainage Report 10
The runoff generated from the central drive corridor will be treated through a
combination of the paver section and StormTech Chambers.
The landscape areas surrounding the project (Sub-basin ON1, ON2, OS1, and
OS2) will be treated by use of a grass buffer, as the run on area is less that 1:1.
2. The release rate for the undeveloped land (pre-development) was established by
calculating the 2-year peak runoff rate of the existing pervious area and the 100-year
peak runoff rate of the existing impervious area located within the project area,
resulting in an overall release of 23.68 cfs. In excluding all portions of the proposed
project that releases undetained (Sub-basins N1, N2, S6, OS1, OS2, ON1, and
ON2), the overall allowable peak runoff rate for the remaining site was calculated at
15.47 cfs. This remaining release rate was divided among Sub-Basins N2, S1, S2,
S3, S4 and S5. This release rates were utilized in the FAA method for design of
Ponds S1-S5 and N3. (Refer to Appendix B for these calculations).
3. Detention Pond Calculations
Pond N3
Calculations for Pond N3, based on the characteristics of Sub-basin N3 and an
adjusted release rate of 9.58 cfs, indicate a detention volume of 3,225 cu. ft. This
does not included the Water Quality Capture Volume (WQCV) of 2,484 cu. ft.,
resulting in an overall detention volume of 5,709 cu. ft. Water quality will be treated
through the use of a sand filter and discharge into West Lake Street, while overall
quantity detention will be released into West Prospect Road.
Pond S1
Calculations for Pond S1, based on the characteristics of Sub-basin S1 and an
adjusted release rate of 1.96 cfs, indicate a detention volume of 1,230 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (327 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond S2
Calculations for Pond S2, based on the characteristics of Sub-basin S2 and an
adjusted release rate of 1.01 cfs, indicate a detention volume of 1,123 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (224 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond S3
Calculations for Pond S3, based on the characteristics of Sub-basin S3 and an
adjusted release rate of 1.03 cfs, indicate a detention volume of 1,123 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (232 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
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Final Drainage Report 11
Pond S4
Calculations for Pond S4, based on the characteristics of Sub-basin S4 and an
adjusted release rate of 0.88 cfs, indicate a detention volume of 1,123 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (215 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond S5
Calculations for Pond S5, based on the characteristics of Sub-basin S5 and an
adjusted release rate of 1.01 cfs, indicate a detention volume of 620 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (239 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
4. Detention Pond Results
Pond N3
The total storage available within Pond N3 is 5,780 cu. ft at a High Water Surface
Elevation (HWSE) of 5030.4. The top of the structure will provide more than the
required 12-inches of freeboard. The WQCV is achieved at a water surface elevation
of 5028.5 feet, while the 100-year detention volume is achieved at a water surface
elevation of 5028.90 feet. In the case that the outlet structure within Pond N1 were
to clog, stormwater will exit the pond structure through vents within the exterior wall
and discharge into the drainage swale to the east that was designed for The Slab.
Once within this swale, the emergency flow will discharge directly into West Lake
Street.
Pond S1
The storage volume available within StormTech Vault Structure within Pond S1 is
1,230 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 16 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 469 cu. ft., while the volume achieved within
only the chambers of the isolator row is 235 cu. ft. In the case that the area inlet
within Sub-basin S1 should clog or backwatering should occur, stormwater would
overtop the inlet and discharge directly into West Prospect Road.
Pond S2
The storage volume available within StormTech Vault Structure within Pond S2 is
1,123 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 4 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 300 cu. ft., while the volume achieved within
only the chambers of the isolator row is 184 cu. ft. In the case that the outlet
structure within Sub-basin S2 should clog or backwatering should occur, stormwater
will bubble up from the outlet structure and overtop the wall located at the south end
of the courtyard and discharge directly into West Prospect Road.
The Standard @ Fort Collins
Final Drainage Report 12
Pond S3
The storage volume available within StormTech Vault Structure within Pond S3 is
1,123 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 4 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 300 cu. ft., while the volume achieved within
only the chambers of the isolator row is 184 cu. ft. In the case that the outlet
structure within Sub-basin S3 should clog or backwatering should occur, stormwater
will bubble up from the outlet structure and overtop the wall located at the south end
of the courtyard and discharge directly into West Prospect Road.
Pond S4
The storage volume available within StormTech Vault Structure within Pond S4 is
1,123 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 4 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 300 cu. ft., while the volume achieved within
only the chambers of the isolator row is 184 cu. ft. In the case that the outlet
structure within Sub-basin S4 should clog or backwatering should occur, stormwater
will bubble up from the outlet structure and overtop the wall located at the south end
of the courtyard and discharge directly into West Prospect Road.
Pond S5
The storage volume available within StormTech Vault Structure within Pond S5 is
620 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 4 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 117 cu. ft., while the volume achieved within
only the chambers of the isolator row is 59 cu. ft. In the case that the outlet
structure within Sub-basin S2 should clog or backwatering should occur, stormwater
bubble up from the outlet structure and overtop into the central drive aisle, where it
will be routed directly into West Prospect Road.
The Standard @ Fort Collins
Final Drainage Report 13
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with The Standard @ Fort Collins project complies with
the City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with The Standard @ 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 Standard @ Fort Collins
development.
4. The drainage plan and stormwater management measures proposed with The
Standard @ 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 Standard @ Fort Collins will detain for the
pervious area converted to impervious areas by releasing at the 2-year existing rate
during the developed100-year storm.
2. The proposed The Standard @ Fort Collins development will not impact the Master
Drainage Plan recommendations for the Old Town major drainage basin.
The Standard @ Fort Collins
Final Drainage Report 14
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.
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Standard @ Fort Collins
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: C. Snowdon
Asphalt ……....……………...……….....…...……………….………………………………….. 0.95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….. 0.50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
HN1 87709 2.01 0.84 0.27 0.61 0.00 0.30 0.83 0.83 1.00 81%
HS1 96447 2.21 0.00 0.14 0.25 0.24 1.58 0.33 0.33 0.41 20%
Total 184156 4.23 0.84 0.41 0.86 0.24 1.88 0.57 0.57 0.71 49%
HN1 (Impervious) 74619 1.71 0.84 0.27 0.61 0.00 0.00 0.95 0.95 1.00 95%
HN1 (Pervious) 13090 0.30 0.00 0.00 0.00 0.00 0.30 0.15 0.15 0.19 0%
HS2 (Impervious) 27620 0.63 0.00 0.14 0.25 0.24 0.00 0.78 0.78 0.97 71%
HS2 (Pervious) 68827 1.58 0.00 0.00 0.00 0.00 1.58 0.15 0.15 0.19 0%
HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Notes
October 18, 2016
Overland Flow, Time of Concentration:
Project: Standard @ Fort Collins
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
Rational Method Equation: Project: Standard @ Fort Collins
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
hn1 HN1 2.01 8 8 5 0.83 0.83 1.00 2.46 4.21 9.95 4.11 7.03 20.03
hs1 HS1 2.21 15 15 14 0.33 0.33 0.41 1.87 3.19 6.82 1.36 2.33 6.21
N/A HN1 (Impervious) 1.71 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 4.64 7.93 17.04
N/A HN1 (Pervious) 0.30 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.13 0.22 0.56
N/A HS2 (Impervious) 0.63 6 6 5 0.78 0.78 0.97 2.67 4.56 9.95 1.31 2.25 6.12
N/A HS2 (Pervious) 1.58 20 20 19 0.15 0.15 0.19 1.61 2.74 5.75 0.38 0.65 1.70
Total Release = 23.68
HISTORIC RUNOFF COMPUTATIONS
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
C. Snowdon
October 18, 2016
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
C2
Total allowable release from Basin Hs1
= 6.51
Total allowable release from Basin HN1
= 17.17
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C10 C
100
Q = C f ( C )( i )( A )
Page 3 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Hist-Direct-Runoff
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Standard @ Fort Collins
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt ……....……………...……….....…...……………….………………………………….0.. 95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….0.. 50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
N1 9556 0.219 0.000 0.152 0.000 0.000 0.020 0.047 0.73 0.73 0.91 62%
N2 6619 0.152 0.000 0.087 0.000 0.000 0.042 0.023 0.68 0.68 0.84 51%
N3 66237 1.521 0.000 0.000 1.520 0.000 0.000 0.000 0.95 0.95 1.00 90%
S1 17810 0.409 0.000 0.051 0.265 0.000 0.024 0.069 0.78 0.78 0.98 70%
S2 11793 0.271 0.000 0.038 0.179 0.000 0.000 0.054 0.79 0.79 0.99 72%
S3 11790 0.271 0.000 0.043 0.180 0.000 0.000 0.048 0.81 0.81 1.00 74%
S4 10923 0.251 0.000 0.031 0.174 0.000 0.000 0.045 0.81 0.81 1.00 74%
Overland Flow, Time of Concentration:
Project: Standard @ Fort Collins
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = T
i + Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Rational Method Equation: Project: Standard @ Fort Collins
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
n1 N1 0.22 5 5 5 0.73 0.73 0.91 2.85 4.87 9.95 0.45 0.78 1.98 1.98
n2 N2 0.15 5 5 5 0.68 0.68 0.84 2.85 4.87 9.95 0.29 0.50 1.28 1.28
n3 N3 1.52 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 4.12 7.03 15.13 9.58
s1 S1 0.41 5 5 5 0.78 0.78 0.98 2.85 4.87 9.95 0.91 1.56 3.98 1.96
s2 S2 0.27 5 5 5 0.79 0.79 0.99 2.85 4.87 9.95 0.61 1.04 2.67 1.01
s3 S3 0.27 5 5 5 0.81 0.81 1.00 2.85 4.87 9.95 0.62 1.07 2.69 1.03
s4 S4 0.25 5 5 5 0.81 0.81 1.00 2.85 4.87 9.95 0.58 0.98 2.50 0.88
s5 S5 0.21 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.56 0.95 2.04 1.01
s6 S6 0.18 7 7 5 0.68 0.68 0.85 2.60 4.44 9.95 0.32 0.55 1.53 1.53
on1 ON1 0.13 5 5 5 0.45 0.45 0.56 2.85 4.87 9.95 0.16 0.28 0.71 0.71
on2 ON2 0.15 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.06 0.11 0.28 0.28
os1 OS1 0.40 5 5 5 0.46 0.46 0.58 2.85 4.87 9.95 0.52 0.90 2.29 2.29
os2 OS2 0.08 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.03 0.06 0.14 0.14
Total 23.68
DEVELOPED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
C. Snowdon
October 18, 2016
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
100-year
Release Rate
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
n1 N1 0.219 0.73 0.91 5.0 5.0 0.45 1.98
n2 N2 0.152 0.68 0.84 5.0 5.0 0.29 1.28
n3 N3 1.521 0.95 1.00 5.0 5.0 4.12 15.13
s1 S1 0.409 0.78 0.98 5.0 5.0 0.91 3.98
s2 S2 0.271 0.79 0.99 5.0 5.0 0.61 2.67
s3 S3 0.271 0.81 1.00 5.0 5.0 0.62 2.69
s4 S4 0.251 0.81 1.00 5.0 5.0 0.58 2.50
s5 S5 0.205 0.95 1.00 5.0 5.0 0.56 2.04
s6 S6 0.182 0.68 0.85 6.9 5.0 0.32 1.53
on1 ON1 0.126 0.45 0.56 5.0 5.0 0.16 0.71
on2 ON2 0.150 0.15 0.19 5.0 5.0 0.06 0.28
os1 OS1 0.396 0.46 0.58 5.0 5.0 0.52 2.29
os2 OS2 0.076 0.15 0.19 5.0 5.0 0.03 0.14
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
hn1 HN1 2.014 0.83 1.00 7.7 5.0 4.11 20.03
hs1 HS1 2.214 0.33 0.41 15.1 13.8 1.36 6.21
Page 7 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\SUMMARY-TABLE
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers
B.2 – Inlets
B.3 – Detention Facilities
APPENDIX B.1
STORM SEWERS (FOR FUTURE USE)
APPENDIX B.2
INLETS (FOR FUTURE USE)
APPENDIX B.3
DETENTION FACILITIES
Pond No :
N2
100-yr
1.00
5.00 min 3225 ft3
1.52 acres 0.074 ac-ft
Max Release Rate = 9.50 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 4540 1.00 9.50 2850 1690
10 7.720 7045 0.75 7.13 4275 2770
15 6.520 8925 0.67 6.33 5700 3225
20 5.600 10221 0.63 5.94 7125 3096
25 4.980 11362 0.60 5.70 8550 2812
30 4.520 12375 0.58 5.54 9975 2400
35 4.080 13032 0.57 5.43 11400 1632
40 3.740 13652 0.56 5.34 12825 827
45 3.460 14209 0.56 5.28 14250 -41
50 3.230 14738 0.55 5.23 15675 -937
55 3.030 15208 0.55 5.18 17100 -1892
60 2.860 15660 0.54 5.15 18525 -2865
65 2.720 16135 0.54 5.12 19950 -3815
70 2.590 16545 0.54 5.09 21375 -4830
75 2.480 16974 0.53 5.07 22800 -5826
80 2.380 17376 0.53 5.05 24225 -6849
85 2.290 17764 0.53 5.03 25650 -7886
90 2.210 18152 0.53 5.01 27075 -8923
95 2.130 18466 0.53 5.00 28500 -10034
100 2.060 18800 0.53 4.99 29925 -11125
105 2.000 19165 0.52 4.98 31350 -12185
110 1.940 19475 0.52 4.97 32775 -13300
115 1.890 19835 0.52 4.96 34200 -14365
120 1.840 20150 0.52 4.95 35625 -15475
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Pond No :
s1
100-yr
0.98
5.00 min 1230 ft3
0.41 acres 0.028 ac-ft
Max Release Rate = 1.96 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 1196 1.00 1.96 588 608
10 7.720 1857 0.75 1.47 882 975
15 6.520 2352 0.67 1.31 1176 1176
20 5.600 2694 0.63 1.23 1470 1224
25 4.980 2994 0.60 1.18 1764 1230
30 4.520 3261 0.58 1.14 2058 1203
35 4.080 3434 0.57 1.12 2352 1082
40 3.740 3598 0.56 1.10 2646 952
45 3.460 3744 0.56 1.09 2940 804
50 3.230 3884 0.55 1.08 3234 650
55 3.030 4008 0.55 1.07 3528 480
60 2.860 4127 0.54 1.06 3822 305
65 2.720 4252 0.54 1.06 4116 136
70 2.590 4360 0.54 1.05 4410 -50
75 2.480 4473 0.53 1.05 4704 -231
80 2.380 4579 0.53 1.04 4998 -419
85 2.290 4681 0.53 1.04 5292 -611
90 2.210 4783 0.53 1.03 5586 -803
95 2.130 4866 0.53 1.03 5880 -1014
100 2.060 4954 0.53 1.03 6174 -1220
105 2.000 5050 0.52 1.03 6468 -1418
110 1.940 5132 0.52 1.02 6762 -1630
115 1.890 5227 0.52 1.02 7056 -1829
120 1.840 5310 0.52 1.02 7350 -2040
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S1
A =
Pond No :
s2
100-yr
0.99
5.00 min 1123 ft3
0.27 acres 0.026 ac-ft
Max Release Rate = 1.01 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 801 1.00 1.01 303 498
10 7.720 1243 0.75 0.76 454 789
15 6.520 1574 0.67 0.67 605 969
20 5.600 1803 0.63 0.63 757 1046
25 4.980 2004 0.60 0.61 908 1096
30 4.520 2183 0.58 0.59 1059 1123
35 4.080 2299 0.57 0.58 1211 1088
40 3.740 2408 0.56 0.57 1362 1046
45 3.460 2506 0.56 0.56 1514 993
50 3.230 2600 0.55 0.55 1665 935
55 3.030 2683 0.55 0.55 1816 866
60 2.860 2762 0.54 0.55 1968 795
65 2.720 2846 0.54 0.54 2119 727
70 2.590 2918 0.54 0.54 2270 648
75 2.480 2994 0.53 0.54 2422 573
80 2.380 3065 0.53 0.54 2573 492
85 2.290 3133 0.53 0.53 2724 409
90 2.210 3202 0.53 0.53 2876 326
95 2.130 3257 0.53 0.53 3027 230
100 2.060 3316 0.53 0.53 3178 138
105 2.000 3380 0.52 0.53 3330 51
110 1.940 3435 0.52 0.53 3481 -46
115 1.890 3499 0.52 0.53 3632 -134
120 1.840 3554 0.52 0.53 3784 -229
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Pond No :
s3
100-yr
1.00
5.00 min 1123 ft3
0.27 acres 0.026 ac-ft
Max Release Rate = 1.03 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 809 1.00 1.03 309 500
10 7.720 1255 0.75 0.77 464 792
15 6.520 1590 0.67 0.69 618 972
20 5.600 1821 0.63 0.64 773 1049
25 4.980 2024 0.60 0.62 927 1097
30 4.520 2205 0.58 0.60 1082 1123
35 4.080 2322 0.57 0.59 1236 1086
40 3.740 2432 0.56 0.58 1391 1042
45 3.460 2532 0.56 0.57 1545 987
50 3.230 2626 0.55 0.57 1700 926
55 3.030 2710 0.55 0.56 1854 856
60 2.860 2790 0.54 0.56 2009 782
65 2.720 2875 0.54 0.55 2163 712
70 2.590 2948 0.54 0.55 2318 630
75 2.480 3024 0.53 0.55 2472 552
80 2.380 3096 0.53 0.55 2627 469
85 2.290 3165 0.53 0.55 2781 384
90 2.210 3234 0.53 0.54 2936 299
95 2.130 3290 0.53 0.54 3090 200
100 2.060 3350 0.53 0.54 3245 105
105 2.000 3415 0.52 0.54 3399 16
110 1.940 3470 0.52 0.54 3554 -84
115 1.890 3534 0.52 0.54 3708 -174
120 1.840 3590 0.52 0.54 3863 -272
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Pond No :
s4
100-yr
1.00
5.00 min 1123 ft3
0.25 acres 0.026 ac-ft
Max Release Rate = 0.88 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 749 1.00 0.88 263 487
10 7.720 1163 0.75 0.66 394 769
15 6.520 1473 0.67 0.58 525 948
20 5.600 1687 0.63 0.55 656 1030
25 4.980 1875 0.60 0.53 788 1087
30 4.520 2042 0.58 0.51 919 1123
35 4.080 2151 0.57 0.50 1050 1101
40 3.740 2253 0.56 0.49 1181 1072
45 3.460 2345 0.56 0.49 1313 1032
50 3.230 2432 0.55 0.48 1444 988
55 3.030 2510 0.55 0.48 1575 935
60 2.860 2584 0.54 0.47 1706 878
65 2.720 2663 0.54 0.47 1838 825
70 2.590 2730 0.54 0.47 1969 762
75 2.480 2801 0.53 0.47 2100 701
80 2.380 2867 0.53 0.46 2231 636
85 2.290 2931 0.53 0.46 2363 569
90 2.210 2995 0.53 0.46 2494 502
95 2.130 3047 0.53 0.46 2625 422
100 2.060 3102 0.53 0.46 2756 346
105 2.000 3163 0.52 0.46 2888 275
110 1.940 3214 0.52 0.46 3019 195
115 1.890 3273 0.52 0.46 3150 123
120 1.840 3325 0.52 0.46 3281 44
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Pond No :
s5
100-yr
1.00
5.00 min 620 ft3
0.21 acres 0.014 ac-ft
Max Release Rate = 1.01 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 612 1.00 1.01 304 308
10 7.720 950 0.75 0.76 456 494
15 6.520 1203 0.67 0.68 608 595
20 5.600 1378 0.63 0.63 760 618
25 4.980 1531 0.60 0.61 912 620
30 4.520 1668 0.58 0.59 1064 604
35 4.080 1756 0.57 0.58 1216 541
40 3.740 1840 0.56 0.57 1368 473
45 3.460 1915 0.56 0.56 1520 396
50 3.230 1986 0.55 0.56 1671 315
55 3.030 2050 0.55 0.55 1823 226
60 2.860 2111 0.54 0.55 1975 135
65 2.720 2175 0.54 0.55 2127 47
70 2.590 2230 0.54 0.54 2279 -49
75 2.480 2288 0.53 0.54 2431 -143
80 2.380 2342 0.53 0.54 2583 -241
85 2.290 2394 0.53 0.54 2735 -341
90 2.210 2446 0.53 0.53 2887 -441
95 2.130 2489 0.53 0.53 3039 -550
100 2.060 2534 0.53 0.53 3191 -657
105 2.000 2583 0.52 0.53 3343 -760
110 1.940 2625 0.52 0.53 3495 -870
115 1.890 2673 0.52 0.53 3647 -973
120 1.840 2716 0.52 0.53 3799 -1083
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S5
A =
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 70.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.220 in
A = 0.41 ac
V = 0.0075 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
327 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins June 22, 2016
1290-001 C. Snowdon
Landmark
S1
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
ø
Pond No :
s1
WQ
0.78
5.00 min 229 ft3
0.41 acres 0.01 ac-ft
Max Release Rate = 0.14 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 136 1.00 0.14 41 95
10 1.105 212 1.00 0.14 82 129
15 0.935 268 0.67 0.09 82 186
20 0.805 308 0.63 0.09 103 205
25 0.715 342 0.60 0.08 123 219
30 0.650 373 0.58 0.08 144 229
35 0.585 392 0.57 0.08 165 227
40 0.535 410 0.56 0.08 185 225
45 0.495 426 0.56 0.08 206 221
50 0.460 440 0.55 0.08 226 214
55 0.435 458 0.55 0.07 247 211
60 0.410 471 0.54 0.07 267 203
65 0.385 479 0.54 0.07 288 191
70 0.365 489 0.54 0.07 309 181
75 0.345 495 0.53 0.07 329 166
80 0.330 505 0.53 0.07 350 156
85 0.315 513 0.53 0.07 370 142
90 0.305 525 0.53 0.07 391 135
95 0.290 527 0.53 0.07 411 116
100 0.280 536 0.53 0.07 432 104
105 0.270 543 0.52 0.07 452 90
110 0.260 547 0.52 0.07 473 74
115 0.255 561 0.52 0.07 494 68
120 0.245 563 0.52 0.07 514 49
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Client :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia I
a = 51.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 0.510
C) Tributary Watershed Area ATotal
= 6,619 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 1,843 sq ft
(Minimum recommended permeable pavement area = 1345 sq ft)
E) Impervious Tributary Ratio RT
= 1.3
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 92 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal
= cu ft
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 16.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.30
D) Slope of the Base Course/Subgrade Interface S = ft / ft
E) Length Between Lateral Flow Barriers L = ft
F) Volume Provided Based on Depth of Base Course V = 691 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sloped: V = P * [(Dmin - (D
min - 6*SL-1)) / 12] * Area
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells =
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
The Standard @ Fort Collins - Basin N2
Fort Collins, CO
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
October 18, 2016
Choose One
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = 2.0 ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
A) Depth of WQCV in the Reservoir DWQCV
= 2.00 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice
= inches
(Use a minimum orifice diameter of 3/8-inches)
Notes:
Fort Collins, CO
The Standard @ Fort Collins - Basin N2
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
October 18, 2016
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
WQ - Basin N2 - UD-BMP_v3.03.xlsm, PPS 10/18/2016, 11:14 AM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia I
a = 51.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 0.510
C) Tributary Watershed Area ATotal
= 6,619 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 1,843 sq ft
(Minimum recommended permeable pavement area = 1345 sq ft)
E) Impervious Tributary Ratio RT
= 1.3
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 92 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal
= cu ft
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 16.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.30
D) Slope of the Base Course/Subgrade Interface S = ft / ft
E) Length Between Lateral Flow Barriers L = ft
F) Volume Provided Based on Depth of Base Course V = 691 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sloped: V = P * [(Dmin - (D
min - 6*SL-1)) / 12] * Area
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells =
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
The Standard @ Fort Collins - Basin N2
Fort Collins, CO
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
October 18, 2016
Choose One
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = 2.0 ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
A) Depth of WQCV in the Reservoir DWQCV
= 2.00 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice
= inches
(Use a minimum orifice diameter of 3/8-inches)
Notes:
Fort Collins, CO
The Standard @ Fort Collins - Basin N2
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
October 18, 2016
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
WQ - Basin N3 - UD-BMP_v3.03.xlsm, PPS 10/18/2016, 11:14 AM
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 72.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.227 in
A = 0.27 ac
V = 0.0051 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
224 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins June 22, 2016
1290-001 C. Snowdon
Landmark
S2
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
ø
Pond No :
s2
WQ
0.78
5.00 min 176 ft3
0.27 acres 0.00 ac-ft
Max Release Rate = 0.07 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 90 1.00 0.07 21 69
10 1.105 140 1.00 0.07 42 98
15 0.935 178 0.67 0.05 42 135
20 0.805 204 0.63 0.04 53 151
25 0.715 227 0.60 0.04 64 163
30 0.650 247 0.58 0.04 74 173
35 0.585 260 0.57 0.04 85 175
40 0.535 271 0.56 0.04 96 176
45 0.495 283 0.56 0.04 106 176
50 0.460 292 0.55 0.04 117 175
55 0.435 303 0.55 0.04 127 176
60 0.410 312 0.54 0.04 138 174
65 0.385 317 0.54 0.04 149 169
70 0.365 324 0.54 0.04 159 165
75 0.345 328 0.53 0.04 170 158
80 0.330 335 0.53 0.04 180 154
85 0.315 340 0.53 0.04 191 149
90 0.305 348 0.53 0.04 202 146
95 0.290 349 0.53 0.04 212 137
100 0.280 355 0.53 0.04 223 132
105 0.270 360 0.52 0.04 233 126
110 0.260 363 0.52 0.04 244 119
115 0.255 372 0.52 0.04 255 117
120 0.245 373 0.52 0.04 265 108
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S2
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 74.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.235 in
A = 0.27 ac
V = 0.0053 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
232 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins June 22, 2016
1290-001 C. Snowdon
Landmark
S3
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
ø
Pond No :
s3
WQ
0.78
5.00 min 148 ft3
0.27 acres 0.00 ac-ft
Max Release Rate = 0.09 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 90 1.00 0.09 28 62
10 1.105 140 1.00 0.09 57 84
15 0.935 178 0.67 0.06 57 121
20 0.805 204 0.63 0.06 71 133
25 0.715 227 0.60 0.06 85 142
30 0.650 247 0.58 0.06 99 148
35 0.585 260 0.57 0.05 113 146
40 0.535 271 0.56 0.05 127 144
45 0.495 283 0.56 0.05 142 141
50 0.460 292 0.55 0.05 156 136
55 0.435 303 0.55 0.05 170 134
60 0.410 312 0.54 0.05 184 128
65 0.385 317 0.54 0.05 198 119
70 0.365 324 0.54 0.05 212 112
75 0.345 328 0.53 0.05 226 102
80 0.330 335 0.53 0.05 241 94
85 0.315 340 0.53 0.05 255 85
90 0.305 348 0.53 0.05 269 79
95 0.290 349 0.53 0.05 283 66
100 0.280 355 0.53 0.05 297 58
105 0.270 360 0.52 0.05 311 48
110 0.260 363 0.52 0.05 325 37
115 0.255 372 0.52 0.05 340 32
120 0.245 373 0.52 0.05 354 19
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S3
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 74.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.235 in
A = 0.25 ac
V = 0.0049 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
215 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins June 22, 2016
1290-001 C. Snowdon
Landmark
S4
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
ø
Pond No :
s4
WQ
0.78
5.00 min 156 ft3
0.25 acres 0.00 ac-ft
Max Release Rate = 0.07 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 84 1.00 0.07 21 62
10 1.105 130 1.00 0.07 42 87
15 0.935 165 0.67 0.05 42 122
20 0.805 189 0.63 0.04 53 136
25 0.715 210 0.60 0.04 64 146
30 0.650 229 0.58 0.04 74 155
35 0.585 241 0.57 0.04 85 156
40 0.535 251 0.56 0.04 96 156
45 0.495 262 0.56 0.04 106 156
50 0.460 270 0.55 0.04 117 153
55 0.435 281 0.55 0.04 127 154
60 0.410 289 0.54 0.04 138 151
65 0.385 294 0.54 0.04 149 145
70 0.365 300 0.54 0.04 159 141
75 0.345 304 0.53 0.04 170 134
80 0.330 310 0.53 0.04 180 130
85 0.315 315 0.53 0.04 191 123
90 0.305 322 0.53 0.04 202 121
95 0.290 324 0.53 0.04 212 111
100 0.280 329 0.53 0.04 223 106
105 0.270 333 0.52 0.04 233 100
110 0.260 336 0.52 0.04 244 92
115 0.255 344 0.52 0.04 255 90
120 0.245 345 0.52 0.04 265 80
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S4
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 90.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.321 in
A = 0.21 ac
V = 0.0055 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
239 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins June 22, 2016
1290-001 C. Snowdon
Landmark
S5
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
ø
Pond No :
s5
WQ
0.78
5.00 min 50 ft3
0.21 acres 0.00 ac-ft
Max Release Rate = 0.14 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 68 1.00 0.14 42 26
10 1.105 106 1.00 0.14 85 21
15 0.935 135 0.67 0.09 85 50
20 0.805 154 0.63 0.09 106 48
25 0.715 171 0.60 0.08 127 44
30 0.650 187 0.58 0.08 149 38
35 0.585 196 0.57 0.08 170 27
40 0.535 205 0.56 0.08 191 14
45 0.495 214 0.56 0.08 212 1
50 0.460 221 0.55 0.08 233 -13
55 0.435 230 0.55 0.08 255 -25
60 0.410 236 0.54 0.08 276 -40
65 0.385 240 0.54 0.08 297 -57
70 0.365 245 0.54 0.08 318 -73
75 0.345 248 0.53 0.08 340 -91
80 0.330 253 0.53 0.08 361 -108
85 0.315 257 0.53 0.07 382 -125
90 0.305 263 0.53 0.07 403 -140
95 0.290 264 0.53 0.07 425 -160
100 0.280 269 0.53 0.07 446 -177
105 0.270 272 0.52 0.07 467 -195
110 0.260 274 0.52 0.07 488 -214
115 0.255 281 0.52 0.07 509 -228
120 0.245 282 0.52 0.07 531 -249
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S5
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 62.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.194 in
A = 0.22 ac
V = 0.0035 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins June 22, 2016
1290-001 C. Snowdon
Landmark
N1
155 cu. ft.
Drain Time
a =
i =
WQCV =
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
ø
Pond No :
n1
WQ
0.78
5.00 min 128 ft3
0.22 acres 0.00 ac-ft
Max Release Rate = 0.07 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 73 1.00 0.07 21 52
10 1.105 113 1.00 0.07 41 72
15 0.935 144 0.67 0.05 41 103
20 0.805 165 0.63 0.04 51 114
25 0.715 183 0.60 0.04 62 122
30 0.650 200 0.58 0.04 72 128
35 0.585 210 0.57 0.04 82 128
40 0.535 219 0.56 0.04 93 127
45 0.495 228 0.56 0.04 103 125
50 0.460 236 0.55 0.04 113 123
55 0.435 245 0.55 0.04 123 122
60 0.410 252 0.54 0.04 134 118
65 0.385 256 0.54 0.04 144 113
70 0.365 262 0.54 0.04 154 108
75 0.345 265 0.53 0.04 165 101
80 0.330 271 0.53 0.04 175 96
85 0.315 274 0.53 0.04 185 89
90 0.305 281 0.53 0.04 195 86
95 0.290 282 0.53 0.04 206 77
100 0.280 287 0.53 0.04 216 71
105 0.270 291 0.52 0.04 226 64
110 0.260 293 0.52 0.04 237 57
115 0.255 301 0.52 0.04 247 54
120 0.245 301 0.52 0.04 257 44
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
C =
Tc =
A =
N1
Input Variables Results
Vault ID
Total
Required
WQ Volume
(cf)
Flow,
WQ
(cfs)
Chamber
Type
Chamber Release
Ratea
(cfs)
Chamber
Volumeb
(cf)
Installed Camber
w/ Aggregatec
(cf)
Mimimum
No. of
Chambersd
Total Release
Ratee
(cfs)
Required
Storage
Volume by
FAA Method
(cf)
Mimimum
No. of
Chambersf
Storage
Provided
within the
Chambersg
(cf)
Total
Installed
System
Volumeh
(cf)
S1 327 0.46 SC-160 0.011 14.70 29.30 12 0.14 229 16 235 469
S2 224 0.31 SC-740 0.024 45.90 74.90 3 0.07 176 4 184 300
S3 232 0.31 SC-740 0.024 45.90 74.90 4 0.09 148 4 184 300
S4 215 0.29 SC-740 0.024 45.90 74.90 3 0.07 156 4 184 300
S5 239 0.28 SC-310 0.016 14.70 29.30 9 0.14 50 4 59 117
N1 155 0.23 SC-160 0.011 14.70 29.30 6 0.07 128 9 132 264
a. Release rate per chamber, limited by flow through geotextile with accumulated sediment.
b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.
c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.
d. Number of chambers required to provide full WQCV within total installed system, including aggregate.
e. Release rate per chamber times number of chambers.
f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage).
g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume.
e. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV.
Chamber Configuration Summary
\\broncos\engineers\Projects\1290-001\Drainage\WatQual\1290-001 Chamber Summary.xlsx
Chamber Dimensions SC-310 SC-310 SC-740
Width (in) 25.0 34.0 51.0
Length (in) 84.4 85.4 85.4
Height (in) 12.0 16.0 30.0
Floor Area (sf) 14.7 20.2 30.2
Chamber Volume (cf) 6.9 14.7 45.9
Chamber/Aggregate Volume (cf) 15.0 29.3 74.9
Flow Rate* 0.35 gpm/sf
1 cf = 7.48052 gal
1 gallon = 0.133681 cf
1 GPM = 0.002228 cfs
*Flow rate based on 1/2 of Nov 07 QMAX in Figure 17 of UNH Testing Report
SC-160 SC-310 SC-740
Flow Rate/chamber (cfs) 0.011426 0.015724 0.023586
StormTech Chamber Data
Chamber Flow Rate
Chamber Flow Rate Conversion (gpm/sf to cfs)
\\broncos\engineers\Projects\1290-001\Drainage\WatQual\1290-001 Chamber Summary.xlsx
Design
Point Basin ID Basin Area Treatment Type
LID
System
Area
Treated by
LID System
Percent of Site
Treated by LID
System
Area of
Pavers
Area of
Asphalt
Parking
Percent
Pavers
Run-on Area
for Paver
Section
Run-on Area
Ratio
n1 N1 0.219 ac. StormTech
Chambers Yes 0.219 ac. 5% 0.020 ac. 0.152 ac. 13.16% 0.064 3.2
n2 N2 0.152 ac. Pavers Yes 0.152 ac. 4% 0.042 ac. 0.087 ac. 48.28% 0.087 2.1
n3 N3 1.521 ac. Sand Filter Yes 1.521 ac. 36% 0.000 ac. 0.000 ac. N/A 0 N/A
s1 S1 0.409 ac. StormTech
Chambers Yes 0.409 ac. 10% 0.024 ac. 0.051 ac. 47.06% 0 N/A
s2 S2 0.271 ac. StormTech
Chambers Yes 0.271 ac. 6% 0.000 ac. 0.038 ac. N/A 0 N/A
s3 S3 0.271 ac. StormTech
Chambers Yes 0.271 ac. 6% 0.000 ac. 0.043 ac. N/A 0 N/A
s4 S4 0.251 ac. StormTech
Chambers Yes 0.251 ac. 6% 0.000 ac. 0.031 ac. N/A 0 N/A
s5 S5 0.205 ac. StormTech
Chambers Yes 0.205 ac. 5% 0.000 ac. 0.000 ac. N/A 0 N/A
s6 S6 0.182 ac. Pavers Yes 0.182 ac. 4% 0.023 ac. 0.113 ac. 20.35% 0.0719 3.1
on1 ON1 0.126 ac. Grass Buffer No N/A 0% 0.000 ac. 0.047 ac. N/A 0 N/A
on2 ON2 0.150 ac. Grass Buffer No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
os1 OS1 0.396 ac. Grass Buffer No N/A 0% 0.000 ac. 0.155 ac. N/A 0 N/A
os2 OS2 0.076 ac. Grass Buffer No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
Total 4.23 ac. 3.481 ac. 82% 0.109 ac. 0.717 ac. 15.20%
APPENDIX D
EROSION CONTROL REPORT
Lake Avenue Apartments
Final Erosion Control Report
A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included
with the final construction drawings. It should be noted, however, that any such Erosion and
Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of
the BMPs depicted, and additional or different BMPs from those included may be necessary during
construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented
during construction, as well as permanent erosion control protection. Best Management Practices
from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are
not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways
and inlet protection at proposed storm inlets. Vehicle tracking control pads, spill containment and
clean-up procedures, designated concrete washout areas, dumpsters, and job site restrooms shall
also be provided by the Contractor.
Grading and Erosion Control Notes can be found on Sheet CS2 of the Utility Plans. The Utility
Plans at final design will also contain a full-size Erosion Control Plan as well as a separate sheet
dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets, the
Contractor shall be aware of, and adhere to, the applicable requirements outlined in any existing
Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior
to issuance of the Development Construction Permit. Also, the Site Contractor for this project will
be required to secure a Stormwater Construction General Permit from the Colorado Department of
Public Health and Environment (CDPHE), Water Quality Control Division – Stormwater Program,
before commencing any earth disturbing activities. Prior to securing said permit, the Site Contractor
shall develop a comprehensive StormWater Management Plan (SWMP) pursuant to CDPHE
requirements and guidelines. The SWMP will further describe and document the ongoing activities,
inspections, and maintenance of construction BMPs.
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
UP
D.S.
D.S.
R.D.
D.S.
D.S. D.S.
D.S.
D.S.
D.S.
D.S.
R.D.
D.S.
X X
X
X X X
X
X X X X
X
X X
X X
X
X
X X X X
X
X
X
UD UD UD UD
UD
UD
UD
W
UD
UD UD UD UD UD
UD UD
UD
MAJOR STORM EVENT
OUTLET FROM INTERNAL
POND STRUCTURE
WATER QUALITY EVENT
OUTLET FROM INTERNAL
POND STRUCTURE
s1
s1 s1
s1
s1
s2
s2 s3 s3
s4 s4
s5
s5
s6
n3
n3
n2
on1
on2
os2
os1
N3
ON1
S1
OS1
S3
S2
S4
OS2
N2
S5
S6
ON2
POND S4
(SC-740 CHAMBERS)
POND S3
(SC-740 CHAMBERS)
POND S2
(SC-740 CHAMBERS)
POND S1
(SC-160 CHAMBERS)
POND S5
(SC-310 CHAMBERS)
POND N2
(WITH SAND FILTER)
PROSPECT ROAD
(30' PUBLIC ROW)
LAKE STREET
(60' PUBLIC ROW)
THE SLAB
STADIUM APARTMENTS
STORM LINE C2
STORM LINE C1
STORM LINE B
STORM LINE A
UNDERDRAIN PERMEABLE
PAVERS
UNDERDRAIN
PERMEABLE
PAVERS
WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
POND OUTLET
STRUCTURE
POND OUTLET
STRUCTURE
POND OUTLET
STRUCTURE
POND OUTLET
STRUCTURE
POND OUTLET
STRUCTURE
WATER QUALITY
STRUCTURE
ROOF
LEADER
ROOF LEADER ROOF LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
AREA INLET
AREA INLET
STORM LINE A
OUTFALL
STORM LINE B
OUTFALL
SIDEWALK CHASE
SIDEWALK CHASE
SIDEWALK CHASE
STORM LINE C
OUTFALL
AREA INLET
AREA INLET W/
WATER QUALITY
PLATE
21 SC-160 CHAMBERS
FOR WATER QUALITY
N1
INFLOW CURB
& GUTTER
n1
THE SLAB
STORM WATER OUTFALL
STADIUM APARTMENTS
STORM WATER OUTFALL
Sheet
of 14
STANDARD AT FORT COLLINS These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
REVIEW SET
301 North Howes Street, Suite 100
Fort Collins, Colorado 80521
E NGINEER ING
N O R T H E RN
PHONE: 970.221.4158
www.northernengineering.com
C5.00
DRAINAGE EXHIBIT
GRAPHIC SCALE:
LEGEND:
ST
4950
4:1
NORTH
( IN FEET )
0
1 INCH = 20 FEET
20 20 40 60
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
Call before you dig.
R
A2
a3
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
NOTES:
14
RUNOFF SUMMARY TABLE:
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
Q2
(cfs)
Q100
(cfs)
N1 0.219 0.73 0.91 0.45 1.98
N2 0.152 0.68 0.84 0.29 1.28
N3 1.521 0.95 1.00 4.12 15.13
S1 0.409 0.78 0.98 0.91 3.98
S2 0.271 0.79 0.99 0.61 2.67
S3 0.271 0.81 1.00 0.62 2.69
S4 0.251 0.81 1.00 0.58 2.50
S5 0.205 0.95 1.00 0.56 2.04
S6 0.182 0.68 0.85 0.32 1.53
ON1 0.126 0.45 0.56 0.16 0.71
ON2 0.150 0.15 0.19 0.06 0.28
OS1 0.396 0.46 0.58 0.52 2.29
OS2 0.076 0.15 0.19 0.03 0.14
Design Point
Design Storm Required Detention Volume
Page 12 of 14
1290-001 Chamber Summary.xlsx
ö
ç
è
= æ
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 10 of 14
1290-001 Chamber Summary.xlsx
ö
ç
è
= æ
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 8 of 14
1290-001 Chamber Summary.xlsx
ö
ç
è
= æ
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 6 of 14
1290-001 Chamber Summary.xlsx
ö
ç
è
= æ
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 4 of 14
1290-001 Chamber Summary.xlsx
ö
ç
è
= æ
12 hr
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
WQ - Basin N3 - UD-BMP_v3.03.xlsm, PPS 10/18/2016, 11:14 AM
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
WQ - Basin N2 - UD-BMP_v3.03.xlsm, PPS 10/18/2016, 11:14 AM
Landmark
The Standard @ Fort Collins
1290-001
Project Name :
Project Number :
S1
Page 2 of 14
1290-001 Chamber Summary.xlsx
ö
ç
è
= æ
12 hr
Tc =
Project Location :
Design Point
C =
Design Storm
Page 1 of 1
1290-001_Pond S5_DetentionVolume_FAAModified Method.xls
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S4
Page 1 of 1
1290-001_Pond S4_DetentionVolume_FAAModified Method.xls
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S3
Page 1 of 1
1290-001_Pond S3_DetentionVolume_FAAModified Method.xls
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S2
Page 1 of 1
1290-001_Pond S2_DetentionVolume_FAAModified Method.xls
Tc =
Project Location :
Design Point
C =
Design Storm
Page 1 of 1
1290-001_Pond S1_DetentionVolume_FAAModified Method.xls
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond N2
Page 1 of 1
1290-001_Pond N2_DetentionVolume_FAAModified Method.xls
Q = C f ( C )( i )( A )
Page 6 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Direct-Runoff
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
n1 N1 No 0.73 0.73 0.91 25 9.40% 1.7 1.7 0.8 174 1.01% 2.01 1.4 0.5 N/A N/A 5 5 5
n2 N2 No 0.68 0.68 0.84 27 3.85% 2.6 2.6 1.6 157 1.70% 2.61 1.0 1.5 N/A N/A 5 5 5
n3 N3 No 0.95 0.95 1.00 N/A N/A N/A N/A 345 2.00% 2.83 2.0 1.5 N/A N/A 5 5 5
s1 S1 No 0.78 0.78 0.98 N/A N/A N/A N/A 80 2.00% 2.83 0.5 N/A N/A N/A 5 5 5
s2 S2 No 0.79 0.79 0.99 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s3 S3 No 0.81 0.81 1.00 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s4 S4 No 0.81 0.81 1.00 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s5 S5 No 0.95 0.95 1.00 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s6 S6 No 0.68 0.68 0.85 100 2.47% 5.8 5.8 3.5 120 0.93% 1.93 1.0 N/A N/A N/A 7 7 5
on1 ON1 No 0.45 0.45 0.56 19 5.05% 3.1 3.1 2.5 N/A N/A N/A N/A N/A N/A 5 5 5
on2 ON2 No 0.15 0.15 0.19 12 16.50% 2.4 2.4 2.3 N/A N/A N/A N/A N/A N/A 5 5 5
os1 OS1 No 0.46 0.46 0.58 41 3.56% 5.0 5.0 4.1 N/A N/A N/A N/A N/A N/A 5 5 5
os2 OS2 No 0.15 0.15 0.19 13 18.38% 2.4 2.4 2.3 N/A N/A N/A N/A N/A N/A 5 5 5
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter/Internal Building Flow Swale Flow
Design
Point
Basin
Overland Flow
C. Snowdon
October 18, 2016
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
Page 5 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr
S5 8937 0.205 0.000 0.000 0.205 0.000 0.000 0.000 0.95 0.95 1.00 90%
S6 7925 0.182 0.000 0.113 0.000 0.000 0.023 0.046 0.68 0.68 0.85 56%
ON1 5475 0.126 0.000 0.047 0.000 0.000 0.000 0.078 0.45 0.45 0.56 34%
ON2 6520 0.150 0.000 0.000 0.000 0.000 0.000 0.150 0.15 0.15 0.19 0%
OS1 17264 0.396 0.000 0.155 0.000 0.000 0.000 0.241 0.46 0.46 0.58 35%
OS2 3296 0.076 0.000 0.000 0.000 0.000 0.000 0.076 0.15 0.15 0.19 0%
TOTAL 184145 4.23 0.000 0.718 2.524 0.000 0.109 1.095 0.78 0.78 0.97 69%
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf = 1.00
October 18, 2016
**Soil Classification of site is Sandy Loam**
C. Snowdon
Page 4 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\C-Values
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
hn1 HN1 No 0.83 0.83 1.00 77 0.40% 6.0 6.0 2.2 205 1.01% 2.01 1.7 N/A N/A N/A 8 8 5
hs1 HS1 No 0.33 0.33 0.41 118 1.96% 12.5 12.5 11.2 N/A N/A N/A 113 0.23% 0.72 2.6 15 15 14
N/A HN1 (Impervious) No 0.95 0.95 1.00 77 0.40% 3.3 3.3 2.2 205 1.01% 2.01 1.7 N/A N/A N/A 5 5 5
N/A HN1 (Pervious) No 0.15 0.15 0.19 22 4.23% 5.2 5.2 4.9 N/A N/A N/A N/A N/A N/A 5 5 5
N/A HS2 (Impervious) No 0.78 0.78 0.97 84 2.13% 4.3 4.3 1.7 N/A N/A N/A 130 0.50% 1.06 2.0 6 6 5
N/A HS2 (Pervious) No 0.15 0.15 0.19 80 0.50% 20.0 20.0 19.2 N/A N/A N/A N/A N/A N/A 20 20 19
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
C. Snowdon
October 18, 2016
Design
Point
Basin
Overland Flow Gutter Flow Swale Flow Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
Page 2 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Hist-Tc-10-yr_&_100-yr
10-year Cf = 1.00
**Soil Classification of site is Sandy Loam**
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
Existing Impervious Area Breakdown
Page 1 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Hist-C-Values