HomeMy WebLinkAboutMULBERRY CONNECTION - PDP190015 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTCity of Fort Collins
Mulberry Connection
(Redman Drive and I-25 Frontage Road)
Preliminary Drainage Report
SEPTEMBER 2019 | VERSION 1
Prepared By:
4582 South Ulster Street, Suite 1500
Denver, CO 80237
Dan L. Skeehan
Registered Professional Engineer
State of Colorado No. 46391
2
INTRODUCTION
The proposed Mulberry Connection Project is located within the Northeast Quarter of Section 9, Township
7 North, Range 68 West of the Sixth Principal Meridian, City of Fort Collins, County of Larimer, Colorado.
The site is bound by:
· North: Existing Farmland
· East: Interstate 25 (“I-25”) Frontage Road
· South: Redman Drive
· West: Existing Farmland
A vicinity map is provided below.
Preliminary Drainage Report
Mulberry Connection – Fort Collins, Colorado
3
PROPOSED DEVELOPMENT
The site is approximately 13 acres and is existing farm land. The proposed site includes two industrial
buildings with associated parking and landscape improvements.
EXISTING SITE INFORMATION
The soil on the site is primarily Nunn loam (73) and Garrett loam (0), which are classified as Hydrologic Soil
Group C and B, respectively. The soil Classification Map can be found in Appendix A. This Site is a part
of the Boxelder Creek & Cooper Slough Master Drainage Plan, which is currently under revision and has
not been referenced in this design. The existing site is utilized as agricultural land with ground cover
primarily made up of crop.
According to the Geotechnical Evaluation performed by Ninyo & Moore on July 2, 2019, groundwater was
encountered at depths ranging between approximately 8.5 to 12 feet below ground surface.
HISTORIC DRAINAGE
The existing Site is relativity flat with slopes ranging from 0.5% to 3%. There are currently no existing on-
site water quality or detention improvements. The majority of the site currently slopes to the southwest,
conveying water into an existing roadside ditch adjacent to Redman Drive, which discharges into Copper
Slough approximately 600 feet west of the Site. The site directly north of the Site is collected by an existing
drainage ditch along the northern property line, routing all discharges around the Site. I-25 Frontage Road
is adjacent to the Site. The width of the Frontage Road drains west onto the Site in the existing condition.
The site is located within City of Fort Collins Federal Emergency Management Agency (FEMA) Flood
Insurance Rate Map Number 08069C0984H and is designated as an area outside of the 100-year
floodplain. The updated FEMA maps is included in Appendix A.
DESIGN CRITERIA
The City of Fort Collins “Stormwater Criteria Manual, December 2018 Edition,” (Criteria Manual) and the
“Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual” Volumes 1, 2, and 3
(Drainage Manual), with latest revisions, were used to prepare the storm calculations. Weighted impervious
values were calculated and used for the site area in accordance with the Criteria Manual and Drainage
Manual.
This Site is a part of the Boxelder Creek & Cooper Slough Master Drainage Plan, which is currently under
revision and has not been referenced in this design. Existing storm sewer infrastructure is not present on
the Site. An existing drainage ditch is present on both sides of Redman Drive, in addition to the existing
concrete irrigation ditch on the northern adjacent property.
Hydrologic Criteria
The 2-year and 100-year storm event were evaluated for this Site. Rainfall intensity values provided in the
Criteria Manual were utilized for the analysis. Impervious values for pavement, roof, and landscape area
were taken from the Criteria Manual. Runoff coefficients were calculated per the Criteria Manual. The
Rational Method was utilized to calculate the peak runoff values for the minor and major storm event.
4
Peak runoff values were calculated for the existing conditions of the Site, which the 2-year existing peak
runoff informed the allowable release from the Site in the proposed conditions in the 100-year storm event.
Topographic survey of the Site was utilized to delineate existing sub-basins for the Site. An Existing
Drainage Map is provided in Appendix B and all hydrologic calculations are provided in Appendix C.
The proposed site layout and grading was utilized to delineate sub-basins for the proposed condition, as
shown in the Proposed Drainage Map included in Appendix B. Peak runoff values for the proposed sub-
basins were calculated using the Rational Method. Hydrologic calculations are provided in Appendix C.
Water Quality Capture Volumes for each on-site sub-basin was calculated per the methods described in
the Criteria Manual. The Modified FAA Method, as described in the Criteria Manual, was utilized to calculate
the required detention volume for the Site in the proposed conditions. Water quality and detention
calculations are provided in Appendix C.
DRAINAGE PLAN
GENERAL CONCEPT
The Site in the proposed conditions was divided into five onsite sub-basins which are described in greater
detail in the following section. BMPs were selected utilizing the four step process outlined in Volume 3,
Chapter 1, Section 4 of the Drainage Manual:
1. Employ runoff reduction practices - The redevelopment on an urban site provides limited
opportunities to employ runoff reduction practices. The Site has been developed to install
landscaping wherever pavement (or building) is not required. Additionally, impervious areas have
been disconnected from storm sewer infrastructure at all feasible locations.
2. Implement BMPs that provide a water quality capture volume with a slow release – 7.66 acres of
the Site (Drainage Basins B and C) will be treated with bioretention via three rain gardens. The
total proposed impervious surface area is 9.12 acres (including pavement and roofs), with 5.39
acres of that being treated with bioretention. Thus, 59% of the Site’s impervious area will be treated
with LIDs. A variance request has been included with this report for not meeting the required
75% treatment of impervious areas with LID. The three proposed rain gardens are shown on
the Proposed Drainage Map in Appendix B and calculations are provided in Appendix D.
3. Stabilize streams – Not applicable.
4. Implement site specific and other source control BMPs – During construction, the site will include
silt fence to reduce potential for contamination discharges at the perimeter. Site access will be
provided through an area of vehicle tracking control to reduce tracking of contamination offsite
which will be further controlled with street sweeping and rock socks along Redman Drive. Proposed
storm sewer will have inlet protection. Additionally, diversion ditches routing water to a sediment
basin will be installed at the beginning of construction.
SPECIFIC DETAILS
Runoff generated by three of the five on-site basins (12.75 acres of the total 13.07 acres – 98% of the Site)
will be routed to LID features and the proposed extended detention pond via surface flow and limited storm
sewer. The proposed extended detention pond will outfall to an existing drainage swale directly upstream
of Cooper Slough. Two on-site basins (0.32 acres – 2% of the Site) will surface flow off-site and not be
treated for water quality or be detained. The 100-year release rate from the proposed extended detention
pond was calculated to take into account these undetained flows. Two offsite sub-basins are included in
the drainage analysis to properly size all proposed drainage features. The Proposed Drainage Map included
Preliminary Drainage Report
Mulberry Connection – Fort Collins, Colorado
5
in Appendix B shows the five sub-basins and each basin is described in further detail below. Table 1
summarizes the tributary areas, impervious areas, imperviousness, and peak flows from each sub-basin.
Full calculations are included in Appendix C.
Sub-basin A
Sub-basin A is 5.09 acres and consists of on-site parking, sidewalk, one of the buildings, and landscape
areas that surface flow to two curb cuts routing flows into the proposed extended detention pond. Water
quality treatment for runoff from this sub-basin will occur within the proposed extended detention pond.
Sub-basin B
Sub-basin B is 3.86 acres and consists of on-site parking, sidewalk, loading dock, and landscaped areas.
Runoff within this sub-basin surface flow to a proposed 8-foot valley gutter routing water south to a proposed
curb cut. The curb cut is connected to proposed Rain Garden B2. A culvert beneath the access drive will
allow Rain Garden B2 to be utilized for water quality treatment of this runoff as well. Storm events greater
than the water quality volume will be routed through Rain Garden B2 and B1 into the proposed extended
detention pond via storm pipe.
Sub-basin C
Sub-basin C is 3.80 acres and consists of on-site parking, sidewalk, on of the buildings, and landscaped
areas. Runoff within this sub-basin will surface flow east into Rain Garden C, which will provide water quality
treatment. Storm events greater than the water quality volume will be routed through Rain Garden C, into
Rain Gardens B1 and B2 and finally into the proposed extended detention pond via storm pipe.
Sub-basin O1
Sub-basin O1 is 0.21 acres and consists of on-site landscaped area and a portion of the west access drive.
Runoff within this sub-basin will surface flow offsite and water quality treatment nor detention will be
provided for this sub-basin.
Sub-basin O2
Sub-basin O2 is 0.11 acres and consists of on-site landscaped areas. Runoff within this sub-basin will
surface flow offsite to the proposed swale on the eastern property boundary. Water quality treatment nor
detention will be provided for this sub-basin.
Sub-basin OS1
Sub-basin OS1 is 0.22 acres and consists of off-site landscaped area and I-25 Frontage Road. Runoff
within this sub-basin will flow to the proposed drainage swale on the eastern property boundary, following
historic drainage patterns. Areal imagery indicates that an existing culvert is at the corner of I-25 Frontage
Road and Redman Drive, convey flows south to an existing roadside swale. Water quality treatment nor
detention will be provided for this sub-basin on the proposed site. Additionally, this basin is not included as
a part of the total Site improvement area, as proposed off-site improvements will improve existing conditions
and maintain historic drainage patterns.
6
Sub-basin OS2
Sub-basin OS is 0.70 acres and consists of a portion of Redman Drive and offsite landscape area. Runoff
within this sub-basin will surface flow to the existing drainage ditch on the north side of Redman Drive.
Water quality treatment nor detention will be provided for this sub-basin. Additionally, this basin is not
included as a part of the total Site improvement area, as proposed off-site improvements will improve
existing conditions and maintain historic drainage patterns.
Table 1. Summary of proposed drainage sub-basins.
Basin ID Total
Tributary
Area (acres)
Impervious
Area (acres)1
Imperviousness 2-Year Peak
Flow (CFS)
100-Year
Peak Flow
(CFS)
A 5.09 3.69 69% 7.62 33.20
B 3.86 2.80 73% 6.00 24.79
C 3.80 2.59 64% 5.52 24.13
O1 0.21 0.04 21% 0.14 0.59
O2 0.11 0.00 2% 0.04 0.16
OS1 0.22 0.00 2% 0.07 0.31
OS2 0.70 0.23 34% 0.62 2.68
Total On-Site 13.07 9.12 67% 19.32 82.87
Total On-Site
to Detention
12.75 9.08 69% 19.14 82.12
Total Off-Site 0.92 0.23 26% 0.18 0.75
1. Includes pavement and roof areas.
VARIANCE REQUESTS
Site constraints, including the relative flatness of the Site and proximity to the ultimate outfall require
variances to the standard criteria, as described in the Criteria Manual, to be requested. The following
variances are requested.
Section 6.0: Low Impact Development: “…2) 75% of all newley added or modified impervious area must be
treated by LID techniques…”
Water quality treatment through the design of LID features was utilized to the extent practicable. As
currently proposed, 59% of the Site’s impervious area will be treated with LIDs.
Chapter 8, Section 3.4: Freeboard: “…Twelve inches (12”) of freeboard is to be provided within the
detention basin, measured vertically from the 100-year water surface elevation to the top of the basin, or
Preliminary Drainage Report
Mulberry Connection – Fort Collins, Colorado
7
measured from the emergency spillway elevation (if it is higher than the 100-year water surface elevation)
to the top of the basin…”
The proposed extended detention basin 100-year water surface elevation is less than 1-foot from the top
of berm along the east side of the proposed basin. Freeboard in this area is measured going into the parking
lot. A minimum of 1-foot of freeboard from the 100-year water surface elevation and all proposed building
finished floor elevations is provided.
EROSION CONTROL
The Erosion Control Criteria and all Erosion Control Materials will be provided in the Final Drainage Report.
CONCLUSIONS
COMPLIANCE WITH STANDARDS
Except for the two variances listed above, the Mulberry Connection project is in compliance with City of
Fort Collins criteria for storm drainage design. The “Fort Collins Stormwater Criteria Manual, December
2018 Edition,” and the Urban Drainage Flood Control District “Urban Storm Drainage Criteria Manual
Volumes 1, 2, and 3 have been utilized for reference.
SUMMARY OF CONCEPT
The proposed drainage concept is to surface flow runoff from impervious areas to pervious area to the
extent practicable. Three rain gardens are proposed to treat the WQCV from as much of the Site as
possible. An extended detention pond is proposed to detain the on-site 100-year runoff volume to the 2-
year historic on-site flow and treat the WQCV for the remainder of the Site. Downstream impacts due to the
development of this Site are not anticipated.
REFERENCES
Fort Collins Stormwater Criteria Manual, December 2018 Edition, City of Fort Collins.
Urban Storm Drainage Criteria Manual, Volume 1-3, Urban Drainage and Flood Control District, Denver,
CO; January 2016, with latest revisions.
APPENDICES
A. NRCS Data and FEMA Map
B. Existing and Proposed Drainage Map
C. Hydrologic Calculations
D. Hydraulic Calculations
8
APPENDIX A
United States
Department of
Agriculture
A product of the National
Cooperative Soil Survey,
a joint effort of the United
States Department of
Agriculture and other
Federal agencies, State
agencies including the
Agricultural Experiment
Stations, and local
participants
Custom Soil Resource
Report for
Larimer County
Natural Area, Colorado
Resources
Conservation
Service
August 15, 2019
6
Custom Soil Resource Report
Soil Map
4493280 4493330 4493380 4493430 4493480 4493530 4493580
4493280 4493330 4493380 4493430 4493480 4493530 4493580
499430 499480 499530 499580 499630 499680 499730 499780 499830 499880
499430 499480 499530 499580 499630 499680 499730 499780 499830 499880
40° 35' 35'' N
105° 0' 25'' W
40° 35' 35'' N
105° 0' 4'' W
40° 35' 24'' N
105° 0' 25'' W
40° 35' 24'' N
105° 0' 4'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 100 200 400 600
Feet
0 30 60 120 180
Meters
Map Scale: 1:2,260 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
40 Garrett loam, 0 to 1 percent
slopes
5.6 27.8%
53 Kim loam, 1 to 3 percent slopes 0.0 0.0%
63 Longmont clay, 0 to 3 percent
slopes
0.6 2.8%
73 Nunn clay loam, 0 to 1 percent
slopes
13.9 69.4%
76 Nunn clay loam, wet, 1 to 3
percent slopes
0.0 0.1%
Totals for Area of Interest 20.0 100.0%
Map Unit Descriptions
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions, along
with the maps, can be used to determine the composition and properties of a unit.
A map unit delineation on a soil map represents an area dominated by one or more
major kinds of soil or miscellaneous areas. A map unit is identified and named
according to the taxonomic classification of the dominant soils. Within a taxonomic
class there are precisely defined limits for the properties of the soils. On the
landscape, however, the soils are natural phenomena, and they have the
characteristic variability of all natural phenomena. Thus, the range of some
observed properties may extend beyond the limits defined for a taxonomic class.
Areas of soils of a single taxonomic class rarely, if ever, can be mapped without
including areas of other taxonomic classes. Consequently, every map unit is made
up of the soils or miscellaneous areas for which it is named and some minor
components that belong to taxonomic classes other than those of the major soils.
Most minor soils have properties similar to those of the dominant soil or soils in the
map unit, and thus they do not affect use and management. These are called
noncontrasting, or similar, components. They may or may not be mentioned in a
particular map unit description. Other minor components, however, have properties
and behavioral characteristics divergent enough to affect use or to require different
management. These are called contrasting, or dissimilar, components. They
generally are in small areas and could not be mapped separately because of the
scale used. Some small areas of strongly contrasting soils or miscellaneous areas
are identified by a special symbol on the maps. If included in the database for a
given area, the contrasting minor components are identified in the map unit
descriptions along with some characteristics of each. A few areas of minor
components may not have been observed, and consequently they are not
mentioned in the descriptions, especially where the pattern was so complex that it
was impractical to make enough observations to identify all the soils and
miscellaneous areas on the landscape.
Custom Soil Resource Report
8
19
Custom Soil Resource Report
Map—Hydrologic Soil Group
4493280 4493330 4493380 4493430 4493480 4493530 4493580
4493280 4493330 4493380 4493430 4493480 4493530 4493580
499430 499480 499530 499580 499630 499680 499730 499780 499830 499880
499430 499480 499530 499580 499630 499680 499730 499780 499830 499880
40° 35' 35'' N
105° 0' 25'' W
40° 35' 35'' N
105° 0' 4'' W
40° 35' 24'' N
105° 0' 25'' W
40° 35' 24'' N
105° 0' 4'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 100 200 400 600
Feet
0 30 60 120 180
Meters
Map Scale: 1:2,260 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
Table—Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
40 Garrett loam, 0 to 1
percent slopes
B 5.6 27.8%
53 Kim loam, 1 to 3 percent
slopes
B 0.0 0.0%
63 Longmont clay, 0 to 3
percent slopes
D 0.6 2.8%
73 Nunn clay loam, 0 to 1
percent slopes
C 13.9 69.4%
76 Nunn clay loam, wet, 1 to
3 percent slopes
C 0.0 0.1%
Totals for Area of Interest 20.0 100.0%
Rating Options—Hydrologic Soil Group
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Custom Soil Resource Report
21
9
APPENDIX B
MULBERRY CONNECTION
CITY OF FORT COLLINS
UTILITY PLANS
FOR REVIEW ONLY
NOT FOR
Kimley-Horn and Associates, Inc.
CONSTRUCTION
OF 6
R
Know what's below.
Call before you dig. 096501004_DRN_PROP
LEGEND
NORTH
6
10
APPENDIX C
POUDRE VALLEY DEVELOPMENT DATE: 9/20/2019
096501004
HMO
DLS
TYPE B/C SOIL
ASPHALT/C
ONCRETE ROOFTOP GRAVEL
LAWNS, SANDY
SOIL, FLAT SLOPE
LAWNS, SANDY SOIL,
AVG SLOPE
LAND USE: AREA AREA AREA AREA AREA
2-YR RUNOFF COEFFICIENT 0.95 0.95 0.50 0.10 0.15
5-YR RUNOFF COEFFICIENT 0.95 0.95 0.50 0.10 0.15
100-YR RUNOFF COEFFICIENT 1.19 1.19 0.63 0.13 0.19
IMPERVIOUS % 100% 90% 40% 2% 2%
ASPHALT/CONCRERTOEOFTOP GRAVEL
LAWNS, SANDY
SOIL, FLAT SLOPE
LAWNS, SANDY SOIL,
AVG SLOPE TOTAL
DESIGN DESIGN AREA AREA AREA AREA AREA AREA
BASIN POINT (AC) (AC) (AC) (AC) (AC) (AC) Cc(2) Cc(5) Cc(100) Imp %
EX1 EX1 0.29 0.00 0.00 0.00 12.81 13.10 0.17 0.17 0.21 4%
EX2 EX2 0.23 0.00 0.00 0.00 0.47 0.69 0.41 0.41 0.52 34%
EX3 EX3 0.46 0.00 0.00 0.00 0.20 0.66 0.71 0.71 0.88 70%
A A 1.54 2.15 0.00 1.40 0.00 5.09 0.72 0.72 0.90 69%
B B 2.80 0.00 0.00 0.00 1.06 3.86 0.73 0.73 0.91 73%
C C 0.87 1.63 0.00 0.00 1.21 3.72 0.69 0.69 0.86 64%
O1 O1 0.04 0.00 0.00 0.00 0.17 0.21 0.30 0.30 0.38 21%
O2 O2 0.00 0.00 0.00 0.00 0.14 0.14 0.15 0.15 0.19 2%
TOTAL ON-SITE 13.02 0.70 0.70 0.87 67%
TOTAL TO DETENTION 12.67 0.71 0.71 0.89 69%
OS1 OS1 0.00 0.00 0.00 0.00 0.22 0.22 0.15 0.15 0.19 2%
OS2 OS2 0.23 0.00 0.00 0.00 0.47 0.70 0.42 0.42 0.52 34%
CHECKED BY:
PROJECT NUMBER:
CALCULATED BY:
NOTE: C2-YR*1.00 PER FCSCM TABLE 3-2-3
OFF-SITE BASINS
ON-SITE BASINS
RUNOFF COEFFICIENTS - IMPERVIOUS CALCULATION
PROJECT NAME:
COMPOSITE RUNOFF
COEFFICIENT
NOTE: C2-YR*1.25 PER FCSCM TABLE 3-2-3
EXISTING BASINS
POUDRE VALLEY DEVELOPMENT DATE: 9/20/2019
096501004
HMO
DLS
FINAL
Tc
DESIGN AREA C2 LENGTH SLOPE Ti LENGTH SLOPE R VEL Tt MAX Tc MIN Tc
BASIN Ac Ft % Min. Ft. % fps Min. Min. Min. Min. Min.
EX1 13.10 0.17 500 0.6% 210.0 600 0.6% 0.654 6.9 1.4 211.4 12.8 5.0 12.8
EX2 0.69 0.41 62 0.4% 62.8 1,434 0.5% 0.654 5.9 4.0 66.8 10.3 5.0 10.3
EX3 0.66 0.71 75 3.0% 20.5 465 0.6% 0.654 6.8 1.1 21.6 10.4 5.0 10.4
A 5.09 0.72 275 3.0% 38.3 -- 0.0% 0.195 0.0 -- 38.3 11.5 5.0 11.5
B 3.86 0.73 190 1.3% 41.1 2,000 0.5% 0.195 2.7 12.2 53.3 11.1 5.0 11.1
C 3.72 0.69 260 2.3% 43.5 -- 0.0% 0.195 0.0 -- 43.5 11.4 5.0 11.4
O1 0.21 0.30 40 5.1% 25.4 -- 0.0% 0.195 0.0 -- 25.4 10.2 5.0 10.2
O2 0.14 0.15 75 3.0% 49.5 465 0.6% 0.195 3.0 2.5 52.1 10.4 5.0 10.4
OS1 0.220 0.15 83 14.0% 31.2 480 1.0% 0.654 8.6 0.9 32.1 10.5 5.0 10.5
OS2 0.700 0.42 200 2.0% 66.7 585 0.5% 0.654 6.1 1.6 68.3 11.1 5.0 11.1
TIME OF CONCENTRATION
MAXIMUM & MINIMUM
TIME OF CONCENTRATION
PROJECT NAME:
PROJECT NUMBER:
DATA
INITIAL/OVERLAND
TIME (Ti)
CHANNELIZED TIME
(Tt)
SUB-BASIN
CALCULATED BY:
ON-SITE BASINS
CHECKED BY:
Tc
2-YEAR
OFF-SITE BASINS
EXISTING BASINS
ܶ = 1.87(1.1 − ܮ (ܥݔܥ
య ܵ ܸ = 1.49 ܶ = ܶ + ܶ௧
݊ ܴଶ/ଷܵଵ/ଶ
ܶ,௫ = 1 80ܮ
10 +
POUDRE VALLEY DEVELOPMENT DATE: 9/20/2019
096501004
HMO
DLS
FINAL
Tc
DESIGN AREA C100 LENGTH SLOPE Ti LENGTH SLOPE R VEL Tt MAX Tc MIN Tc
BASIN Ac Ft % Min. Ft. % fps Min. Min. Min. Min. Min.
EX1 13.10 0.21 500 0.6% 200.5 600 0.6% 0.654 6.9 1.4 202.0 12.8 5.0 12.8
EX2 0.69 0.52 62 0.4% 53.4 1,434 0.5% 0.654 5.9 4.0 57.4 10.3 5.0 10.3
EX3 0.66 0.88 75 3.0% 11.3 465 0.6% 0.654 6.8 1.1 12.4 10.4 5.0 10.4
A 5.09 0.90 275 0 20.5 -- 0 0.654 0.0 -- 20.5 11.5 5.0 11.5
B 3.86 0.91 190 0 20.8 2,000 0 0.654 6.1 5.5 26.3 11.1 5.0 11.1
C 3.72 0.86 260 0 25.3 -- 0 0.654 0.0 -- 25.3 11.4 5.0 11.4
O1 0.21 0.38 40 0 23.0 -- 0 0.654 0.1 -- 23.0 10.2 5.0 10.2
O2 0.14 0.19 75 0 47.6 465 0 0.654 6.8 1.1 48.7 10.4 5.0 10.4
OS1 0.220 0.19 83 14.0% 29.9 480 1.0% 0.654 8.6 0.9 30.9 10.5 5.0 10.5
OS2 0.700 0.52 200 2.0% 56.6 585 0.5% 0.654 6.1 1.6 58.2 11.1 5.0 11.1
CHECKED BY:
TIME OF CONCENTRATION
100-YEAR
PROJECT NAME:
PROJECT NUMBER:
CALCULATED BY:
EXISTING BASINS
ON-SITE BASINS
OFF-SITE BASINS
SUB-BASIN INITIAL/OVERLAND CHANNELIZED TIME
Tc
MAXIMUM & MINIMUM
DATA TIME (Ti) (Tt) TIME OF CONCENTRATION
ܶ = 1.87(1.1 − ܮ (ܥݔܥ
య ܵ ܸ = 1.49 ܶ = ܶ + ܶ௧
݊ ܴଶ/ଷܵଵ/ଶ
ܶ,௫ = 1 80ܮ
10 +
PROJECT NAME: POUDRE VALLEY DEVELOPMENT DATE:
PROJECT NUMBER: 096501004
CALCULATED BY: HMO
CHECKED BY: DLS
REMARKS
DESIGN
POINT
DESIGN
BASIN
AREA
(AC)
RUNOFF
COEFF
C2
tc (min)
C*A(ac)
I
(in/hr)
Q
(cfs)
tc(max)
S(C*A)
(ac)
I
(in/hr)
Q
(cfs)
SLOPE
(%)
STREET
FLOW(cfs
DESIGN
FLOW(cfs
)
SLOPE
(%)
PIPE
SIZE (in)
LENGTH
(ft)
VELOCIT
Y
tt
(min)
(2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
EX1 EX1 13.10 0.17 12.78 2.20 2.00 4.40
EX2 EX2 0.69 0.41 10.34 0.29 2.18 0.62
EX3 EX3 0.66 0.71 10.42 0.47 2.18 1.01
A A 5.09 0.72 11.53 3.65 2.09 7.62
B B 3.86 0.73 11.06 2.82 2.13 6.00
C C 3.72 0.69 11.44 2.56 2.09 5.36
O1 O1 0.21 0.30 10.22 0.06 2.19 0.14
O2 O2 0.14 0.15 10.42 0.02 2.18 0.05
OS1 OS1 0.22 0.15 10.46 0.03 2.17 0.07
OS2 OS2 0.70 0.42 11.11 0.29 2.12 0.62
ON-SITE BASINS
OFF-SITE BASINS
EXISTING BASINS
STORM
LINE
PROJECT NAME: POUDRE VALLEY DEVELOPMENT DATE:
PROJECT NUMBER: 096501004
CALCULATED BY: HMO
CHECKED BY: DLS
REMARKS
DESIGN
POINT
DESIGN
BASIN
AREA
(AC)
RUNOFF
COEFF
C100
tc (min)
C*A(ac)
I
(in/hr)
Q
(cfs)
tc(max)
S(C*A)
(ac)
I
(in/hr)
Q
(cfs)
SLOPE
(%)
STREET
FLOW(cfs)
DESIGN
FLOW(cfs)
SLOPE
(%)
PIPE
SIZE (in)
LENGTH
(ft)
VELOCITY
(fps)
tt
(min)
(2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
EX1 EX1 13.10 0.21 12.78 2.75 6.79 18.66
EX2 EX2 0.69 0.52 10.34 0.36 7.62 2.72
EX3 EX3 0.66 0.88 10.42 0.58 7.59 4.42
A A 5.09 0.90 11.53 4.56 7.28 33.20
B B 3.86 0.91 11.06 3.52 7.04 24.79
C C 3.72 0.86 11.44 3.21 7.31 23.43
O1 O1 0.21 0.38 10.22 0.08 7.65 0.59
O2 O2 0.14 0.19 10.42 0.03 7.59 0.20
OS1 OS1 0.22 0.19 10.46 0.04 7.58 0.31
OS2 OS2 0.70 0.52 11.11 0.36 7.39 2.68
STANDARD FORM SF-3
STORM DRAINAGE DESIGN - RATIONAL METHOD 100 YEAR EVENT
9/20/2019
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE TRAVEL TIME
STORM
LINE
PROJECT NAME: POUDRE VALLEY DEVELOPMENT DATE: 9/20/2019
PROJECT NUMBER:096635000
CALCULATED BY: HMO
CHECKED BY: DLS
Q2 Q100
EX1 EX1 13.10 4.40 18.66
EX2 EX2 0.69 0.62 2.72
EX3 EX3 0.66 1.01 4.42
14.46 6.03 25.80
A A 5.09 7.62 33.20
B B 3.86 6.00 24.79
C C 3.72 5.36 23.43
O1 O1 0.21 0.14 0.59
O2 O2 0.14 0.05 0.20
13.02 19.17 82.21
12.67 18.98 81.42
OS1 OS1 0.22 0.07 0.31
OS2 OS2 0.70 0.62 2.68
0.92 0.69 3.00
ON-SITE BASINS
OFF-SITE BASINS
TOTAL
TOTAL
TOTAL
TOTAL ON-SITE TO DETENTION
EXISTING BASINS
DESIGN POINT
RATIONAL CALCULATIONS SUMMARY
TRIBUTARY
BASINS
TRIBUTARY AREA
(AC)
PEAK FLOWS (CFS)
4582 S. Ulster Street - Suite 1500
Denver, Colorado 80237
Project: Mulberry Connection Prepared By: HMO
Project Number: 096501004 Checked By: DLS
Date: 20-Sep-19
Water Quality Capture Volume - Basin A
Contributing Basin Characteristics
Site Area = 5.09 61% - -
Hydrologic Soil Group A =
Hydrologic Soil Group B =
Hydrologic Soil Group C =
Hydrologic Soil Group D =
Water Quality Capture Volume
FCSCM Equation 7-1 WQ Watershed Inches = a*(0.91i
3
-1.19i
2
+.078i)
a12 = 0.8 (12-Hr Drain Time)
a40 = 1.0 (40-Hr Drain Time)
FCSCM Equation 7-2 WQCV = (WQCV/12)*(Area)*1.2
WQCV Impervious (Site) = 61%
a = 0.8
WQ Watershed Inches (Site) = 0.192
WQCV Area (Site) = 5.09
WQ Capture Volume (Site) = 0.098 AC-FT
0.098 AC-FT
4,249 CU-FT
Area
(AC)
Impervious
(%)
Watershed Flow
Length (ft)
Watershed Flow
Slope (ft/ft)
Site WQ Volume
WQCV A - 9/18/2019
4582 S. Ulster Street - Suite 1500
Denver, Colorado 80237
Project: Mulberry Connection Prepared By: HMO
Project Number: 096501004 Checked By: DLS
Date: 20-Sep-19
Water Quality Capture Volume - Basin B
Contributing Basin Characteristics
Site Area = 3.86 73% - -
Hydrologic Soil Group A =
Hydrologic Soil Group B =
Hydrologic Soil Group C =
Hydrologic Soil Group D =
Water Quality Capture Volume
FCSCM Equation 7-1 WQ Watershed Inches = a*(0.91i
3
-1.19i
2
+.078i)
a12 = 0.8 (12-Hr Drain Time)
a40 = 1.0 (40-Hr Drain Time)
FCSCM Equation 7-2 WQCV = (WQCV/12)*(Area)*1.2
WQCV Impervious (Site) = 73%
a = 0.8
WQ Watershed Inches (Site) = 0.231
WQCV Area (Site) = 3.86
WQ Capture Volume (Site) = 0.089 AC-FT
0.089 AC-FT
3,891 CU-FT
Site WQ Volume
Area
(AC)
Impervious
(%)
Watershed Flow
Length (ft)
Watershed Flow
Slope (ft/ft)
WQCV B - 9/18/2019
4582 S. Ulster Street - Suite 1500
Denver, Colorado 80237
Project: Mulberry Connection Prepared By: HMO
Project Number: 096501004 Checked By: DLS
Date: 20-Sep-19
Water Quality Capture Volume - Basin C
Contributing Basin Characteristics
Site Area = 3.72 64% - -
Hydrologic Soil Group A =
Hydrologic Soil Group B =
Hydrologic Soil Group C =
Hydrologic Soil Group D =
Water Quality Capture Volume
FCSCM Equation 7-1 WQ Watershed Inches = a*(0.91i
3
-1.19i
2
+.078i)
a12 = 0.8 (12-Hr Drain Time)
a40 = 1.0 (40-Hr Drain Time)
FCSCM Equation 7-2 WQCV = (WQCV/12)*(Area)*1.2
WQCV Impervious (Site) = 64%
a = 0.8
WQ Watershed Inches (Site) = 0.200
WQCV Area (Site) = 3.72
WQ Capture Volume (Site) = 0.074 AC-FT
0.074 AC-FT
3,245 CU-FT
Site WQ Volume
Area
(AC)
Impervious
(%)
Watershed Flow
Length (ft)
Watershed Flow
Slope (ft/ft)
WQCV C - 9/18/2019
PROJECT NAME: Mulberry Connection
PROJECT NUMBER: 096501004
CALCULATED BY: HMO
CHECKED BY: DLS 2-yr Historic Flow 4.4 CFS
DATE: 9/20/2019 O1 100-yr Flow 0.59 CFS
O2 100-yr Flow 0.2 CFS
Allowed Release Rate 3.61 CFS
12.75
3.61
0.89
Duration, Td Rainfall Intensity, I Inflow Volume, Vi Outflow Volume, Vo Storage Volume, Vs Storage Volume, Vs
(min) (in/hr) (CF) (CF) (CF) (AC)
5 9.95 33872 1083 32789 0.75
10 7.72 52562 2166 50396 1.16
15 6.52 66587 3249 63338 1.45
20 5.60 76255 4332 71923 1.65
25 4.98 84766 5415 79351 1.82
30 4.52 92323 6498 85825 1.97
35 4.08 97225 7581 89644 2.06
40 3.74 101855 8664 93191 2.14
45 3.46 106008 9747 96261 2.21
50 3.23 109957 10830 99127 2.28
55 3.03 113464 11913 101551 2.33
60 2.86 116834 12996 103838 2.38
65 2.71 119932 14079 105853 2.43
70 2.59 123438 15162 108276 2.49
75 2.48 126638 16245 110393 2.53
80 2.38 129634 17328 112306 2.58
85 2.29 132527 18411 114116 2.62
90 2.21 135421 19494 115927 2.66
95 2.13 137770 20577 117193 2.69 Basin WQCV (ac-ft)
100 2.06 140255 21660 118595 2.72 A 0.098
105 2.00 142979 22743 120236 2.76 B 0.089
110 1.94 145293 23826 121467 2.79 C 0.074
115 1.88 147200 24909 122291 2.81
120 1.84 150332 25992 124340 2.85 Required: 2.95 100-yr Detention + Basin A WQCV
MODIFIED FAA DETENTION SIZING
BASIN A 100-YEAR
Area (A)
DETENTION VOLUME BY MODIFIED FAA METHOD - 100 YEAR
acres (Basins A, B, & C)
ALLOWED RELEASE RATE CALCULATION
Release Rate (R)'
100-Year Runoff Coefficient (C)'
CALCULATIONS
cfs (Historic 2-yr flow)
Composite of entire proposed area
11
APPENDIX D
990 South Broadway - Suite 200
Denver, Colorado 80209
Project: Mulberry Connection
Project Number: 96501004
Date:
Prepared By: HMO
Checked By: DLS
BioRetention B
WQCV Required 3,891 cf
Infiltration Rate 300 min/inch
Drain Time 12 hours
Drian Time 720 min
Infiltration Depth 2 inches
Infiltration Depth 0.2 ft
Raingarden B1 Raingarden B2
Total Volume of Basin 3276 cf Total Volume of Basin 596 cf
Area of Bottom 860 sf Area of Bottom 106 sf
Ponding Depth 1 ft Ponding Depth 0.4 ft
Volume at 1 ft Depth 3276 cf Volume at 1 ft Depth 596 cf
Bioretention Sand Media Depth 18 in Bioretention Sand Media Depth 18 in
Bioretention Sand Media Void Ratio 0.14 Bioretention Sand Media Void Ratio 0.14
Volume w/in 1-ft Ponding Depth 3,276 cf Volume w/in Ponding Depth 596 cf
Volume w/in Bioretention Media 181 cf Volume w/in Bioretention Media 22 cf
Volume Infiltrated 172 cf Volume Infiltrated 21 cf
TOTAL VOLUME 3,629 cf TOTAL VOLUME 639 cf
TOTAL WQCV PROVIDED 4,268 cf
September 20, 2019
990 South Broadway - Suite 200
Denver, Colorado 80209
Project: Mulberry Connection
Project Number: 96501004
Date:
Prepared By: HMO
Checked By: DLS
BioRetention C
WQCV Required 3,245 cf
Infiltration Rate 300 min/inch
Drain Time 12 hours
Drian Time 720 min
Infiltration Depth 2 inches
Infiltration Depth 0.2 ft
Total Volume of Basin 6701 cf
Area of Bottom 3800 sf
Ponding Depth 1 ft
Volume at 1 ft Depth 6701 cf
Bioretention Sand Media Depth 18 in
Bioretention Sand Media Void Ratio 0.14
Volume w/in 1-ft Ponding Depth 6,701 cf
Volume w/in Bioretention Media 798 cf
Volume Infiltrated - cf Assume no infiltration
TOTAL VOLUME 7,499 cf
WQCV 7,499 cf
WQCV Water Surface 4,953.00 ft
September 20, 2019
PROJECT NAME:
PROJECT NUMBER: 096755001
CALCULATED BY: HMO
CHECKED BY: DLS
DATE: 9/20/2019
PRISMOIDAL METHOD
Prismoidal Calculation Method = (1/3)*(ELEV1-ELEV2)*(AREA1+AREA2)+(SQRT(AREA1*AREA2))
ELEV. AREA VOLUME ACCUM. VOL. ACCUM. VOL.
(FT) (SQ FT.) (CU FT) (CU FT) (AC-FT)
4947.5 4,662 0 0 0.00
4948 11,657 3,948 3,948 0.09 WQCV (0.097 AC-FT) = 4950.59
4948.5 18,361 7,441 11,390 0.26
4949 22,999 10,318 21,708 0.50
4949.5 25,418 12,099 33,807 0.78
4950 27,819 13,305 47,112 1.08
4950.5 30,279 14,520 61,632 1.41
4951 32,798 15,765 77,397 1.78
4951.5 35,376 17,039 94,437 2.17
4952 38,012 18,343 112,780 2.59
4952.5 40,707 19,676 132,456 3.04 100-YR (2.85 AC-FT) = 4952.29
4953 43,470 21,040 153,496 3.52
STAGE-STORAGE ANALYSIS
BASIN A
BASIN A
PROJECT NAME:
PROJECT NUMBER: 096755001
CALCULATED BY: HMO
CHECKED BY: DLS
DATE: 9/20/2019
PRISMOIDAL METHOD
Prismoidal Calculation Method = (1/3)*(ELEV1-ELEV2)*(AREA1+AREA2)+(SQRT(AREA1*AREA2))
ELEV. AREA VOLUME ACCUM. VOL. ACCUM. VOL.
(FT) (SQ FT.) (CU FT) (CU FT) (AC-FT)
4949 860 0 0 0.00
4949.5 3,620 1,041 1,041 0.02
4950 5,378 2,235 3,276 0.08 Orifice plate at Elev 4950 1-ft of ponding
4950.5 7,075 3,104 6,379 0.15 100-yr grate at Elev 4950.5
ELEV. AREA VOLUME ACCUM. VOL. ACCUM. VOL.
(FT) (SQ FT.) (CU FT) (CU FT) (AC-FT)
4949.8 106 0 0 0.000
4950 1,520 135 135 0.003
4950.2 3,194 461 596 0.014 Orifice plate at Elev 4950.2 - 0.4-ft of ponding
100-yr grate at Elev 4950.2
1176 0.09
3872 0.16
STAGE-STORAGE ANALYSIS
BASIN B
RAINGARDEN B1
RAINGARDEN B2
WQ TOTAL
100-YR TOTAL
PROJECT NAME:
PROJECT NUMBER: 096755001
CALCULATED BY: HMO
CHECKED BY: DLS
DATE: 9/20/2019
PRISMOIDAL METHOD
Prismoidal Calculation Method = (1/3)*(ELEV1-ELEV2)*(AREA1+AREA2)+(SQRT(AREA1*AREA2))
ELEV. AREA VOLUME ACCUM. VOL. ACCUM. VOL.
(FT) (SQ FT.) (CU FT) (CU FT) (AC-FT)
4952 3,800 0 0 0.00
4953 10,106 6,701 6,701 0.15 Outlet at 4953 - 1-ft of ponding
STAGE-STORAGE ANALYSIS
BASIN C
RAINGARDEN C
(1)
EXISTING BASINS
ON-SITE BASINS
OFF-SITE BASINS
(1)
STANDARD FORM SF-3
STORM DRAINAGE DESIGN - RATIONAL METHOD 2 YEAR EVENT
9/20/2019
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE TRAVEL TIME
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 13, Sep 10, 2018
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Aug 11, 2018—Aug
12, 2018
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Custom Soil Resource Report
20
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 13, Sep 10, 2018
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Aug 11, 2018—Aug
12, 2018
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Custom Soil Resource Report
7