HomeMy WebLinkAboutTHE SAVOY - PDP210019 - DOCUMENT MARKUPS - ROUND 2 - DRAINAGE REPORT
PRELIMINARY DRAINAGE REPORT
THE SAVOY
FORT COLLINS, COLORADO
NOVEMBER 18, 2021
NORTHERNENGINEERING.COM
970.221.4158
FORT COLLINS
GREELEY
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FORT COLLINS | GREELEY COVER LETTER
November 18, 2021
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, CO 80526
RE: PRELIMINARY DRAINAGE REPORT FOR
THE SAVOY (514-003)
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage Report for your review. This report
accompanies the Preliminary Development Review submittal for The Savoy.
This report has been prepared in accordance with the Fort Collins Stormwater Criteria Manual (FCSCM) and
serves to document the stormwater impacts associated with the proposed The Savoy multi-family project. We
understand review by the City of Fort Collins is to assure general compliance with standardized criteria
contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
BLAINE MATHISEN, PE
Project Engineer
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FORT COLLINS | GREELEY TABLE OF CONTENTS
TABLE OF CONTENTS
GENERAL LOCATION AND DESCRIPTION .......................................................... 1
DRAIN BASINS AND SUB-BASINS ..................................................................... 3
DRAINAGE DESIGN CRITERIA .......................................................................... 4
DRAINAGE FACILITY DESIGN ........................................................................... 7
CONCLUSIONS .............................................................................................. 9
REFERENCES .............................................................................................. 10
TABLES AND FIGURES
FIGURE 1 - VICINITY MAP ..................................................................................................1
FIGURE 2 - AERIAL PHOTO ................................................................................................2
FIGURE 3 - FIRMETTE MAP 08069C0994F .........................................................................3
TABLE 1 - LID SUMMARY TABLE .......................................................................................9
APPENDICES
APPENDIX A – HYDROLOGIC COMPUTATIONS
APPENDIX B – HYDRAULIC CALCULATIONS – FOR FUTURE USE
APPENDIX C –WATER QUALITY/LID COMPUTATIONS
APPENDIX D – EROSION CONTROL REPORT
APPENDIX E – EXCERPTS FROM PREVIOUS REPORTS AND USDA SOILS REPORT
MAP POCKET
DR1 – DRAINAGE EXHIBIT
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GENERAL LOCATION AND DESCRIPTION
A. LOCATION
Vicinity Map
The Savoy project site is located in the northeast quarter of Section 4, Township 6 North, Range
68 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado.
The project site (refer to Figure 1) is bordered to the west, east, and south by other multi-family
complexes and to the north by a vacant lot.
There are no major drainageways located adjacent to the project site.
B. DESCRIPTION OF PROPERTY
The Savoy project is comprised of ±8.34 acres plus some additional right-of-way dedications.
The site is currently vacant with native grasses.
The existing on-site runoff generally drains from the north-to-south across flat grades (e.g.,
<2.00%) into either Brookfield Drive or Precision Drive. Once runoff has entered the right-of-
way, it is routed to a 15' Type R inlet at the northwest corner of the Brookfield Drive and
Precision Drive intersection. From there, the drainage is routed to Detention Pond A –
Brookfield via a series of RCP pipes. The Savoy is proposing to alter this existing drainage
pattern to align with the master planning put forth with the Banner Medical Center and
Brookfield projects. The site will be split, with roughly 5.90 acres routed north of the ODP Pond,
associated with Banner Medical Center. The remaining runoff will be routed to Detention Pond
A – Brookfield. Additional information regarding these changes will be provided in the
Figure 1 - Vicinity map
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following sections. In addition, excerpts from both drainage reports have been provided in
Appendix F for further clarification.
According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey website:
http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx), the site consists entirely of
Nunn clay loam (Hydrologic Soil Group C).
There is no major drainageway within or adjacent to the project site. However, Fossil Creek
Reservoir Inlet Ditch runs adjacent to the ODP Pond and Detention Pond A – Brookfield.
The proposed development will consist of eight multi-family buildings containing a total of 240
units. Other proposed improvements include new asphalt concrete drive aisles, new sidewalks,
and new landscaping.
The proposed land use is multi-family dwellings. This use is permitted in the Harmony Corridor
District (H-C).
Figure 2 - Aerial Photo
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C. FLOODPLAIN
The subject property is not located in a FEMA regulatory floodplain. In particular, the project
site is not located within a FEMA-designated 100-year floodplain per Map Number
08069CO994F (Effective date: December 19, 2006). Additionally, the project site is not
located in a City of Fort Collins regulated floodplain.
DRAIN BASINS AND SUB-BASINS
A. MAJOR BASIN DESCRIPTION
The Savoy Project is located within the City of Fort Collins McClelland's major drainage
basin. Specifically, the project site is situated in the eastern third of this major drainage
basin. This basin is located in southeast Fort Collins and has a drainage area of
approximately 3.4 square miles and includes drainage originating near the College and
Harmony intersection and draining through the Oakridge, Willow Springs, Stetson Creek,
and Harvest Park developments. The McClelland's major drainage basin generally drains
from northwest to southeast. Runoff from the major drainage basin drains to the Fossil
Creek Reservoir.
Figure 3 - FIRMette Map 08069C0994F
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B. SUB-BASIN DESCRIPTION
There are two separate outfalls for the project. However, both outfalls are routed to the Fossil
Creek Reservoir Inlet Ditch.
The existing subject site can be defined with one (1) major sub-basins that encompasses the
entire project site and the adjacent ROW.
The existing site runoff generally drains from northwest to southeast and into either Precision
Drive or Brookfield Drive. An existing 15' Type R inlet is routing all the runoff to Detention Pond
A – Brookfield via a series of RCP pipes.
The project site does not receive runoff from contiguous off-site properties.
DRAINAGE DESIGN CRITERIA
A. ORIGINAL PROVISIONS AND PREVIOUS STUDIES
There are no optional provisions outside of the FCSCM proposed with The Savoy. The Savoy
project site has been included in several drainage studies for this area. The "East Harmony
Portion of McClelland's Creek Master Drainage Plan Update" (ICON Engineering, Inc., August
1999), "Final Drainage Report for Brookfield" (TST, Inc. Consulting Engineers, December
2001), "Final Drainage and Erosion Control Report Banner Health Medical Campus"
(Northern Engineering, September 2013), "Final Drainage and Erosion Control Report for
Presidio Apartments" (Northern Engineering, December 2009), and "Final Drainage Report
for Milestone Apartments" (Northern Engineering, May 2014). All these reports were
reviewed before the preparation of this report.
It is noted, City Stormwater previously agreed the off-site ODP Pond and Detention Pond A –
Brookfield were to provide all water quality and detention requirements for The Savoy
project site. Per "Final Drainage Report and Erosion Control Report Banner Health Medical
Campus," the ODP Pond is responsible for detaining 5.90 acres of The Savoy project site.
Basin O-2 from the Banner Health Medical Campus Master Drainage Exhibit depicts this.
During the design of the ODP Pond, Basin O-2 was assumed to be 85% impervious. Per "Final
Drainage Report for Brookfield," Detention Pond A – Brookfield was designed to detain and
treat 9.93 acres, with an assumed impervious of 85%, of The Savoy project site. Basins D9
and D5 from the "Final Drainage Report for Brookfield" are the basins associated with The
Savoy project site.
The "Final Drainage and Erosion Control Report Banner Health Medical Campus" and "Final
Drainage Report for Brookfield" contradict one another regarding which pond is responsible
for detaining and treating The Savoy site. Banner Health Medical Campus specifies the ODP
Pond, north of the project site, is responsible for detaining 5.90 acres of The Savoy project
site. However, Brookfield specifies Detention Pond A – Brookfield is responsible for
detaining and treating 9.93 acres of the project site and adjacent rights-of-way. Because
"Final Drainage and Erosion Control Report Banner Health Medical Campus" was published
after "Final Drainage Report for Brookfield," The Savoy will be relying on the ODP Pond to
detain 5.90 acres of the project site, while the remaining portion of the site is routed towards
Detention Pond A – Brookfield for detention.
After reviewing all the reports mentioned above, it became clear that The Savoy would be
responsible for providing on-site Low Impact Development (LID) methods to treat
stormwater quality to bring the site into compliance with the Land Use Code. LID will be
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provided via Stormtech isolator chambers and a rain garden. Additional information on LID
sizing will be provided below.
Please refer to Appendix F for excerpts from previous drainage studies. Complete copies can
be provided at request.
B. STORMWATER MANAGEMENT STRATEGY
The overall stormwater management strategy employed with The Savoy utilizes the "Four
Step Process" to minimize adverse impacts of urbanization on receiving waters. The
following is a description of how the proposed development has incorporated each step.
Step 1 – Employ Runoff Reduction Practices.
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use of implementing multiple Low Impact Development (LID) strategies, including:
· Providing vegetated open areas throughout the site to reduce the overall
impervious area and to minimize directly connected impervious areas.
· Routing runoff through the drain rock within the Stormtech system and rain garden
to increase concentration-time and promote infiltration.
Step 2 – Implement BMPs that Provide a Water Quality Capture Volume (WQCV) with
Slow Release.
The efforts taken in Step 1 will help to minimize excess runoff from frequently occurring
storm events; however, urban development of this intensity will still have stormwater runoff
leaving the site. Water quality treatment will occur in the underground vault on the north
side of the site and a rain garden on the site's south side.
Step 3 – Stabilize Drainageways.
As stated in Section I. B. 5. above, there is no major drainageway adjacent to the subject site.
While this step may not seem applicable to The Savoy, the proposed project indirectly helps
achieve stabilized drainageways, nonetheless. Once again, site selection has a positive effect
on stream stabilization. Developing an infill site with existing stormwater infrastructure,
combined with LID and MDCIA strategies, reduces the likelihood of bed and bank erosion.
Furthermore, this project will pay one-time stormwater development fees and ongoing
monthly stormwater utility fees, both of which help achieve Citywide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs. This step typically
applies to industrial and commercial developments. However, localized trash enclosures
with gates will reduce the potential impacts of garbage making its way downstream.
C. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
The subject property is part of an Overall Development Plan (ODP) drainage study or similar
"development/project" drainage master plan. Refer to Section III. A. and Appendix F for a list of
all previous drainage studies that include The Savoy project site.
The site plan is constrained on all four sides by public streets. It is bound by Cinequefoil Lane
to the west, Le Fever Drive to the north, Brookfield Drive to the east, and Precision Drive to the
south.
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D. HYDROLOGICAL CRITERIA
The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure
3.4-1 of the FCSCM, serves as the source for all hydrologic computations associated with The
Savoy development. Tabulated data contained in Table 3.4-1 has been utilized for Rational
Method runoff calculations.
The Rational Method has been employed to compute stormwater runoff utilizing coefficients
contained in Tables RO-11 and RO-12 of the FCSCM.
The Rational Formula-based Federal Aviation Administration (FAA) procedure has not been
utilized for detention storage calculations since detention is provided off-site at the ODP Pond
or Detention Pond A – Brookfield.
Three separate design storms have been utilized to address distinct drainage scenarios. The
first event analyzed is the "Minor" or "Initial" Storm, with a 2-year recurrence interval. The
second event considered is the "Major Storm," which has a 100-year recurrence interval. The
final event analyzed was the 10-year recurrence interval for comparative analysis only.
E. HYDRAULIC CRITERIA
The drainage facilities proposed with The Savoy project are designed in accordance with
criteria outlined in the FCSCM and/or the Mile High Flood District's (UDFCD) Urban Storm
Drainage Criteria Manual.
As stated in Section I. C. 1. above, the subject property is not located within a FEMA or a City of
Fort Collins designated floodplain.
F. FLOODPLAIN REGULATIONS COMPLIANCE
As stated in Section I. C. 1. above, the subject property is not located within a FEMA or a City
of Fort Collins designated floodplain.
G. MODIFICATIONS OF CRITERIA
No formal modifications are requested at this time. However, as previously stated, The
Savoy will not provide detention on-site. Two regional detention ponds will provide
detention.
H. CONFORMANCE WITH WATER QUALITY TREATMENT CRITERIA
City Code requires 100% of runoff from a project site to receive water quality treatment. This
project proposes to provide water quality treatment by using an underground infiltration
gallery (aka – underground chambers) located at the north end of the project and a rain
garden at the south end of the site. Stormtech isolator chambers are considered a LID
treatment method. Due to the physical constraints associated with an infill project of this
nature and the prohibition of providing water quality facilities within the public right-of-way,
some areas around the perimeter of the project cannot be captured and adequately routed
to either the rain garden or the Stormtech chambers. However, these areas have been
accounted for within the ODP Pond and Detention Pond A – Brookfield to receive water
quality.
Additionally, when the ODP Pond was installed, it did meet the current LID requirements set
forth by the Land Use Code. The ODP Pond has a sand filter along the entire length of the
bottom. However, the ODP Pond is also used for detention, and thus that is why it no longer
meets current LID standards.
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I. CONFORMANCE WITH LOW IMPACT DEVELOPMENT (LID)
The project site will conform with the requirement to treat a minimum of 75% of the site
using a LID technique. Please see Appendix C for LID design information, table, and
exhibit(s). As shown in the LID table provided in the appendix, 79.55% of the proposed site,
including adjacent right-of-way, will receive LID Treatment, which exceeds the minimum
required.
J. SIZING OF LID FACILITIES
The Stormtech isolator chambers were sized by determining the required water quality
capture volume (WQCV) for Major Basin A. A 12-hour drain time was used in this calculation.
Once the WQCV was identified, the minimum number of vaults needed to achieve this volume
was calculated. The required WQCV for Major Basin A is 5,590 cf. The number of MC-4500
chambers required is 38, which provides 5,691 cf of WQCV. Each isolator row will have an
inspection port and a Nyloplast basin at the end for easy maintenance and cleanout.
The rain garden was sized by determining the required water quality capture volume for Major
Basin B. The Mile High Flood District's criteria and online tools yielded a required WQCV of
2,077 cf. However, The Savoy proposes installing a rain garden with a total WQCV of 2,227 cf.
A volume calculation utilizing the WQ flow rate into the chamber and the calculated release
rate through the fabric was completed. The number of chambers has been increased as
needed to confirm the resulting volume is provided within the empty volume of the
underground chambers. This is intended to ensure the chambers do not become overwhelmed
in the water quality storm event before "discharging" flows into the surrounding aggregates.
For additional clarification, please refer to Appendix C.
DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
The main objective of The Savoy drainage design is to bring the project site into compliance
with existing drainage studies the site is associated with.
No notable off-site runoff passes directly through the project site.
A list of tables and figures used within this report can be found in the Table of Contents at the
front of this document. The tables and figures are located within the sections to which the
content best applies.
Drainage for the project site has been analyzed using four (4) Major Drainage Basins,
designated as Basins A, B, ODP, and BF. Basins A, B, and ODP all have associated sub-basins.
The drainage patterns anticipated for the basins are further described below.
Major Basin A
Major Basin A has twelve (12) sub-basins (A1-A12) associated with the north side of The
Savoy site. Major Basin A has a total area of 5.05 acres and an impervious value of 76%. All
runoff generated within Major Basin A is routed via a combination of overland flow, storm
line conveyance, and curb and gutter routing to the Stormtech system. Major Basin A will
receive LID treatment within the Stormtech system. Once treated or any event greater than
the WQ event, the runoff will be routed via HDPE pipes to the ODP Pond for detention.
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Major Basin B
Major Basin B has seven (7) sub-basins (B1-B7) and is associated with the south side of The
Savoy site. Major Basin B has a total area of 2.30 acres and an impervious value of 77%. All
runoff generated within Major Basin B is routed via a combination of overland flow, storm
line conveyance, and curb and gutter routing to the rain garden at the southeast corner of
the site. An overflow inlet will be set at the WQCV water surface elevation (WSEL) to allow
storm events larger than the WQ event to bypass the rain garden without draining across
public sidewalks. All runoff from Major Basin B will be routed to the existing 15' Type R Inlet
at the northwest corner of the Brookfield Drive and Precision Drive intersection. This existing
inlet has been acting as the "interim" outfall location for the entire Savoy property. Once
runoff has been routed to the existing Type R inlet, it is conveyed to Detention Pond A –
Brookfield via a series of RCP pipes gradually upsized as it moves downstream.
Major Basin ODP
Major Basin ODP has three (3) sub-basins (ODP1-ODP3) and is associated with the area along
the north side of the property that cannot be captured and treated for LID on The Savoy
project site but is being routed to the ODP Pond. Sub-Basin ODP1 is associated with the
north side of Le Fever Drive and, therefore, it is not counted toward any of The Savoy's LID
requirements or detention requirements. Sub-Basin ODP2 is on the south side of the Le
Fever Drive, and, therefore, The Savoy would be responsible for detaining and treating this
basin if it had not been included in the ODP Pond calculations. Sub-Basin ODP3 is associated
with a small portion of the east side of Cinequefoil Lane. Existing drainage patterns for Sub-
Basin ODP3 are being maintained with The Savoy Development. Water quality, LID, and
detention for Sub-Basin ODP3 are being provided in the ODP Pond.
As previously stated in Section III. A., per "Final Drainage Report and Erosion Control Report
Banner Health Medical Campus," the ODP Pond is responsible for detaining 5.90 acres of The
Savoy project site. Basin O-2 from the Banner Health Medical Campus Master Drainage
Exhibit depicts this. During the design of the ODP Pond, Basin O-2 was assumed to be 85%
impervious. The Savoy proposes utilizing the ODP Pond for 5.91 acres with an impervious
value of 77%. The 5.91 (5.05+0.61+0.25=5.05) acres come from Major Basin A (5.05 ac) plus
Sub-Basin ODP2 (0.61 ac) and Sub-Basin ODP3 (0.25 ac). Sub-Basin ODP1 was not included
in this calculation because it is on the north side of Le Fever Drive and thus not associated
with Basin O-2, but rather Basin O-3 per "Final Drainage Report and Erosion Control Report
Banner Health Medical Campus." Therefore, The Savoy is meeting the requirements set forth
by "Final Drainage Report and Erosion Control Report Banner Health Medical Campus."
Major Basin BF1
Major Basin BF1 has no sub-basins and is associated with the area along the east, west, and
south sides of The Savoy property that cannot be brought into the project site for LID
treatment. Major Basin BF1 has an area of 1.03 acres and an impervious value of 52%. Major
Basin BF1 will maintain existing runoff patterns, with all runoff being routed to the existing
15' Type R Inlet at the northwest corner of the Brookfield Drive and Precision Drive
intersection. Runoff generated in Major Basin BF1 will be detained and treated within
Detention Pond A – Brookfield.
As previously stated in Section III. A., per "Final Drainage Report for Brookfield," Detention
Pond A – Brookfield was designed to detain and treat 9.93 acres, with an assumed
impervious of 85% of The Savoy project site. Basins D9 and D5 from the "Final Drainage
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Report for Brookfield" are the basins associated with The Savoy project site. However, The
Savoy project is proposing to route 3.33 acres, with an impervious value of 69%, to
Detention Pond A – Brookfield. The remaining portion of the site will be routed to the ODP
Pond.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report.
In addition, excerpts from earlier drainage reports referenced in this Section can be found in
Appendix E.
B. SPECIFIC DETAILS
Since detention is not required with this site, the existing impervious area has not been
considered in determining allowable release from the property. Instead, the site was designed
to send roughly 5.90 acres to the ODP Pond while the rest of the runoff would be routed to
Detention Pond A – Brookfield.
LID treatment will be provided for Major Basin A and Major Basin B. Major Basin ODP will be
treated in the ODP Pond, and Major Basin BF1 will be treated in Detention Pond A – Brookfield.
CONCLUSIONS
A. COMPLIANCE WITH STANDARDS
The design elements comply without variation and meet all LID requirements.
The drainage design proposed for The Savoy complies with the City of Fort Collins Master
Drainage Plan, "Final Drainage Report and Erosion Control Report Banner Health Medical
Campus," and "Final Drainage Report for Brookfield." Excerpts from referenced reports can be
found in Appendix F.
There are no FEMA regulatory floodplains associated with The Savoy development.
The drainage plan and stormwater management measures proposed with The Savoy project
are compliant with all applicable State and Federal regulations governing stormwater
discharge.
LID SUMMARY TABLE
Area Treated by Stormtech LID Pond (ac) 5.05
Area Treated by Rain Garden (ac) 2.30
Total LID (ac) 7.35
*Total Drainage Area (ac) 9.24
% Treated by LID 79.55%
% Treated by ODP Pond and Detention Pond A - Brookfield 20.45%
*Includes Major Basin A, Major Basin B, Major Basin BF1, Sub-Basin
ODP2, and Sub-Basin ODP3. Excludes Sub-Basin ODP1.
Table 1 - LID Summary Table
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B. DRAINAGE CONCEPT
The drainage design proposed with this project will effectively limit potential damage
associated with its stormwater runoff. The Savoy project will provide on-site LID treatment for
runoff but will not be detaining any flows. Detention is provided either in the ODP Pond or
Detention Pond A- Brookfield.
The Savoy development will not impact the Master Drainage Plan recommendations for the
McClelland Major Drainage Basin.
REFERENCES
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities,
November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, adopted by Ordinance No.
159, 2018, and referenced in Section 26-500 of the City of Fort Collins Municipal Code.
3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service,
United States Department of Agriculture.
4. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District,
Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
5. Final Drainage Report for Milestone Apartments, Northern Engineering, Fort Collins, Colorado, May
2014.
6. Final Drainage and Erosion Control Report Banner Health Medical Campus, Northern Engineering,
Fort Collins, Colorado, September 2013.
7. Final Drainage and Erosion Control Report for Presidio Apartments, Northern Engineering, Fort
Collins, Colorado, December 2009.
8. Final Drainage Report for Brookfield, TST, Inc. Consulting Engineers, Fort Collins, Colorado,
December 2001.
9. East Harmony Portion of McClelland's Creek Master Drainage Plan Update Final Report, ICON
Engineering, Inc., Englewood, Colorado, August 1999.
Project Title Date:
Project Number Calcs By:
City
Basins
1
WQCV = Watershed inches of Runoff (inches)76%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100)0.305 in
A =5.05 ac
V = 0.1283 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
The Savoy November 11, 2021
514-003 B. Mathisen
Fort Collins
Stormtech LID Pond
5590 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
00.10.20.30.40.50.60.70.80.91WQCV (watershed inches)Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
()iii78.019.10.91aWQCV 23 +-=
()iii78.019.10.91aWQCV 23 +-=
AV*
12
WQCV
=
12 hr
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =77.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.770
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.25 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 100,339 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 =0.43 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =2,077 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 =12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =1545 sq ft
D) Actual Flat Surface Area AActual =1874 sq ft
E) Area at Design Depth (Top Surface Area)ATop =2580 sq ft
F) Rain Garden Total Volume VT=2,227 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
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 =2.5 ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =2,077 cu ft
iii) Orifice Diameter, 3/8" Minimum DO =1 in
Design Procedure Form: Rain Garden (RG)
Blaine Mathisen
Northern Engineering
November 11, 2021
The Savoy
Fort Collins, CO
UD-BMP (Version 3.07, March 2018)
Choose One
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18" Rain Garden Growing Media
Other (Explain):
YES
NO
Major Basin B - Raingarden.xlsm, RG 11/11/2021, 3:24 PM
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?
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)
Blaine Mathisen
Northern Engineering
November 11, 2021
The Savoy
Fort Collins, CO
Choose One
Choose One
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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
Major Basin B - Raingarden.xlsm, RG 11/11/2021, 3:24 PM