HomeMy WebLinkAboutDrainage Reports - 12/23/2019City of Fort Collins Approved Plans
Approved by:
Date:
Matt Simpson
12/23/2019
October 30, 2019
Revised: December 5, 2019
Revised: December 19, 2019
Mr. Shane Boyle, Civil Engineer
Water Utilities Engineering
City of Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80521
Re: Final Drainage Report
Garcia House: A Circle Program by SummitStone
Project No. 0060.0002.00
Dear Mr. Boyle,
We are pleased to submit this revised Final Drainage Report for the Garcia House: A Circle
Program by SummitStone located at the corner of Patton, East Elizabeth, and McHugh Streets.
This report was prepared based on the City of Fort Collins Stormwater Criteria Manual adopted
in December 2018.
Please let me know if you have any questions or comments.
Sincerely,
COLORADO CIVIL GROUP, INC.
Edward J. Jansury Jr., PE
Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
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Table of Contents
1 Project Summary ...................................................................................................................................................... 1
1.1 Site Location ..................................................................................................................................................... 1
1.2 Existing Site Conditions .................................................................................................................................... 2
1.3 Master Drainage Plan Description .................................................................................................................... 2
1.4 Floodplain Information ..................................................................................................................................... 3
1.5 Project Description ........................................................................................................................................... 3
2 Proposed Drainage Facilities .................................................................................................................................... 4
2.1 General Flow Patterns ...................................................................................................................................... 4
2.2 On-Site Basin Description ................................................................................................................................. 4
2.2.1 On-Site Basin Description ......................................................................................................................... 5
2.3 Off-Site Basin Description ................................................................................................................................. 5
2.4 Water Quantity Detention ................................................................................................................................ 6
2.5 Water Quality Capture Volume ...................................................................................................................... 10
2.6 LID Treatment ................................................................................................................................................. 11
2.7 Maintenance Access ....................................................................................................................................... 13
2.8 Easements ...................................................................................................................................................... 13
3 Proposed Drainage Design Criteria ......................................................................................................................... 13
3.1 Drainage Studies ............................................................................................................................................. 13
3.2 Four-Step Process ........................................................................................................................................... 13
3.2.1 Step 1: Runoff Reduction ........................................................................................................................ 14
3.2.2 Step 2: Treat and Slowly Release Runoff ................................................................................................ 14
3.2.3 Step 3: Stabilize Drainageways ............................................................................................................... 14
3.2.4 Step 4: Implementation of Source Controls ........................................................................................... 14
3.3 BMP Selection Considerations ........................................................................................................................ 15
3.3.1 Soils ......................................................................................................................................................... 15
3.3.2 Watershed Size ....................................................................................................................................... 15
3.3.3 Base Flows .............................................................................................................................................. 15
3.4 BMP Design ..................................................................................................................................................... 16
3.5 Hydrologic Criteria .......................................................................................................................................... 16
3.6 Hydraulic Criteria ............................................................................................................................................ 16
4 Variance Requests .................................................................................................................................................. 17
5 Erosion Control ....................................................................................................................................................... 17
6 Conclusions ............................................................................................................................................................. 18
7 References .............................................................................................................................................................. 18
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8 Appendices ............................................................................................................................................................. 18
Appendix A: Existing Soil Properties ................................................................................................................................. A
Appendix B: Hydrologic Calculations ................................................................................................................................ B
Appendix C: Hydraulic Calculations .................................................................................................................................. C
Appendix D: StormTech System Plans and Details .......................................................................................................... D
Appendix E: Historic and Developed Drainage Basin Plans .............................................................................................. E
Index of Figures and Tables
Figure 1-1: Vicinity Map ................................................................................................................................................... 1
Figure 1-2: Spring Creek Drainage Basin .......................................................................................................................... 3
Figure 2-1: Off-Site Basins ................................................................................................................................................ 6
Table 2-1: FCSCM Runoff Coefficients .............................................................................................................................. 7
Table 2-2: FCSCM Frequency Adjustment Factors ........................................................................................................... 8
Table 2-3: Impervious Percentages .................................................................................................................................. 8
Table 2-4: Existing Condition Basin Summary .................................................................................................................. 9
Table 2-5: Developed Basin Summary .............................................................................................................................. 9
Table 2-6: Developed Sub-Basin Summary .................................................................................................................... 10
Table 2-7: Detention Pond Summary Table ................................................................................................................... 10
Table 2-8: LID Treatment ................................................................................................................................................ 12
Table 2-9: Water Quality Chambers ............................................................................................................................... 12
Figure 2-2: LID Exhibit ..................................................................................................................................................... 13
Table3-1: Grate Inlet Capacities ..................................................................................................................................... 17
Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
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1 Project Summary
1.1 Site Location
Garcia House: A Circle Program by SummitStone site is Lot 2 of the East Elizabeth
Subdivision and is in the Southwest Quarter of Section 18, Township 7 North, Range
68 West of the 6
th Principal Meridian, City of Fort Collins, County of Larimer, Colorado.
The site is bounded on the north by East Elizabeth Street, on the west by Patton
Street, on the northeast by McHugh Street and on the south by property owned by
Hanlon Bush Investments, LLC. A vicinity map is presented in Figure 1-1. The project
area is generally located at 40° 34’26” North Latitude and 105° 3’14” West
Longitude.
Figure 1-1: Vicinity Map
E ELIZABETH ST
PROJECT
AREA
E PITKIN ST
RIVERSIDE AVE
UCHEALTH
POUDRE
VALLEY
HOSPITAL
MCHUGH ST
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1.2 Existing Site Conditions
The parcel contains 0.635 acres in area as in currently undeveloped with a natural
grass groundcover. The parcel in located in the Spring Creek Drainage Basin. The
soils on site are listed as Kim Loam with 1-3% slopes on the National Resources
Conservation Service Web Soil Survey website. Kim Loam soils are considered well
drained and in Hydrologic Soil Group B. This soils on this site are in wind erodibility
group 4L on a scale of 1 to 8 with group 1 being the most susceptible to wind
erosion. Groundwater depths were found to be 16 feet deep per the geotechnical
report prepared by Earth Engineering Company, Inc.
1.3 Master Drainage Plan Description
As previously mentioned, this site is located within the Spring Creek Drainage Basin
and is part of the Spring Creek Master Drainage Plan. The Spring Creek drainage
basins encompasses approximately 9 square miles. Spring Creek flows from the
Spring Canyon Dam at Horsetooth Reservoir to the Poudre River. This site is in the
northeast corner of the basin in an area where the water quality was not evaluated as
the runoff drains into an existing irrigation system. See Figure 1-2 below and
Appendix A. The area surrounding this site is fully developed with no known master
planning improvements at or near this site.
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Figure 1-2: Spring Creek Drainage Basin
1.4 Floodplain Information
The project site is located within Zone‘X’ of Community-Panel Number 08069C0983H,
revised May 2, 2012. Zone‘X’is defined as “Areas determined to be outside the
0.2% annual chance floodplain.” A portion of the referenced map can be found in
Appendix A of this report.
1.5 Project Description
Garcia House: A Circle Program by SummitStone project includes the complete
development of one parcel (8718312002). This parcel contains 0.635 acres. A building,
parking, and walkways will be built on the currently undeveloped lot. The construction
on this site include an entrance from McHugh Street, an exit onto Patton Street for
emergency and service vehicles, walkways, and an underground detention pond.
PROJECT AREA
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2 Proposed Drainage Facilities
2.1 General Flow Patterns
The site and surrounding properties were reviewed to determine existing drainage
patterns. Runoff generally flows from a high point near the center of the southern
edge of the property westerly and northerly to Patton, E. Elizabeth and McHugh
Streets. Runoff travels northerly along the flow line of Patton Street to its’ intersection
with E. Elizabeth Street and then easterly and southeasterly along the flow line of E.
Elizabeth and McHugh Streets. Off-site flow from a portion of the property south of this
site developed as a rehabilitation and nursing center enters in two locations near the
southeast corner of the site and flows undetained overland northerly to McHugh Street.
No drainage report is available for this adjacent property. Based on the aerial photo,
off-site basins have been delineated and assumptions have been made about slope
based on the slope on Garcia House property. Developed drainage basins were
delineated based on existing and proposed improvements. The Final Drainage Plan is
in Appendix D. Three on-site basins and two off-site basins were delineated.
Descriptions of the delineated basins are listed below. The physical parameters and
hydrologic calculations for the basins can be found in Appendix B.
2.2 On-Site Basin Description
Basin A consists of sidewalks and landscape areas between the north and west sides
of the building and the rights-of-way of Patton, E. Elizabeth, and McHugh Streets. The
basin boundary runs along the street right-of-way, per City of Fort Collins direction.
Basin A flows via sheet flow to Patton, East Elizabeth, and McHugh Streets without
detention.
Basin B consists of the proposed commercial building, courtyard area, the majority of
the parking lot pavement, concrete walks, and landscaped area. From the existing
condition to the proposed condition, the imperviousness for the basin is increased by
replacing the natural grass area with parking lot pavement, buildings, and concrete
walks. The basin drains to the StormTech system which then releases flow to a
proposed storm drain prior to outflowing on McHugh Street through the sidewalk chase.
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Basin C includes a portion of an existing commercial parking lot which will provide
access to the site and a portion of landscaped area. Runoff from Basin C flows via
sheet flow to McHugh Street without detention.
2.2.1 On-Site Basin Description
Sub basins were created for Basin B to determine flows into specific components of
the storm drain system, specifically the roof drains, area inlets and curb inlets in the
parking lot.
2.3 Off-Site Basin Description
Basin OS-1 includes a portion of the nursing center property drains to on-site Basin B.
The flows from this basin are accounted for in the storm drain sizing and are conveyed
through the property to McHugh Street undetained.
Basin OS-2 includes the remaining portion of the nursing center property that drains to
the Garcia House property drains to on-site Basin C. As no drainage facilities are
proposed for Basin C, runoff from this basin passes through the site and enters
McHugh Street undetained, which is consistent with the existing drainage pattern.
Figure 2-1 presents the delineation of the off-site basins and Appendix B presents the
hydrologic calculations for the basins.
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Figure 2-1: Off-Site Basins
2.4 Water Quantity Detention
In order to determine the quantity of stormwater detention and treatment necessary for the
project site, the existing and proposed conditions were calculated and compared. Surface
Type Runoff Coefficients (Cx) found in Table 3.2.2 of the Fort Collins Stormwater Criteria
Manual (FCSCM) adopted in December 2018 were utilized to determine the composite runoff
coefficients of each basin. Values from this table are presented in Table 2-1 below.
E ELIZABETH ST
MCHUGH STPROJECT
AREA
BASIN
OS-1 BASIN
OS-2
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Table 2-1: FCSCM Runoff Coefficients
Source: Table 3.2.2 Fort Collins Stormwater Criteria Manual, December 2018
Composite coefficients were determined utilizing Equation 5-2 found in the Fort Collins
Stormwater Criteria Manual (FCSCM) adopted in December 2018.
Where: C = Composite Runoff Coefficient
Ci = Runoff Coefficient for Specific Area (Ai), dimensionless
Ai = Area of Surface with Runoff Coefficient of Ci, acres or square feet
n = Number of different surfaces to be considered
At = Total Area over which C is applicable, acres or square feet
The composite runoff coefficients were adjusted by applying frequency adjustment factors (Cf)
for the appropriate design storm event. Composite coefficients Frequency Adjust Factors
found in Table 3.2-3 of the Fort Collins Stormwater Criteria Manual (FCSCM) adopted in
December 2018 utilized are presented in Table 2-2 below.
Hardscape or Hard Surface
Asphalt, Concrete 0.95
Rooftop 0.95
Recycled Asphalt 0.80
Gravel 0.50
Pavers 0.50
Landscape or Pervious Surface
Lawns, Sandy Soil, Flat Slope <2% 0.10
Lawns, Sandy Soil, Avg Slope 2%-7% 0.15
Lawns, Sandy Soil, Steep Slope >7% 0.20
Lawns, Clayey Soil, Flat Slope <2% 0.20
Lawns, Clayey Soil, Avg Slope 2%-7% 0.25
Lawns, Clayey Soil, Steep Slope >7% 0.35
Surface Type Runoff Coefficient (Cx)
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Table 2-2: FCSCM Frequency Adjustment Factors
Source: Table 3.2-3 Fort Collins Stormwater Criteria Manual, December 2018
The adjusted composite runoff coefficient value was determined utilizing the following
equation.
C=Cx*Cf
Maximum adjusted composite runoff coefficient value is limited to 1.00.
Imperviousness was calculated for Basin B using the impervious percent Table 4.1.3 in
FCSWM criteria. The impervious percentages as shown in Table 2-3 below.
Table 2-3: Impervious Percentages
The existing condition represents the current project site with no improvements or changes.
The proposed condition represents the project site with the proposed improvements. Basin
categories and area computations can be found in Appendix B. Tables 2-4 and 2-5 below
provide a summary of the existing and developed basin characteristics.
2, 5, 10 1.00
25 1.10
50 1.20
100 1.25
Storm Return Period (years)Frequency
Adjustment Factor (Cf)
Hardscape or Hard Surface
Asphalt, Concrete 100
Rooftop 90
Recycled Asphalt 80
Gravel 40
Pavers 40
Landscape or Pervious Surface
Playgrounds 25
Lawns, Sandy Soil 2
Lawns, Clayey Soil 2
Surface Type Percent Impervious
(%)
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Table 2-4: Existing Condition Basin Summary
Table 2-5: Developed Basin Summary
Water quantity detention is required for Garcia House: A Circle Program by SummitStone.
During a meeting about the project, the City of Fort Collins staff indicated that due to
existing conditions on site flows from Basins A and C could be released from the site
without detention. Basin A is primarily a landscaped area. Basin C contains the existing
parking lot, which currently drains to the street without detention.
Runoff from Basin B enters the StormTech system before being released to the street. The
StormTech system detention pond has been sized using the Modified FAA Method equations
found in Chapter 6 of the FCSCM. The water quantity detention required was determined to
be 4599 cubic feet or 0.106 acre-feet. Adding the water quantity detention required to the
Water Quality Volume, as required by the FCSCM, results in a detention pond total volume
of 5170 cubic feet or 0.119 acre-feet. The IDF data and detention pond calculations can be
found in Appendix B.
Basin B was further divided into four (4) sub-basins, as noted above, to evaluate flow to
structures connected to the underground detention pond. Table 2-6 below shows the
Design Point 100-Year 2-Year 100-Year
I100 Q2 Q100
(acres) (minutes) (in./hour) (in./hour)(ft3/s)(ft3/s)
A 1 0.54 11.9 0.10 0.13 2.1 7.4 0.12 0.50
B 2 0.05 5.0 0.95 1.00 2.9 10.0 0.12 0.45
2-Year
C2
Basin
Area
Rainfall Intensity Runoff
2-Year
I2
Runoff Coefficients
100-Year
C100
Basin I.D.
Time of
Concentration
100-Year 2-Year 100-Year
I100 Q2 Q100
(acres) (minutes) (in./hour) (in./hour)(ft3/s)(ft3/s)
A 1 0.11 8.6 0.34 0.42 2.4 8.4 0.09 0.38
B 2 0.41 5.0 0.90 1.00 2.9 10.0 1.04 4.03
C 3 0.06 5.0 0.74 0.92 2.9 10.0 0.12 0.51
D 4 0.02 5.0 0.20 0.25 2.9 10.0 0.01 0.05
Runoff Coefficients Rainfall Intensity Runoff
2-Year
C2
100-Year
C100
2-Year
I2
Basin I.D.
Basin
Area
Time of
ConcentrationDesign Point
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developed condition sub-basin characteristics. Basin categories and area computations can
be found in Appendix B.
Table 2-6: Developed Sub-Basin Summary
A small area, approximately 900 square feet, located south of the proposed parking lot has
been delineated as Basin D. This landscaped area, due to grades, will combine with the
off-site flow from OS1 prior to entering the storm drain which will convey it to the outfall on
McHugh Street.
The StormTech system will utilize SC-310 chambers, has a proposed volume of 5265 cubic
feet, and release at the 2-yr Historic rate of 0.12 cfs. This will be accomplished using an
orifice plate in the StormTech system outlet structure.
Table 2-7: Detention Pond Summary Table
2.5 Water Quality Capture Volume
Equations in Chapter 7 of the FCSCM were used for the calculation of Water Quality
Capture Volume (WQCV) required for Garcia House: A Circle Program by SummitStone
project and are presented below.
The Water Quality Capture Volume is calculated based on the imperviousness of the project
site and the drain time. Most of the new impervious area on Garcia House: A Circle
Program by SummitStone project site will drain to the StormTech system. The most
0.95 0.95 0.80 0.50 0.50 0.10 0.15 0.20 0.20 0.25 0.35 (acres)
B1 2,932 0 0 0 0 108 0 0 0 0 0 0.07
B2 4,564 0 0 0 0 310 0 0 0 0 0 0.11
B3 0 8,540 0 0 0 0 0 0 0 0 0 0.20
B4 649 0 0 252 0 301 0 0 0 0 0 0.03
TOTAL (acres) 0.19 0.20 0.00 0.01 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.41
Lawns, Sandy,
Slope <2%
Lawns, Sandy,
Slope 2-7%
Lawns, Sandy,
Slope >7%
Lawns,
Clayey, Slope
Lawns,
Clayey, Slope
Lawns,
Clayey, Slope
Basin I.D.
Basin Categories and Areas (SF)
Basin AreaHardscape or Hard Surface Landscape or Pervious Surface
Asphalt,
Concrete Rooftop Recycled
Asphalt Gravel Pavers
(acres) (hours) (in) (ac-ft) (cu-ft)
B 0.41 90% 12 0.323 0.013 571
WQCV
Volume 2
WQCV
VolumeBasin I.D.
Basin
Area
Percent
Impervious Drain Time WQCV1
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conservative drain time presented in the FCSCM, 12 hours, has been used in the sizing
calculations for Garcia House: A Circle Program by SummitStone.
WQCV = (0.91 3-1.19 2+0.78 ) Equation 7-1 FCSCM
Where: WQCV = Water Quality Capture Volume (watershed inches)
= Drain Time Coefficient (0.8 for a drain time of 12 hours)
= Imperviousness, %/100 (0.90 for Basin B)
For Garcia House: A Circle Program by SummitStone, the resulting WQCV is 0.323
watershed inches.
The FCSCM uses the WQCV above to find the basin storage volume based on the following
equation:
V = (WQCV/12)*A*1.2 Equation 7-2 FCSCM
Where: V = Basin Design Volume (cubic feet)
WQCV = Water Quality Capture Volume (watershed inches)
A = Area of Watershed Tributary to the Basin (square feet)
With a total tributary area of 18,559 square feet, the Basin Design Volume required is 571
cubic feet or 0.013 acre-feet.
2.6 LID Treatment
The City of Fort Collins LID ordinance requires that for 75% of all newly added or modified
impervious areas be treated by LID techniques. Runoff from a small portion of the new or
modified impervious area on the project site flows directly to McHugh Street and is therefore
not treated by the StormTech system. Table 2-8 shows how the LID requirements have
been met for this project.
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Table 2-8: LID Treatment
The isolation chamber rows in the StormTech system have been designed to meet the City
of Fort Collins criteria. Table 2-9 indicates the minimum number of isolation chambers
required is 20. Isolation chambers proposed for this StormTech system is 30. The isolation
chambers will be in 2 rows of 15, such that each row can handle runoff from approximately
75% of the site. StormTech chamber plans and details can be found in Appendix D.
Table 2-9: Water Quality Chambers
Figure 2-2 shows the location of the StormTech system.
PROJECT AREA
TOTAL NET NEW IMPERVIOUS AREA 16,221 SF
REQUIRED MINIMUM AREA TO BE TREATED BY LID
(75% OF NEW IMPERVIOUS AREA)12,166 SF
NET NEW IMPERVIOUS AREA TREATED BY LID 15,946 SF
PERCENT OF NEW IMPERVIOUS AREA TREATED BY LID 98%
75% ON-SITE TREATMENT BY LID
(cf) (cfs) (sf) (cfs) (cf) (cf) (units) (cfs)
B 571 0.52 SC-310 20.2 0.016 14.70 29.30 20 0.32
Chamber
Volume per unit
with Aggregate4
Minimum
Number of
Chambers5
Minimum
Release
Rate6
Chamber
Volume per
Unit3Basin I.D.
Required
WQCV
Volume
WQ Flow1 Chamber
Type
Chamber
Release Rate2
Chamber
Bottom
Area
(cf) (units) (cf) (cf) (units) (cfs) (cf) (cf)
62 5 294 586 30 0.32 441 879
Proposed Storage in
Chambers12
Proposed Total
WQCV Volume13
Minimum WQCV
Volume10
Modified FAA
Storage Volume
Required
Minimum FAA
Number of
Chambers8
Minimum Storage
Required in
Chambers9
Proposed
Release
Rate11
Isolation
Chamber Units
Proposed
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Figure 2-2: LID Exhibit
2.7 Maintenance Access
The drainage facilities on this site will be privately maintained.
2.8 Easements
A 10-foot-wide drainage easement will be granted to the property owner to the south to
allow for off-site conveyance through the property.
A drainage easement around the Stormtech System will be granted to the City of Fort
Collins.
3 Proposed Drainage Design Criteria
3.1 Drainage Studies
There are no available previous drainage studies for this site or the site to the south.
Storm runoff from the property to the south has been analyzed and accounted for as
part of the design for this site.
3.2 Four-Step Process
This section of the report presents the design of drainage facilities related to Garcia
House: A Circle Program by SummitStone project. The drainage design has been
explained as it pertains to the “Four-Step Process for Stormwater Quality Management”
as outlined in the FCSCM.
STORMTECH
SYSTEM
LID TREATMENT
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3.2.1 Step 1: Runoff Reduction
The first step in stormwater quality management is to reduce runoff peaks,
volumes, and pollutant loads from urbanizing areas by implementing Low Impact
Development (LID) strategies. LID practices include reducing unnecessary
impervious areas and routing runoff from impervious surfaces over permeable
areas to slow runoff and promote infiltration.
Garcia House: A Circle Program by SummitStone project includes an increase in
impervious area with the construction of the building, concrete walks and asphalt
drives. Runoff from most of the new impervious areas will be routed through a
StormTech detention system. The Isolator Row in the StormTech system acts as
a LID practice by allowing sediment to collect as stormwater infiltrates through
the cloth barrier into the StormTech detention system.
3.2.2 Step 2: Treat and Slowly Release Runoff
After reducing the runoff from a site, the second step in stormwater quality
management is to route the water quality volume through the Stormtech isolator
rows which will capture sediment before releasing it.
3.2.3 Step 3: Stabilize Drainageways
Although steps 1 and 2 help to minimize the effects of runoff on downstream
drainageways, natural drainageways are often subject to bed and bank erosion
due to increases in the frequency, rate, duration, and volume of runoff. Step 3
includes measures to prevent drainageway erosion.
There are no drainageways on Garcia House: A Circle Program by SummitStone
site. By implementing steps 1 and 2, the project site does its part to reduce
drainageway erosion downstream.
3.2.4 Step 4: Implementation of Source Controls
The final step in stormwater quality management is source control. Site specific
needs such as material storage or other site operations require consideration of
targeted source control Best Management Practices (BMPs). These BMPs are
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shown on the Erosion Control Plan and explained in the Erosion Control Report
which has been submitted to the City of Fort Collins by separate document.
3.3 BMP Selection Considerations
The following sections discuss the considerations for determining the best BMP or LID
solution to implement for the project.
3.3.1 Soils
The existing soil condition on the project site must be considered when designing
BMPs. Soils with good permeability provide opportunities for infiltration of runoff
and are well-suited for infiltration based BMPs such as dry wells, permeable
pavement, and grass swales. The soils on Garcia House: A Circle Program by
SummitStone site are in Hydrologic Soil Group B, which is defined as soils
having a moderate infiltration when thoroughly wet. For this reason, infiltration
based BMPs were considered a good option for the project site. Soil information
for the site may be found in Appendix A.
3.3.2 Watershed Size
The contributing drainage area is an important consideration for the design of
BMPs. For a small site, such as Garcia House: A Circle Program by
SummitStone, it is not feasible to design a detention pond that releases the
WQCV over a 12-hour drain time due to the small orifices that would be
required. Instead, it is recommended that small watersheds use filtering BMPs,
such as the StormTech system designed for the project site.
3.3.3 Base Flows
BMPs such as constructed wetlands ponds, retention ponds, and wetland
channels require a base flow to prevent the BMPs from becoming dry and
unable to support wetland vegetation. No base flow exists for Garcia House: A
Circle Program by SummitStone site, so no BMPs that require a base flow were
considered for the site.
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3.4 BMP Design
The StormTech chamber system utilizes infiltration to reduce the transportation of
pollutants to downstream receiving waters. The system is equipped with an “isolator
row” which consists of wrapping the row of chambers that filters the first flush of storm
runoff with fabric. This row captures the sediment which can be removed and
disposed of as part of the maintenance process.
3.5 Hydrologic Criteria
Per City of Fort Collins criteria, the Rational Formula Method was used for the
hydrologic analysis of Garcia House: A Circle Program by SummitStone project site.
The rainfall intensities (IDF Data) from the FCSCM were used for the calculation of
runoff for the 2-year and 100-year storm events. The IDF Data can be found in
Appendix B. Detention Volumes were determined utilizing the Modified FAA procedure
as described in Chapter 6 of the FCSCM.
3.6 Hydraulic Criteria
The City of Fort Collins criteria and UDFCD were utilized for different components of
the storm sewer system. Equations 9-8 (weir flow) and 9-9 (orifice flow) of the
FCSCM were used to determine inlet capacities of the combination inlets in the parking
lot and the area inlets in the courtyard area. Both grates have excess capacity as
depicted in Table 3-1.
Qi = CwLwd1.5 Equation 9-8 FCSCM
Where: Cw = Weir Discharge Coefficient
Lw = Weir Length, ft
d = Flow Depth, ft
Qi = CoAo(2gd)0.5 Equation 9-9 FCSCM
Where: Co = Orifice Discharge Coefficient
Ao = Orifice Area, ft2
d = Characteristic Depth as defined in Table 3.4.3-1, ft
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d = Characteristic Depth as defined in Table 3.4.3-1, ft
g = 32.2 ft/sec2
Table3-1: Grate Inlet Capacities
UD-Sewer software was utilized to analyze the capacities of the storm sewer lines for
the 100-year storm event. All lines were analyzed assuming that the Stormtech
chambers were at capacity. The analysis indicates that the lines on the west side (B1)
will operate with a maximum surcharge of 3 inches above the top of the pipe and the
line on the east side (B2) will have a surcharge of 8 inches, both of which are well
below the inlet grate elevations.
The underground detention pond inlet structures weir elevations were determined by the
WQCV volume requirements in conjunction with the stage-storage tables for the
Stormtech Isolator Rows. The WQCV Orifice Plate is not required as the Stormtech
Isolation chambers are sized for the 12 hour water quality volume.
The outlet structure will be equipped with a quantity detention orifice plate (restrictor
plate) as requested by the City of Fort Collins. The restrictor plate will be set at 0.06
feet above the outlet pipe invert to restrict the flow to 0.12 cfs. The restrictor plate
calculations can be found in Appendix B.
4 Variance Requests
No variance requests are anticipated with this project.
5 Erosion Control
This project complies with the City of Fort Collins Erosion Control Criteria. The complete
Stormwater Management Plan meeting all of the requirements in Chapter 4 has been
provided by separate document.
Inlet Inlet Type
Design
Flow
Flow
Depth (d)
Weir
Discharge
Coefficient
(Cw)
Grate
Length (L)
Grate
Width (W)
Weir Length
(Lw) = L+2W
Clear
Opening of
Grate (A0)
Weir
Equation
Valid for
d<1.79(A0/Lw)
Weir
Equation
Valid
Inlet
Capacity1 (Qi)
(Qi)=CwLwd^
1.5
(cfs) (feet) (feet) (feet) (feet) square feet) (cfs)
B1 Grate Inlet 0.69 0.27 3 1.91 1.41 4.73 1.02 0.39 YES 1.99
B2 Grate Inlet 1.11 0.32 3 1.91 1.41 4.73 1.02 0.39 YES 2.57
Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
18
6 Conclusions
The final drainage design for Garcia House: A Circle Program by SummitStone project, as
outlined in this Drainage Report, is in compliance with City of Fort Collins Stormwater
Criteria Manual, Master Drainage Plans, Floodplain Regulations, and/or State and Federal
Regulations. The design safely and effectively collects and conveys runoff per the applicable
criteria and mimics existing drainage patterns where possible.
7 References
City of Fort Collins Stormwater Criteria Manual adopted December 2018
City of Fort Collins Isolation Chamber calculation criteria
Advanced Drainage Systems Inc. design criteria for StormTech Chamber Systems
8 Appendices
Appendix A contains the Soil Survey Information, Floodplain Map, and Spring Creek Basin
Management Proposed Condition BMP Map.
Appendix B contains the hydrologic calculations, detention basin – volume calculations, water
quality capture volume calculations, IDF Data, StormTech isolation chamber calculations, LID
Calculations, and LID Exhibit.
Appendix C contains the hydraulic calculations for inlet sizing, storm sewer sizing, WQCV
orifice sizing, and outlet structure orifice plate sizing.
Appendix D contains the StormTech System Plans and Details
Appendix E contains the Historic and Developed Drainage Basin Plans.
Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
A
Appendix A: Existing Soil Properties
Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
B
Appendix B: Hydrologic Calculations
GARCIA HOUSE: A CIRCLE PROGRAM BY SUMMITSTONE
TABLE B 7: LID REQUIREMENTS
PROJECT AREA
TOTAL NET NEW IMPERVIOUS AREA 16,222 SF
REQUIRED MINIMUM AREA TO BE TREATED BY LID
(75% OF NEW IMPERVIOUS AREA)
12,166 SF
NET NEW IMPERVIOUS AREA TREATED BY LID 15,946 SF
PERCENT OF NEW IMPERVIOUS AREA TREATED BY LID 98%
75% ON SITE TREATMENT BY LID
10/28/2019
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GARCIA HOUSE: A CIRCLE PROGRAM BY SUMMITSTONE
TABLE B 11: DETENTION VOLUME
DETENTION VOLUME BY THE MODIFIED FAA METHOD (FORT COLLINS)
Project:
Design Point:
0.41 Acres
1.00
0.12 CFS
5 Minutes
5 9.95 1223.85 34.70 1189
6 9.31 1374.16 41.64 1333
7 8.80 1515.36 48.58 1467
8 8.38 1649.18 55.53 1594
9 8.03 1777.84 62.47 1715
10 7.72 1899.12 69.41 1830
11 7.42 2007.85 76.35 1932
12 7.16 2113.63 83.29 2030
13 6.92 2213.02 90.23 2123
14 6.71 2310.92 97.17 2214
15 6.52 2405.88 104.11 2302
16 6.30 2479.68 111.05 2369
17 6.10 2551.02 117.99 2433
18 5.92 2621.38 124.93 2496
19 5.75 2687.55 131.87 2556
20 5.60 2755.20 138.81 2616
21 5.46 2820.64 145.75 2675
22 5.32 2879.18 152.70 2726
23 5.20 2942.16 159.64 2783
24 5.09 3005.14 166.58 2839
25 4.98 3062.70 173.52 2889
26 4.87 3114.85 180.46 2934
27 4.78 3174.88 187.40 2987
28 4.69 3230.47 194.34 3036
29 4.60 3281.64 201.28 3080
30 4.52 3335.76 208.22 3128
31 4.42 3370.69 215.16 3156
32 4.33 3408.58 222.10 3186
33 4.24 3442.03 229.04 3213
34 4.16 3479.42 235.98 3243
35 4.08 3512.88 242.92 3270
36 4.01 3551.26 249.86 3301
37 3.93 3577.09 256.81 3320
38 3.87 3617.68 263.75 3354
39 3.80 3645.72 270.69 3375
40 3.74 3680.16 277.63 3403
41 3.68 3711.65 284.57 3427
42 3.62 3740.18 291.51 3449
43 3.56 3765.77 298.45 3467
44 3.51 3799.22 305.39 3494
45 3.46 3830.22 312.33 3518
46 3.41 3858.76 319.27 3539
47 3.36 3884.83 326.21 3559
48 3.31 3908.45 333.15 3575
49 3.27 3941.66 340.09 3602
50 3.23 3972.90 347.03 3626
51 3.18 3989.63 353.98 3636
52 3.14 4016.69 360.92 3656
53 3.10 4041.78 367.86 3674
54 3.07 4078.19 374.80 3703
55 3.03 4099.59 381.74 3718
56 2.99 4119.02 388.68 3730
57 2.96 4150.51 395.62 3755
58 2.92 4166.26 402.56 3764
59 2.89 4194.55 409.50 3785
60 2.86 4221.36 416.44 3805
65 2.71 4333.29 451.14 3882
70 2.59 4459.98 485.85 3974
75 2.48 4575.60 520.55 4055
80 2.38 4683.84 555.26 4129
85 2.29 4788.39 589.96 4198
90 2.21 4892.94 624.66 4268
95 2.13 4977.81 659.37 4318
100 2.06 5067.60 694.07 4374
105 2.00 5166.00 728.77 4437
110 1.94 5249.64 763.48 4486
115 1.88 5318.52 798.18 4520
120 1.84 5431.68 832.88 4599
GARCIA HOUSE: A CIRCLE PROGRAM BY SUMMITSTONE
BASIN B
Design Information (Input)
Rainfall Intensity
I (inches/hour)
Outflow Volume
Vo (Cubic Feet)
Required
Detention
Volume
Vs (Cubic Feet)
Catchment Area:
Runoff Coefficent:
Allowable Maximum Release Rate:
Time of Concentration:
Storm Duration
T (minutes)
Inflow Volume
Vi (Cubic Feet)
10/28/2019
GARCIA HOUSE: A CIRCLE PROGRAM BY SUMMITSTONE
TABLE B 12: ISOLATION CHAMBER VOLUME
Project:
Design Point:
0.41 Acres
0.90
0.32 CFS
5 Minutes
5 1.43 156.27 94.54 62
6 1.34 175.68 113.44 62
7 1.26 193.44 132.35 61
8 1.20 210.55 151.26 59
9 1.15 227.00 170.16 57
10 1.11 242.35 189.07 53
11 1.07 256.93 207.98 49
12 1.03 269.76 226.89 43
13 0.99 282.27 245.79 36
14 0.96 294.77 264.70 30
15 0.94 307.60 283.61 24
16 0.91 317.58 302.52 15
17 0.88 326.24 321.42 5
18 0.85 335.56 340.33 5
19 0.83 343.79 359.24 15
20 0.81 353.11 378.14 25
21 0.78 359.25 397.05 38
22 0.77 369.12 415.96 47
23 0.75 375.81 434.87 59
24 0.73 384.25 453.77 70
25 0.72 392.04 472.68 81
26 0.70 399.16 491.59 92
27 0.69 405.63 510.49 105
28 0.67 411.45 529.40 118
29 0.66 419.78 548.31 129
30 0.65 427.68 567.22 140
31 0.64 431.73 586.12 154
32 0.62 435.13 605.03 170
33 0.61 441.49 623.94 182
34 0.60 443.69 642.84 199
35 0.59 449.06 661.75 213
36 0.58 453.99 680.66 227
37 0.58 470.66 699.57 229
38 0.56 462.55 718.47 256
39 0.55 466.17 737.38 271
40 0.54 469.35 756.29 287
41 0.53 472.09 775.20 303
42 0.52 479.00 794.10 315
43 0.51 480.97 813.01 332
44 0.51 487.33 831.92 345
45 0.50 488.54 850.82 362
46 0.49 494.35 869.73 375
47 0.48 494.79 888.64 394
48 0.48 500.05 907.55 407
49 0.47 505.10 926.45 421
50 0.46 504.44 945.36 441
51 0.46 508.93 964.27 455
52 0.45 513.21 983.17 470
53 0.45 517.27 1002.08 485
54 0.44 521.11 1020.99 500
55 0.44 524.72 1039.90 515
56 0.43 528.12 1058.80 531
57 0.43 531.30 1077.71 546
58 0.42 534.27 1096.62 562
59 0.42 537.01 1115.52 579
60 0.41 539.53 1134.43 595
65 0.39 555.98 1228.97 673
70 0.37 560.36 1323.50 763
75 0.35 575.72 1418.04 842
80 0.33 579.01 1512.58 934
85 0.32 596.55 1607.11 1011
90 0.31 602.04 1701.65 1100
95 0.29 604.23 1796.18 1192
100 0.28 614.10 1890.72 1277
105 0.27 621.77 1985.26 1363
110 0.26 627.26 2079.79 1453
115 0.26 643.16 2174.33 1531
120 0.25 644.80 2268.86 1624
ISOLATION CHAMBER VOLUME BY THE MODIFIED FAA METHOD (FORT
COLLINS)
Time of Concentration:
Storm Duration
T (minutes)
Rainfall Intensity
I (inches/hour)
Inflow Volume
Vi (Cubic Feet)
Outflow Volume
Vo (Cubic Feet)
Required
Detention Volume
Vs (Cubic Feet)
GARCIA HOUSE: A CIRCLE PROGRAM BY SUMMITSTONE
BASIN B
Design Information (Input)
Catchment Area:
Runoff Coefficent:
Release Rate:
10/28/2019
Area must be at least value listed to right -sf Min. Area -
(inches) (cubic feet) (cubic feet) (cubic feet) (cubic feet) (cubic feet) (feet)
712 sf min. area
GARCIA HOUSE: A CIRCLE PROGRAM BY SUMMITSTONE
TABLE B-13 QUANTITY DETENTION ORIFICE PLATE SIZING
Outlet Structure Weir
Circular Orifice
Q = C0A(2gh)1/2
Maximim Orifice Discharge (Q)0.12 cfs
C0 0.61
g 32.2 ft/sec^2
Orifice Diameter 1.75 inches
Cross Sectional Area (A) 0.016703
ft2
Upstream Water Surface Elevation 4960.41 ft
Orifice Invert Elevation 4958.11 ft
Orifice Centroid Elevation 4958.183 ft
Effective Head (h)2.227083 ft
Q 0.12 cfs
12/17/2019
Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
C
Appendix C: Hydraulic Calculations
MANNING'S EQUATION for OPEN CHANNEL FLOW
Project: Garcia House Location: Basin B1
By: EJJ Date: 10/25/2019
Chk By: EJJ Date: 10/25/2019 version 12-2004
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 12
b (btm width, ft)= 0
Q = (1.486/n)ARh
2/3S1/2 d (depth, ft)= 0.27
R = A/P S (slope, ft/ft) 0.005
A = cross sectional area n low =0.016
P= wetted perimeter n high =0.016
S = slope of channel V = (1.49/n)Rh
2/3S1/2
n = Manning's roughness coefficient Q = V x A
Depth, ft Area, sf
Wetted
Perimeter, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.27 0.44 3.52 0.12 1.63484474 0.71508 1.634845 0.71508 T = 3.24
Dm = 0.135
Sc low = 0.0081 Sc high = 0.0081
sc =critical slope ft / ft
T = top width of the stream .7 Sc 1.3 Sc .7 Sc 1.3 Sc
dm =a/T = mean depth of flow 0.0057 0.0106 0.0057 0.0106
Created by: Mike O'Shea
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
MANNING'S EQUATION for OPEN CHANNEL FLOW
Project: Garcia House Location: Basin B2
By: EJJ Date: 10/25/2019
Chk By: EJJ Date: 10/25/2019 version 12-2004
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 12
b (btm width, ft)= 0
Q = (1.486/n)ARh
2/3S1/2 d (depth, ft)= 0.32
R = A/P S (slope, ft/ft) 0.005
A = cross sectional area n low =0.016
P= wetted perimeter n high =0.016
S = slope of channel V = (1.49/n)Rh
2/3S1/2
n = Manning's roughness coefficient Q = V x A
Depth, ft Area, sf
Wetted
Perimeter, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.32 0.61 4.17 0.15 1.83092175 1.12492 1.830922 1.12492 T = 3.84
Dm = 0.160
Sc low = 0.0077 Sc high = 0.0077
sc =critical slope ft / ft
T = top width of the stream .7 Sc 1.3 Sc .7 Sc 1.3 Sc
dm =a/T = mean depth of flow 0.0054 0.0100 0.0054 0.0100
Created by: Mike O'Shea
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Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
D
Appendix D: StormTech System
Plans and Details
OU
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Garcia House: A Circle Program by SummitStone Final Drainage Report December 2019
E
Appendix E: Historic and Developed
Drainage Basin Plans
DATE DESCRIPTION
REVISIONS
OF
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2204 HOFFMAN DRIVE
LOVELAND, COLORADO 80538
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