HomeMy WebLinkAboutSEVEN GENERATIONS MULTIFAMILY - MJA220002 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT
PRELIMINARY DRAINAGE REPORT
FOR
Seven Generations Multifamily
Prepared by:
Highland Development Services
6355 Fairgrounds Ave, Suite 100
Windsor, Colorado 80550
Phone: 970.674.7550
Prepared for:
Black Timber Builders
417 Jefferson Street
Fort Collins, CO 80524
Office: 970.657.2399
September 14, 2022
Job Number 22-1057-00
Highland Development Services, Inc.
6355 Fairgrounds Avenue, Suite 100 | Windsor, CO 80550 | 970.674.7550
September 14, 2022
Fort Collins Utilities – Stormwater Department
700 Wood Street
Fort Collins, CO 80522
RE: Preliminary Drainage Report for Heartside Hill
Fort Collins Stormwater Department,
We are pleased to submit for your review, the Preliminary Drainage Report for the
redevelopment project Seven Generations Multifamily residential housing project. This report
describes the drainage design intent to be in accordance with the City of Fort Collins
Stormwater Criteria Manual.
We appreciate your time and consideration in reviewing this submittal. Please call if you have
any questions.
Sincerely,
Highland Development Services
Jason T. Claeys, P.E., LEED AP
Page i
TABLE OF CONTENTS
Table of Contents ............................................................................................................................. i
Engineer Certification ......................................................................................................................ii
General Description and Location .................................................................................................. 1
Site Description and Location ...................................................................................................... 1
Site Soils ....................................................................................................................................... 2
Storm Drainage Criteria .................................................................................................................. 3
Hydrologic Criteria ....................................................................................................................... 3
Hydraulic Criteria ......................................................................................................................... 3
Drainage Basins ............................................................................................................................... 4
Drainage Facility Design .................................................................................................................. 5
Drainage Conveyance Design ...................................................................................................... 5
Detention/Water Quality Pond Design ....................................................................................... 5
Low Impact Development ............................................................................................................... 6
Stormwater Pollution Prevention ................................................................................................... 8
Conclusions ..................................................................................................................................... 9
References .................................................................................................................................... 10
Appendix ....................................................................................................................................... 11
Appendix A – Site Descriptions, Characteristics, & References .................................................. A
Appendix B – Rational Calculations ............................................................................................. B
Appendix C – Low Impact Development Calculations ................................................................. C
Page ii
ENGINEER CERTIFICATION
I hereby certify that this report (plan) for the preliminary drainage design of Seven Generations
Multifamily was prepared by me (or under my direct supervision) in accordance with the
provisions of the City of Fort Collins Stormwater Criteria Manual and Construction of Public and
Private Improvements for the Responsible Parties thereof. I understand that the City of Fort
Collins does not and shall not assume liability for drainage facilities designed by others.
________________________________________
Jason T. Claeys, PE
Registered Professional Engineer
State of Colorado No. 42122
Page 1
GENERAL DESCRIPTION AND LOCATION
SITE DESCRIPTION AND LOCATION
The project site is situated in the southeast quarter of Section 30, Township 7 North, Range 68
West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, in the State of
Colorado. The property consists of Lot 2 and the south 85 feet of the west 410 feet of Lot 4 of
the New Hampshire Subdivision, west of the intersection of Vermont Drive and Eastbrook
Drive. It is bounded by open space owned by the City of Fort Collins to the north, Eastbrook
Drive to the east, commercial development to the south, and the Union Pacific Railroad to the
west.
The site was previously developed as commercial office spaces with one building, the parking
lot, and all of the utility infrastructure currently constructed. The total site, including the
existing improvements and commercial office building is approximately 3.64 acres. The area of
proposed redevelopment, approximately 1.28 acres, is currently unimproved and was originally
approved for two additional commercial office buildings and plaza space. The Seven
Generations Multifamily proposes to redevelop this area with the construction of a single 75-
unit multifamily building and supporting access and plaza spaces. The existing infrastructure,
parking and utilities, is to generally be protected in place and utilized to support the proposed
redevelopment. The project site generally slopes from the southeast to the northwest at
approximately 2% toward an existing water quality pond in the northwest corner of the
property. The water quality pond was designed and constructed to support the previous
commercial office development and is well established with vegetation. The intent is to protect
the existing water quality pond and be utilized to provide water quality enhancement for the
existing improvements.
No wetlands are located within the area of proposed redevelopment.
The project site is not located within the FEMA floodway or floodplain and is within the non-
printed FEMA FIRM panel 08069C1000F, effective 12/19/2006. The site is within the City of Fort
Collins Foothill Master Drainage Basin and the 100-yr floodplain is located along the west and
north sides of the property. The redevelopment area is outside of the City’s 100-yr floodplain.
Due to the vicinity of the site to this floodplain, timing of the peak runoff, and proposed
impervious area, on site detention was not required.
The proposed redevelopment includes a single 75-unit multifamily building and plaza space that
will provide the required emergency access. The existing improvements will generally be
protected in place and will provide the required parking, utility services, and standard water
Page 2
quality. A filtration gallery is proposed to provide additional the stormwater quality
enhancement and is intended to satisfy the low impact development (LID) requirement.
The site was previously analyzed within the “Final Drainage and Erosion Control Report for
Seven Generations Office,” prepared by Interwest Consulting Group, revised October 12, 2006.
SITE SOILS
The Seven Generations Multifamily redevelopment project site consists primarily of Nunn clay
loam and a small portion of Fort Collins loam both classified as Type C hydrologic group.
According to USDA/Natural Resource Conservation Group, Type C soils a have slow infiltration
rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the
downward movement of water or soils of moderately fine texture or fine texture. These soils
also have a slow rate of water transmission.
Per the “Preliminary Subsurface Exploration Report, 3400 Eastbrook Drive, Fort Collins,
Colorado,” prepared by Earth Engineering Consultants, Inc. dated March 2, 2006:
“A thin mantle of topsoil/vegetation was encountered at the surface at boring locations. The
topsoil/vegetation was underlain by clayey sand and in boring B-1 and sandy lean clay in
borings B-2 and B-3. The clayey sand and sandy lean clay showed low swell potential in
laboratory testing at present moisture and density. The essentially granular soils extended to
the bottom of borings B-1 while moderately cohesive soils extended to depths of approximately
14 and 8 ft, respectively, in borings B-2 and B-3.
The lean clay soils in boring B-2 and B-3 were underlain in poorly graded sand and gravel. The
granular soils were loose to medium dense with cobbles observed with depth. The sand and
gravel extended to the bottom of the borings at depths of approximately 15 feet below present
site grades.”
Groundwater was also observed during the subsurface soil exploration:
“Observations were made while drilling and after completion of the borings to detect the
presence and depth to the hydrostatic groundwater table. At the time of drilling, no free
groundwater was observed in the test borings.”
Page 3
STORM DRAINAGE CRITERIA
This preliminary drainage report was prepared to meet or exceed the City of Fort Collins
Stormwater Criteria Manual. The Criteria Manual and amendments to the Urban Drainage
Flood Control District’s (UDFCD) Drainage Criteria Manual (USDCM) Volumes 1, 2 and 3 were
referenced as guidelines for this design.
HYDROLOGIC CRITERIA
The rational method was performed to calculate the peak runoff rates for each basin. Percent
imperviousness and runoff coefficients were calculated for each basin using the surface
characteristics of each basin. The time of concentration was calculated using City of Fort Collins
initial time of concentration and the intensity was calculated using the corresponding storm
rainfall depth and the City of Fort Collins’ Intensity-Duration-Frequency Curve. The City of Fort
Collins area has a 2-yr, 1-hr rainfall depth of 0.82 inches and a 100-yr, 1-hr rainfall depth of 2.86
inches. These depths do account for the 1999 adjusted rainfall depths.
The proposed redevelopment rational calculations are compared to the pervious rational
calculations to review the impacts of this proposal.
HYDRAULIC CRITERIA
The existing storm drainage system will be reanalyzed to confirm conveyance of the minor and
major storm events through the combination of private drives, storm sewer pipes and swales.
Runoff flows determined with the rational method will be attenuated through the site. Inlet
capacities will be calculated using UDFCD’s spreadsheet UD-Inlet_v4.05.xlsm.
The Autodesk Hydraflow Express program will be used to compute the open channel hydraulics
and check the capacities of the drainage swales throughout the site. Flow velocities within
these swales will be reviewed and where flows are found to be supercritical, the swales will be
lined with turf reinforcement mat.
All swale and pipe outlets will be protected with riprap or suitable erosion protection methods.
Storm sewer pipe outlets will be protected using the requirements set by the USDCM for the
protection downstream of culverts.
All supporting calculations are located in the Appendix.
Page 4
DRAINAGE BASINS
The Seven Generations Multifamily drainage basins are delineated by areas draining through
the site and also in reference to previous basin delineation for comparison and review of
impacts. The site is divided into 4 main drainage basins:
Drainage Basin 1A:
Drainage Basin 1A is approximately 0.35 acres and 65.1% impervious. This basin consists of the
existing commercial office building and the adjacent existing landscape and walks. Runoff is
conveyed via existing storm drains to the existing water quality pond.
Drainage Basin 1B:
Drainage Basin 1A is approximately 0.98 acres and 77.6% impervious. This basin consists of
most of the redevelopment area. Runoff is conveyed to the Filtration Gallery and to the existing
water quality pond.
Drainage Basins 1A & 1B combined correlate to the previous Basin 1 of the Seven Generations
Office drainage study. Combined these basins are 1.33 acres and 74.4% impervious. This is an
increase in area of approximately 0.32 acres and increase of approximately 6% impervious.
There is an increase in runoff rates and the proposed Filtration Gallery offsets with impacts to
the existing water quality pond.
Drainage Basin 2:
Drainage Basin 2 is approximately 1.72 acres and 71.1% impervious. This basin consists of the
existing parking area, existing water quality pond, and the areas adjacent to the
south/west/north sides of the proposed multifamily building. Runoff is conveyed via surface
curb and pans to the existing water quality pond.
Majority of the existing and proposed redevelopment improvements are contained within
Basins 1A, 1B, and 2. Combined these basins are 3.05 acres and 72.5% impervious. Relating
back to the previous Seven Generations Office drainage study, this is a decrease in area of
approximately 0.12 acres and increase of approximately 6% impervious. There is a slight
increase in runoff rates that may be considered negligible.
Drainage Basin 3:
Drainage Basin 3 is approximately 0.83 acres and 32.8% impervious. This basin consists of the
existing west half of Eastbrook Drive, and open space to the north and west. Runoff is conveyed
offsite via curbs and overland surface flows.
Comparing the combination of all the drainage basins, there is an increase in 3% impervious
area.
Page 5
DRAINAGE FACILITY DESIGN
DRAINAGE CONVEYANCE DESIGN
The existing storm infrastructure to convey runoff includes swales, inlets, and storm drain
pipes. Stormwater water quality enhancement is achieved through the use of the existing water
quality pond and the proposed Filtration Gallery.
DETENTION/WATER QUALITY POND DESIGN
The existing water quality pond is intended to be protected with this proposed redevelopment
project and utilized to provide water quality enhancement for the existing improvements.
Similar to the previously approved Seven Generations Office project, this project is proposing to
provide water quality only with no detention with the following justifications:
- This site peaks at approximately 8.2 minutes, and the peak flow within the Foothills
Master Drainage Basin channel is over 3 hours. Runoff from this site does not contribute
to the peak flow (detained or undetained.) [the updated timing of the basin peak needs
to be confirmed but do not expect it to impact this justification]
The increase of impervious with this redevelopment proposal is not significant enough to
invalidate the previous detention waiver justification. Thus, this redevelopment proposal
anticipates that the detention waiver remains justified and supported.
Page 6
LOW IMPACT DEVELOPMENT
The City of Fort Collins updated the Low Impact Development ordinance in 2016 (Ordinance No.
007, 2016) to require:
· Treat at least 75% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques, or
· Treat at least 50% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques when 25% of private driveable surfaces are permeable.
To satisfy the required implementation of Low Impact Development (LID) techniques, Seven
Generations Multifamily proposes to utilize a Filtration Gallery to provide water quality
enhancement of the redevelopment area. The impervious area treated by the proposed
Filtration Gallery will exceed the required area of treatment.
Below is a description of the 4-step process for selecting structural BMPs:
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for
receiving water protection that focuses on reducing runoff volumes, treating the water quality
capture volume (WQCV), stabilizing drainageways and implementing long-term source controls.
The Four Step Process applies to the management of smaller, frequently occurring events.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low
Impact Development (LID) strategies, including Minimizing Directly Connected Impervious
Areas (MDCIA).
Captured runoff from strategic areas are routed through the filtration gallery. Filtration galleries
will slow runoff, promote infiltration, and filter runoff prior to being released into the adjacent
storm drain system.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release
The filtration gallery is designed to provide water quality capture volume per the City of Fort
Collins recommendations and supporting calculations.
Step 3: Stabilize Drainageways
Page 7
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate and volume of runoff during and following development. Because the site will
drain to an existing storm system, bank stabilization is unnecessary with this project.
Step 4: Implement Site Specific and Other Source Control BMPs
The proposed project will implement site specific source controls by managing the existing
localized trash enclosures within the development for disposal of solid waste; a filtration gallery
for water treatment prior to flows entering storm systems; and additional water quality
measures to protect and prolong the design life of BMPS delineated in Step 1.
All calculations are attached for reference.
Page 8
STORMWATER POLLUTION PREVENTION
Erosion and sedimentation will be controlled on-site by use of sediment control logs, inlet
protection, and gravel construction entrances. The measures are designed to limit the overall
sediment yield increase due to construction as required by the City of Fort Collins. During
overlot and final grading the soil will be roughened and furrowed perpendicular to the
prevailing winds.
During the performance of the work required by these specifications or any operations
appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the
contractor shall furnish all labor, equipment, materials, and means required. The Contractor
shall carry out proper efficient measures wherever and as necessary to reduce dust nuisance,
and to prevent dust nuisance that has originated from his operations from damaging crops,
orchards, cultivated fields, and dwellings, or causing nuisance to persons. The Contractor will be
held liable for any damage resulting from dust originating from his operations under these
specifications on right-of-way or elsewhere.
It is unlawful to track or cause to be tracked mud or other debris onto public streets or rights-
of-way. Wherever construction vehicles access routes or intersect paved public roads,
previsions must be made to minimize the transport of sediment by runoff or vehicles tracking
onto the paved surface. Stabilized construction entrances are required with base material
consisting of 6” coarse aggregate. The contractor will be responsible for clearing mud tracked
onto public streets on a daily basis.
All temporary and permanent erosion and sediment control practices must be maintained and
repaired as needed to assure continued performance of their intended function. Maintenance
is the responsibility of the contractor.
All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation
shall not be considered established until a ground cover is achieved which is demonstrated to
be mature enough to control soil erosion to the satisfaction of the City Inspector and to survive
severe weather condition.
Page 9
CONCLUSIONS
This Preliminary Drainage Report for Seven Generations Multifamily has been prepared to
comply with the stormwater criteria set by the City of Fort Collins. The proposed drainage
system will be designed to convey the developed peak 100-yr storm water runoff through the
site, and ultimately to the existing drainage features. Drainage conveyance systems will be
designed to convey drainage to the proposed roadways and collect onsite drainage and treat it
in accordance with LID requirements before discharging to the existing water quality pond and
offsite. This preliminary drainage report anticipates the implementation of best management
practices for erosion control, temporary and permanent, and on-site construction facilities.
It can therefore be concluded that development of Seven Generations Multifamily will comply
with the storm water jurisdictional criteria and the approved City of Fort Collins Stormwater
Criteria Manual and will not adversely affect the adjacent properties, streets, storm drain
system and/or detention/water quality facilities.
Page 10
REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood
Control District, June 2001, Revised January 2016.
2. Fort Collins Stormwater Criteria Manual, Fort Collins Utilities, City of Fort Collins,
Colorado, Dated December 2018, Adopted January 2019.
3. “Hydrologic Group Rating for Larimer County Area, Colorado”, USDA-Natural Resources
Conservation Service, National Cooperative Soil Survey. Web Soil Survey URL:
http://websoilsurvey.nrcs.usda.gov. [9/6/2022]
4. “Preliminary Subsurface Exploration Report, 3400 Eastbrook Drive, Fort Collins,
Colorado,” prepared by Earth Engineering Consultants, Inc. dated March 2, 2006.
5. Final Drainage and Erosion Control Report for Seven Generations Office,” prepared by
Interwest Consulting Group, revised October 12, 2006.
Page 11
APPENDIX
Appendix A – Site Descriptions, Characteristics, & References
Appendix B – Rational Calculations
Appendix C – Low Impact Development Calculations
Appendix A
APPENDIX A – SITE DESCRIPTIONS, CHARACTERISTICS, & REFERENCES
SITE
E. DRAKE RD
UNION PACIFIC RAILROADS. TIMBERLINE RDE. HORSETOOTH RDS. LEMAYAVEVicinity Map
Scale: 1" = 1000'
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK #43-01
EAST SIDE OF TIMBERLINE ROAD, AT THE SOUTH ENTRANCE TO C.S.U. RIGDEN FARM, ON THE NORTH END OF THE
HEAD WALL OF A STORM DITCH
ELEV= 4937.02
CITY OF FORT COLLINS BENCHMARK #12-93
NORTHWEST CORNER OF HORSETOOTH ROAD AND TIMBERLINE ROAD, ON A SIGNAL POLE BASE
ELEV= 4957.08
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 EQUATIONS SHOULD BE USED:
NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) = 4937.02 (NAVD88 DATUM) - 3.18'
NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) = 4957.08 (NAVD88 DATUM) - 3.19'
Hydrologic Soil Group—Larimer County Area, Colorado
(Seven Generations)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/6/2022
Page 1 of 44487940448796044879804488000448802044880404488060448808044879404487960448798044880004488020448804044880604488080496300496320496340496360496380496400496420496440496460496480496500496520
496300 496320 496340 496360 496380 496400 496420 496440 496460 496480 496500 496520
40° 32' 36'' N 105° 2' 37'' W40° 32' 36'' N105° 2' 27'' W40° 32' 31'' N
105° 2' 37'' W40° 32' 31'' N
105° 2' 27'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 45 90 180 270
Feet
0 10 20 40 60
Meters
Map Scale: 1:1,010 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 16, Sep 2, 2021
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 2, 2021—Aug 25,
2021
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
(Seven Generations)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/6/2022
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
36 Fort Collins loam, 3 to 5
percent slopes
C 0.2 4.8%
74 Nunn clay loam, 1 to 3
percent slopes
C 3.7 79.0%
76 Nunn clay loam, wet, 1
to 3 percent slopes
C 0.8 16.2%
Totals for Area of Interest 4.6 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Hydrologic Soil Group—Larimer County Area, Colorado Seven Generations
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/6/2022
Page 3 of 4
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado Seven Generations
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/6/2022
Page 4 of 4
National Flood Hazard Layer FIRMette
0 500 1,000 1,500 2,000250
Feet
Ü
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or DepthZone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mileZone X
Future Conditions 1% Annual
Chance Flood HazardZone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood HazardZone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 9/12/2022 at 7:11 PM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
8
B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
105°2'51"W 40°32'48"N
105°2'14"W 40°32'20"N
Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020
2,257
376.2
Seven Generations Multifamily
This map is a user generated static output from the City of Fort Collins FCMaps
Internet mapping site and is for reference only. Data layers that appear on this
map may or may not be accurate, current, or otherwise reliable.
City of Fort Collins - GIS
286.0
1:
WGS_1984_Web_Mercator_Auxiliary_Sphere
Feet286.00143.00
Notes
Legend
1,715
FEMA Floodplain
FEMA High Risk - Floodway
FEMA High Risk - 100 Year
FEMA Moderate Risk - 100 / 500 Year
City Floodplains
City High Risk - Floodway
City High Risk - 100 Year
City Moderate Risk - 100 Year
City Limits
NearMap Logo
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
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
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
FOOTHILLS BASIN HYDROLOGY UPDATE
AND ALTERNATIVE ANALYSIS AT DRAKE
RD. AND LEMAY AVE.
Prepared by: Prepared for:
Enginuity Engineering Solutions, LLC (Enginuity) City of Fort Collins – Utility Department
10106 W. San Juan Way, Ste 215 700 Wood St.
Littleton, CO 80127 Fort Collins, CO 80522
February 2020
FOOTHILLS BASINS
UPDATE
SUB624
SUB621
SUB64
SUB63
SUB650
SUB58SUB59
SUB584
SUB53
SUB57
SUB55
SUB47
SUB56
SUB54SUB48
SUB46
SUB671SUB66
SUB67
SUB581
SUB583SUB582
SUB68 SUB691
SUB69
SUB681
SUB682
SUB651
SUB622
SUB61
SUB60
SUB52
SUB150
SUB50
SUB51
SUB49
SUB45
SUB144
SUB44
SUB40
SUB142
SUB43
SUB37
SUB39SUB38
SUB26
SUB29
SUB30
SUB28
SUB36
SUB33
SUB35
SUB34
SUB25N
SUB24
SUB22
SUB15
SUB19
SUB17
SUB14
SUB16
SUB12
SUB11SUB8SUB7SUB6
SUB10
SUB105
SUB5
SUB4
SUB78
SUB75
SUB2
SUB3 SUB31
SUB70SUB71
SUB18 SUB27
SUB65
SUB623
SUB32
SUB252
SUB255
SUB249
SUB251
SUB250
SUB248
SUB254
SUB253
SUB243
SUB240
SUB241
SUB242
SUB247
SUB246
SUB244
SUB245
SUB25S
Esri, HERE, Garmin, (c) OpenStreetMap contributors, and the GIS user community, Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community
0 0.5 10.3
Miles ¹
Foothills Impervious Update
Difference in Impervious
(Updated - MODSWMM)
≤-30
≤-15
≤-5
≤5
≤15
≤40
Development_Change_Areas
DRAKE RD.COLLEGE RD.LEMAY AVE.
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Apr-12-2022 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
Appendix B
APPENDIX B – RATIONAL CALCULATIONS
Design Engineer:
Design Firm:
Project Number:
Date:
DRAINAGE SUMMARY:
Q2
(ft3/s)
Q10
(ft3/s)
Q100
(ft3/s)
Q2
(ft3/s)
Q10
(ft3/s)
Q100
(ft3/s)
Q2
(ft3/s)
Q10
(ft3/s)
Q100
(ft3/s)
1 1.01 68% 2.2 3.7 9.6 1A+1B 1.33 74% 2.7 4.6 13.2 0.32 6% 0.5 0.9 3.6
2 2.15 67% 3.5 6.0 16.4 2 1.72 71% 2.8 4.7 13.1 -0.43 4% -0.7 -1.3 -3.3
1+2 3.17 67%5.1 8.9 24.6 1A+1B+2 3.05 73%5.2 8.9 24.8 -0.12 6%0.1 0.0 0.2
3 0.71 35%0.9 1.5 3.9 3 0.83 33%0.8 1.4 3.7 0.12 -2%-0.1 -0.1 -0.2
Totals 3.88 61%Totals 3.88 64%0.00 3%
J.Claeys
Highland Development Services, Inc.
22-1057-00
September 13, 2022
Seven Generations Multifamily
DRAINAGE SUMMARY
Peak Runoff
Comparison
Seven Generations
Multifamily Basins
Area
(acres)
%
Imprevious
Area
(acres)
%
Imprevious
Previous Redeveloped
Peak Runoff Peak RunoffSeven Generations
Office Park Basins
Area
(acres)
%
Imprevious
22-1057-00 Rational Calcs.xlsx Page 1 of 5 Interwest Consulting Group
Design Engineer:
Design Firm:
Project Number:
Date:
%
Impervious
Runoff
Coefficient C
Return
Period
Frequency
Adjustment
Factor (Cf)
100% 0.95
2-year to
10-year 1.00
90% 0.95 100-year 1.25
90% 0.95
40% 0.50
0% 0.20
C2 to C10 C100
1A 15,031 0.35 0 10,034 845 0 4,152 65.1% 0.74 0.93
1B 42,894 0.98 8,146 27,640 312 0 6,797 77.6% 0.83 1.00
1A+1B 57,925 1.33 8,146 37,674 1,157 0 10,948 74.4% 0.81 1.00
2 74,920 1.72 52,663 0 687 0 21,571 71.1% 0.73 0.92
1A+1B+2 132,846 3.05 60,809 37,674 1,844 0 32,519 72.5% 0.77 0.96
3 35,984 0.83 10,907 0 980 0 24,097 32.8% 0.45 0.56
Total 168,830 3.88 71,716 37,674 2,823 0 56,617 64.1% 0.70 0.87
COMPOSITEApaved
(sq feet)
Aroof
(sq feet)
Awalk
(sq feet)
Alawn
(sq feet)
Agravel/pavers
(sq feet)
Lawns
(Flat, < 2% Slope)
Sub-basin
Designation
Atotal
(sq feet)
Atotal
(acres)
Weighted %
Impervious
Gravel/Pavers
Paved
Roof
Walks
Land Use
Seven Generations Multifamily
DEVELOPED IMPERVIOUS AREA CALCULATION
DESIGN CRITERIA:
Fort Collins Stormwater Criteria Manual
BASINS:
Highland Development Services, Inc.
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
% Impervious values from Table 3.2.2 in the Fort Collins Stormwater Criteria Manual
J.Claeys
22-1057-00
September 13, 2022
22-1057-00 Rational Calcs.xlsx Page 2 of 5 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 5-3 -Equation 5-4 -Urbanized Check Equation 3.3-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (2-yr to 10-yr)
1A 1A 65.1% 0.74 0.35 63 0.0200 4.20 159 0.0070 0.10 0.016 1.68 1.58 5.78 222 11.23 5.78
1B 1B 77.6% 0.83 0.98 103 0.0200 4.04 234 0.0050 0.10 0.016 1.42 2.75 6.79 337 11.87 6.79
1A+1B 1A+1B 74.4% 0.81 1.33 103 0.0200 4.39 234 0.0050 0.10 0.016 1.42 2.75 7.14 337 11.87 7.14
2 2 71.1% 0.73 1.72 55 0.0200 4.04 599 0.0065 0.10 0.016 1.62 6.17 10.21 654 13.63 10.21
2 1A+1B+2 72.5% 0.77 3.05 55 0.0200 3.68 599 0.0065 0.10 0.016 1.62 6.17 9.86 654 13.63 9.86
3 3 32.8% 0.45 0.83 41 0.0200 6.19 372 0.0065 0.10 0.016 1.62 3.84 10.02 413 12.30 10.02
OVERALL LENGTH
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
VELOCITY
(ft/s)
ROUGHNESS
COEFFICIENT
HYDRAULIC
RADIUS
(ft)
LENGTH
(ft)
DESIGN CRITERIA:
City of Fort Collins Stormwater Criteria Manual
Overland Flow Equations for City of Fort Collins Stormwater Criteria Manual
SUB-BASIN DATA INITIAL/OVERLAND TIME
(ti)TRAVEL TIME (tt)
tc=ti+tt
(min)
Urban Check Final
tc
(min)DESIGN
POINT Sub-basin %
Impervious C2-10
AREA
(acres)
tt
(min)
September 13, 2022
Seven Generations Multifamily
DEVELOPED TIME OF CONCENTRATION
J.Claeys
22-1057-00
Highland Development Services, Inc.
ticttt+=
V
Ltt60
=1.871.1
10
180
+=LtcV.R2/3 S 1/2
22-1057-00 Rational Calcs.xlsx Page 3 of 5 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 5-3 -Equation 5-4 -Urbanized Check Equation 3.3-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (100-yr)
1A 1A 65.1% 0.93 0.35 63 0.0200 2.02 159 0.0070 0.10 0.016 1.68 1.58 5.00 222 11.23 5.00
1B 1B 77.6% 1.00 0.98 103 0.0200 1.50 234 0.0050 0.10 0.016 1.42 2.75 5.00 337 11.87 5.00
1A+1B 1A+1B 74.4% 1.00 1.33 103 0.0200 1.50 234 0.0050 0.10 0.016 1.42 2.75 5.00 337 11.87 5.00
2 2 71.1% 0.92 1.72 55 0.0200 2.01 599 0.0065 0.10 0.016 1.62 6.17 8.19 654 13.63 8.19
2 1A+1B+2 72.5% 0.96 3.05 55 0.0200 1.57 599 0.0065 0.10 0.016 1.62 6.17 7.74 654 13.63 7.74
3 3 32.8% 0.56 0.83 41 0.0200 5.13 372 0.0065 0.10 0.016 1.62 3.84 8.96 413 12.30 8.96
OVERALL LENGTH
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
VELOCITY
(ft/s)
HYDRAULIC
RADIUS
(ft)
ROUGHNESS
COEFFICIENT
LENGTH
(ft)
DESIGN CRITERIA:
City of Fort Collins Stormwater Criteria Manual
Overland Flow Equations for City of Fort Collins Stormwater Criteria Manual
SUB-BASIN DATA INITIAL/OVERLAND TIME
(ti)TRAVEL TIME (tt)
tc=ti+tt
(min)
Urban Check Final
tc
(min)DESIGN
POINT Sub-basin %
Impervious C100
AREA
(acres)
tt
(min)
September 13, 2022
Seven Generations Multifamily
DEVELOPED TIME OF CONCENTRATION
J.Claeys
22-1057-00
Highland Development Services, Inc.
ticttt+=
V
Ltt60
=1.871.1
10
180
+=LtcV.R2/3 S 1/2
22-1057-00 Rational Calcs.xlsx Page 4 of 5 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
P 1-2yr =0.82 in
P 1-10yr =1.40 in
P 1-100yr =2.86 in
BASIN SUMMARY:
tc
(min)
Runoff Coeff
(C2-10)
C(A)
(acres)
Intensity
(in/hr)
Q2
(ft3/s)
tc
(min)
Runoff Coeff
(C2-10)
C(A)
(acres)
Intensity
(in/hr)
Q10
(ft3/s)
tc
(min)
Runoff Coeff.
(C100)
C(A)
(acres)
Intensity
(in/hr)
Q100
(ft3/s)
1A 1A 0.345 65.1% 5.78 0.74 0.26 2.67 0.68 5.78 0.74 0.26 4.55 1.17 5.00 0.93 0.32 9.95 3.19
1B 1B 0.985 77.6% 6.79 0.83 0.82 2.54 2.08 6.79 0.83 0.82 4.34 3.55 5.00 1.00 0.98 9.95 9.80
1A+1B 1A+1B 1.330 74.4% 7.14 0.81 1.07 2.50 2.69 7.14 0.81 1.07 4.27 4.59 5.00 1.00 1.33 9.95 13.23
2 2 1.720 71.1% 10.21 0.73 1.26 2.20 2.77 10.21 0.73 1.26 3.75 4.73 8.19 0.92 1.58 8.32 13.13
2 1A+1B+2 3.050 72.5% 9.86 0.77 2.34 2.23 5.20 9.86 0.77 2.34 3.80 8.89 7.74 0.96 2.92 8.49 24.80
3 3 0.826 32.8% 10.02 0.45 0.37 2.21 0.82 10.02 0.45 0.37 3.78 1.40 8.96 0.56 0.46 8.05 3.72
C n = n -yr runoff coefficient
I n = n -yr rainfall intensity (in/hr)
A n = Basin drainage area (ac)
I = rainfall intensity (in/hr)
P 1 = one-hour point rainfall depth (in)
t c = time of concentration (min)
10-yr Peak Runoff 100-yr Peak Runoff
Seven Generations Multifamily
DEVELOPED PEAK RUNOFF
DESIGN CRITERIA:
Design
Point Sub-basin Area
(acres)
J.Claeys
Highland Development Services, Inc.
22-1057-00
September 13, 2022
2-yr Peak Runoff
City of Fort Collins Stormwater Criteria Manual
%
Impervious
Q n = n -yr peak discharge (cfs)
nnnnAICQ=(0.786651)
1
)10(
5.28
ct
PI
+
=
22-1057-00 Rational Calcs.xlsx Page 5 of 5 Highland Development Services
Appendix C
APPENDIX C – LOW IMPACT DEVELOPMENT CALCULATIONS
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Low Impact Development Summary
Sq-Ft Acres
Impervious Area
(sq-ft)
% of Impervious
Area Requiring
LID Treatment
Impervious Area
Requiring
LID Treatment
55,874 1.28 42,152 75% 31,614
LID
Facility
Contributing
Basins
Area Drainage
to LID
(sq-ft)
% Impervious
Impervious
Area Treated
(sq-ft)
WQCV12-hr
(watershed inches)
WQCV12-hr
(cu-ft)
Treatment
Method
1B 1B 42,894 77.6% 36,098 0.25 898 Storm Chamber
31,614
36,098
114.2%
Area (sq-ft) Area (acres) Treatment Ratio
42,894 0.98 76.8%
12,979 0.30 23.2%
55,874 1.28
Seven Generations Multifamily
Low Impact Development
Total % Required Treatment
Development Area Breakdown
City of Fort Collins - Ordinance No. 007, 2016
- Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or
- Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are
permeable.
Impervious Area Treated (sq-ft)
Impervious Area Required for LID Treatment (sq-ft)
LID Treatment Summary
LID Treatment Areas
J.Claeys
Highland Development Services, Inc.
22-1057-00
September 14, 2022
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Description
Total Redeveloped Area
Total Improvement Area
Water Quality Area Treatment Summary
Description
Total Redevelopment Area Treated by LID
Total Redevelopment Area Treated by Existing Water Quality Pond
Allowed FilterFabric Flow Ratea(cfs)0.35 gpm/sq-ftSC-106LP 14 10 6 6 85.4 25 12 14.8 0.012 6.9 15.0SC-310 18 8 6 6 85.4 34 16 20.2 0.016 14.7 31.0SC-740 18 8 6 6 85.4 51 30 30.2 0.024 45.9 74.9DC-780 18 12 6 9 85.4 51 30 30.2 0.024 46.2 78.4MC-3500 24 8 12 9 90 77 45 48.1 0.038 109.9 178.9 14.9 46MC-4500 24 7 12 9 52 100 60 36.1 0.028 106.5 162.6 35.7 108.7LIDFacilityChamberTypeTotalRelease Ratef(cfs) WQ Flowg(cfs)Req'd StorageVolumeh(cu-ft)Minimum No. of ChambersiChamberStoragej(cu-ft)No. ofEndcapskEndcapStoragel(cu-ft)Total ChamberVolumem(cu-ft)Total InstalledSystem Volumen(cu-ft)WQCV12-hr(cu-ft)1B SC-310 0.38 0.95355 24 355 4 0 355 921 898NegligibleEndcapVolumed(cu-ft)Min InstalledEndcap/AggregateVolumee(cu-ft)NegligibleNegligibleNegligibleMin InstalledChamber/AggregateVolumec(cu-ft)Seven Generations MultifamilyLow Impact DevelopmentStormTech Chamber Configuration SummaryStormTech Chamber DataDesign Engineer:Design Firm:Project Number:Date:Length(in)Width(in)Height(in)Floor Area(sq-ft)ChamberVolumeb(cu-ft)MinAggregate Base(in)Min Aggregate Cover(in)Max Cover(ft)Min Cover(in)ChamberModelJ.ClaeysHighland Development Services, Inc.22-1057-00September 14, 2022Note:a. Release rate per chamber, limited by flow through geotextile with accumulated sediment. City acceptable flow rates determined to be approximately 1/2 of the Nov-07 Qmaxfrom Figure 17 of the "Final Report on Field Verification Testing of the StormTech Isoloator Row Treatement Unit", prepard by the University of New Hamphire Stormwater Center, dated Setpember 2010.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. Volume within endcap only, not accounting for void spaces in surrounding aggregate.e. Volume includes endcap and void spaces (40%) in surrounding aggregate, per chamber unit.f. Release rate per chamber times number of chambers. This is used as the allowed release rate for the FAA calculations.g. WQ flow, equal to 1/2 of the 2-yr peak runoff rate, referenced to size flow control structure.h. Required detention volume determined using the FAA Method based on the acceptable release rate of sediment accumulated filter fabric of the chambers and the 1/2 of the 2yr in flow rate.i. Number of chambers required to provide required FAA storage volume stored within the chamber and endcaps only (no aggregate storage).j. Total volume provided in chambers only (no aggregate storage).k. Number of endcaps based on desired chamber layout.l. Total volume provided in endcaps only (no aggregate storage).m. Total chamber and endcap storage (not aggregate storage). This number must meet or exceed the required FAA storage volume.n. System volume includes total chambervolumeplus surrounding aggregate volume,assumes a 40% void ratio for aggregate storage.This totalis provided from ADS Design Tool.
DESIGN CRITERIA
0.84
1.00
0.84 ft3 acre-ft
0.99 acres 355 0.01
0.38 cfs
Time
(min)
1/2 2-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Accumulative
Release Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.000 0.00 0 0 0 0.00
5 1.425 1.18 354 114 240 0.01
10 1.105 0.91 549 228 321 0.01
15 0.935 0.77 696 342 355 0.01
20 0.805 0.67 799 455 344 0.01
25 0.715 0.59 887 569 318 0.01
30 0.650 0.54 968 683 285 0.01
35 0.585 0.48 1,016 797 220 0.01
40 0.535 0.44 1,062 911 152 0.00
45 0.495 0.41 1,106 1,025 81 0.00
50 0.460 0.38 1,142 1,138 3 0.00
55 0.435 0.36 1,188 1,252 -64 0.00
60 0.410 0.34 1,221 1,366 -145 0.00
September 14, 2022
Design Engineer:
Design Firm:
Project Number:
Date:
Seven Generations Multifamily
WQ Treatment Volume - FAA Method
J.Claeys
Highland Development Services, Inc.
22-1057-00
Adjusted Runoff Coefficient (CC f )
Area (A )
Allowed Release Rate
- City of Fort Collins - Storm Water Criteria Manual
- City of Fort Collins accepts 1/2 of the 2-yr runoff as the WQ inflow rate
WQ Treatment Volume Calculation - 1B Filtration Chamber
Runoff Coefficient (C )
Frequency Factor (C f )Required Detention
User Inputs
Chamber Model: SC-310
Outlet Control Structure: Yes
Project Name: Seven Generations
Multifamily
Engineer: Jason Claeys
Project Location: Colorado
Measurement Type: Imperial
Required Storage Volume: 850 cubic ft.
Stone Porosity: 40%
Stone Foundation Depth: 6 in.
Stone Above Chambers: 6 in.
Average Cover Over Chambers: 18 in.
Design Constraint Dimensions:(20 ft. x 50 ft.)
Results
System Volume and Bed Size
Installed Storage Volume: 920.60 cubic ft.
Storage Volume Per Chamber: 14.70 cubic ft.
Number Of Chambers Required: 24
Number Of End Caps Required: 8
Chamber Rows: 4
Maximum Length:49.22 ft.
Maximum Width: 15.43 ft.
Approx. Bed Size Required: 759.56 square ft.
System Components
Amount Of Stone Required: 53 cubic yards
Volume Of Excavation (Not Including
Fill):
66 cubic yards
Total Non-woven Geotextile Required:243 square yards
Woven Geotextile Required (excluding
Isolator Row):
12 square yards
Woven Geotextile Required (Isolator
Row):
24 square yards
Total Woven Geotextile Required:35 square yards
SHEET
OFDATE:PROJECT #:DRAWN:CHECKED:THIS DRAWING HAS BEEN PREPARED BASED ON INFORMATION PROVIDED TO ADS UNDER THE DIRECTION OF THE SITE DESIGN ENGINEER OR OTHER PROJECT REPRESENTATIVE. THE SITE DESIGN ENGINEER SHALL REVIEW THIS DRAWING PRIOR TO CONSTRUCTION. IT IS THE ULTIMATERESPONSIBILITY OF THE SITE DESIGN ENGINEER TO ENSURE THAT THE PRODUCT(S) DEPICTED AND ALL ASSOCIATED DETAILS MEET ALL APPLICABLE LAWS, REGULATIONS, AND PROJECT REQUIREMENTS.4640 TRUEMAN BLVDHILLIARD, OH 43026ADVANCED DRAINAGE SYSTEMS, INC.R1 105-10-19KRKRSTANDARD CROSS SECTIONSC-310DATEDRWNCHKDDESCRIPTION70 INWOOD ROAD, SUITE 3 | ROCKY HILL | CT | 06067860-529-8188 |888-892-2694 | WWW.STORMTECH.COMDetention Retention Water QualityACCEPTABLE FILL MATERIALS: STORMTECH SC-310 CHAMBER SYSTEMS
PLEASE NOTE:
1.THE LISTED AASHTO DESIGNATIONS ARE FOR GRADATIONS ONLY. THE STONE MUST ALSO BE CLEAN, CRUSHED, ANGULAR. FOR EXAMPLE, A SPECIFICATION FOR #4 STONE WOULD STATE: "CLEAN, CRUSHED, ANGULAR NO. 4 (AASHTO M43) STONE".
2.STORMTECH COMPACTION REQUIREMENTS ARE MET FOR 'A' LOCATION MATERIALS WHEN PLACED AND COMPACTED IN 6" (150 mm) (MAX) LIFTS USING TWO FULL COVERAGES WITH A VIBRATORY COMPACTOR.
3.WHERE INFILTRATION SURFACES MAY BE COMPROMISED BY COMPACTION, FOR STANDARD DESIGN LOAD CONDITIONS, A FLAT SURFACE MAY BE ACHIEVED BY RAKING OR DRAGGING WITHOUT COMPACTION EQUIPMENT. FOR SPECIAL LOAD DESIGNS, CONTACT STORMTECH FOR
COMPACTION REQUIREMENTS.
4.ONCE LAYER 'C' IS PLACED, ANY SOIL/MATERIAL CAN BE PLACED IN LAYER 'D' UP TO THE FINISHED GRADE. MOST PAVEMENT SUBBASE SOILS CAN BE USED TO REPLACE THE MATERIAL REQUIREMENTS OF LAYER 'C' OR 'D' AT THE SITE DESIGN ENGINEER'S DISCRETION.
NOTES:
1.CHAMBERS SHALL MEET THE REQUIREMENTS OF ASTM F2922 (POLETHYLENE) OR ASTM F2418-16a (POLYPROPYLENE), "STANDARD SPECIFICATION FOR CORRUGATED WALL STORMWATER COLLECTION
CHAMBERS".
2.SC-310 CHAMBERS SHALL BE DESIGNED IN ACCORDANCE WITH ASTM F2787 "STANDARD PRACTICE FOR STRUCTURAL DESIGN OF THERMOPLASTIC CORRUGATED WALL STORMWATER COLLECTION
CHAMBERS".
3.THE SITE DESIGN ENGINEER IS RESPONSIBLE FOR ASSESSING THE BEARING RESISTANCE (ALLOWABLE BEARING CAPACITY) OF THE SUBGRADE SOILS AND THE DEPTH OF FOUNDATION STONE WITH
CONSIDERATION FOR THE RANGE OF EXPECTED SOIL MOISTURE CONDITIONS.
4.PERIMETER STONE MUST BE EXTENDED HORIZONTALLY TO THE EXCAVATION WALL FOR BOTH VERTICAL AND SLOPED EXCAVATION WALLS.
5.REQUIREMENTS FOR HANDLING AND INSTALLATION:
·TO MAINTAIN THE WIDTH OF CHAMBERS DURING SHIPPING AND HANDLING, CHAMBERS SHALL HAVE INTEGRAL, INTERLOCKING STACKING LUGS.
·TO ENSURE A SECURE JOINT DURING INSTALLATION AND BACKFILL, THE HEIGHT OF THE CHAMBER JOINT SHALL NOT BE LESS THAN 2”.
·TO ENSURE THE INTEGRITY OF THE ARCH SHAPE DURING INSTALLATION, a) THE ARCH STIFFNESS CONSTANT AS DEFINED IN SECTION 6.2.8 OF ASTM F2922 SHALL BE GREATER THAN OR EQUAL TO 400
LBS/IN/IN. AND b) TO RESIST CHAMBER DEFORMATION DURING INSTALLATION AT ELEVATED TEMPERATURES (ABOVE 73° F / 23° C), CHAMBERS SHALL BE PRODUCED FROM REFLECTIVE GOLD OR
YELLOW COLORS.
MATERIAL LOCATION DESCRIPTION AASHTO MATERIAL
CLASSIFICATIONS COMPACTION / DENSITY REQUIREMENT
D
FINAL FILL: FILL MATERIAL FOR LAYER 'D' STARTS FROM THE TOP OF
THE 'C' LAYER TO THE BOTTOM OF FLEXIBLE PAVEMENT OR
UNPAVED FINISHED GRADE ABOVE. NOTE THAT PAVEMENT SUBBASE
MAY BE PART OF THE 'D' LAYER.
ANY SOIL/ROCK MATERIALS, NATIVE SOILS, OR PER ENGINEER'S PLANS.
CHECK PLANS FOR PAVEMENT SUBGRADE REQUIREMENTS.N/A
PREPARE PER SITE DESIGN ENGINEER'S PLANS. PAVED
INSTALLATIONS MAY HAVE STRINGENT MATERIAL AND
PREPARATION REQUIREMENTS.
C
INITIAL FILL: FILL MATERIAL FOR LAYER 'C' STARTS FROM THE TOP
OF THE EMBEDMENT STONE ('B' LAYER) TO 18" (450 mm) ABOVE THE
TOP OF THE CHAMBER. NOTE THAT PAVEMENT SUBBASE MAY BE A
PART OF THE 'C' LAYER.
GRANULAR WELL-GRADED SOIL/AGGREGATE MIXTURES, <35% FINES OR
PROCESSED AGGREGATE.
MOST PAVEMENT SUBBASE MATERIALS CAN BE USED IN LIEU OF THIS
LAYER.
AASHTO M145¹
A-1, A-2-4, A-3
OR
AASHTO M43¹
3, 357, 4, 467, 5, 56, 57, 6, 67, 68, 7, 78, 8, 89, 9, 10
BEGIN COMPACTIONS AFTER 12" (300 mm) OF MATERIAL OVER
THE CHAMBERS IS REACHED. COMPACT ADDITIONAL LAYERS IN
6" (150 mm) MAX LIFTS TO A MIN. 95% PROCTOR DENSITY FOR
WELL GRADED MATERIAL AND 95% RELATIVE DENSITY FOR
PROCESSED AGGREGATE MATERIALS. ROLLER GROSS
VEHICLE WEIGHT NOT TO EXCEED 12,000 lbs (53 kN). DYNAMIC
FORCE NOT TO EXCEED 20,000 lbs (89 kN).
B EMBEDMENT STONE: FILL SURROUNDING THE CHAMBERS FROM THE
FOUNDATION STONE ('A' LAYER) TO THE 'C' LAYER ABOVE.CLEAN, CRUSHED, ANGULAR STONE AASHTO M43¹
3, 357, 4, 467, 5, 56, 57 NO COMPACTION REQUIRED.
A FOUNDATION STONE: FILL BELOW CHAMBERS FROM THE SUBGRADE
UP TO THE FOOT (BOTTOM) OF THE CHAMBER.CLEAN, CRUSHED, ANGULAR STONE AASHTO M43¹
3, 357, 4, 467, 5, 56, 57 PLATE COMPACT OR ROLL TO ACHIEVE A FLAT SURFACE.2,3
D
C
B
A
18"
(450 mm) MIN*
8'
(2.4 m)
MAX
6" (150 mm)
MIN
12" (300 mm) MIN 12" (300 mm) MIN34" (864 mm)6"
(150 mm) MIN
ADS GEOSYNTHETICS 601T NON-WOVEN GEOTEXTILE ALL AROUND
CLEAN CRUSHED, ANGULAR STONE IN A & B LAYERS
*TO BOTTOM OF FLEXIBLE PAVEMENT. FOR UNPAVED
INSTALLATIONS WHERE RUTTING FROM VEHICLES MAY
OCCUR, INCREASE COVER TO 24" (600 mm).
PERIMETER STONE
(SEE NOTE 4)
EXCAVATION WALL
(CAN BE SLOPED OR VERTICAL)
SC-310
END CAP SUBGRADE SOILS
(SEE NOTE 3)
PAVEMENT LAYER (DESIGNED
BY SITE DESIGN ENGINEER)
DEPTH OF STONE TO BE DETERMINED
BY SITE DESIGN ENGINEER 6" (150 mm) MIN
16"
(406 mm)total depth=18+16+6=40/12=3.33'