HomeMy WebLinkAboutINNOVATION ISLAND, FIRST FILING - PDP - 40-05A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTSoil Survey of Latimer County Area, Colorado INNOVATION ISLAND
Map Unit Legend Summary
Larimer County Area, Colorado
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
4 Altvan-Satanta loams, 3 to 9 0.3 6.0
percent slopes
91 Renohill-Midway clay 0.4 9.0
loams, 3 to 15 percent slopes
USDA NahwA Ye..rn Web Soil Survey 1.0
c..e.raswvke National Cooperative Soil Survey
9/28/2005
Page 3 of 3
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MAP LEGEND
I_. Soil Map Units
® Cities
Detailed Counties
Interstate Highways
Roads
Rails
Water
Hydrography
Oceans
USDA NataW Baov�e
W USDA cmurnt6n SaAm
MAP INFORMATION
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL: http://websoilsurvey.nres.usda.gov
Coordinate System: UTM Zone 13
Soil Survey Area: Larimer County Area, Colorado
Spatial Version of Data: 1
Soil Map Compilation Scale: 1:24000
The orthophoto or other base map on which the soil lines were compiled and
digitized probably differs from the background imagery displayed on these mi
As a result, some minor shifting of map unit boundaries may be evident.
9ngn00s
Page 2 of 3
—1
SOIL SURVEY OF LARIMER COUNTY AREA, COLORADO
INNOVATION ISLAND
� Meters
0 10 20 40
0 35 70
Feet
140 210 280
USDA Nxh" Raomon
comar"AmsaAm
rmo Irxo
Iww
MEMO
uTIRAL FL004 NSIMAACE PROGRAM
FIRM
FLB00 IMSURANCE RATE MAP
CITY OF
FORT COLONS,
COLIRADO
LABBM COUNTY
MAP INDEX
PANELS PRINTED: 3. R. 4
COMMUNITY -PANEL NUMBERS
GOO162 Dam-0007
MAP REVISED:
FEBRUARY 15, 1984
FtlonI E�m Mn l AA
i
small grain straw and processed materials such as erosion control blankets. Vegetation will
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
Isevere weather conditions. Contech Pyramat or other approved turf reinforcement matting is
required at the outlets of all proposed stormwater pipes in order to prevent soil erosion and
Iundercutting of the pipes.
6. REFERENCES
1. City of Fort Collins, "Storm Drainage Design Criteria and Construction Standards"
(SDDCCS), May 1984.
2. Soil Survey of Larimer County Area, Colorado. United States Department of
Agriculture Soil Conservation Service and Forest Service, 1980.
3. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual', Volumes 1 and 2, dated June 2001, and Volume 3, dated September 1992.
4. City of Fort Collins Municipal Code and Charter, Chapter 10, "Flood Prevention and
Protection".
5. "Preliminary/Master Drainage Study for Woodridge", RBD, Inc. Engineering
Consultants, December 2, 1991.
6. "Final Drainage and Erosion Control Study for the Overlook at Woodridge Fourth
Filing, Phase One" RBD, Inc. Engineering Consultants, June 14, 1995.
Drainage and Erosion Control Report OctobPage 5
er 5, 2005
' Innovation Island
located closest to Harmony will be directed to flow to the south. Since the source of the
majority of pollutants in stormwater runoff comes from driveway and parking areas, this
small amount of untreated runoff should have a negligible effect on the overall pollutant
load.
4.3 Outlet Structure Design
The proposed outlet structure is a drop box structure with a flow control plate designed to
release frequently occurring storm events over a 40-hour period. The top of the drop box
structure is equipped with a grated inlet that will pass the 100-year storm. The outlet pipe for
the drop box is an 18-inch reinforced concrete pipe which will be connected to the back of
the existing 15' type R inlet on Harmony Road. An orifice plate will restrict the flows into
the outlet pipe in accordance with the allowable release rate. In case the outlet is plugged, an
emergency overflow spillway will pass the 100-year peak flows on the north side of the EDB
and onto Harmony Road. Detailed design of the outlet structure including sizing of the
orifice plate will be completed with final design.
5. EROSION & SEDIMENTATION CONTROL
5.1 Erosion and Sediment Control Measures
The erosion and sedimentation control plan for the site meets requirements for development
in the City of Fort Collins and meets or exceeds those set by the United Stated
Environmental Protection Agency (EPA) Document No. EPA 832/R-92-005 (September
1992), Stormwater Management for Construction Activities, Chapter 3. The purpose of the
erosion and sedimentation control plan is to limit the overall sediment yield and reduce the
negative impacts on air quality during construction. Measures that are included in the plan
include the use of silt fences, wattles, inlet protection, gravel construction entrances, and
seeding and mulch on -site. During overlot and final grading, the soil will be roughened and
furrowed perpendicular to the prevailing winds. Wattles will be placed along proposed
swales. Erosion control effectiveness calculations, rainfall performance calculations and a
construction schedule will be completed with final design.
5.2 Permanent Stabilization
A vegetative cover shall be established soon after grading is completed in order to reduce
erosion and prevent the movement of sediments from the site. Suitable vegetative cover
includes sod or using cover crops with mulch. Mulches that can be used include grass hay,
Page 8
Drainage and Erosion Control Report October 5, 2005
Innovation Island
known as design point 10 of this report. The designed peak flow to this inlet was Q(2) = 5.1-
cfs and Q(100) = 17.6 cfs of direct runoff. The calculated peak flow with the Innovation
Island site is Q(2) = 3.05 cfs and Q(100) =15.1 cfs. The difference in the peak flow rates is
due to more accurate time of concentration calculations with the detailed site layout for
Innovation Island. The same results were found at the second 15' Type R inlet which is
known as design point 21 in the Woodridge plan. Thus, the downstream conveyance system
is adequately sized to handle fully developed flows from the Innovation Island site under the
minor and major storms and additional detention is not warranted.
4.2 Extended Detention Basin Design
Water quality enhancement is being provided for fully commercial developed conditions for
Basin A which includes the majority of the multi -family portion of the Innovation Island site
and the future commercial site on the east side. Two water quality enhancement measures
will be used with the primary water quality enhancement method is an Extended Detention
Basin (EDB) designed using guidelines set forth in the Urban Storm Drainage Criteria
Manual, Volume 3 (2004). The proposed EDB is a sedimentation facility which will capture
stormwater runoff from frequently occurring rainfall events and extend the emptying time to
allow for pollutant removal through gravity settling. The EDB pond was sized
conservatively to include runoff from the entire site, although at this time all of this area will
not drain to the pond. This will allow the future commercial development to drain to the
proposed pond without reshaping or redesigning it.
The second water quality enhancement measure is to minimize the amount of directly
connected impervious areas by detaching sidewalks and passing water through grassy swales
to prior to entering the EDB. The bottom of the swales and the low flow channel of the EDB
will not be concrete lined in order to further enhance pollutant removal. A permanent micro -
pool is not being provided in order to minimise maintenance costs for the Habitat for
Humanity homeowners. Thus, in between stormwater events the majority of the basin will
remain dry. Calculations for the required water quality capture volume are included in the
Appendix.
There is a small portion of the site immediately adjacent to Harmony Drive which will not
pass through the EDB facility but will flow directly to the street gutter and into the
stormwater system. The majority of this area is landscaped with grass and plantings and only
a small amount of impervious area from the sidewalk is included. The roofs of the buildings
Island
October 5, 2005
4. STORMWATER DETENTION & WATER QUALITY TREATMENT
4.1 Stormwater Detention
Developed commercial flows from this site were accounted for in the design of the storm
drainage detention pond for the Overlook at Woodridge Fourth Filing (1995). Since the time
that the Final Drainage Study for the Overlook was completed, the City of Fort Collins
(CFC) has modified their stormwater design criteria to include stormwater quality
enhancement requirements and the use of a larger design storm based on a 1998 precipitation
study. The peak discharge using the old rainfall data for the site only (4.4 acres) was
calculated to be 39.6-cfs. The required detention volume under the new rainfall conditions
with a release rate set to the peak discharge under the old rainfall conditions was calculated.
The result was a detention requirement of 0.06 ac-ft at with storm duration of 5 minutes.
Since water quality is being provided for this site (see following section) with a calculated
release over 40-hours, adequate stormwater detention, in essence, is being provided for the
short, first flush of rainwater. Therefore, additional detention is not required based on the
increase in the design rainfall rates.
Figure 4 - Existing Regional Detention Pond
Adjacent to Webber Jr. High
The downstream capacity of the stormwater system was also considered in determining if
detention would be required for this site. As stated in the previous section, runoff from the
site enters the two existing 15' Type R inlets along the south side of Harmony Road. The
upstream inlet was designed with the Overlook at Woodridge, P.U.D. Fourth Filing and it
Drainage and Erosion Control Report Page 6
Innovation Island October 5, 2005
MI
11
3. PROPOSED (POST -DEVELOPMENT) HYDROLOGY & HYDRAULICS
3.1 General Flow Routing
For this preliminary 50% submittal, the site hydrology was analyzed in order to size the
proposed water quality pond and the drainage swale on the south boundary of the site. The
proposed site generally follows the existing drainage patterns and is divided into three major
drainage basins as follows:
I Basin A includes the majority of the site. Stormwater is conveyed via overland flow and
gutter flow to the proposed drainage swale that runs west to east along the southern property
I boundary. This south swale discharges into the proposed Extended Detention Basin (EDB)
in the southeast corner of the property. The outlet pipe for the EDB discharges to the
existing storm drain inlet located on the south side of Harmony Road.
Basin B includes the northwest corner of the site and half of the roadway of Harmony Road.
This basin is conveyed via overland and gutter flow to the existing 15' Type R inlet in
Harmony Road.
Basin C includes the northeast portion of the site and half of the roadway of Harmony Road.
This basin is conveyed via overland and gutter flow to another existing 15' Type R inlet in
Harmony Road.
3.2 Hydrologic Computations
The Rational Method was used to determine the 2-year and 100-year peak runoff values for
each Basin per guidelines in the SDDCCS Manual. Runoff coefficients were assigned using
Table 3-2 "Rational Method Minor Storm Runoff Coefficients for Zoning Classifications" of
the SDDCCS Manual. All hydrologic calculations for the Basins shown on the attached
drainage plan are included in the Appendix this report.
3.3 Hydraulic Computations
Preliminary hydraulic calculations for sizing of the proposed stormwater swale along the
south site boundary was completed and it is sized to convey the 100-year flows from the site.
Sizing of smaller swales, gutters and pipes were not completed with this preliminary report.
Design and capacity verification of the street sections, inlets and pipes will be completed
with the next submittal and they will be sized to convey the minor storm.
Drainage and Erosion Control Report Page 5
Innovation Island October 5, 2005
1.5
4
Variances from Criteria
A variance is being requested to allow a small portion of the site (0.8 acres) to be released
without water quality enhancement. The area includes landscaping and a small amount of
sidewalk and street. More information on the water quality enhancements proposed for this
site is included in the following section.
HISTORIC (PRE -DEVELOPMENT) HYDROLOGY
The southern portion of the site drains to an existing swale which carries stormwater runoff
along the south property line to a depression and into a concrete pipe located in Tract A of
the Overlook at Woodridge. The remaining portion of the site drains via overland flow to the
curb and gutter along Harmony Road and into two existing 15' type R inlets on the south side
of Harmony Road. All of the stormwater runoff from the site is conveyed to the existing
stormwater conveyance system in Harmony Road which passes to the existing concrete lined
drainage channel north of Seneca Drive and then to the existing regional detention pond
located adjacent to Webber Jr. High.
Figure 3 - Downstream Concrete Channel north
of Seneca Drive
w
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Drainage and Erosion Control Report Page 4
October 5, 2005
Innovation Island
The site is located outside of any Federal Emergency Management Agency (FEMA)
designated floodplain. The applicable Flood Insurance Rate Map (FIRM) is the City of Fort
Collins, Larimer County, Colorado, Community Panel Number 080102 0003 A, revised
February 15, 1984. The site lies in Zone C, areas of minimal flooding. A copy of the FIRM
map is included in the Appendix.
1.3 Design Criteria
This report was prepared to meet or exceed the submittal requirements established in the City
of Fort Collins' "Storm Drainage Design Criteria and Construction Standards" (SDDCCS),
dated May 1984 and revised in January 1997. Where applicable, the criteria established in
the "Urban Storm Drainage Criteria Manual" (UDFCD) dated 1984, developed by the
Denver Regional Council of Governments have been utilized.
In accordance to the City of Fort Collins SDDCCS guidelines for residential multi -family
zoning, the initial or minor storm return period of 2-years and a major storm return period of
100-years were used for the stormwater management system design. In general the initial
storm drainage system includes curb and gutter, storm sewer pipes and storm inlets and its
purpose is to minimize inconvenience and protect against recurring water damage. The
major storm drainage system includes overflow swales and stormwater detention facilities
and its purpose is to eliminate substantial property damage and loss of life.
I 1.4 Master Drainage Basins and Offsite Hydrology
Il The site is located on the upper end of the Mail Creek Drainage Basin. This site is known as
sub -basin 89 in the master drainage plan and there are no offsite flows that pass through this
site. Excerpts from the "Mail Creek Basin Baster Drainage Plan Hydrology Technical
Appendix" are included in the Appendix of this report.
This site is also included in the "Master Drainage Study for Woodridge" (1991) and the
I"Final Drainage and Erosion Control Study for the Overlook at Woodridge, Fourth Filing"
(1995). In the Final Drainage Report for the Overlook at Woodridge Fourth Filing, this site
is known as Basin 1 and 2A. Fully developed commercial flows from this site were
considered in the stormwater system plan design for the Overlook at Woodridge. Details of
the site drainage are included in the following section.
Drainage and Erc
Innovation Island
October 5, 2005
The total size of the proposed Innovation Island site is approximately 4.4-acres and will be
divided into two lots. An Overall Development Plan for the entire 4.4-acre parcel is being
submitted in conjunction with this PDP report. This PDP report includes stormwater system
plans for the west lot which is approximately 3.2-acres in size and will contain 27 multi-
family units and a small park The east lot is approximately 1.3-acres in size and will be sold
separately for a future commercial development. This report details the proposed storm
water conveyance system for the 3.2-acre mulit-family development on the west side.
1.2 Existing Site Characteristics
The site currently consists of open space and is sparsely vegetated with native plants and
grasses.
Figure 2 - Site Photo looking west
Existing swale along south border
The soils in the area are predominately Renohill clay loam, 3-9 percent slopes (soil number
90) and Fort Collins loam, 1-3 percent slopes (soil number 35) as reported in the Soil Survey
of Larimer County Area, Colorado. Renohill clay loam has rapid runoff and severe water
erosion hazard. Fort Collins loam has slow runoff and moderate to slight hazard of wind and
water erosion.
Page 2
Drainage and Erosion Control Report October 5, 2005
Innovation Island
1. INTRODUCTION
This Project Development Plan (PDP) report describes and provides supporting calculations
for the proposed stormwater management system and the erosion and sedimentation control
plan for Innovation Island. This plan is intended to limit the impact of the proposed project
on the natural water flows and air quality during construction and throughout the life of the
building. Stormwater management measures include a combination of Best Management
Practices (BMPs) which control the quantity and quality of the rainfall runoff from the site.
Project Description
Innovation Island, hereafter referred to as "site", is located in the southeast corner of
Harmony Road (County Road 38E) and Taft Hill Road in southwest Fort Collins, Colorado.
More specifically the project lies in the Southwest 1/4 of Section 34, Township 7 North,
Range 69 West of the 6 h Principal Meridian in the City of Fort Collins, Larimer County,
Colorado. The site is bounded by Harmony Road on the north and east, Taft Hill Road on
the west, and The Overlook at Woodridge Fourth Filing on the south. Adjacent to the
northeast corner of the site is a water pump station owned by the Fort Collins -Loveland
Water District.
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Drainage and Erosion Control Report Page 1
Innovation Island October 5, 2005
TABLE OF CONTENTS
OF CONTENTS
PAGE
ii
INTRODUCTION..................................................................................................................1
1.1 Project Description..........................................................................................................1
Figure1— Vicinity Map............................................................................................................1
1.2 Existing Site Characteristics...........................................................................................2
Figure 2 - Site Photo looking west..........................................................................................2
Existing swale along south border...........................................................................................2
1.3 Design Criteria................................................................................................................3
1.4 Master Drainage Basins and Offsite Hydrology..............................................................3
1.5 Variances from Criteria...................................................................................................4
HISTORIC (PRE -DEVELOPMENT) HYDROLOGY......................................................4
Figure 3 - Downstream Concrete Channel north of Seneca Drive..........................................4
PROPOSED (POST -DEVELOPMENT) HYDROLOGY & HYDRAULICS..................5
3.1 General Flow Routing.....................................................................................................5
3.2 Hydrologic Computations................................................................................................1
3.3 Hydraulic Computations.................................................................................................
STORMWATER DETENTION & WATER QUALITY TREATMENT .........................6
4.1 Stormwater Detention.....................................................................................................6
Figure 4 - Existing Regional Detention Pond.........................................................................6
4.2 Extended Detention Basin Design..................................................................................7
4.3 Outlet Structure Design...................................................................................................8
EROSION & SEDIMENTATION CONTROL...................................................................8
5.1 Erosion and Sediment Control Measures........................................................................8
5.2 Permanent Stabilization..................................................................................................8
REFERENCES............. ............ ......................................................... ».............................. .....9
APPENDIX:
Maps and Figures
Hydrologic and Hydraulic Calculations
Detention Pond Analysis
Extended Detention Basin Design
Excerpts from other Reports
INTERWEST M CONSULTING G R O U P
5, 2005
Basil Hamdan
of Fort Collins
mwater Utility
Wood Street
:Collins, CO 80521
Drainage and Erosion Control Report
Innovation Island
Basil:
We are pleased to submit for your review this 50% Submittal Drainage and Erosion Control Report
for the Project Development Plans (PDP) for Innovation Island. This site is located in the southeast
comer of the intersection of Harmony Road and Taft Hill Road. All computations within this report
have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria.
We greatly appreciate your time and consideration in reviewing this submittal. Please call if you
have any questions.
Sincerely,
Jennifer Zung
Project Engineer
olorado Professional
ngineer No. 34767
SH, STE. C . WINDSOR, COLORADO 80550
4.3300 • rnx.970.674.3303
�.L
PROJECT DEVELOPMENT PLAN
DRAINAGE AND EROSION
CONTROL REPORT
FOR
INNOVATION ISLAND
Prepared for:
Habitat for Humanity
4001 South Taft Hill Road
Fort Collins, CO 80526
Ph. 970.223.4522
Prepared by:
Interwest Consulting Group
1218 W. Ash, Suite C
Windsor, Colorado 80550
Ph. 970.674.3300
Fax 970.674.3303
October 5, 2005
INTERWEST = CONSULTING GROUP