HomeMy WebLinkAboutPACIFIC COAST SUPPLY WAREHOUSE - FDP200019 - - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL REPORT
FOR
PACIFIC COAST SUPPLY
A TRACT OF LAND LOCATED IN THE SOUTHWEST QUARTER OF SECTION 3,
TOWNSHIP 7 NORTH, RANGE 68 WEST OF THE 6TH P.M.,
CITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADO
ZP#: Z19-050
September 2, 2020
Rev. January 28, 2021
FINAL DRAINAGE AND EROSION CONTROL REPORT
FOR
PACIFIC COAST SUPPLY
A TRACT OF LAND LOCATED IN THE SOUTHWEST QUARTER OF SECTION 3,
TOWNSHIP 7 NORTH, RANGE 68 WEST OF THE 6TH P.M.,
CITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADO
ZP#: Z19-050
September 2, 2020
Rev. January 28, 2021
Prepared for: Pacific Coast
12860 W. Cedar Dr.
Lakewood, CO 80228
Contact: Stuart Nielson
303-659-2313
Prepared by: ZP Architects Engineers, Inc.
2727 Bryant Street, Suite 610
Denver, CO 80211
(303) 455-3322
William J. Logan, P.E.
Project Engineer
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Engineers Certification Statement
“I hereby attest that this report for the final drainage design for the Pacific Coast Supply
was prepared by me or under my direct supervision, in accordance with the provisions
of the Fort Collins Stormwater Criteria Manual. I understand that the City of Fort Collins
does not and will not assume liability for drainage facilities designed by others.”
Registered Professional Engineer Date
State of Colorado No.31705
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TABLE OF CONTENTS
PHASE II DRAINAGE REPORT
I. GENERAL LOCATION AND DESCRIPTION
A. Location ................................................................................................................. 1
B. Description of Property .......................................................................................... 2
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description ......................................................................................... 2
B. Sub-Basin Description ........................................................................................... 2
III. DRAINAGE DESIGN CRITERIA
A. Regulations............................................................................................................ 3
B. Development Criteria Reference and Constraints ................................................. 3
C. Hydrological Criteria .............................................................................................. 3
D. Hydraulic Criteria ................................................................................................... 3
E. Waivers from the Criteria ....................................................................................... 4
F. Low Impact Development Four Step Process ........................................................ 4
IV. DRAINAGE FACILITY DESIGN
A. General Concept ................................................................................................... 5
B. Specific Details ...................................................................................................... 7
V. CONCLUSIONS
A. Compliance with Standards ................................................................................... 7
B. Drainage Concept .................................................................................................. 7
VI. LIST OF REFERENCES ............................................................................................ 8
APPENDIX A ................................................................................................................... 9
Hydrologic & Hydraulic Computations
APPENDIX B ................................................................................................................. 29
Charts and Tables
APPENDIX C ................................................................................................................ 38
FIRM Map, Drainage Plan
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I. GENERAL LOCATION AND DESCRIPTION
A. Location
The proposed Pacific Coast Supply building is located in a Tract of land located
in the Southwest Quarter of Section 3, Township 7 North, Range 68 West of the
6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado.
The site is specifically located at 1012 NE I-25 Frontage Road.
Vicinity Map
A new structure is to be located north of the existing Pacific Coast Supply
buildings. Site access is off Northeast I-25 Frontage Road to the west. To the
north and east is cultivated land with further development beyond the boundary
of the proposed site. To the south, the property is separated from the cultivated
property by an existing 30-feet public access right-of-way. A private irrigation
ditch lies along the easterly boundary. The Larimer and Weld Canal also lies to
the north and east of the property, (Reference 4).
A number of easements exist within the proposed property improvements. The
easements consist of a 20’ water line easement, and two 15’ and 10’ easements
per the plate from the K-2 Industrial Park; no description of the last two is given.
The existing 10’ easement shall be removed from the property.
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B. Description of Property
The site consists of two tracts for an approximate area of 4.263 acres. The
existing southern tract is currently developed, and includes the three buildings
used by Pacific Coast Supply. The recently obtained north tract is undeveloped
and will contain most of the new improvements. The plan is to construct a new
20,000 square-foot metal building with approximately 45,000 square-feet of hard
surfaces on both tracts. The proposed development will provide additional
storage space for the Pacific Coast Supply operations.
The existing topography of the site slopes over a combination of native and
gravel yards from the east to the west at an average slope of 1.2%. New
detention and access easements for detention, maintenance and fire access are
proposed.
The web soil survey describes the site soils primarily as Longmont Clay and
Nunn Clay Loam to Satanta Loam with a Hydrologic Soil Group C and D. Group
C/D soils have a slow infiltration rate when thoroughly wet, and consist chiefly of
layers that impedes the downward movement of water or soils of moderately fine
to fine texture (Reference appendix B for Soil Survey Map Information). The site
also has a high water table per the Geotechnical Evaluation Report by American
Geoservices (Reference 6).
The Larimer and Weld Canal to the east and north flows easterly under I-25 to
the west. An irrigation ditch lies along the easterly most boundary and will not be
affected by the proposed improvements.
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
The site is located within the Cooper Slough/Box Elder Basin Master Drainage
Study. (Reference 3 and hereafter called Master).
This site is located within a 100-year floodplain as defined by the Federal
Emergency Management Agency Community Panel numbers 08069C1001F,
(Reference 4) and 08069C0982F, (Reference 5), both dated December 19, 2006.
B. Sub-Basin Description
Both tracts currently surface drain to the west into the ditch along NE I-25
Frontage Road. Runoff into the ditch drains south and crosses under I-25
through an existing culvert leading to the west. Offsite runoff to the site is limited
from the east basins labeled OS1 and OS2.
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The proposed site improvements will collect and surface drain the majority of the
site to a water quality Bioretention pond in the middle of the site. Stormwater,
along with most of the site’s proposed improvements will be directed to the
detention pond located at the northwest corner of the property. The runoff
collected in the pond will be directed to the west into the frontage ditch.
An existing sump condition exists along the frontage ditch near the northwest
corner of the property. The low spot has been identified and corrected in the
proposed plans. In order to correct the low spot, some minor over lot grading is
needed at the northern neighbor’s southwest corner.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
The primary criteria for this development is the “Fort Collins Stormwater Criteria
Manual”, (Reference 1 and hereafter called Criteria), and the Urban Drainage
Flood Control District’s Urban Storm Drainage Criteria Manuals (Reference 2 and
hereafter called Manual).
B. Development Criteria References and Constraints
The subject area is identified within the Master drainage study. In addition to the
Criteria, additional physical site restraints are realized due to this property being
partially developed with three buildings already on site. See waivers below.
C. Hydrological Criteria
The design rainfall for the runoff generated on-site was based on the Rational
Method for the 2 and 100-year rainfall events for developed conditions as
established in the Criteria and Manual. The runoff results are summarized on the
Drainage Plan and in Appendix A. Rainfall intensities were determined from the
Criteria by using the 1-hour point rainfall values of 0.82 in/hr. for the 2-year storm
event and 2.86 in/hr. for the 100-year storm event.
The detention and discharge limits are based on the 2-year historic runoff, with
the allowance that the existing impervious areas are limited to the 100-year
recurrence.
D. Hydraulic Criteria
The capacity of the detention facility is based on the FAA method outlined in the
Criteria. The proposed Bioretention pond and Extended Drainage Basin water
quality volumes are per the Manual.
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E. Waivers from the Criteria
The site contains unique conditions that make development per the Criteria with
LID features extremely difficult. Within the proposed site, two existing buildings
with floor elevations surveyed at 4973.00 feet establish an upper limit to design.
At the other end, the need to eliminate the existing sump condition and still drain
to the ditch establishes the lower design elevation at 4968.40 feet. The
combination of full detention, an Extended Detention Basin, a Bioretention pond,
Forbay, an emergency overflow depth, and a free board forces the drainage
facility within a vertical design limit of 4.6 feet. This is further reduced to about
4.0 feet once a connection to the ditch is made. Due to the existing site
limitations, five (5) variances are requested from the Criteria and Manual.
1. Ground Cover of drainage Box:
Variance: Due to insufficient ground cover across the drive lane, a structural
concrete box culvert is proposed to accommodate drainage between the
Bioretention to the detention pond.
2. Bioretention Details D-53 and D-53A:
Variance: Details D-53 and D-53A depicts a 30” deep Bioretention pond
filtration structure. Due to vertical site limitations and the need to control
flooding, these details cannot be achieved. Therefor a Bioretention pond
(Raingarden) with an 18” growing and drainage media similar to the Manual,
Volume 3 is prosed.
F. Low Impact Development Four Step Process
The overall stormwater management strategy for the proposed project utilizes the
Four Step Process to minimize adverse impacts of urbanization on receiving
waters. The follow is a description of how the proposed development has
incorporated each step:
Step 1 – Runoff Reduction Practices
Bioretention and Extended Detention Basin Water Quality Systems are
employed to reduce peak runoff, volume, and pollutants as part of a Low
Impact Development (LID) strategy.
Step 2 – Implement BMPs that Provide a Water Quality Capture Volume (WQCV)
with Slow Release
The features identified in Step 1 will facilitate the reduction of runoff. The
majority of the stormwater runoff from the proposed improvements will be
intercepted through the LID features prior to exiting the site.
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Step 3 – Stabilized Drainageways
No drainageways lie within the subject property; however, the prosed LID
features will reduce sediment and potential erosion to the drainage ditch and
downstream drainageway systems.
Step 4 – Implement Site Specific and Other Source Control BMPs
The proposed BMPs will intercept most of the north proposed improvements
and approximately half the existing historic site conditions. These
improvements will treat the tributary surface runoff through a forbay, followed
by a Bioretention pond. Runoff from the Bioretention pond will then drain to
the detention facility and further be treated by the Extended Detention Basin
before exiting the site.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
Currently the surface drains primarily over native vegetation and existing gravel
from the east to west into the frontage drainage ditch. The proposed improvements
will maintain the same drainage patterns by collecting the majority of the
improvements into the detention pond along the frontage road. Minor offsite runoff
will contribute to the detention pond from basin OS1.
Appendix B contains the tables and charts from the Criteria and the Manual.
Rainfall is based on the rational method and the City’s rainfall intensities with the
site grading divided into seven onsite drainage basins. Basins A through C and
OS1 define the areas directly tributary to the detention pond. Basins of direct
runoff are designated DRS, DRE, DRN, DRW and OS2 are limited to the perimeter
areas about the site.
Basin A:
Basin A comprises of the center of the property and the east storage yard area.
Water collected along with basin OS1 will drain first to the Bioretention pond before
transferring to the detention pond.
Basin B:
Basin B consists of the north roof of the building. Water off the north roof is
collected in underground drain lines and discharged in the detention near the
northeast corner of the building.
Basin C:
Basin C contains the detention pond area. Water collected in basin C is combined
with basins A, B and OS1 for design point DET, the emergency overflow weir.
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Basin DRS:
The area of Direct Runoff South (DRS) represents the existing surfaces on the
south side of the property. This runoff is existing and is not changed due to the
proposed improvements.
Basin DRE:
Direct Runoff East (DRE) represents the small area of runoff intercepted by the
existing irrigation ditch. The proposed improvements due not change the ditch and
are the surrounding banks along the easterly property line.
Basin DRN:
The area of Direct Runoff North (DRN) represents the surface behind the building.
The surface runoff to the north is over native vegetation is insignificant.
Basin DRW:
The area of Direct Runoff West (DRW) represents the surface tributary to the
frontage road. This are is the result of the berm created for the detention pond and
the existing landscaped area south of the access drive lane.
The detention facility is made up of four volumes. Two water quality volumes, and
the 2-year and 100-year detention volumes. As part of the LID criteria, a
Bioretention pond is proposed in the middle of basin A. 75% of the new hard
surfaces are collected in the Bioretention pond. Water through the Bioretention
pond is directed through a discharge box into a structural box culvert that leads to
the detention pond. The detention pond consists of an Extended Detention Basin
volume and the 2-year and 100-year detention volumes. The Extended Detention
Basin is reduced by the Bioretention volume. A Forebay is established at the
entrance to the Bioretention pond, and is based on the total detention area
tributary to the detention pond. Specific volumes and elevations are tabulated in
appendix A and on the drainage plan.
The detention ponds outlet box uses a water quality plate to restrict runoff to a
maximum 40-hour discharge limit. The 2-year stormwater volume is in turn
discharged through the weir. The 100-year volume is then controlled by a restrictor
plate over the 15” outlet pie from the drainage box. Both storm release rates are
based on the Criteria’s limits. For the minor storm, the discharge is limited to 3.63
cfs for the combined pond outlet and the areas of direct runoff. The 100-year
storm discharge from the pond and areas of direct runoff is limited to 11.78 cfs.
This limit is derived from the 2-year historic pervious areas of 1.19 cfs and the
historic impervious areas of 10.60 cfs. Total 100-year combined direct runoff is
5.08 cfs for an allowed discharge limit from the pond of 6.70 cfs. In the event the
outlet box is blocked by debris, an emergency overflow weir is set at the 100-year
water elevation of 4971.50 feet. This weir is designed to discharge the 100-year
runoff (20.48 cfs) to the ditch along the frontage road. In addition, flood control
from the Bioretention pond is managed both through the concrete box culvert, and
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over and through the drainage swale set across the drive lane.
B. Specific Details
Access and maintenance to the outlet structures and to the detention features is
obtained from an access and drainage easement located off the frontage road.
The area of access and detention is contained in the designated easement.
V. CONCLUSIONS
A. Compliance with Standards
The runoff calculations are based on the Criteria and Manual for the 2-year and
100-year storm recurrences. In addition, water quality volumes are provided in the
form of a Bioretention pond and an Extended Detention Basin per the Manual. The
storm detention volumes are based on the Modified FAA method for the 2-year and
100-year storm events. The emergency overflow and storm outlet pipe drain to the
right-of-way and are sized for the 100-year storm event.
B. Drainage Concept
The drainage system has been designed to convey the developed runoff to the
designated detention pond in a safe and effective manner. In addition, all on site
flows as well as the detention pond and its components have been sized to
transfer stormwater to the drainage ditch. The proposed release rates from the
detention pond will reduce the peak runoff to the 2-year historic limit. In its current
condition, runoff from the site runs un-detained. The improvements being made will
detain a large amount of stormwater and reduce runoff from the site so that the
100-year storm event can be conveyed safely downstream. As a result, no
negative impacts are anticipated to any downstream stormwater facilities.
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VI. REFERENCES
1. “Fort Collins Stormwater Criteria Manual”, dated revised November 2017.
2. "Urban Storm Drainage Criteria Manual", by Urban Drainage and Flood Control
District, Vol. 1 and 2 dated January 2016, and Vol. 3 dated November 2010.
3. “Cooper Slough/Box Elder Basin Master Drainage Study”
4. Federal Emergency Management Agency Community Panel Number
08069C1001F, dated December 19, 2006.
5. Federal Emergency Management Agency Community Panel Number
08069C0982F, dated December 19, 2006.
6. Geotechnical Evaluation Report, Project No. 0281-D20, by American
Geoservices, dated June 30, 2020
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APPENDIX A
Hydrologic & Hydraulic Computations
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Fort Collins Stormwater Rational MethodProject Name:Pacific Coast Supply Historic RunoffCoefficentImperviousBasin Surface Types C(%)Hard SurfacesAsphalt, Conc 0.95100Rooftops 0.9590Recycled Asphalt 0.8080Gravel or Pavers 0.5040Landscape (Lawns)Playgrounds25Lawns, Sandy Soil, Flat Slope < 2% 0.102Lawns, Sandy Soil, Avg Slope 2-7% 0.152Lawns, Sandy Soil, Steep Slope > 7% 0.202Lawns, Clayey Soil, Flat Slope < 2% 0.202Lawns, Clayey Soil, Avg Slope 2-7% 0.252Lawns, Clayey Soil, Steep Slope >7% 0.352Dominant Predevelopement NRCS Soils Group: C/DAsphaltRecycled Gravel orLawns, SandyLawns, Clayey AreaAreaTotal & Conc. Rooftops Asphalt Pavers Playgrnds Flat Average Steep Flat Average Steep AverageAverage TotalArea Area Areas Areas Area Area Area Area Area Area Area Area Area Coeff. 1.00 1.00 1.00 1.10 1.20 1.25 Impervs AreaBasin Description (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (C)C2C5C10C25C50C100(%) (acre) BasinH1Historic Site (Pervious Area)96685 0 0 0 0 0 0 0 0 0 103547 0 0.27 0.27 0.27 0.27 0.29 0.32 0.33 2.1 2.220 H1H2Historic Site (Impervious Area)88990 4192 6550 0 78248 0 0 0 0 0 0 0 0.55 0.55 0.55 0.55 0.61 0.67 0.69 46.5 2.043 H2Runoff CoefficientsFrequency Adjustment Factor Cf10
TIME OF CONCENTRATIONProject Name:Pacific Coast Supply Historic RunoffCalculated By:WJLDATE:1/15/2021SUB-BASIN INITIAL/OVERLANDINITIALFINAL REMARKSDATATIME (ti)TIMEtcTOTALtc;ti+ttDESIGN C*Cf = AREALENGTHSLOPEtiLENGTHSLOPECHANNELVEL.ttti+ttLENGTHtc=(L/180)+10minimumC5(Ac) (ft) (ft/ft) (min) (ft) (ft/ft)CONSTANT(fps) (min) (min) (ft) (min) (min)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (12) (13) (14)H1 0.27 2.22 300 0.018 103 200 0.008 10 0.89 4 107 500 12.8 12.8H20.55 2.04 114 0.003 7979 114 10.6 10.6ti=1.87(1.1-CxCf)(L^0.5)/S^1/3tt=L/(60V)tc CHECK(URBANIZED BASINS)TRAVEL TIME(tt)11
STANDARD FORM SF-3Calculated By: WJLJOB NO:Z19-050DATE:STORM DRAINAGE SYSTEM DESIGNPROJECT :NameCHECKED BY:______________ (RATIONAL METHOD PROCEDURE)DESIGN STORM:2 YearAREA DESIGNAREA (AC)RUNOFF COEFFtc (MIN)C*A (AC)I (IN/HR)Q (CFS)tc (MIN)SUM(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)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)1H1 H1 H12.22 0.27 12.8 0.59 1.99 1.192H2 H2 H22.04 0.55 10.6 1.13 2.16 2.4434Total 2-year Historic Runoff = 3.63567891011121314TRAVEL TIMEREMARKS1/15/2021STREETDESIGN POINTDIRECT RUNOFFTOTAL RUNOFF STREET PIPE
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STANDARD FORM SF-3Calculated By: WJLJOB NO:Z19-050DATE:STORM DRAINAGE SYSTEM DESIGNPROJECT :NameCHECKED BY:______________ (RATIONAL METHOD PROCEDURE)DESIGN STORM:100 YearAREA DESIGNAREA (AC)RUNOFF COEFFtc (MIN)C*A (AC)I (IN/HR)Q (CFS)tc (MIN)SUM(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)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)1H1 H1 H12.22 0.33 12.8 0.74 6.96 5.12H2 H2 H22.04 0.69 10.6 1.41 7.52 10.6034Total 100-year Historic Runoff 1.19cfs + 10.60cfs = 11.785678910111213121/15/2021STREET PIPE TRAVEL TIMEREMARKSSTREETDESIGN POINTDIRECT RUNOFFTOTAL RUNOFF13
Fort Collins Stormwater Rational MethodProject Name:Pacific Coast SupplyCoefficentImperviousBasin Surface Types C(%)Hard SurfacesAsphalt, Conc 0.95100Rooftops 0.9590Recycled Asphalt 0.8080Gravel or Pavers 0.5040Landscape (Lawns)Playgrounds25Lawns, Sandy Soil, Flat Slope < 2% 0.102Lawns, Sandy Soil, Avg Slope 2-7% 0.152Lawns, Sandy Soil, Steep Slope > 7% 0.202Lawns, Clayey Soil, Flat Slope < 2% 0.202Lawns, Clayey Soil, Avg Slope 2-7% 0.252Lawns, Clayey Soil, Steep Slope >7% 0.352Dominant Predevelopement NRCS Soils Group: C/D179566AsphaltRecycled Gravel orLawns, SandyLawns, Clayey AreaAreaTotal & Conc. Rooftops Asphalt Pavers Playgrnds Flat Average Steep Flat Average Steep AverageAverage TotalArea Area Areas Areas Area Area Area Area Area Area Area Area Area Coeff. 1.00 1.00 1.00 1.10 1.20 1.25 Impervs AreaBasin Description (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (C)C2C5C10C25C50C100(%) (acre) BasinA Center/Storage 94372 36517 16285 0 20377 0 0 0 0 21193 0 0 0.68 0.68 0.68 0.68 0.75 0.82 0.85 63.3 2.166 AB North Roof 10000 0 10000 0 0 0 0 0 0 0 0 0 0.95 0.95 0.95 0.95 1.00 1.00 1.00 90.0 0.230 BCWest Front Area19994 3260 0 0 0 0 0 0 0 16734 0 0 0.32 0.32 0.32 0.32 0.35 0.39 0.40 18.0 0.459 CDRSDirect Runoff South33741 4402 3286 0 15647 0 0 0 0 10406 0 0 0.51 0.51 0.51 0.51 0.56 0.61 0.63 41.0 0.775 DRSDREDirect Runoff East2264 0 0 0 0 0 0 0 0 2264 0 0 0.20 0.20 0.20 0.20 0.22 0.24 0.25 2.0 0.052 DREDRNDirect Runoff North11130 0 0 0 5676 0 0 0 0 5454 0 0 0.35 0.35 0.35 0.35 0.39 0.42 0.44 21.4 0.256 DRNDRWDirect Runoff West8065 812 0 0 0 0 0 0 0 7253 0 0 0.28 0.28 0.28 0.28 0.30 0.33 0.34 11.9 0.185 DRWOS1 Offsite 1 15231 0 0 0 0 0 0 0 0 15231 0 0 0.20 0.20 0.20 0.20 0.22 0.24 0.25 2.0 0.350 OS1OS2 Offsite 2 5949 0 0 0 0 0 0 0 0 5949 0 0 0.20 0.20 0.20 0.20 0.22 0.24 0.25 2.0 0.137 OS2DetDetention+EDB179566 44991 29570.59 0 41700 0 0 0 0 63304.41 0 0 0.58 0.58 0.58 0.58 0.64 0.70 0.72 49.9 4.122 DetRGA+OS1 Rain Garden109603 36517 16285 0 20377 0 0 0 0 36424 0 0 0.62 0.62 0.62 0.62 0.68 0.74 0.77 54.8 2.516 RG Sec. 6.0 Low Impact Development (LID) Option 2 Impervious SurfacesPavement RoofPavement RoofACenter/Storage36517 1300036517 13000BNorth Roof0 100000 0CWest Front Area3260 00 0DRSDirect Runoff South2477 00 0DREDirect Runoff East0 00 0DRNDirect Runoff North0 00 0DRWDirect Runoff West812 00 0Sub-Totals =43066 2300036517 13000Total New = 66066sq.ft. Total Captured =49517 sq.ft.Percent of New Hard Surfaces Tributary to RG = 75.0%Runoff CoefficientsFrequency Adjustment Factor CfTotal New HardsurfacesRG Capture Area14
TIME OF CONCENTRATIONProject Name:Pacific Coast SupplyCalculated By:WJLDATE:1/15/2021SUB-BASININITIAL/OVERLANDINITIALFINAL REMARKSDATATIME (ti)TIMEtcTOTALtc;ti+ttDESIGN C*Cf = AREALENGTHSLOPEtiLENGTHSLOPECHANNELVEL.ttti+ttLENGTHtc=(L/180)+10minimumC5(Ac) (ft) (ft/ft) (min) (ft) (ft/ft)CONSTANT(fps) (min) (min) (ft) (min) (min)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (12) (13) (14)A 0.68 2.17 206 0.005 65.88 160 0.009 20 1.85 1.44 67.31 366 12.0312.03B 0.95 0.23 50 0.020 7.317.31 50 10.28 7.31C 0.32 0.46 144 0.036 52.6352.63 144 10.80 10.80DRS 0.51 0.77 198 0.005 90.4990.49 198 11.10 11.10DRE 0.20 0.05 22 0.068 19.3219.32 22 10.12 10.12DRN 0.35 0.26 35 0.086 18.7418.74 35 10.19 10.19DRW 0.28 0.19 17 0.250 10.0910.09 17 10.09 10.09OS1 0.20 0.35 183 0.011 102.59102.59 183 11.02 11.02OS2 0.20 0.14 102 0.010 79.4279.42 102 10.57 10.57Det 0.58 4.12 206 0.014 57.85 362 0.007 20 1.64 3.68 61.53 568 13.16 13.16RG 0.62 2.52 206 0.014 53.83 160 0.007 20 1.64 1.63 55.46 366 12.03 12.03ti=1.87(1.1-CxCf)(L^0.5)/S^1/3tt=L/(60V)tc CHECK(URBANIZED BASINS)TRAVEL TIME(tt)15
STANDARD FORM SF-3Calculated By: WJLJOB NO:Z19-050DATE:STORM DRAINAGE SYSTEM DESIGNPROJECT :NameCHECKED BY:______________ (RATIONAL METHOD PROCEDURE)DESIGN STORM:2 YearAREA DESIGNAREA (AC)RUNOFF COEFFtc (MIN)C*A (AC)I (IN/HR)Q (CFS)tc (MIN)SUM(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)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)1A A A2.17 0.68 12.0 1.48 2.05 3.04 11.0 1.55 2.12 3.302B B B0.23 0.95 7.3 0.22 2.48 0.543C C C0.46 0.32 10.8 0.15 2.14 0.3245DRS DRS DRS0.77 0.51 11.1 0.40 2.12 0.846DRE DRE DRE0.05 0.20 10.1 0.01 2.20 0.027DRN DRN DRN0.26 0.35 10.2 0.09 2.19 0.208DRW DRW DRW0.19 0.28 10.1 0.05 2.20 0.119OS1 OS1 OS10.35 0.20 11.0 0.07 2.12 0.1510OS2 OS2 OS20.14 0.20 10.6 0.03 2.16 0.0611Det Det Det4.12 0.58 13.2 2.40 1.97 4.7212RG RG RG2.52 0.62 12.0 1.55 2.05 3.181314Maximum allowed discharge = 3.63 cfs Total Runoff from basins DRS, DRE, DRN, DRW = 1.17cfs Allowable Detention release = 2.46 cfs TRAVEL TIMEREMARKS1/15/2021STREETDESIGN POINTDIRECT RUNOFFTOTAL RUNOFF STREET PIPE
16
STANDARD FORM SF-3Calculated By: WJLJOB NO:Z19-050DATE:STORM DRAINAGE SYSTEM DESIGNPROJECT :NameCHECKED BY:______________ (RATIONAL METHOD PROCEDURE)DESIGN STORM:100 YearAREA DESIGNAREA (AC)RUNOFF COEFFtc (MIN)C*A (AC)I (IN/HR)Q (CFS)tc (MIN)SUM(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)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)1A A A2.17 0.85 12.0 1.85 7.14 13.2 12.0 1.93 7.14 13.82B B B0.23 1.00 7.3 0.23 8.63 1.983C C C0.46 0.40 10.8 0.18 7.47 1.3845DRS DRS DRS0.77 0.63 11.1 0.49 7.39 3.636DRE DRE DRE0.05 0.25 10.1 0.01 7.67 0.107DRN DRN DRN0.26 0.44 10.2 0.11 7.65 0.868DRW DRW DRW0.19 0.34 10.1 0.06 7.68 0.499OS1 OS1 OS10.35 0.25 11.0 0.09 7.41 0.6510OS2 OS2 OS20.14 0.25 10.6 0.03 7.54 0.2611Det Det Det4.12 0.72 13.2 2.98 6.87 20.4812RG RG RG2.52 0.77 12.0 1.93 7.14 13.801312Maximum allowed discharge =11.78cfs Total Runoff from basins DRS, DRE, DRN, DRW = 5.08cfs Allowable Detention release = 6.70 cfs 1/15/2021STREET PIPE TRAVEL TIMEREMARKSSTREETDESIGN POINTDIRECT RUNOFFTOTAL RUNOFF17
Fort Collins Modified FAA Detention
Project Name: Pacific Coast Supply
Design Informtion (Input):
Tributary Area: 4.12 acres
Imperviousness: 49.87 %
Tc: 11.02 min.
Allowable Release Rate Qout: 2.46 cfs (2-year Historic) Allowable Release Rate Qout: 6.70 cfs (Adjstd 2-year Historic)
2-Year Minor Detention 100-Year Major Detention
Runoff Coefficient C2:0.58 Runoff Coefficient C100:0.72
Inflow Peak Runoff Qin:4.72 cfs Inflow Peak Runoff Qin:20.48
Duration Duration
Results:(cu.ft.) (acre-ft) (min.) Results:(cu.ft.) (acre-ft) (min.)
Max. Minor Storage Vol: 1817 0.042 15 Max. Major Storage Vol: 12240 0.281 28
WQCV (EDB): 1308 0.030 WQCV (EDB): 1308 0.030
Total Minor Storm Vol: 3125 0.072 Total Major Storm Vol: 13548 0.311
1 (min) Duration Interval 1 (min) Duration Interval
Rainfall Rainfall Inflow Outflow Storage Storage Rainfall Rainfall Inflow Outflow Storage Storage
Duration Intensity Volume Volume Volume Volume Duration Intensity Volume Volume Volume Volume
minutes inches / hr cubic feet cubic feet cubic feet acre feet minutes inches / hr cubic feet cubic feet cubic feet acre feet
(input) (output) (output) (output) (output) (output) (input) (output) (output) (output) (output) (output)
5 2.85 2048 738 1310 0.0301 5 9.95 8902 2010 6892 0.1582
6 2.67 2302 886 1417 0.0325 6 9.31 9995 2412 7583 0.1741
7 2.52 2535 1033 1502 0.0345 7 8.80 11023 2815 8208 0.1884
8 2.40 2760 1181 1579 0.0362 8 8.38 11996 3217 8779 0.2015
9 2.30 2975 1329 1646 0.0378 9 8.03 12932 3619 9313 0.2138
10 2.21 3176 1476 1700 0.0390 10 7.72 13814 4021 9793 0.2248
11 2.13 3367 1624 1744 0.0400 11 7.42 14605 4423 10182 0.2337
12 2.05 3536 1772 1764 0.0405 12 7.16 15374 4825 10549 0.2422
13 1.98 3699 1919 1780 0.0409 13 6.92 16097 5227 10870 0.2495
14 1.92 3863 2067 1797 0.0412 14 6.71 16809 5629 11180 0.2567
15 1.87 4031 2214 1817 0.0417 15 6.52 17500 6031 11469 0.2633
16 1.81 4162 2362 1800 0.0413 16 6.30 18037 6433 11604 0.2664
17 1.75 4276 2510 1766 0.0405 17 6.10 18556 6835 11720 0.2691
18 1.70 4398 2657 1741 0.0400 18 5.92 19068 7237 11830 0.2716
19 1.65 4506 2805 1701 0.0390 19 5.75 19549 7640 11909 0.2734
20 1.61 4628 2953 1675 0.0385 20 5.60 20041 8042 11999 0.2755
21 1.56 4708 3100 1608 0.0369 21 5.46 20517 8444 12073 0.2772
22 1.53 4838 3248 1590 0.0365 22 5.32 20943 8846 12097 0.2777
23 1.49 4925 3395 1530 0.0351 23 5.20 21401 9248 12153 0.2790
24 1.46 5036 3543 1493 0.0343 24 5.09 21859 9650 12209 0.2803
25 1.43 5138 3691 1448 0.0332 25 4.98 22278 10052 12226 0.2807
26 1.40 5232 3838 1393 0.0320 26 4.87 22657 10454 12203 0.2801
27 1.37 5316 3986 1330 0.0305 27 4.78 23094 10856 12237 0.2809
28 1.34 5393 4134 1259 0.0289 28 4.69 23498 11258 12240 0.2810
29 1.32 5502 4281 1221 0.0280 29 4.58 23755 11660 12094 0.2776
30 1.30 5605 4429 1176 0.0270 30 4.49 24091 12062 12028 0.2761
31 1.27 5658 4576 1082 0.0248 31 4.40 24416 12465 11952 0.2744
32 1.24 5703 4724 979 0.0225 32 4.32 24732 12867 11865 0.2724
33 1.22 5786 4872 915 0.0210 33 4.24 25038 13269 11769 0.2702
34 1.19 5815 5019 796 0.0183 34 4.16 25335 13671 11664 0.2678
35 1.17 5886 5167 719 0.0165 35 4.09 25624 14073 11551 0.2652
36 1.15 5950 5315 636 0.0146 36 4.02 25904 14475 11429 0.2624
37 1.13 6009 5462 547 0.0126 37 3.95 26177 14877 11300 0.2594
38 1.11 6062 5610 453 0.0104 38 3.89 26443 15279 11164 0.2563
39 1.09 6110 5757 352 0.0081 39 3.83 26702 15681 11021 0.2530
40 1.07 6151 5905 246 0.0057 40 3.77 26955 16083 10872 0.2496
41 1.05 6187 6053 135 0.0031 41 3.71 27202 16485 10716 0.25
42 1.04 6278 6200 78 0.0018 42 3.65 27443 16887 10555 0.24
43 3.60 27678 17290 10389 0.24
44 3.54 27908 17692 10217 0.23
45 3.49 28134 18094 10040 0.23
46 3.44 28354 18496 9858 0.23
47 3.40 28570 18898 9672 0.22
48 3.35 28782 19300 9482 0.22
49 3.31 28989 19702 9287 0.21
50 3.26 29193 20104 9089 0.21
51 3.22 29393 20506 8887 0.20
52 3.18 29589 20908 8681 0.20
53 3.14 29782 21310 8472 0.19
54 3.10 29972 21712 8260 0.19
55 3.06 30159 22115 8044 0.18
56 3.03 30343 22517 7826 0.18
57 2.99 30524 22919 7605 0.17
58 2.96 30702 23321 7381 0.17
59 2.92 30878 23723 7155 0.16
60 2.89 31051 24125 6926 0.16
18
0
1000
2000
3000
4000
5000
6000
7000
5 10 15 20 25 30 35 40Volume (Cubic Feet)Duration (Minutes)
2-Year Modified FAA Storm Detention
2-Vol
2-Inflow
2-Outflow
19
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
55000
5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59Volume (Cubic Feet)Duration (Minutes)
100-Year Modified FAA Stom Detention
100-Vol
100-Inflow
100-Outflow
20
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =54.8 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.548
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.18 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area)Area = 109,603 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =1,606 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =4.20 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical)Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =1201 sq ft
D) Actual Flat Surface Area AActual =5071 sq ft
E) Area at Design Depth (Top Surface Area)ATop =5071 sq ft
F) Rain Garden Total Volume VT=1,775 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
Note: The City standard depth is 24", but cannot be achieved.
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =1.380 ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =1,606 cu ft
iii) Orifice Diameter, 3/8" Minimum DO =1 in
Design Procedure Form: Rain Garden (RG)
W. Logan
ZP Architects Engineers
January 29, 2021
Pacific Coast Supply
Fort Collins Bioretention
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
21
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
PROVIDE A 30 MIL (MIN) PVC LINER WITH CDOT CLASS B
GEOTEXTILE ABOVE IT. USE THE SAME GEOTEXTILE BELOW
THE LINER IF THE SUBGRADE IS ANGULAR
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
W. Logan
ZP Architects Engineers
January 29, 2021
Pacific Coast Supply
Fort Collins Bioretention
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
22
Sheet 1 of 3
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =49.9 %
B) Tributary Area's Imperviousness Ratio (i = Ia / 100 )i = 0.499
C) Contributing Watershed Area Area = 4.122 ac
D) For Watersheds Outside of the Denver Region, Depth of Average d6 = in
Runoff Producing Storm
E) Design Concept
(Select EURV when also designing for flood control)1
F) Design Volume (WQCV) Based on 40-hour Drain Time VDESIGN= ac-ft
(VDESIGN = (1.0 * (0.91 * i3 - 1.19 * i2 + 0.78 * i) / 12 * Area )
G) For Watersheds Outside of the Denver Region, VDESIGN OTHER= ac-ft
Water Quality Capture Volume (WQCV) Design Volume
(VWQCV OTHER = (d6*(VDESIGN/0.43))
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VDESIGN USER=0.0300 ac-ft
(Only if a different WQCV Design Volume is desired)
I) NRCS Hydrologic Soil Groups of Tributary Watershed
i) Percentage of Watershed consisting of Type A Soils HSG A =%
ii) Percentage of Watershed consisting of Type B Soils HSG B =%
iii) Percentage of Watershed consisting of Type C/D Soils HSG C/D =%
J) Excess Urban Runoff Volume (EURV) Design Volume
For HSG A: EURVA = 1.68 * i1.28 EURVDESIGN = ac-f t
For HSG B: EURVB = 1.36 * i1.08
For HSG C/D: EURVC/D = 1.20 * i1.08
K) User Input of Excess Urban Runoff Volume (EURV) Design Volume EURVDESIGN USER= ac-f t
(Only if a different EURV Design Volume is desired)
2. Basin Shape: Length to Width Ratio L : W = 2.0 : 1
(A basin length to width ratio of at least 2:1 will improve TSS reduction.)
3. Basin Side Slopes
A) Basin Maximum Side Slopes Z = 4.00 ft / ft
(Horizontal distance per unit vertical, 4:1 or flatter preferred)
4. Inlet
A) Describe means of providing energy dissipation at concentrated
inflow locations:
0.030
5. Forebay
A) Minimum Forebay Volume VFMIN =0.001000 ac-ft
(VFMIN = 2% of the WQCV)
B) Actual Forebay Volume VF =0.00404 ac-ft
C) Forebay Depth
(DF = 18 inch maximum)DF =6.0 in
D) Forebay Discharge
i) Undetained 100-year Peak Discharge Q100 =13.80 cfs
ii) Forebay Discharge Design Flow QF =0.28 cfs
(QF = 0.02 * Q100)
E) Forebay Discharge Design
F) Discharge Pipe Size (minimum 8-inches)Calculated DP =in
G) Rectangular Notch Width Calculated WN =4.0 in
Flow too small for berm w/ pipe
Design Procedure Form: Extended Detention Basin (EDB)
Pacific Coast Supply
ZP Architects Engineers
January 29, 2021
Vdesign = 0.07076acres-1775/43560 = 0.030ac-ft=1308 ft^3
W. Logan
UD-BMP (Version 3.07, March 2018)
Riprap field
Choose One
Excess Urban Runoff Volume (EURV)
Choose One
Wall with Rect. Notch
Berm With Pipe
Water Quality Capture Volume (WQCV)
Wall with V-Notch Weir
\23
Detention Pond Volume Calculations
Incremental Area =(A1+A2+SQRT(A1*A2))*D/3
Pond Incremental Accumulated Design Design Design
Stage Elev. Cont. Area Vol. Vol. Vol. Vol. Stage Vol. Elev.
(ft) (ft) (ft^2) (ft^3) (ft^3) (ft^3) (ft) (ft)
0 69.08 0 0 0
0.42 69.5 1171 164 164
0.92 70 3570 1131 1295
1.42 70.5 6992 2593 3888 1308 0.92 70.00
1.92 71 9904 4203 8091 3125 1.33 70.41
2.42 71.5 11898 5443 13534
2.92 72 13811 6421 19955 13548 2.67 71.50
BioRetention (Rain Garden) Volume Calculations
Pond Incremental Accumulated Design Design Design
Stage Elev. Cont. Area Vol. Vol. Vol. Vol. Stage Vol. Elev.
(ft) (ft) (ft^2) (ft^3) (ft^3) (ft^3) (ft) (ft)
0 71.40 5071 0 0
0.35 71.75 5071 1775 1775 1660 0.33 71.73
Forebay Volume Calculations
Pond Incremental Accumulated Design Design Design
Stage Elev. Cont. Area Vol. Vol. Vol. Vol. Stage Vol. Elev.
(ft) (ft) (ft^2) (ft^3) (ft^3) (ft^3) (ft) (ft)
0 71.50 0 0 0
0.50 72.00 1054 176 176 44 0.12 71.62
24
Use stainless steel well screen #93 Vee w/ 0.139 " wire opening, # 156 VEE
support rods on 3/4" o.c., screen thickness 0.31" w/ 6" wide min. opening.
(44 in^2)
At 0.31ft2=At Aot 77 e 0.124-D( ):=
Aot 0.004ft2=Aot
0.0521 ft( )2
4
2:=D 9
16
in:=
Trashrack Opening Area:
Provide 2 rows at 4" o.c. vertically in face of drainage box with
(1) one 9/16-inch diameter holes per row.
(approxiomatly)Drain_Time 30.2hr=
Drain_Time WQCV
Qwqcv
1hr
3600sec
:=Approximate WQCV Drain Time:
Qwqcv 0.0120 ft3
sec
=Qwqcv
d 1
2
4
Cd 2 g h 1
d1
2
-
d 2
2
4
Cd 2 g h2
d2
2
-
+:=
Discharge from water quality plate:
h 2 0.393ft=d 2 0.0469ft=
Two 3/4" diameter outlets:h 1 0.727ft=d 1 0.0469ft=
WQCV 1308ft3=Cd 0.60:=where
WQCV Release Plate:
25
Detention Outlet Structure:
2-year discharge
Use a retangular contracted weir:
Q2weir Cw L 0.0 H-( )Hb:=
where Cw 3.3:=
b 3
2
:=
Use top of 3ft square box:L 3.0 ft:=
Detention Flow Through runoff is:Qof Q2weir:=Q2weir
Required width of weir for a maximum flow height of 3":
Height root Cw L 0.2 H-( )Hb Q2weir-H,:=
Height 0.401ft2=Set crest of weir at 0.401 ft (4.809in) below
top of 2-year volume at Elev = 70.01 ft.
26
Project:
Basin ID:
X
1
#1 Vertical #2 Vertical
Sizing the Restrictor Plate for Circular Vertical Orifices or Pipes (Input)Orifice Orifice
Water Surface Elevation at Design Depth Elev: WS = 71.50 feet
Pipe/Vertical Orifice Entrance Invert Elevation Elev: Invert = 69.00 feet
Required Peak Flow through Orifice at Design Depth Q = 6.70 cfs
Pipe/Vertical Orifice Diameter (inches)Dia = 15.0 inches
Orifice Coefficient Co = 0.65
Full-flow Capacity (Calculated)
Full-flow area Af = 1.23 sq ft
Half Central Angle in Radians Theta = 3.14 rad
Full-flow capacity Qf = 8.8 cfs
Percent of Design Flow = 131%
Calculation of Orifice Flow Condition
Half Central Angle (0<Theta<3.1416)Theta = 1.95 rad
Flow area Ao = 0.89 sq ft
Top width of Orifice (inches)To = 13.97 inches
Height from Invert of Orifice to Bottom of Plate (feet)Yo = 0.85 feet
Elevation of Bottom of Plate Elev Plate Bottom Edge = 69.85 feet
Resultant Peak Flow Through Orifice at Design Depth Qo = 6.7 cfs
Width of Equivalent Rectangular Vertical Orifice Equivalent Width = 1.05 feet
Centroid Elevation of Equivalent Rectangular Vertical Orifice Equiv. Centroid El. = 69.43 feet
Pacific Coast
Detention Outlet
RESTRICTOR PLATE SIZING FOR CIRCULAR VERTICAL ORIFICES
27
Emergency overflow from pond:
Use a retangular contracted weir:
Qof Cw L 0.2 H-( )Hb:=
where Cw 3.33:=
b 3
2
:=
Hw 6.00 in:=
Detention Flow Through runoff is:Qof 20.48 cfs:=
Required width of weir for a maximum flow height of 4":
Width root Cw L 0.2 Hw-( )
Hw
b Qof-L,:=
Width 17.5ft= Use an 18' wide emergency overflow
wier from detention pond.
28
APPENDIX B
Charts and Tables
29
30
31
32
33
Hydrologic Soil Group—Larimer County Area, Colorado
(Pacific Coast Supply)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 1 of 44494360449438044944004494420449444044944604494480449450044943604494380449440044944204494440449446044944804494500499900499920499940499960499980500000500020500040500060500080500100500120
499900 499920 499940 499960 499980 500000 500020 500040 500060 500080 500100 500120
40° 36' 4'' N 105° 0' 4'' W40° 36' 4'' N104° 59' 54'' W40° 35' 59'' N
105° 0' 4'' W40° 35' 59'' N
104° 59' 54'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 50 100 200 300
Feet
0 15 30 60 90
Meters
Map Scale: 1:1,070 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.34
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 15, Jun 9, 2020
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 19, 2018—Aug
10, 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.
Hydrologic Soil Group—Larimer County Area, Colorado
(Pacific Coast Supply)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 2 of 435
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
53 Kim loam, 1 to 3 percent
slopes
B 0.0 0.1%
63 Longmont clay, 0 to 3
percent slopes
D 1.3 29.3%
74 Nunn clay loam, 1 to 3
percent slopes
C 2.2 51.5%
94 Satanta loam, 0 to 1
percent slopes
C 0.8 19.1%
Totals for Area of Interest 4.3 100.0%
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 Pacific Coast Supply
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 3 of 4
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Rating Options
Aggregation Method: Dominant Condition
Aggregation is the process by which a set of component attribute values is
reduced to a single value that represents the map unit as a whole.
A map unit is typically composed of one or more "components". A component is
either some type of soil or some nonsoil entity, e.g., rock outcrop. For the
attribute being aggregated, the first step of the aggregation process is to derive
one attribute value for each of a map unit's components. From this set of
component attributes, the next step of the aggregation process derives a single
value that represents the map unit as a whole. Once a single value for each map
unit is derived, a thematic map for soil map units can be rendered. Aggregation
must be done because, on any soil map, map units are delineated but
components are not.
For each of a map unit's components, a corresponding percent composition is
recorded. A percent composition of 60 indicates that the corresponding
component typically makes up approximately 60% of the map unit. Percent
composition is a critical factor in some, but not all, aggregation methods.
The aggregation method "Dominant Condition" first groups like attribute values
for the components in a map unit. For each group, percent composition is set to
the sum of the percent composition of all components participating in that group.
These groups now represent "conditions" rather than components. The attribute
value associated with the group with the highest cumulative percent composition
is returned. If more than one group shares the highest cumulative percent
composition, the corresponding "tie-break" rule determines which value should
be returned. The "tie-break" rule indicates whether the lower or higher group
value should be returned in the case of a percent composition tie. The result
returned by this aggregation method represents the dominant condition
throughout the map unit only when no tie has occurred.
Component Percent Cutoff: None Specified
Components whose percent composition is below the cutoff value will not be
considered. If no cutoff value is specified, all components in the database will be
considered. The data for some contrasting soils of minor extent may not be in the
database, and therefore are not considered.
Tie-break Rule: Higher
The tie-break rule indicates which value should be selected from a set of multiple
candidate values, or which value should be selected in the event of a percent
composition tie.
Hydrologic Soil Group—Larimer County Area, Colorado Pacific Coast Supply
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 4 of 4
37
APPENDIX C
FIRM Map, Drainage Plan and Details
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