HomeMy WebLinkAboutKECHTER TOWNHOMES - PDP200010 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT
AND EROSION CONTROL REPORT
July 22, 2020
Kechter Townhomes
Fort Collins, Colorado
Prepared for:
TWG
Ryan Kelly, Acquisitions Director
1301 East Washington Street, Suite 100
Indianapolis, IN 46202
317‐559‐7009
Prepared by:
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158
www.northernengineering.com
Project Number: 1664‐003
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.
301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com
July 17, 2020
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
Kechter Townhomes
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for your
review. This report accompanies the Preliminary Development Plan submittal for the proposed Kechter
Townhomes development.
This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM), and
serves to document the stormwater impacts associated with the proposed 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.
Deborah Spaustat, PE
Design Engineer
Kechter Townhomes
Final Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND EXISTING SITE INFORMATION ................................................................ 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 1
C. Existing Sub‐Basin Description .......................................................................................................... 2
II. Master Drainage Basin Information ................................................................................................. 3
III. Floodplain ........................................................................................................................................ 3
IV. Project Description .......................................................................................................................... 4
A. Overall Description ........................................................................................................................... 4
B. Sub‐Basin Description ....................................................................................................................... 5
V. PROPOSED DRAINAGE FACILITIES .................................................................................................... 5
A. Detention Basin and Outlet Design ................................................................................................... 5
B. Existing Storm Sewer in Kechter Road .............................................................................................. 6
C. WQCV design .................................................................................................................................... 6
D. LID Systems and design ..................................................................................................................... 6
E. Maintenance Access ......................................................................................................................... 7
F. Drainage Easements ......................................................................................................................... 7
VI. DRAINAGE DESIGN CRITERIA ........................................................................................................... 7
A. Regulations ........................................................................................................................................ 7
G. Four Step Process .............................................................................................................................. 7
H. Development Criteria Reference and Constraints ............................................................................ 8
I. Hydrological Criteria ......................................................................................................................... 8
J. Hydraulic Criteria .............................................................................................................................. 9
K. Detention Calculation Method ......................................................................................................... 9
L. Floodplain Regulations Compliance .................................................................................................. 9
M. Modifications of Criteria ............................................................................................................... 9
VII. CONCLUSIONS .................................................................................................................................. 9
A. Compliance with Standards .............................................................................................................. 9
N. Drainage Concept .............................................................................................................................. 9
References .................................................................................................................................................. 11
Kechter Townhomes
Final Drainage Report
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Detention Ponds
B.2 – Water Quality
B.3 – Storm Sewers
APPENDIX C – Erosion Control Report
APPENDIX D – LID Exhibit
APPENDIX F – References
LIST OF FIGURES:
Figure 1 – Aerial Photograph ........................................................................................................................ 2
Figure 2 – Existing Floodplapins .................................................................................................................... 3
Figure 3– Proposed Site Plan ........................................................................................................................ 4
MAP POCKET:
DR1 ‐ Drainage Exhibit
Kechter Townhomes
Final Drainage Report 1
I. GENERAL LOCATION AND EXISTING SITE INFORMATION
A. Location
1. Vicinity Map
2. A tract located in the southwest quarter of Section 4, Township 6 North, Range 68 West of
the 6th Prime Meridian, City of Fort Collins, County of Larimer, State of Colorado.
3. The project site is 4.68‐acres located at 3620 Kechter Road approximately one mile west of
the Kechter Road/I‐25 interchange. The site is situated between the Twin Silo Community
Park to the west and Observatory Village to the east with Radiant Park located directly south
across Kechter Road.
4. The project is located in the McClellands Creek drainage basin in the Master Drainage Study.
The direct outfall for stormwater from the site is the existing stormwater system in Kechter
Road, which discharges to the Muskrat Ditch on the south side of Kechter Road in Radiant
Park.
B. Description of Property
1. The project site is located in the Low Density Mixed‐Use Neighborhood District. Currently
the lot is mostly undeveloped containing one single family home and several outbuildings.
No stormwater infrastructure exists onsite.
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Final Drainage Report 2
2. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey the project site consists of Nunn clay loam and Fort
Collins loam, which fall into Hydrologic Soil Group C.
Figure 1 – Aerial Photograph
3. The existing site is generally comprised of undeveloped land with natural grasses and
vegetation. A house, gravel drive, and out‐buildings exist on the site.
4. This site will employ water quality features and runoff reduction facilities including rain
gardens, minimization of directed connected areas of imperviousness, and an extended
detention basin.
5. An irrigation ditch runs outside of the property along the north and east boundary lines to
Kechter Road.
6. There is an existing stormwater system in Kechter Road that was designed and installed as
part of the Willow Brook development (Observatory Neighborhood). The system comprises
storm manholes and 18” RCP pipe.
7. The Final Drainage Report for Willow Brook shows this storm sewer as the point of discharge
for detention pond E with a 100‐year release rate of 4.55‐cfs. The Developed Drainage Plan
in the report shows the discharge rate at 4.3‐cfs. The analysis of the storm sewer for the
current project uses 4.55‐cfs to be conservative.
C. Existing Sub‐Basin Description
1. Historically the property drains in four directions, as shown in the Existing Drainage Exhibit.
Kechter Townhomes
Final Drainage Report 3
The southwest quarter of the site (basin A) sheet flows offsite to the pond in Twin Silo Park.
The north half of the site (basin B) drains to a low spot in the center of the field and either
infiltrates into the ground or evaporates. Basin C at the south east corner of the site sheet
flows to Kechter Road and a small basin D sheet flows to the existing irrigation ditch
adjacent to the site.
2. A full analysis of the existing hydrology was not conducted since the detention requirements
are based on the McLellend Basin master plan and not historical release rates.
3. A full‐size copy of the Existing Drainage Exhibit and Proposed Drainage Exhibit can be found
in the Map Pocket at the end of this report.
II. Master Drainage Basin Information
1. Kechter Townhomes is located within the McClellands Basin, which encompasses 3.4 square
miles in Southeast Fort Collins. McClellands Creek conveys flow from upper end of the basin
northeast of College Avenue and Harmony road to down to its point of discharge to the
Fossil Creek Reservoir Inlet Ditch.
2. There are no recommended improvements in the master plan for the Kechter Townhomes
site. Onsite detention is being provided per the McClellands Basin master plan’s
requirement of 0.2‐cfs per acre for the minor storm event and 0.5‐cfs per acre for the major
storm event.
III. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
Figure 2 – Existing Floodplains
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Final Drainage Report 4
IV. Project Description
A. Overall Description
1. The project is proposing to create an affordable housing neighborhood with 60 townhomes
and a public loop road on a 4.68‐acre parcel of land off of Kechter Road. Vehicular
connections to the adjacent Observatory Neighborhood will be made at Eclipse Lane and
Quasar Way.
2. Two raingardens will treat 68% of the newly created impervious areas and an extended
detention basin will provide additional water quality treatment and detain runoff to
allowable release rates as allowed in the McClelland Basin Master Plan.
3. The site will discharge from the extended detention basin (EDB) to the existing stormwater
system in Kechter Road.
4. All runoff from the site will be diverted to the extended detention basin an. No runoff will
be allowed to flow directly to the irrigation ditch or adjacent properties.
Figure 3– Proposed Site Plan
Kechter Townhomes
Final Drainage Report 5
B. Sub‐Basin Description
1. The site is broken into ten sub‐basins that drain to one of three locations.
2. Runoff from sub‐basins A.1‐A.3 flows to Rain Garden A located in the southwest corner of
the site. Runoff in sub‐basin A.1 is collected in a grass swale and flows south along the
property line to the rain garden. A valley pan conveys runoff from the low point in A.3 to
A.2, where a chase drain under the sidewalk allows flow to enter the rain garden from the
gutter in A.2. The outlet of rain garden A discharges flow to the extended detention basin in
C.5.
3. Runoff from sub‐basin B.1 is collected in the open space in between the townhomes and
conveyed to rain garden B. Flow from sub‐basin B.2 is collected in curb and gutter and is
conveyed to the rain garden via a chase drain under the sidewalk at the southern end of the
open space. The outlet of rain garden B discharges flow to the extended detention basin in
C.5.
4. Runoff from sub‐basins C.1‐C.4 collect in swales and curb& gutter and directly to the
extended detention basin in C.5. The outfall of the EDB is the existing 18” RCP stormwater
system in Kecther Road. This storm system ultimately discharges to the Muskrat Ditch.
5. Table 1 summarizes the hydrologic characteristics of each subbasin and the total site.
Table 1 – Proposed Basin Hydrology Summary
Basin ID Basin
Area (ac)
Composite %
Imperv. C2 C100
Tc
(min)
Q2
(cfs)
Q100
(cfs)
A.1 0.50 52% 0.64 0.80 5.0 0.91 3.98
A.2 0.53 78% 0.82 1.00 5.0 1.23 5.28
A.3 0.53 77% 0.80 1.00 5.0 1.23 5.32
B.1 0.37 61% 0.71 0.89 5.0 0.75 3.26
B.2 0.60 77% 0.81 1.00 5.0 1.39 6.01
C.1 0.18 37% 0.53 0.66 5.0 0.27 1.18
C.2 0.11 71% 0.74 0.93 5.0 0.23 1.00
C.3 0.25 53% 0.65 0.82 5.0 0.46 2.01
C.4 1.24 72% 0.77 0.96 5.0 2.71 11.81
C.5 0.40 12% 0.33 0.41 5.0 0.38 1.65
Total Site 4.72 63%
V. PROPOSED DRAINAGE FACILITIES
A. Detention Basin and Outlet Design
1. The Extended Detention Basin was designed to limit release rates to the site to 0.2‐cfs/acres
for the minor storm event and 0.5cf/acres for the major event.
2. The major storm event release rate was calculated to be 2.34‐cfs based on the total onsite
area of 4.68‐acres. This results in a required detention volume of 38,279 ft3, or 0.879‐acre‐
ft.
3. The total volume provided in the extended detention basin in C.5 is 41,684 ft3, or 0.97‐acre‐
ft. Table 2 summarizes the onsite detention:
Kechter Townhomes
Final Drainage Report 6
Table 2: Extended Detention Basin Summary
Area of
Site
(acres)
Allowable
Q2 (cfs)
Allowable
Q100(cfs)
Water
Quality
Capture
Volume
(ft3)
Total
Volume
Required
(ft3)
Total
Volume
Provided
(ft3)
4.68 0.94 2.34 5,091 38,279 41,684
B. Existing Storm Sewer in Kechter Road
1. The existing storm sewer in Kechter road was modeled in Storm and Sanitary Analysis using
as‐built data from the existing conditions survey for pipe sizes and inverts and the proposed
connection from the extended detention basin in C.5.
2. The 100‐year flow from the existing detention pond C was assumed to be 4.55‐cfs and the
flow from the current project was assumed to be 2.34‐cfs.
3. The existing storm sewer has the capacity to convey the increase in flow from the current
project.
4. The results of the hydraulic model are included in the appendices.
C. WQCV design
1. The water quality capture volume for the extended basin was based on a 40‐hour drain
time.
2. Outletworks design that will address both the WQCV minor and major storm allowable
release rates will be provided with the Final Development Plan.
D. LID Systems and design
1. The LID for this project will be provided by two rain gardens, which will treat 59.3% of the
newly created impervious area.
2. The rain garden required volumes were based on a 12‐hour drain time. Table 3 summarizes
the rain gardens:
Table 3: Rain Garden Summary
Basin Area
(acre)
%
Imperv
Volume
(ft3)
Min Flat
Area
(ft2) Contributing Basins
Rain Garden A 1.57 69 1,480 944 A.1, A.2, A.3
Rain Garden B 0.97 71 944 599 B.1, B.2
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Final Drainage Report 7
3. Table 4 Summarizes the LID Project Requirements:
Table 4: LID Project Requirements
Project Summary
Total Impervious Area 133,658 sf
Target Treatment Percentage 50%
Minimum Area to be Treated by LID
measures 66,829 sf
Rain Garden A
Impervious Treatment Area 49,189 sf
Rain Garden B
Impervious Treatment Area 31,623 sf
Total Treatment Area 80,813 sf
Offsite Treatment Area 1,578 sf
Onsite Treatment Area 79,235 sf
Percent Total Project Area Treated 59.3%
4. Basins A.2 and A.3 include 1,578‐ft2 of offsite impervious area from Quasar Drive that will be
treated in Rain Garden A. While the Rain Garden is designed to include this area, the
calculations for required and provided treatment of imperviousness areas omit it.
E. Maintenance Access
5. The EDB and both rain gardens can be accessed directly from the Loop Road and an
easement on lots 4 and 5, block 3 for maintenance.
F. Drainage Easements
1. There is an
VI. DRAINAGE DESIGN CRITERIA
A. Regulations
1. There are no optional provisions outside of the FCSCM proposed with the Kechter project.
2. The project site has not been a part of any known previous drainage study, however, the
Final Drainage Report for Willow Brook, July 27, 2001, was referred to for the capacity
analysis of the offsite receiving storm system in Kechter Road.
G. Four Step Process
The overall stormwater management strategy employed with the Kechter Townhomes 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:
Kechter Townhomes
Final Drainage Report 8
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 rain gardens to provide additional
infiltration.
Providing on‐site detention to increase time of concentration, promote infiltration and
reduce loads on existing storm infrastructure.
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. A
majority of stormwater runoff from the site will ultimately be intercepted and treated in
proposed rain gardens and an extended detention basin. Water quality for areas not routed
through the rain gardens will be provided within the extended detention basin volume.
Step 3 – Stabilize Drainageways
This property discharges detained stormwater to an existing storm sewer system in Kechter
Road. The project does not directly impact any drainageways.
Step 4 – Implement Site Specific and Other Source Control BMPs.
The proposed project will improve upon site specific source controls compared to historic
conditions:
Trash receptacles within home will allow for the disposal of solid waste.
Rain Gardens and extended detention basins to provide for water treatment prior to flows
being released to existing drainageways and storm infrastructure.
Standard Operating Procedures (SOPs) for BMP maintenance of Rain Gardens, Detention
ponds, and associated drainage infrastructure to remove sediment accumulation regularly.
H. Development Criteria Reference and Constraints
1. The proposed site is a part of the McClelland Drainage Basin, which requires onsite
detention with a 0.2‐cfs.ac release rate for the 10‐year storm and a 0.5‐cfs/acre release rate
for the 100‐year storm.
2. City of Fort Collins standard water quality requirements include treatment of 50% of the site
runoff to be treated using the standard water quality treatment as described in the Fort
Collins Stormwater Manual, Volume 3‐Best Management Practices.
3. This site is subject to the LID requirements per the City of Fort Collins. Please see the LID
Exhibit located in the Appendix for calculations concerning LID treatment. For residential
neighborhoods with public streets, the City requires 50% of new or modified impervious
areas to be treated with LID methods.
I. Hydrological Criteria
1. The Rational Method was used to compute stormwater runoff using runoff coefficients from
Table 3.2‐2 of the FCSCM.
2. Storm intensities based on time of concentration were interpolated from The City of Fort
Collins Rainfall Intensity‐Duration‐Frequency Curves shown in Figure 3.4‐1 and Table 3.4‐1 of
the FCSCM.
3. Required detention storage was calculated using The Modified Federal Aviation
Administration (FAA) Procedure.
Kechter Townhomes
Final Drainage Report 9
4. The 2‐year storm event and the 100‐year storm event were used as the minor and major
design storms.
5. No other assumptions or calculation methods have been used with this development that
are not referenced by current City of Fort Collins criteria.
J. Hydraulic Criteria
1. All drainage facilities proposed with the Kechter Townhomes project are designed in
accordance with criteria outlined in the FCSCM.
2. Street capacity, inlet capacity, stormsewer capacity and swale sizing calculations will be
provided with the Final Development Plans.
K. Detention Calculation Method
1. Onsite detention is required to restrict the 10‐year storm release rate to 0.2‐cfs/ac and the
100‐year storm release rate to 0.5‐cfs/acre.
2. The Modified FAA Procedure was used to calculate the required detention volume based on
the area of the site as outlined in the FCSCM.
3. The volume of the pond was calculated using FCSCM Equation 6‐4 for conical stage storage
volume approximation.
L. Floodplain Regulations Compliance
1. The subject property is located outside of all FEMA regulated and local floodplains and is not
subject to any floodplain regulations.
M. Modifications of Criteria
1. No modifications to criteria are requested at this time.
VII. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the Kechter Townhomes project complies with the City
of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with the Kechter Townhomes project complies with the City
of Fort Collins’ Master Drainage Plan for the McLelland Basin.
3. There are no regulatory floodplains associated with the development.
4. The drainage plan and stormwater management measures proposed with the development
are compliant with all applicable State and Federal regulations governing stormwater
discharge.
5. The site achieves LID treatment for 59.3% of total impervious areas. This is 9.3% above the
requirements set forth by the City of Fort Collins for Low Impact Development (LID). Please
see LID Exhibit located in the Appendix.
N. Drainage Concept
1. The drainage design for Kechter Townhomes effectively captures runoff from the entire site
and safely conveys it via curb & gutter, swales, and storm sewer to two rain gardens and an
extended detention basin.
Kechter Townhomes
Final Drainage Report 10
2. Project LID requirements to treat a minimum of 50% of the newly created or modified
impervious areas is exceeded by 9.3%
3. Detention to achieve allowable release rates is provided by an extended detention basin,
which also provides water quality treatment.
4. 100% of the site is treated for water quality either by rain gardens and/or the extended
detention basin.
Kechter Townhomes
Final Drainage Report 11
References
1. 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.
2. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
4. Urban Storm Drainage Criteria Manual, Volumes 1‐3, Urban Drainage and Flood Control District,
Wright‐McLaughlin Engineers, Denver, Colorado, Revised April 2008.
5. Final Drainage Report for Willow Brook, TST Inc., Consulting Engineers, July 27, 2001.
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient1
Percentage
Impervious1 Project:
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt …………………........................... ................................................................................... 0.95 100% Date:
Concrete ……………… ........................... ................................................................................... 0.95 100%
Gravel (packed) ………........................... ................................................................................... 0.50 40%
Roofs………………….. ........................... ................................................................................... 0.95 90%
Pavers…………………. ........................... ................................................................................... 0.50 40%
Recycled Asphalt ........................... ................................................................................... 0.80 80%
Lawns and Landscaping
Playgrounds 25%
Sandy Soil
Flat <2% ………….. ........................... ................................................................................... 0.10 2%
Average 2% to 7% ........................... ................................................................................... 0.15 2%
Steep >7% ………… ........................... ................................................................................... 0.20 2%
Clayey Soil
Flat <2% ………….. ........................... ................................................................................... 0.20 2%
Average 2% to 7% ........................... ................................................................................... 0.25 2%
Steep >7% ………… ........................... ................................................................................... 0.35 2% 2-year Cf
= 1.00 10-year Cf = 1.00
USDA SOIL TYPE: C
Sub-Basin ID
Sub-Basin
Area
(sq. ft.)
Sub-Basin
Area
(ac.)
Area of
Asphalt &
Concrete
(ac.)
Area of Roofs
(ac.)
Area of
Pavers
(ac.)
Area of
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
A.1 21,897 0.50 0.049 0.228 0.000 0.225 0.64 0.64 0.80 52%
A.2 23,101 0.53 0.240 0.188 0.000 0.102 0.82 0.82 1.00 78%
A.3 23,281 0.53 0.290 0.133 0.000 0.111 0.80 0.80 1.00 77%
Project:
Calculations By:
Date:
A.1 A.1 0.50 5 5 0.64 0.80 2.85 9.95 0.91 3.98
A.2 A.2 0.53 5 5 0.82 1.00 2.85 9.95 1.23 5.28
A.3 A.3 0.53 5 5 0.80 1.00 2.85 9.95 1.23 5.32
B.1 B.1 0.37 5 5 0.71 0.89 2.85 9.95 0.75 3.26
B.2 B.2 0.60 5 5 0.81 1.00 2.85 9.95 1.39 6.01
C.1 C.1 0.18 5 5 0.53 0.66 2.85 9.95 0.27 1.18
C.2 C.2 0.11 5 5 0.74 0.93 2.85 9.95 0.23 1.00
C.3 C.3 0.25 5 5 0.65 0.82 2.85 9.95 0.46 2.01
C.4 C.4 1.24 5 5 0.77 0.96 2.85 9.95 2.71 11.81
C.5 C.5 0.40 5 5 0.33 0.41 2.85 9.95 0.38 1.65
DPA A.1,A.2, A.3, A.4 1.57 5 5 0.75 0.94 2.85 9.95 3.37 14.71
DPB B.1, B.2 0.97 5 5 0.77 0.97 2.85 9.95 2.14 9.34
DPC 1, C.2, C.3, C.4, C 4.72 5 5 0.71 0.89 2.85 9.95 9.55 41.69
D. Spaustat
Ketcher Townhomes
PROPOSED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
2-yr
Tc
(min)
C2
Intensity,
i100
(in/hr)
Sub-Basin(s)
Rational Method Equation:
Rainfall Intensity:
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
DESIGN PONTS
July 22, 2020
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
Q C f C i A
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 DETENTION POND
B.2 WATER QUALITY
B.3 STORM SEWER
APPENDIX B.1
DETENTION POND
Project No. BD-20-051
D.Spaustat
Pond No : Pond 1
1
100-yr
0.89
Area (A)= 4.68 acres 38279 ft
3
Max Release Rate = 2.34 cfs 0.879 ac-ft
Time Time 100-yr
Intensity Q
100
Inflow
(Runoff)
Volume
Outflow
(Release)
Volume
Storage
Detention
Volume
(mins) (secs) (in/hr) (cfs) (ft
3
) (ft
3
) (ft
3
)
5 300 9.950 41.38 12413 702.0 11711.4
10 600 7.720 32.10 19263 1404.0 17858.7
15 900 6.520 27.11 24403 2106.0 22296.7
20 1200 5.600 23.29 27946 2808.0 25137.8
25 1500 4.980 20.71 31065 3510.0 27554.8
30 1800 4.520 18.80 33834 4212.0 29622.4
35 2100 4.080 16.97 35631 4914.0 30716.9
40 2400 3.740 15.55 37328 5616.0 31711.6
45 2700 3.460 14.39 38850 6318.0 32531.7
50 3000 3.230 13.43 40297 7020.0 33276.9
55 3300 3.030 12.60 41582 7722.0 33859.9
60 3600 2.860 11.89 42817 8424.0 34393.0
65 3900 2.720 11.31 44114 9126.0 34988.5
70 4200 2.590 10.77 45237 9828.0 35409.3
75 4500 2.480 10.31 46410 10530.0 35880.0
80 4800 2.380 9.90 47508 11232.0 36275.9
85 5100 2.290 9.52 48568 11934.0 36634.3
90 5400 2.210 9.19 49629 12636.0 36992.8
95 5700 2.130 8.86 50490 13338.0 37151.6
100 6000 2.060 8.57 51400 14040.0 37360.4
105 6300 2.000 8.32 52398 14742.0 37656.4
110 6600 1.940 8.07 53247 15444.0 37802.8
115 6900 1.890 7.86 54232 16146.0 38086.4
120 7200 1.840 7.65 55093 16848.0 38245.2
125 7500 1.790 7.44 55829 17550.0 38279.3
130 7800 1.740 7.24 56441 18252.0 38188.6
135 8100 1.690 7.03 56927 18954.0 37973.1
Project Location : Fort Collins
Input Variables Results
Calculations By:
DETENTION POND CALCULATION; FAA METHOD
Project Name : Ketcher Housing
Project No. BD-20-051
D.Spaustat
Pond No : Pond 1
Detention Basin Volume- Conic Volume Approximation
Elevation Depth
(ft)
Area
(ft2)
Volume
(ft3)
Cumulative
Volume
(ft3)
Cumulative
Volume
(acre-ft)
4892 0.0 6,438 0 0 0.00
4893 1.0 6,769 6,602 6,602 0.15
4894 1.0 7,098 6,933 13,535 0.31
4895 1.0 8,723 7,897 21,432 0.49
4896 1.0 9,085 8,904 30,336 0.70
4897 1.0 13,774 11,348 41,684 0.96
Calculations By:
DETENTION POND CALCULATION; FAA METHOD
Project Name : Ketcher Housing
Date : July 22, 2020
Project Location : Fort Collins
APPENDIX B.2
WATER QUALITY
WATER QUALITY CAPTURE VOLUME DESIGN CALCULATIONS
40-Hour Detention (Extended Detention Basin)
Project: 1664-003
By: DCS
Date: 7/22/2020
EDB
REQUIRED STORAGE:
BASIN AREA = 4.72 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 63 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.6333 <-- CALCULATED
WQCV (watershed inches) = 0.25 <-- CALCULATED from USDCM Vol.3, Equation 3-1
V (ft
3
) = 5,091 <-- CALCULATED from USDCM Vol.3, Equation B-1
WATER QUALITY CAPTURE VOLUME DESIGN CALCULATIONS
12-Hour Detention (Rain Garden)
Project: 1664-003
By: DCS
Date: 7/2/2020
RAIN GARDEN A
REQUIRED STORAGE & SAND FILTER SIZE:
BASIN AREA = 1.57 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 69 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.6909 <-- CALCULATED
WQCV (watershed inches) = 0.22 <-- CALCULATED from USDCM Vol.3, Equation 3-1
V (ft
3
) = 1,480 <-- CALCULATED from USDCM Vol.3, Equation B-1
Af, Minimum Flat Filter Area (ft
2
) 944 <-- CALCULATED from USCDM Vol.3, Equation B-2
RAIN GARDEN B
REQUIRED STORAGE & SAND FILTER SIZE:
BASIN AREA = 0.97 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 71 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.7085 <-- CALCULATED
WQCV (watershed inches) = 0.22 <-- CALCULATED from USDCM Vol.3, Equation 3-1
V (ft
3
) = 944 <-- CALCULATED from USDCM Vol.3, Equation B-1
Af, Minimum Flat Filter Area (ft
2
) 599 <-- CALCULATED from USCDM Vol.3, Equation B-2
APPENDIX B.3
STORM SEWERS
APPENDIX C
EROSION CONTROL REPORT
Mountain’s Edge
Preliminary 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 existing and 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.
APPENDIX D
LID EXHIBIT
GAS
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
S
VAULT
ELEC
ELEC W
F
E
S
D
S
S S
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
D
E
VAULT
ELEC
T
VAULT
C ELEC
X
G
T
T
E
E
W
W W
W
W
W
W
T T
T
E
E
E E
E
X X X
X X X X X
X
X
X
X
X
X
E E
E
APPENDIX F
REFERENCES
Hydrologic Soil Group—Larimer County Area, Colorado
(Ketcher Townhomes)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
6/25/2020
Page 1 of 4
4483600 4483800 4484000 4484200 4484400 4484600 4484800
4483600 4483800 4484000 4484200 4484400 4484600 4484800
498300 498500 498700 498900 499100 499300 499500 499700 499900 500100
498300 498500 498700 498900 499100 499300 499500 499700 499900 500100
40° 30' 51'' N
105° 1' 18'' W
40° 30' 51'' N
104° 59' 52'' W
40° 30' 8'' N
105° 1' 18'' W
40° 30' 8'' N
104° 59' 52'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 450 900 1800 2700
Feet
0 100 200 400 600
Meters
Map Scale: 1:9,340 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
35 Fort Collins loam, 0 to 3
percent slopes
C 83.8 29.7%
36 Fort Collins loam, 3 to 5
percent slopes
C 28.4 10.1%
73 Nunn clay loam, 0 to 1
percent slopes
C 6.0 2.1%
74 Nunn clay loam, 1 to 3
percent slopes
C 143.8 51.0%
76 Nunn clay loam, wet, 1
to 3 percent slopes
C 17.0 6.0%
103 Stoneham loam, 5 to 9
percent slopes
B 3.1 1.1%
Totals for Area of Interest 282.0 100.0%
Hydrologic Soil Group—Larimer County Area, Colorado Ketcher Townhomes
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
6/25/2020
Page 3 of 4
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
3.0 Rational Method
3.4 Intensity-Duration-Frequency Curves for Rational Method
Page 8
Table 3.4-1. IDF Table for Rational Method
Duration
(min)
Intensity
2-year
(in/hr)
Intensity
10-year
(in/hr)
Intensity
100-year
(in/hr)
Duration
(min)
Intensity
2-year
(in/hr)
Intensity
10-year
(in/hr)
Intensity
100-year
(in/hr)
5 2.85 4.87 9.95
39 1.09 1.86 3.8
6 2.67 4.56 9.31
40 1.07 1.83 3.74
7 2.52 4.31 8.80
41 1.05 1.80 3.68
8 2.40 4.10 8.38
42 1.04 1.77 3.62
9 2.30 3.93 8.03
43 1.02 1.74 3.56
10 2.21 3.78 7.72
44 1.01 1.72 3.51
11 2.13 3.63 7.42
45 0.99 1.69 3.46
12 2.05 3.50 7.16
46 0.98 1.67 3.41
13 1.98 3.39 6.92
47 0.96 1.64 3.36
14 1.92 3.29 6.71
48 0.95 1.62 3.31
15 1.87 3.19 6.52
49 0.94 1.6 3.27
16 1.81 3.08 6.30
50 0.92 1.58 3.23
17 1.75 2.99 6.10
51 0.91 1.56 3.18
18 1.70 2.90 5.92
52 0.9 1.54 3.14
19 1.65 2.82 5.75
53 0.89 1.52 3.10
20 1.61 2.74 5.60
54 0.88 1.50 3.07
21 1.56 2.67 5.46
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
3.0 Rational Method
3.4 Intensity-Duration-Frequency Curves for Rational Method
Page 9
Figure 3.4-1. Rainfall IDF Curve – Fort Collins
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
GAS
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
S
VAULT
ELEC
ELEC W
F
E
S
D
S
S S
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
D
E
VAULT
ELEC
T
VAULT
C ELEC
X
G
T
T
E
E
W
W W
W
W
W
W
T T
T
E
E
E E
E
X X X
X X X X X
X
X
X
X
X
X
E E
E
X
G G G
G
G
G
W
ST
ST ST
ST
ST ST ST
ST
ST ST
ST
ST
ST
ST
SS
SS SS SS SS SS
SS
SS
SS SS
SS
SS
SS
X
X
X X X X X
X
X
X X X X X
X
X
X
X
T
T
T
T
T
C
A.2
0.53 AC
A.3
0.53 AC
A.1
0.50 AC
B.1
0.37 AC
B.2
0.60 AC
C.5
0.40 AC
C.2
0.11 AC
C.1
0.18 AC
C.4
1.25 AC
C.3
0.25 AC
RAIN
GARDEN A
WATER QUALITY POND 1
REQUIRED VOL=38,279 CF
PROVIDED VOL=41,633 CF
PROPOSED
SIDEWALK CHASE
STEPPED WALL
PROPOSED
SIDEWALK
CHASE
PROPOSED
SIDEWALK
CHASE
STORM DRAIN
RAIN GARDEN B
STORM DRAIN
POND OUTFALL
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED
STORM DRAIN
PROPOSED
MILD SWALE
RAIN GARDEN
OUTLET
RAIN GARDEN
OUTLET
ECLIPSE LANE
STREET B
)
STREET C
STREET D
QUASAR WAY
STREET A
PROPOSED CULVERT
(IRRIGATION DITCH)
PROPOSED CULVERT
(IRRIGATION DITCH)
PARCEL X
WILLOW BROOK
PARCEL W
WILLOW BROOK
PARCEL NO.
8604000904
PARCEL NO.
8604000904
VALLEY PAN
B
A
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
HYDROLOGY SUMMARY
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
Call before you dig.
R
NORTH
LID SUMMARY
EXTENDED DETENTION BASIN SUMMARY
A
1.62 AC
LEGEND:
PROPOSED CONTOUR
PROPOSED STORM SEWER
PROPOSED SWALE
EXISTING CONTOUR
PROPOSED CURB & GUTTER
PROPERTY BOUNDARY
PROPOSED INLET
DESIGN POINT A
FLOW ARROW
DRAINAGE BASIN LABEL
DRAINAGE BASIN BOUNDARY
PROPOSED SWALE SECTION
1 1
NOTES:
1. REFER TO THE FINAL DRAINAGE REPORT FOR WILLOW BROOK, JULY 27, 2001 BY
TST, INC. CONSULTING ENGINEERS FOR ADDITIONAL INFORMATION.
PROPOSED UNDERDRAIN UD
BENCHMARK
PROJECT DATUM: NAVD88
BENCHMARK #1:
City of Fort Collins Benchmark 2-03
Location: South side Kechter Road approximately 0.6 miles west of Strauss Cabin Road on the
east end of the south parapet wall of the bridge over the Dixon Canyon Lateral.
Elevation= 4898.14 (NAVD88)
BENCHMARK #2:
City of Fort Collins Benchmark 13-13
Location: On the west side of Strauss Cabin Road, approximately 90-ft south of Kechter Road,
on the northwest corner of a storm inlet.
Elevation= 4887.05 (NAVD88)
Please note: This plan set is using NAVD88 for a vertical datum. Surrounding developments
have used NGVD29 Unadjusted Datum (prior City of Fort Collins Datum) for their vertical
datums.
If NGVD29 Unadjusted Datum (prior City of Fort Collins Datum) is required for any purpose, the
following equation should be used: NGVD29 Unadjusted Datum (prior City of Fort Collins
Datum) = NAVD88 - 3.18'
Basis of Bearings
South line of the Southeast Quarter of Section 4-6-68 as bearing South 88°11'39" East.
EXISTING NATURAL HABITAT BUFFER ZONE
PROPOSED NATURAL HABITAT BUFFER ZONE
EXISTING WETLAND
Sheet
KECHTER TOWNHOMES 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
of 24
DR1
DRAINAGE EXHIBIT
24
DESIGN POINT SUMMARY
55 0.87 1.48 3.03
22 1.53 2.61 5.32
56 0.86 1.47 2.99
23 1.49 2.55 5.20
57 0.85 1.45 2.96
24 1.46 2.49 5.09
58 0.84 1.43 2.92
25 1.43 2.44 4.98
59 0.83 1.42 2.89
26 1.4 2.39 4.87
60 0.82 1.4 2.86
27 1.37 2.34 4.78
65 0.78 1.32 2.71
28 1.34 2.29 4.69
70 0.73 1.25 2.59
29 1.32 2.25 4.60
75 0.70 1.19 2.48
30 1.30 2.21 4.52
80 0.66 1.14 2.38
31 1.27 2.16 4.42
85 0.64 1.09 2.29
32 1.24 2.12 4.33
90 0.61 1.05 2.21
33 1.22 2.08 4.24
95 0.58 1.01 2.13
34 1.19 2.04 4.16
100 0.56 0.97 2.06
35 1.17 2.00 4.08
105 0.54 0.94 2.00
36 1.15 1.96 4.01
110 0.52 0.91 1.94
37 1.16 1.93 3.93
115 0.51 0.88 1.88
38 1.11 1.89 3.87
120 0.49 0.86 1.84
X
G G G
G
G
G
W
ST
ST ST
ST
ST ST ST
ST
ST ST
ST
ST
ST
ST
SS
SS SS SS SS SS
SS
SS
SS SS
SS
SS
SS
X
X
X X X X X
X
X
X X X X X
X
X
X
X
T
T
T
T
T
C
A.2
0.53 AC
A.3
0.53 AC
A.1
0.50 AC
B.1
0.37 AC
B.2
0.60 AC
C.5
0.40 AC
C.2
0.11 AC
C.1
0.18 AC
C.4
1.25 AC
C.3
0.25 AC
RAIN
GARDEN A
WATER QUALITY POND 1
REQUIRED VOL=38,279 CF
PROVIDED VOL=41,633 CF
PROPOSED
SIDEWALK CHASE
STEPPED WALL
PROPOSED
SIDEWALK
CHASE
PROPOSED
SIDEWALK
CHASE
STORM DRAIN
RAIN GARDEN B
STORM DRAIN
POND OUTFALL
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED SWALE
PROPOSED
STORM DRAIN
PROPOSED
MILD SWALE
RAIN GARDEN
OUTLET
RAIN GARDEN
OUTLET
ECLIPSE LANE
STREET B
)
STREET C
STREET D
QUASAR WAY
STREET A
PROPOSED CULVERT
(IRRIGATION DITCH)
PROPOSED CULVERT
(IRRIGATION DITCH)
PARCEL X
WILLOW BROOK
PARCEL W
WILLOW BROOK
PARCEL NO.
8604000904
PARCEL NO.
8604000904
VALLEY PAN
B
A
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
Call before you dig.
R
NORTH
LID PROJECT SUMMARY
A
1.62 AC
LEGEND:
PROPOSED CONTOUR
PROPOSED STORM SEWER
PROPOSED SWALE
EXISTING CONTOUR
PROPOSED CURB & GUTTER
PROPERTY BOUNDARY
PROPOSED INLET
DRAINAGE BASIN LABEL
DRAINAGE BASIN BOUNDARY
NOTES:
1. REFER TO THE FINAL DRAINAGE REPORT FOR WILLOW BROOK, JULY 27, 2001 BY
TST, INC. CONSULTING ENGINEERS FOR ADDITIONAL INFORMATION.
PROPOSED UNDERDRAIN UD
BENCHMARK
PROJECT DATUM: NAVD88
BENCHMARK #1:
City of Fort Collins Benchmark 2-03
Location: South side Kechter Road approximately 0.6 miles west of Strauss Cabin Road on the
east end of the south parapet wall of the bridge over the Dixon Canyon Lateral.
Elevation= 4898.14 (NAVD88)
BENCHMARK #2:
City of Fort Collins Benchmark 13-13
Location: On the west side of Strauss Cabin Road, approximately 90-ft south of Kechter Road,
on the northwest corner of a storm inlet.
Elevation= 4887.05 (NAVD88)
Please note: This plan set is using NAVD88 for a vertical datum. Surrounding developments
have used NGVD29 Unadjusted Datum (prior City of Fort Collins Datum) for their vertical
datums.
If NGVD29 Unadjusted Datum (prior City of Fort Collins Datum) is required for any purpose, the
following equation should be used: NGVD29 Unadjusted Datum (prior City of Fort Collins
Datum) = NAVD88 - 3.18'
Basis of Bearings
South line of the Southeast Quarter of Section 4-6-68 as bearing South 88°11'39" East.
Sheet
KECHTER TOWNHOMES 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
of 1
LID
(LID) EXHIBIT
LOW IMPACT DEVELOPMENT
1
LID BASIN/TREATMENT SUMMARY
LID A
1.57
LID B
0.97
LID BASIN LABEL
DRAINAGE BASIN BOUNDARY
LID B
0.97
Date : July 22, 2020
1.35
Design Point
Design Storm Required Detention Volume
Developed "C" =
B.1 15,992 0.37 0.006 0.237 0.000 0.124 0.71 0.71 0.89 61%
B.2 26,301 0.60 0.290 0.192 0.000 0.121 0.81 0.81 1.00 77%
C.1 7,842 0.18 0.000 0.071 0.000 0.109 0.53 0.53 0.66 37%
C.2 4,695 0.11 0.076 0.000 0.000 0.032 0.74 0.74 0.93 71%
C.3 10,781 0.25 0.000 0.143 0.000 0.105 0.65 0.65 0.82 53%
C.4 53,955 1.24 0.630 0.285 0.000 0.324 0.77 0.77 0.96 72%
C.5 17,558 0.40 0.017 0.028 0.000 0.358 0.33 0.33 0.41 12%
Total Site 205,404 4.72 1.599 1.505 0.000 1.611 0.71 0.71 0.89 63%
DPA 68,280 1.57 0.580 0.550 0.000 0.438 0.75 0.75 0.94 69%
DPB 42,292 0.97 0.296 0.429 0.000 0.245 0.77 0.77 0.97 71%
DPC 205,404 4.72 1.599 1.505 0.000 1.611 0.71 0.71 0.89 63%
Total Treated 110,572 2.54 0.876 0.979 0 0.683
Offsite Treated 1577.73 0.04 0.036 0.000 0 0.000
Total Onsite Treated 108,995 2.50 0.840 0.979 0 0.683
DESIGN POINTS
PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Ketcher Townhomes
D. Spaustat
July 22, 2020
1) Runoff coefficients are taken from the Fort Collins Stormwater Criteria Manaual, Table 4.1-3and Table 3.2-2.
100-year Cf = 1.25
Composite Runoff Coefficient with Adjustment