HomeMy WebLinkAboutHARMONY COTTAGES (AFFORDABLE HOUSING) - PDP - PDP150030 - REPORTS - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT
Harmony Cottages
Prepared for:
Habitat for Humanity
4001 S. Taft Hill Road
Fort Collins, CO 80525
(970) 223-4522
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite A
Windsor, Colorado 80550
(970) 674-3300
January 20, 2016
Job Number 1255-028-00
ii
January 20, 2016
Ms. Heather McDowell
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522-0580
RE: Preliminary Drainage Report for Harmony Cottages
Dear Heather,
I am pleased to submit for your review and approval, this Preliminary Drainage Report for the
Harmony Cottages development. I certify that this report for the drainage design was prepared in
accordance with the criteria in the City of Fort Collins Storm Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Sincerely,
Erika Schneider, P.E. Skylar Brower
Colorado Professional Colorado Professional
Engineer No. 41777 Engineer No. 44248
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TABLE OF CONTENTS
TABLE OF CONTENTS ............................................................................................................ iii
1. GENERAL LOCATION AND DESCRIPTION ................................................................ 1
1.1 Location ........................................................................................................................... 1
1.2 Description of Property ................................................................................................. 1
1.3 Floodplain Submittal Requirements ............................................................................. 2
2. DRAINAGE BASINS AND SUB-BASINS .......................................................................... 2
2.1 Major Basin Description ................................................................................................ 2
2.2 Sub-basin Description .................................................................................................... 2
3. DRAINAGE DESIGN CRITERIA ...................................................................................... 3
3.1 Regulations ...................................................................................................................... 3
3.2 Directly Connected Impervious Area (DCIA) Discussion .......................................... 3
3.3 Development Criteria Reference and Constraints ...................................................... 4
3.4 Hydrological Criteria ..................................................................................................... 5
3.5 Hydraulic Criteria .......................................................................................................... 5
3.6 Floodplain Regulations Compliance ............................................................................. 6
3.7 Modifications of Criteria ............................................................................................... 6
4. DRAINAGE FACILITY DESIGN ....................................................................................... 6
4.1 General Concept ............................................................................................................. 6
4.2 Specific Details ................................................................................................................ 6
4.3 Stormwater Detention .................................................................................................... 7
4.4 Water Quality Treatment .............................................................................................. 7
5. CONCLUSIONS .................................................................................................................... 9
5.1 Compliance with Standards .......................................................................................... 9
5.2 Drainage Concept ........................................................................................................... 9
6. REFERENCES ...................................................................................................................... 9
APPENDIX
VICINITY MAP AND DRAINAGE PLAN .............................................................................. A
HYDROLOGIC COMPUTATIONS .......................................................................................... B
HYDRAULIC COMPUTATIONS (PROVIDED AT FINAL) ................................................. C
STORMWATER DETENTION POND ANALYSIS ............................................................... D
WATER QUALITY AND LID INFORMATION ..................................................................... E
EXCERPTS FROM REFERENCE REPORTS......................................................................... F
SOIL REPORT AND FEMA INFORMATION ....................................................................... G
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1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
The Harmony Cottages development is located in Fort Collins. It is located in the
Southwest ¼ of Section 34, Township 7 North, Range 69 West of the 6th Principal
Meridian in the City of Fort Collins, Larimer County, Colorado. Please refer to the
vicinity map in Appendix A.
The project site is located in the southeast corner of Harmony Road (County Road 38E)
and Taft Hill Road in southwest Fort Collins, Colorado. The site is bounded by
Harmony Road on the north and east, Taft Hill Road on the west, and The Overlook at
Woodridge Fourth Filing on the south. Adjacent to the northeast corner of the site is a
water pump station owned by the Fort Collins-Loveland Water District. The legal
description of the site is a replat of Lots 1 and 2, Innovation Island.
1.2 Description of Property
The project is a site development of a Habitat for Humanity neighborhood. The property
consists of 4.45 acres of land and lots will be designed for single family and duplex
housing units with private drive through aisles and parking areas.
The site currently consists of open space and is sparsely vegetated with native plants and
grasses. Offsite flow contributing to the site includes adjacent public street right-of-way
and the FCLWD parcel.
The soils in the area are predominately Altan-Satanta loams (86.3%), 0-3 percent slopes
(soil number 3), Hydrologic Soil Group B and Fort Collins loam (13.7%), 0-3 percent
slopes (soil number 35), Hydrologic Soil Group C as reported in the Soil Survey of
Larimer County Area, Colorado.
According to FEMA Panel 08069C1000F there are no mapped FEMA Floodways on this
property. Please refer to Appendix G for the NRCS soils report and FEMA information.
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1.3 Floodplain Submittal Requirements
Because the project is not within any FEMA or City of Fort Collins mapped floodway, a
Floodplain Submittal is not required and a “City of Fort Collins Floodplain Review
Checklist for 50% Submittals” has not been included with this report.
2. DRAINAGE BASINS AND SUB-BASINS
2.1 Major Basin Description
The site is located on the upper end of the Mail Creek Drainage Basin. This site is known
as sub-basin 89 in the master drainage plan and there are no offsite flows that pass
through this site. The impervious area for the site was assumed to be 95% in the master
plan. Excerpts from the “Mail Creek Basin Master Drainage Plan Hydrology Technical
Appendix” are included in Appendix F of this report.
This site is also included in the “Master Drainage Study for Woodridge” (1991) and the
“Final Drainage and Erosion Control Study for the Overlook at Woodridge, Fourth
Filing” (1995). In the Final Drainage Report for the Overlook at Woodridge Fourth
Filing, this site is known as Basin 1 and 2A. These basins were considered to be
neighborhood commercial sites with a C-value of 0.85. Fully developed commercial
flows from this site were considered in the stormwater system plan design for the
Overlook at Woodridge. Excerpts from the “Final Drainage and Erosion Control Study
for the Overlook at Woodridge, Fourth Filing” report are included in Appendix F of this
report.
2.2 Sub-basin Description
The southern portion of the site drains to an existing swale which carries stormwater
runoff along the south property line to a depression and into a concrete pipe located in
Tract A of the Overlook at Woodridge. The remaining portion of the site drains via
overland flow to the curb and gutter along Harmony Road and into two existing 15’ type
R inlets on the south side of Harmony Road. All of the stormwater runoff from the site
is conveyed to the existing stormwater conveyance system in Harmony Road which
passes to the existing concrete lined drainage channel north of Seneca Drive and then to
the existing regional detention pond located adjacent to Webber Middle School.
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3. DRAINAGE DESIGN CRITERIA
3.1 Regulations
This report was prepared to meet or exceed the “City of Fort Collins Storm Drainage
Design Criteria Manual” specifications. Where applicable, the criteria established in the
“Urban Storm Drainage Criteria Manual” (UDFCD), developed by the Denver Regional
Council of Governments, has been used.
3.2 Directly Connected Impervious Area (DCIA) Discussion
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process
for receiving water protection that focuses on reducing runoff volumes, treating the water
quality capture volume (WQCV), stabilizing drainageways and implementing long-term
source controls. The Four Step Process applies to the management of smaller, frequently
occurring events.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement
Low Impact Development (LID) strategies, including Minimizing Directly Connected
Impervious Areas (MDCIA).
Runoff for the northern portion of the site will be routed through porous pavement
systems and a rain garden reducing runoff from impervious surfaces over permeable areas
to slow runoff and increase the time of concentration and promote infiltration. Runoff
from the southern portion of the site will be routed through porous pavement systems, a
grass swale, and a second rain garden thereby slowing runoff and also promoting
infiltration.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow
Release
95% of the proposed impervious area will be routed through an LID facility; therefore, no
additional water quality capture volume is proposed with these improvements.
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Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate and volume of runoff during and following development. Because the site
will drain to an existing storm system, bank stabilization is unnecessary with this project.
Step 4: Implement Site Specific and Other Source Control BMPs
Proactively controlling pollutants at their source by preventing pollution rather than
removing contaminants once they have entered the stormwater system or receiving waters
is important when protecting storm systems and receiving waters. This can be
accomplished through site specific needs such as construction site runoff control, post-
construction runoff control and pollution prevention / good housekeeping. It will be the
responsibility of the contractor to develop a procedural best management practice for the
site.
3.3 Development Criteria Reference and Constraints
The runoff from this site has been routed to conform to the requirements of the City
Stormwater Department and the Mail Creek Basin Master Drainage Plan. Water quality
capture volume will be provided on site. The impervious area for the site was assumed to
be 95% in the master plan. The proposed weighted average impervious area for the
proposed site is 50% which is less than the master plan.
Fully developed commercial flows from this site were considered in the stormwater
system plan design for the Overlook at Woodridge. The correlating basins 1 and 2A were
considered to be neighborhood commercial sites with a C-value of 0.85. The proposed
weighted average C-value of the proposed site is 0.55 which is less than the original
design and therefore, downstream stormwater system will have capacity. Please refer to
supporting documentation in Appendix F.
Correlating Basin ID %I C-value
Master Plan 89 95 -
Woodridge 4th 1, 2A - 0.85
Site A, B 50 0.55
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Runoff reduction practices (LID techniques) are also required. No less than fifty percent
of any newly added impervious area must be treated using one or a combination of LID
techniques. The project adds 110,940 sf of new impervious area. Using the porous paver
and rain garden LID techniques, 163,604 sf of new impervious area (147%) will be
treated which exceeds the 50% requirement. In anticipation of the new LID code which
will require 75% of newly added impervious area to be treated by an LID technique, the
rain gardens have been sized to treat the entire site with the assumption that the porous
pavers are removed. Using the rain garden LID technique, 105,796 sf of new impervious
area (95%) will be treated which exceed the 75% requirement.
No less than twenty five percent of any newly added pavement areas must be treated
using a permeable pavement technology. The project adds 27,679 sf of new pavement
area. This project will incorporate 7,427 sf of porous pavers which is 27% of the newly
added pavement which exceeds the required 25%. As previously mentioned, this project
is set up to provide the option of removing the porous pavers during final design with the
assumption that the newly proposed LID code is implemented by the City.
Please refer to Appendix E for LID calculations and information.
3.4 Hydrologic Criteria
Runoff computations were prepared for the 2- and 10-year minor and 100-year major
storm frequency utilizing the rational method.
All hydrologic calculations associated with the basins are included in Appendix B of this
report. Standard Form 8 (SF-8) provides time of concentration calculations for all sub-
basins. Standard Form 9 (SF-9) provides a summary of the design flows for all Sub-
basins and Design Points associated with this site.
3.5 Hydraulic Criteria
All hydraulic calculations will be presented in the final drainage report and prepared in
accordance with the City of Fort Collins Drainage Criteria.
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3.6 Floodplain Regulations Compliance
The project is not within any FEMA or City of Fort Collins mapped floodway; therefore,
Floodplain Regulations Compliance is not required.
3.7 Modifications of Criteria
There are no Modifications of Criteria at this time.
4. DRAINAGE FACILITY DESIGN
4.1 General Concept
The proposed site generally follows the existing drainage patterns and is divided into two
major drainage basins. The site will be further divided into more sub-basins during final
compliance.
4.2 Specific Details
A summary of the drainage patterns within each basin is provided in the following
paragraphs. Please refer to Appendix A for the drainage plan.
Basin A is 1.77 acres and includes the southern portion of the proposed site and a small
off-site area adjacent to Taft Hill Road. Stormwater is conveyed via overland flow to the
proposed grass swale that runs west to east along the southern property boundary. This
south swale discharges into the proposed rain garden in the southeast corner of the
property located at design point a. The outlet pipe for the rain garden discharges to the
existing storm drain inlet #21 located on the south side of Harmony Road.
Basin B is 2.85 acres and includes the northern portion of the site and offsite area from
the FCLWD parcel and area adjacent to Taft Hill Road. This basin is conveyed via
overland flow to the porous paver systems and rain garden located at the southwest corner
of the intersection of the driveway and Harmony Road. The outlet pipe for the rain
garden discharges to the existing 15’ Type R inlet #10 located on the south side of
Harmony Road.
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Basin OS-3 is 0.32 acres and includes the north half of the roofs of 5 lots from the
Overlook at Woodridge, P.U.D. Fourth Filing adjacent to basin A. This basin sheet flows
to the southern grass swale.
Basin OS-10 is 0.94 acres and includes the south half of the roadway of Harmony Road
adjacent to basin B and a small portion of the site adjacent to Harmony Road. This off-
site basin will be further divided showing on-site and off-site areas during final
compliance. This basin is conveyed via gutter flow to the existing 15’ Type R inlet #10
in Harmony Road.
Basin OS-21 is 0.54 acres and includes the south half of the roadway of Harmony Road
adjacent to basin A and a small portion of the site adjacent to Harmony Road. This off-
site basin will be further divided showing on-site and off-site areas during final
compliance. This basin is conveyed via gutter flow to the existing 15’ Type R inlet #21
in Harmony Road.
4.3 Stormwater Detention
Developed commercial flows from this site were accounted for in the design of the storm
drainage detention pond for the Overlook at Woodridge Fourth Filing (1995). Since the
time that the Final Drainage Study for the Overlook was completed, the City of Fort
Collins (CFC) has modified their stormwater design criteria to include stormwater quality
enhancement requirements and the use of a larger design storm based on a 1998
precipitation study. The peak discharge using the old rainfall data for the site only (4.45
acres) and a C 100-year value of 1.00 was calculated to be 40.1-cfs. The required
detention volume under the new rainfall conditions with a release rate set to the peak
discharge under the old rainfall conditions and a developed C 100-year value of 0.70 was
calculated. The result was a detention requirement of -0.04 ac-ft with a storm duration of
5 minutes. Therefore, adequate stormwater detention is being provided and additional
detention is not required based on the increase in the design rainfall rates.
4.4 Water Quality Treatment
Water quality enhancement is being provided for fully developed conditions. Four water
quality enhancement measures will be used on this site. 95% of the impervious area on
8
site will be directed to an LID facility. Therefore, no water quality capture volume is
required for this site.
The first water quality enhancement measure is the rain garden in the east corner of the
site which is referred to as rain garden A. The rain garden is a depressed landscape area
designed to capture and infiltrate the water quality capture volume. This area has an
average depth of 12”, has a flat bottom and will include landscape plantings in 12” depth
of a sand media mixture. Water will be held in the depressed area and slowly drain
through the sand media and then hit a 4” perforated pipe in gravel bedding which will
discharge ultimately to the existing storm system in Harmony Road. This rain garden
will treat 0.02 ac-ft of the water quality capture volume.
The second water quality enhancement measure is the rain garden adjacent to Harmony
and the main driveway which is referred to as rain garden B. The rain garden is a
depressed landscape area designed to capture and infiltrate the water quality capture
volume. This area has an average depth of 12”, has a flat bottom and will include
landscape plantings in 12” depth of a sand media mixture. Water will be held in the
depressed area and slowly drain through the sand media and then hit a 4” perforated pipe
in gravel bedding which will discharge ultimately to the existing storm system in
Harmony Road. This rain garden will treat 0.04 ac-ft of the water quality capture volume.
The third water quality enhancement measure is the grass swale located along the south
property line. The swale has been designed to have a low longitudinal slope in order to
convey flow in a slow and shallow manner promoting sedimentation and filtration and
limiting erosion. The bottom of the swale is not concrete lined in order to further
enhance pollutant removal. The swale will be constructed with a ‘soft pan’ bottom
consisting of a sand/topsoil mix or will be constructed with an underdrain in order to
minimize standing water in the swale.
The fourth water quality enhancement measure is the porous pavement systems located
throughout the pavement area. These systems allow the movement of water into the
layers below the pavement surface where treatment and slow release occurs. These
systems also reduce the effective imperviousness of the site.
There is a small portion of the site immediately adjacent to Harmony Road which will not
9
pass through a water quality feature but will flow directly to the street gutter and into the
stormwater system. The majority of this area is landscaped with grass and plantings and
only a small amount of impervious area from the sidewalk and roof is included. Since the
source of the majority of pollutants in stormwater runoff comes from driveway and
parking areas, this small amount of untreated runoff should have a negligible effect on the
overall pollutant load. Several off-site areas will be conveyed through the site and treated
on-site including the FCLWD parcel and the area adjacent to Taft Hill Road and this
property.
5. CONCLUSIONS
5.1 Compliance with Standards
All computations that have been completed within this report are in compliance with the
City of Fort Collins Storm Drainage Design Criteria Manual.
5.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provides for stormwater quantity and quality treatment of proposed
impervious areas. Conveyance elements have been designed to pass required flows and
to minimize future maintenance.
If, at the time of construction, groundwater is encountered, a Colorado Department of
Health Construction Dewatering Permit will be required.
6. REFERENCES
1. City of Fort Collins, “Fort Collins Stormwater Criteria Manual Amendments to
the Urban Drainage and Flood Control District Criteria Manual”, adopted
December 2011.
2. Urban Drainage and Flood Control District, “Urban Storm Drainage Criteria
Manual”, Volumes 1 and 2, dated June 2001, and Volume 3 dated November
2015.
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3. Ayers Associates, “Alternative Analysis for the Design of the Mason Street
Outfall”, dated November 2010.
4. RBD, Inc. Engineering Consultants, “Preliminary/Master Drainage Study for
Woodridge”, dated December 2, 1991.
5. RBD, Inc. Engineering Consultants, “Final Drainage and Erosion Control Study
for the Overlook at Woodridge Fourth Filing, Phase One”, dated June 14, 1995.
A
APPENDIX A
VICINITY MAP AND DRAINAGE PLAN
B
APPENDIX B
HYDROLOGIC COMPUTATIONS
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/8/2015
Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I
Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I
Type B Soils Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Pavers: 0.50 40
Lawns, sandy soil (Flat <2%) : 0.10 0
SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS CONCRETE LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
Existing
Lot 4.45 193,839 0 0 0 0 193,839 0.10 0
Proposed
Lot 4.45 193,839 46,267 6,641 7,427 47,000 86,504 0.55 50
1, 2A 6.54 0.85
89 5.90 95
Equations
- Calculated C coefficients & % Impervious are area weighted
C = Σ (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
BASED ON MASTER DRAINAGE PLAN
BASED ON WOODRIDGE 4TH FILING
12-8-15 FC FLOW.xls
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/8/2015
Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I
Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I
Type B Soils Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Gravel or Pavers: 0.50 40
Lawns, sandy soil (Flat <2%) : 0.10 0
SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS SIDEWALK LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
A 1.77 77,160 0.55 50
B 2.85 124,007 0.55 50
OS-10 0.94 41,146 223 22,062 0 3,121 15,739 0.62 61
OS-21 0.54 23,355 3,310 9,154 0 2,593 8,298 0.65 63
OS-3 0.49 21,503 0.58
Equations
- Calculated C coefficients & % Impervious are area weighted
C = Σ (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
BASED ON OVERALL LOT CALCS
BASED ON WOODRIDGE 4TH FILING
12-8-15 FC FLOW.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 2 and 10 YR
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/8/2015
2 and 10-yr storm Cf = 1.00 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I
SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASIN) tc
DESIGN SUBBASIN(s) Area C Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10
PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14)
a A 1.77 0.55 20 2.0 3.7 650 1.8 0.016 2.7 4.1 7.7 670 13.7 7.7
b B 2.85 0.55 50 2.0 5.8 880 1.5 0.022 1.8 8.2 14.0 930 15.2 14.0
10 OS-10 0.94 0.62 12 2.0 2.4 575 0.6 0.016 1.6 6.2 8.6 587 13.3 8.6
21 OS-21 0.54 0.65 12 2.0 2.3 225 0.6 0.016 1.6 2.4 4.7 237 11.3 5.0
10 B+OS-10 3.79 0.57 50 2.0 5.6 1455 1.1 0.020 1.8 13.8 19.4 1505 18.4 18.4
21 A+OS-21 2.31 0.57 20 2.0 3.5 875 1.5 0.016 2.4 6.0 9.5 895 15.0 9.5
3 OS-3 0.49 0.58 20 2.0 3.5 600 1.8 0.022 2.0 5.1 8.6 620 13.4 8.6
EQUATIONS:
tc = ti + tt
ti = [1.87 (1.1 - CCf ) L0.5 ] / S 1/3
tt = L/Vel.
Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
12-8-15 FC FLOW.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 100 YR
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/8/2015
100-yr storm Cf = 1.25 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I
SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASIN) tc
DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10
PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14)
a A 1.77 0.55 0.69 20 2.0 2.7 650 1.8 0.016 2.7 4.1 6.8 670 13.7 6.8
b B 2.85 0.55 0.69 50 2.0 4.3 880 1.5 0.022 1.8 8.2 12.5 930 15.2 12.5
10 OS-10 0.94 0.62 0.78 12 2.0 1.6 575 0.6 0.016 1.6 6.2 7.8 587 13.3 7.8
21 OS-21 0.54 0.65 0.81 12 2.0 1.5 225 0.6 0.016 1.6 2.4 3.9 237 11.3 5.0
10 B+OS-10 3.79 0.57 0.71 50 2.0 4.1 1455 1.1 0.020 1.8 13.8 17.9 1505 18.4 17.9
21 A+OS-21 2.31 0.57 0.72 20 2.0 2.5 875 1.5 0.016 2.4 6.0 8.6 895 15.0 8.6
3 OS-3 0.49 0.58 0.73 20 2.0 2.5 600 1.8 0.022 2.0 5.1 7.6 620 13.4 7.6
EQUATIONS:
tc = ti + tt
ti = [1.87 (1.1 - CCf ) L0.5 ] / S 1/3
tt = L/Vel.
Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
12-8-15 FC FLOW.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 2-Yr Storm)
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/8/2015
2 yr storm, Cf = 1.00
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Design Tributary A C Cf tc i Q (2) from Q (2) Q(2)tot
Sub-basin Design
Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
a A 1.77 0.55 7.7 2.45 2.4 2.4 WQ Pond
b B 2.85 0.55 14.0 1.93 3.0 3.0 Rain Garden
10 OS-10 0.94 0.62 8.6 2.36 1.4 1.4 Ex Inlet #10
21 OS-21 0.54 0.65 5.0 2.85 1.0 1.0 Ex Inlet #21
10 B+OS-10 3.79 0.57 18.4 1.69 3.6 3.6 Ex Inlet #10
21 A+OS-21 2.31 0.57 9.5 2.27 3.0 3.0 Ex Inlet #21
3 OS-3 0.49 0.58 8.6 2.36 0.7 0.7 Bioswale
Q = Cf C iA
Q = peak discharge (cfs)
C = runoff coefficient
Cf = frequency adjustment factor
i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99)
A = drainage area (acres) i = 24.221 / (10+ tc)0.7968
12-8-15 FC FLOW.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 10-Yr Storm)
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/8/2015
10 yr storm, Cf = 1.00
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Design Tributary A C Cf tc i Q (10) from Q (10) Q(10)tot
Sub-basin Design
Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
a A 1.77 0.55 7.7 4.19 4.1 4.1 WQ Pond
b B 2.85 0.55 14.0 3.29 5.2 5.2 Rain Garden
10 OS-10 0.94 0.62 8.6 4.03 2.4 2.4 Ex Inlet #10
21 OS-21 0.54 0.65 5.0 4.87 1.7 1.7 Ex Inlet #21
10 B+OS-10 3.79 0.57 18.4 2.88 6.2 6.2 Ex Inlet #10
21 A+OS-21 2.31 0.57 9.5 3.88 5.1 5.1 Ex Inlet #21
3 OS-3 0.49 0.58 8.6 4.04 1.2 1.2 Bioswale
Q = Cf C iA
Q = peak discharge (cfs)
C = runoff coefficient
Cf = frequency adjustment factor
i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99)
A = drainage area (acres) i = 41.44 / (10+ tc)0.7974
12-8-15 FC FLOW.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 100-Yr Storm)
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/8/2015
100 yr storm, Cf = 1.25
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot
Design
Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
a A 1.77 0.69 6.8 8.92 10.9 10.9 WQ Pond
b B 2.85 0.69 12.5 7.06 13.8 13.8 Rain Garden
10 OS-10 0.94 0.78 7.8 8.52 6.3 6.3 Ex Inlet #10
21 OS-21 0.54 0.81 5.0 9.95 4.3 4.3 Ex Inlet #21
10 B+OS-10 3.79 0.71 17.9 5.95 16.0 16.0 Ex Inlet #10
21 A+OS-21 2.31 0.72 8.6 8.24 13.6 13.6 Ex Inlet #21
3 OS-3 0.49 0.73 7.6 9.95 3.6 3.6 Bioswale
Q = C iA
Q = peak discharge (cfs)
C = runoff coefficient
i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99)
A = drainage area (acres) i = 84.682 / (10+ tc)
0.7975
12-8-15 FC FLOW.xls
SUMMARY
DRAINAGE SUMMARY TABLE
Design Tributary Area C (10) C (100) tc (10) tc (100) Q(2)tot Q(10)tot Q(100)tot
Sub-basin REMARKS
Point (ac) (min) (min) (cfs) (cfs) (cfs)
a A 1.77 0.55 0.69 7.7 6.8 2.4 4.1 10.9 WQ Pond
b B 2.85 0.55 0.69 14.0 12.5 3.0 5.2 13.8 Rain Garden
10 OS-10 0.94 0.62 0.78 8.6 7.8 1.4 2.4 6.3 Ex Inlet #10
21 OS-21 0.54 0.65 0.81 5.0 5.0 1.0 1.7 4.3 Ex Inlet #21
3 OS-3 0.49 0.58 0.73 8.6 7.6 0.7 1.2 3.6 Bioswale
Page 8
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C
APPENDIX C
HYDRAULIC CALCULATIONS
(PROVIDED AT FINAL)
D
APPENDIX D
STORMWATER DETENTION POND
ANALYSIS
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 100-Yr Storm - OLD rainfall)
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/5/2015
100 yr storm, Cf = 1.25
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot
Design
Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
1 site 4.45 1.00 5.00 9.00 40.05 40.1 Allowable release under
old reainfall conditions
Q = C
iA
Q = peak discharge (cfs)
C = runoff coefficient
i = rainfall intensity (in/hr) from OLD City of Fort Collins IDF curve
A = drainage area (acres)
DETENTION VOLUME CALCULATIONS
Rational Volumetric (FAA) Method
100-Year Event
LOCATION: Harmony Cottages
PROJECT NO: 1255-028-00
COMPUTATIONS BY: es
DATE: 12/5/15
Equations: Area trib. to pond = 4.45 acre
Developed flow = QD = CIA C (100) = 0.70
Vol. In = Vi = T C I A = T QD Developed C A = 3.1 acre - site only
Vol. Out = Vo =K QPO T Release rate, QPO = 40.1 cfs
storage = S = Vi - Vo K = 0.9 (from fig 2.1)
Rainfall intensity from City of Fort Collins IDF Curve with updated (3.67") rainfall
Storm Rainfall QD Vol. In Vol. Out Storage Storage
Duration, T Intensity, I (cfs) Vi Vo S S
(min) (in/hr) (ft3) (ft3) (ft3) (ac-ft)
5 9.95 31.0 9298 10814 -1515 -0.03
10 7.77 24.2 14515 21627 -7112 -0.16
20 5.62 17.5 21010 43254 -22244 -0.51
30 4.47 13.9 25054 64881 -39827 -0.91
40 3.74 11.6 27960 86508 -58548 -1.34
50 3.23 10.1 30220 108135 -77915 -1.79
60 2.86 8.9 32069 129762 -97693 -2.24
70 2.57 8.0 33634 151389 -117755 -2.70
80 2.34 7.3 34993 173016 -138023 -3.17
90 2.15 6.7 36195 194643 -158448 -3.64
100 1.99 6.2 37273 216270 -178997 -4.11
110 1.86 5.8 38251 237897 -199646 -4.58
120 1.75 5.4 39148 259524 -220376 -5.06
130 1.65 5.1 39977 281151 -241174 -5.54
140 1.56 4.9 40747 302778 -262031 -6.02
150 1.48 4.6 41467 324405 -282938 -6.50
160 1.41 4.4 42144 346032 -303888 -6.98
170 1.35 4.2 42783 367659 -324876 -7.46
180 1.29 4.0 43388 389286 -345898 -7.94
Required Storage Volume: -1515 ft3
-0.03 acre-ft
E
APPENDIX E
WATER QUALITY
AND
LID INFORMATION
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 50.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.500
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.17 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 77,160 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 1,061 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 = 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 = 707 sq ft
D) Actual Flat Surface Area AActual = 725 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 1400 sq ft
F) Rain Garden Total Volume VT= 1,063 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
Standard City of Fort Collins Spec
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Harmony Cottages
Basin A
Design Procedure Form: Rain Garden (RG)
sb
Interwest Consulting Group
January 19, 2016
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Rain Garden Basin A.xls, RG 1/19/2016, 6:48 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)
sb
Interwest Consulting Group
January 19, 2016
Harmony Cottages
Basin A
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
Rain Garden Basin A.xls, RG 1/19/2016, 6:48 PM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 50.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.500
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.17 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 124,007 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 1,705 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 = 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 = 1137 sq ft
D) Actual Flat Surface Area AActual = 1465 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 2567 sq ft
F) Rain Garden Total Volume VT= 2,016 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
Standard City of Fort Collins Spec
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Harmony Cottages
Basin B
Design Procedure Form: Rain Garden (RG)
sb
Interwest Consulting Group
January 19, 2016
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Rain Garden Basin B.xls, RG 1/19/2016, 6:49 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)
sb
Interwest Consulting Group
January 19, 2016
Harmony Cottages
Basin B
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
Rain Garden Basin B.xls, RG 1/19/2016, 6:49 PM
New Impervious Area 110,940 sq. ft.
Required Minimum Impervious Area to be Treated 55,470 sq. ft.
Area Treated by Pavers 57,808 sq. ft.
Area Treated by Rain Garden A 35,370 sq. ft.
Area Treated Rain Garden B 70,426 sq. ft.
Total Impervious Area Treated 163,604 sq. ft.
Actual % On-Site Treated by LID 147 %
New Pavement Area 27,679 sq. ft.
Required Minimum Area of Porous Pavement 6,920 sq. ft.
Area of Paver Section 7,427 sq. ft.
Total Porous Pavement Area 7,427 sq. ft.
Actual % of Porous Pavement Provided 27 %
New Impervious Area 110,940 sq. ft.
Required Minimum Impervious Area to be Treated 83,205 sq. ft.
Area Treated by Rain Garden A 35,370 sq. ft.
Area Treated by Rain Garden B 70,426 sq. ft.
Total Impervious Area Treated 105,796 sq. ft.
Actual % On-Site Treated by LID 95 %
Harmony Cottages
LID Table
75% On-Site Treatment by LID Requirement
50% On-Site Treatment by LID Requirement
25% Porous Pavement Requirement
LID Table
Harmony Cottages
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
HARMONY COTTAGES
LID EXHIBIT - RAIN GARDENS
01/20/16
1"=60'
N/A
RA
RA
1255-028-00
1
HABITAT FOR HUMANITY
4001 S. TAFT HILL ROAD
FORT COLLINS, CO 80525
PHONE: 970.223.4522
LEGEND
IMPERVIOUS AREA TREATED
BY RAIN GARDEN A
(35,370 SF, 32% OF TOTAL IMP. AREA)
IMPERVIOUS AREA TREATED
BY RAIN GARDEN
(70,426 SF, 63% OF TOTAL IMP. AREA)
0
SCALE: 1" = 60'
30 15 60
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
HARMONY COTTAGES
LID EXHIBIT - POROUS PAVEMENT
01/20/16
1"=60'
N/A
RA
RA
1255-028-00
2
HABITAT FOR HUMANITY
4001 S. TAFT HILL ROAD
FORT COLLINS, CO 80525
PHONE: 970.223.4522
LEGEND
AREA TREATED BY
POROUS PAVEMENT LID
(57,808 SF, 52%)
NOTE: AVERAGE RUN-ON AREA IS 8:1 WHICH EXCEEDS
RECOMMENDED 3:1 MAXIMUM. RUNOFF WILL BE
TREATED A SECOND TIME BY THE DOWNSTREAM
RAIN GARDENS.
0
SCALE: 1" = 60'
30 15 60
F
APPENDIX F
EXCERPTS FROM REFERENCE REPORTS
G
APPENDIX G
SOIL REPORT
AND
FEMA INFORMATION
FEMA's National Flood Hazard Layer (Official)
http://fema.maps.arcgis.com/home/webmap/print.html[12/3/2015 11:16:14 AM]
FEMA's National Flood Hazard Layer (Official)
Data from Flood Insurance Rate Maps (FIRMs) where available digitally. Try http://bit.ly/1bPpUjq (Unofficial)
if this map is down
scott.mcafee@fema.dhs.gov | National Geospatial-Intelligence Agency (NGA); Delta State University; Esri