HomeMy WebLinkAboutSTADIUM APARTMENTS (FORMERLY LAKE STREET APARTMENTS) - FDP - FDP160037 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT
Stadium Apartments
Fort Collins, Colorado
September 19, 2016
Prepared for:
Student Housing CSU LLC
2607 Monroe Street
Madison, WI 53711
Prepared by:
301 North Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 1232-001
P This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
September 19, 2016
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
Stadium Apartments
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies the Preliminary Development Review submittal for the
proposed Stadium Apartments. Comments from the Preliminary Development Review Letter dated
April 15, 2016 have been addressed. Written responses thereto can be found in the
comprehensive response to comments letter on file with Current Planning.
This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM),
and serves to document the stormwater impacts associated with the proposed Stadium Apartments
project. We understand that review by the City 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.
Nicholas W. Haws, PE Cody Snowdon
Project Manager Project Engineer
Stadium Apartments
Final Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ....................................................................................................................................... 1
B. Description of Property ................................................................................................................ 2
C. Floodplain .................................................................................................................................... 3
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 5
A. Major Basin Description ............................................................................................................... 5
B. Sub-Basin Description .................................................................................................................. 5
III. DRAINAGE DESIGN CRITERIA ................................................................................... 5
A. Regulations .................................................................................................................................. 5
B. Four Step Process ........................................................................................................................ 5
C. Development Criteria Reference and Constraints ......................................................................... 6
D. Hydrological Criteria .................................................................................................................... 7
E. Hydraulic Criteria ......................................................................................................................... 7
F. Floodplain Regulations Compliance .............................................................................................. 7
G. Modifications of Criteria .............................................................................................................. 7
IV. DRAINAGE FACILITY DESIGN .................................................................................... 7
A. General Concept .......................................................................................................................... 7
B. Specific Details ............................................................................................................................. 9
V. CONCLUSIONS ...................................................................................................... 12
A. Compliance with Standards ........................................................................................................ 12
B. Drainage Concept ...................................................................................................................... 12
References ....................................................................................................................... 13
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers (For Future Use)
B.2 – Inlets (For Future Use)
B.3 – Detention Facilities (For Future Use)
APPENDIX C – Water Quality Design Computations
APPENDIX D – Erosion Control Report
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Final Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2 – Proposed Site Plan ............................................................................................... 3
Figure 3 – Existing FEMA Floodplains .................................................................................... 4
Figure 4 – Existing City Floodplains ....................................................................................... 4
MAP POCKET:
C8.00 - Drainage Exhibit
C8.01 – Historic Drainage Exhibit
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Final Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. Stadium Apartments project is located in the southwest quarter of Section 14,
Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins,
County of Larimer, State of Colorado.
3. The project site is located south of Lake Street and is composed of two properties,
821 and 801 West Lake Street.
4. Currently the existing lots does not have any stormwater or water quality facilities.
The western property consisted of Beebe Christian School and is composed of an
existing building, parking lot and associated walks. The eastern property consist of a
single family residence with a gravel drive and associated walks and accessory
buildings. The project site is composed of 26% imperviousness. The existing site all
drains from the southwest corner of the property to the northeast corner and into West
Lake Street.
5. The project is currently bordered to the south by single family residences, west by
Plymouth Congregational Church, north by West Lake Street and east by Blue Ridge
Apartments.
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Final Drainage Report 2
B. Description of Property
1. Stadium Apartments is approximately 2.45 net acres.
Figure 1 – Aerial Photograph
2. Stadium Apartments consists of two properties with two existing structures and
multiple out buildings. The western lot consist of Beebe Christian School with a
parking lot and associated sidewalks. The eastern lot consist of a single family
residence with a gravel driveway, multiple accessory buildings and associated
sidewalks. There is not off-site drainage entering the existing properties. All runoff
generated from the project drains from the southwest corner of the site to the
northeast corner and is discharged into West Lake Street.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey, 100 percent of the site consists of Altvan-
Satanta loam, which falls into Hydrologic Soil Groups B.
4. The proposed development will include the demolition of the existing structures,
parking lot, gravel drive and associated sidewalks. The proposed project will include
one large multi-family building, an exterior parking lots and associated drive aisle and
sidewalks. The exterior parking lot is planned to be composed of StormTech chambers
underneath the paving. The section of drive constructed on top of the StormTech
Chambers will act as a portion of the project’s water quality and detention facility.
Surrounding green space will act as the remaining water quality and detention facility.
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Final Drainage Report 3
Figure 2– Proposed Site Plan
5. No irrigation facilities or major drainageways are within the property limits.
6. The project site is within the High Density Mixed-Use Neighborhood District (H-M-N)
Zoning District. The proposed use is permitted within the zone district.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
2. The FEMA Panel 0801010979H illustrates the proximity of the project site to the
nearest FEMA delineated regulatory floodplain. It is noted that the vertical datum
utilized for site survey work is the City of Fort Collins Benchmark #29-92
Elevation = 5025.67 (NAVD 88)
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Final Drainage Report 4
Figure 3 – Existing FEMA Floodplains
Figure 4 – Existing City Floodplains
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Final Drainage Report 5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Stadium Apartments is located within the Old Town Basin, which is located primarily
in Old Town Fort Collins.
B. Sub-Basin Description
1. The property historically drains from the southwest corner of the western lot to the
northeast corner of the eastern lot. Stormwater is routed via overland flow across the
existing lots. The project only consists of one basin; Basin H1. Stormwater is
historically discharged directly into West Lake Street (1.75 cfs for the 2-year storm
and 8.15 cfs for the 100-year event). A more detailed description of the projects
proposed drainage patterns follows in Section IV.A.4., below.
2. No drainage is routed onto the property from the surrounding properties.
A full-size copy of the Historic and Proposed Drainage Exhibit can be found in the
Map Pocket at the end of this report.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the Stadium
Apartments project.
B. Four Step Process
The overall stormwater management strategy employed with the Stadium Apartments
project 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 by implementing multiple Low-Impact Development (LID) strategies including:
Selecting a site that has been previously developed and currently consist of a School
building and single family residence, an asphalt parking lot, gravel access drive and
associated sidewalks.
Providing vegetated open areas along the north, south and east portion of the site to
reduce the overall impervious area and to minimize directly connected impervious
areas (MDCIA).
Routing flows, to the extent feasible, through drain rock both within the underground
detention section to increase time of concentration, promote infiltration and provide
initial water quality.
Routing runoff through the drain rock within the underground detention area to
increase time of concentration, promote infiltration and provide water quality.
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Final Drainage Report 6
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release
The efforts taken in Step 1 will facilitate the reduction of runoff; however, this
development will still generate stormwater runoff that will require additional BMPs and
water quality. Stormwater generated from the southeast corner of property and the
courtyard located within the center area of the building will be routed through an extended
detention pond for water quality. Stormwater generated from the roof is routed directly
into isolator rows located in the underground detention sections and drains through the
drain rock surrounding the chambers. Stormwater generated from the majority of the
parking area will be routed via overland flow to an area inlet located south of the parking
area. The stormwater will then be routed directly into isolator rows located in the
underground detention sections and drains through the drain rock surrounding the
chambers. Stormwater generated from the area to the north of the building will be routed
through an extended detention pond for water quality. The areas running off-site to the
west and the east only consist of landscape area and will be routed across landscape
before leaving the site.
Step 3 – Stabilize Drainageways
As stated in Section I.B.5, above, there are no major drainageways in or near the subject
site. While this step may not seem applicable to Stadium Apartments, the proposed
project indirectly helps achieve stabilized drainageways nonetheless. Once again, site
selection has a positive effect on stream stabilization. By repurposing an already
developed, under-utilized site with existing stormwater infrastructure, combined with LID,
the likelihood of bed and bank erosion is greatly reduced. Furthermore, this project will
pay one-time stormwater development fees, as well as 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 and is not
applicable for this project.
C. Development Criteria Reference and Constraints
1. There are no known drainage studies for the existing properties.
2. There are no known drainage studies for any adjacent properties that will have any
effect on the Stadium Apartments project.
3. The subject property is essentially an "in-fill" development project as the property is
surrounded by currently developed properties. As such, several constraints have been
identified during the course of this analysis that will impact the proposed drainage
system including:
Existing elevations along the north property lines adjacent to the West Lake Street
will be maintained. Existing elevations along the south and west will also be
maintained. Areas along the eastern property line will be raised through use of a
landscape wall.
Existing vegetation along a portion of the east and west sides of the subject
property will be preserved.
As previously mentioned, overall drainage patterns of the existing site will be
maintained.
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Final Drainage Report 7
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations
associated with this development. Tabulated data contained in Table RA-7 has been
utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. The Rational Formula-based Modified Federal Aviation Administration (FAA)
procedure has been utilized for detention storage calculations.
4. Three separate design storms have been utilized to address distinct drainage
scenarios. A fourth design storm has also been computed for comparison purposes.
The first design storm considered is the 80th percentile rain event, which has been
employed to design the project’s water quality features. The second event analyzed is
the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third
event considered is the “Major Storm,” which has a 100-year recurrence interval.
The fourth storm computed, for comparison purposes only, is the 10-year event.
5. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
E. Hydraulic Criteria
1. As previously noted, the subject property historically drains into West Lake Street.
The majority of the site drains stormwater via overland flow.
2. All drainage facilities proposed with the Stadium Apartments project are designed in
accordance with criteria outlined in the FCSCM and/or the Urban Drainage and Flood
Control District’s (UDFCD) Urban Storm Drainage Criteria Manual.
3. As stated in Section I.C.1, above, the subject property is not located within any
regulatory floodplain.
4. The Stadium Apartments project does not propose to modify any natural
drainageways.
F. Floodplain Regulations Compliance
1. As previously mentioned, all structures are located outside of any FEMA 100-year or
City floodplain, and thus are not subject to any floodplain regulations.
G. Modifications of Criteria
1. The proposed Stadium Apartments development is not requesting any modification at
this time.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the Stadium Apartments drainage design are to maintain
existing drainage patterns and ensure no adverse impacts to any adjacent properties.
2. As previously mentioned, there are no off-site flows draining onto the existing
property.
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Final Drainage Report 8
3. A list of tables and figures used within this report can be found in the Table of
Contents at the front of the document. The tables and figures are located within the
sections to which the content best applies.
4. The Stadium Apartments project is composed of five major drainage basins,
designated as Basins A, B, C, D and OS. The drainage patterns for each major basin
are further described below.
Basin A
Basin A is further subdivided into two (2) sub-basins, designated as Basins A1 and
A2. Sub-basin A1 is composed primarily of the area located southeast of the building
and consists of landscape surfacing. Stormwater generated from this sub-basin is
routed via overland and swale flow and discharges directly into Pond A. Sub-basin A2
is composed entirely of the courtyard internal to the building and consists of some
landscape surfacing, but predominantly hardscape. Stormwater generated from this
sub-basin is routed via overland flow within the courtyard and discharge through a
pipe internal to the building and into Pond A.
Basin B
Basin B is further subdivided into four (4) sub-basins, designated as Basins B1, B2,
B3 and B4. Sub-basin B1 is composed primarily of the parking area located south of
the building and consists of some landscape surfacing. Stormwater generated from
this sub-basin is routed via overland and gutter flow and discharges through curb cuts
before being intercepted by an area inlet and routed into Underground Detention Pond
B. Sub-basin B2 consists entirely of roof surface. Stormwater generated from this
sub-basin is routed internal to the building through pipe flow and discharged directly
into an isolator row within Underground Pond B. Sub-basin B3 is composed primarily
of the parking area located southwest of the building and consists of some landscape
surfacing, but predominantly hardscape. Stormwater generated from this sub-basin is
routed via overland and gutter flow and discharges through sumped inlet directly into
Underground Pond B. Sub-basin B4 consists entirely of roof surface. Stormwater
generated from this sub-basin is routed internal to the building through pipe flow and
discharged directly into an isolator row within Underground Pond B.
Basin C
Basin C is further subdivided into two (2) sub-basins, designated as Basins C1 and
C2. Sub-basin C1 is composed primarily of the area located north of the building and
consists primarily of landscape surfacing with some hardscape surfaces. Stormwater
generated from this sub-basin is routed via overland and swale flow and discharges
directly into the Underground Pond C. Sub-basin C2 is composed of a small drive
area located towards the northwest corner of the building and consists primarily of
hardscape. Stormwater generated from this sub-basin is routed via overland flow and
is intercepted by a sidewalk culvert and discharged directly into Pond C.
Basin D
Basin D1 is composed of the drive area located northwest of the building and consists
primarily of hardscape. Stormwater generated from this sub-basin is routed via
overland flow and is intercepted by a sumped inlet and discharged directly into
Underground Pond D.
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Final Drainage Report 9
Basin OS
Basin OS is further subdivided into three (3) sub-basins, designated as Basins OS1,
OS2 and OS3. Sub-basin OS1 is composed primarily of the area located northeast of
the building and consists of landscape surfacing. Stormwater generated from this sub-
basin is routed via overland flow and discharges undetained into West Lake Street.
Sub-basin OS2 is composed of a small portion of the drive entrance and consists
primarily of hardscape. Stormwater generated from this sub-basin is routed via
overland flow and discharges undetained into West Lake Street. Sub-basin OS3 is
composed primarily of the area west of the western parking area and consists of
landscape surfacing. Stormwater generated from this sub-basin is routed via overland
flow and discharges undetained into the Plymouth Congregational Church’s parking lot
and ultimately discharging into West Lake Street.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
B. Specific Details
1. The main drainage problem associated with this project site is the deficiency of water
quality present within the existing site. Currently the entire site drains overland and
discharges directly into the West Lake Street without water quality. The proposed site
will mitigate this issue by instituting the following water quality devices:
All of the runoff generated from the proposed building roof (Basin B3) will be
routed into the drain rock surrounding the underground detention.
The runoff generated from the majority of the proposed drive aisle and parking
(Basins B and D) will be routed through an isolator row within the underground
detention area. The remaining runoff (Basins A & C) will be routed to extended
detention ponds.
2. The release rate for the undeveloped land (pre-development) was established by
calculating the 2-year peak runoff rate for the entire project area and excluding all
portions of the proposed project that release undetained (Sub-basins OS1, OS2 and
OS3). The overall 2-year peak runoff rate was calculated at 1.75 cfs, resulting in a
maximum release rate of 1.06 cfs from Basin A, B, C and D. This release rate was
utilized in the FAA procedure detention storage computations (Refer to Appendix B for
these calculations).
3. Detention Pond Calculations
Pond A
The FAA method was used to size the on-site ponds for quantity detention.
Calculations for Pond A, based on the characteristics of Basin A and an adjusted
release rate of 0.36 cfs, indicate a detention volume of 2,015 cu. ft. This does not
included any Water Quality Capture Volume (WQCV) of 255 cu. ft., resulting in an
overall detention volume of 2,270 cu. ft. Water quality will be treated through
extended detention.
Pond B
Calculations for Pond B, based on the characteristics of Basin B and an adjusted
release rate of 0.30 cfs, indicate a detention volume of 20,281 cu. ft. This volume
includes the 12-hour release Water Quality Capture Volume (WQCV) calculated for
Stadium Apartments
Final Drainage Report 10
this basin (1,548 cu. ft.). During a Water Quality storm event, the Water Quality
Capture Volume will be routed directly into an isolator row. The isolator rows were
sized to capture either the 12-hour release Water Quality Capture Volume (WQCV)
within the chambers and the surrounding aggregate or the volume required to detain
the Water Quality storm event only within the chambers, whichever is greater.
Pond C
Calculations for Pond C, based on the characteristics of Basin C and an adjusted
release rate of 0.20 cfs, indicate a detention volume of 697 cu. ft. This does not
included any Water Quality Capture Volume (WQCV) of 147 cu. ft., resulting in an
overall detention volume of 824 cu. ft.
Pond D
Calculations for Pond D, based on the characteristics of Basin D and an adjusted
release rate of 0.20 cfs, indicate a detention volume of 991 cu. ft. This volume
includes the 12-hour release Water Quality Capture Volume (WQCV) calculated for
this basin (121 cu. ft.). During a Water Quality storm event, the Water Quality
Capture Volume will be routed directly into an isolator row. The isolator rows were
sized to capture either the 12-hour release Water Quality Capture Volume (WQCV)
within the chambers and the surrounding aggregate or the volume required to detain
the Water Quality storm event only within the chambers, whichever is greater.
4. Detention Pond Results
Pond A
The total storage available within Pond A is 2,486 cu. ft at a top of pond elevation of
5028.8 feet. The WQCV is achieved at a water surface elevation of 5027.6 feet, the
100-year detention volume is achieved at a water surface elevation of 5028.63 feet
and the overall detention volume is achieved at a high water surface elevation of
5028.72 feet. There is a proposed landscape wall with a top of wall elevation of
5029.34 located along the eastern property line to allow for additional freeboard.
Pond B
The storage volume available within StormTech Vault Structure within Pond B is
20,297 cu. ft. This includes the volume stored in the aggregate surround the
chambers. The achieve water quality, a total of 24 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 1,598 cu. ft., while the volume achieved within
only the chambers of the isolator row is 1,102 cu. ft.
Pond C
The total storage available within Pond C is 984 cu. ft at a top of pond elevation of
5026.4 feet. The WQCV is achieved at a water surface elevation of 5025.78 feet,
the 100-year detention volume is achieved at a water surface elevation of 5026.25
feet and the overall detention volume is achieved at a high water surface elevation of
5026.32 feet.
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Final Drainage Report 11
Pond D
The storage volume available within StormTech Vault Structure within Pond D is 992
cu. ft. This includes the volume stored in the aggregate surround the chambers. The
achieve water quality, a total of 5 chambers are proposed to be wrapped and
installed as isolator rows. The water quality volume achieved within isolator rows
(aggregate included) is 147 cu. ft., while the volume achieved within only the
chambers of the isolator row is 44 cu. ft.
5. Pond A was designed to overtop the pond in the northeast corner. In the case that the
outlet structure should clog, stormwater would overtop and be routed north along the
existing concrete wall/fence bordering the project site to the east. This stormwater
will ultimately be routed and discharged into W. Lake Street. In the case that the
area inlet within Sub-basin B4 should clog or backwatering should occur, stormwater
would overtop from Sub-basin B1 into Sub-basin B2. The excess stormwater from
this basin would continue to overtop and pass through Sub-Basins B2, D1, C2, and
OS2 before it discharges directly into W. Lake Street. In the case that the curb inlet
within Sub-basin B2 should clog or backwatering should occur, stormwater would
overtop from Sub-basin B2 into Sub-basin D1. The excess stormwater from this basin
would continue to overtop and pass through Sub-Basins C2, and OS2 before it
discharges directly into W. Lake Street. Pond C was designed to overtop the pond in
the northeast corner. In the case that the outlet structure should clog, stormwater
would overtop and discharged directly into W. Lake Street. In the case that the curb
inlet within Sub-basin D1 should clog, stormwater would overtop from Sub-basin D1
into Sub-basin C2. The excess stormwater from this basin would continue to overtop
and pass through Sub-Basins OS2 before it discharges directly into W. Lake Street.
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Final Drainage Report 12
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the Stadium Apartments project complies with the
City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with the Stadium Apartments project complies with the
City of Fort Collins’ Master Drainage Plan for the Old Town Basin.
3. There are no regulatory floodplains associated with the Stadium Apartments
development.
4. The drainage plan and stormwater management measures proposed with the Stadium
Apartments development are compliant with all applicable State and Federal
regulations governing stormwater discharge.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit potential damage
associated with its stormwater runoff. Stadium Apartments will detain for the pervious
area converted to impervious areas by releasing at the 2-year existing rate during the
developed100-year storm.
2. The proposed Stadium Apartments development will not impact the Master Drainage
Plan recommendations for the Old Town major drainage basin.
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Final Drainage Report 13
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, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Lake Street Apartments
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: C. Snowdon
Asphalt ……....……………...……….....…...……………….………………………………….. 0.95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….. 0.50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
H1 106750 2.45 0.21 0.12 0.34 0.06 1.72 0.38 0.38 0.47 26%
HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Notes
September 19, 2016
10-year Cf = 1.00
**Soil Classification of site is Sandy Loam**
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
Page 1 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Hist-C-Values
Overland Flow, Time of Concentration:
Project: Lake Street Apartments
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
Rational Method Equation: Project: Lake Street Apartments
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
h1 H1 2.45 15 15 13 0.38 0.38 0.47 1.90 3.24 7.04 1.75 3.00 8.15
HISTORIC RUNOFF COMPUTATIONS
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
C. Snowdon
September 19, 2016
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C2 C
10 C100
Q = C f ( C )( i )( A )
Page 3 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Hist-Direct-Runoff
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Lake Street Apartments
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt ……....……………...……….....…...……………….………………………………….0.. 95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….0.. 50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
A1 6337 0.145 0.000 0.017 0.000 0.000 0.000 0.129 0.24 0.24 0.30 10%
A2 7708 0.177 0.000 0.177 0.000 0.000 0.000 0.000 0.95 0.95 1.00 90%
B1 19564 0.449 0.220 0.037 0.000 0.000 0.000 0.192 0.61 0.61 0.76 56%
B2 18374 0.422 0.000 0.000 0.422 0.000 0.000 0.000 0.95 0.95 1.00 90%
B3 8193 0.188 0.132 0.021 0.000 0.000 0.000 0.036 0.80 0.80 1.00 80%
B4 24252 0.557 0.000 0.000 0.557 0.000 0.000 0.000 0.95 0.95 1.00 90%
C1 4730 0.109 0.000 0.023 0.000 0.000 0.000 0.086 0.32 0.32 0.40 19%
Overland Flow, Time of Concentration:
Project: Lake Street Apartments
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = T
i + Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Rational Method Equation: Project: Lake Street Apartments
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
a1 A1 0.15 6 6 6 0.24 0.24 0.30 2.76 4.72 9.63 0.10 0.17 0.43
a2 A2 0.18 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.48 0.82 1.76
b1 B1 0.45 5 5 5 0.61 0.61 0.76 2.85 4.87 9.95 0.78 1.33 3.39
b2 B2 0.42 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.14 1.95 4.20
b3 B3 0.19 5 5 5 0.80 0.80 1.00 2.85 4.87 9.95 0.43 0.73 1.87
b4 B4 0.56 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.51 2.58 5.54
c1 C1 0.11 5 5 5 0.32 0.32 0.40 2.85 4.87 9.95 0.10 0.17 0.43
c2 C2 0.05 5 5 5 0.88 0.88 1.00 2.85 4.87 9.95 0.13 0.22 0.51
d1 D1 0.14 5 5 5 0.76 0.76 0.96 2.85 4.87 9.95 0.30 0.51 1.29
os1 OS1 0.15 5 5 5 0.24 0.24 0.29 2.85 4.87 9.95 0.10 0.18 0.45
os2 OS2 0.02 5 5 5 0.58 0.58 0.73 2.85 4.87 9.95 0.04 0.07 0.17
os3 OS3 0.04 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.02 0.03 0.07
DEVELOPED RUNOFF COMPUTATIONS
C100 Notes
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
C. Snowdon
September 19, 2016
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
Q = C f ( C )( i )( A )
Page 6 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Direct-Runoff
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Lake Street Apartments
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt ……....……………...……….....…...……………….………………………………….. 0.95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….. 0.50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf
= 1.00 100-year Cf = 1.25
Design Point Basin IDs
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
a1 A1-A2 14045 0.322 0.000 0.194 0.000 0.000 0.000 0.129 0.63 0.63 0.79 54%
b1 B1-B2 37938 0.871 0.220 0.037 0.422 0.000 0.000 0.192 0.77 0.77 0.97 73%
b3 B3-B4 32445 0.745 0.132 0.021 0.557 0.000 0.000 0.192 0.94 0.94 1.00 87%
b1 B1-B4 70383 1.616 0.352 0.058 0.979 0.000 0.000 0.228 0.84 0.84 1.00 79%
c1 C1 & C2 6947 0.159 0.029 0.040 0.000 0.000 0.000 0.121 0.53 0.53 0.66 41%
COMBINED DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
September 19, 2016
Overland Flow, Time of Concentration:
Project: Lake Street Apartments
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = T
i + Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Rational Method Equation: Project: Lake Street Apartments
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
a1 A1-A2 0.32 6 6 6 0.63 0.63 0.79 2.76 4.72 9.63 0.6 1.0 2.4
b1 B1-B2 0.87 5 5 5 0.77 0.77 0.97 2.85 4.87 9.95 1.9 3.3 8.4
b3 B3-B4 0.74 5 5 5 0.94 0.94 1.00 2.85 4.87 9.95 2.0 3.4 7.4
b1 B1-B4 1.62 5 5 5 0.84 0.84 1.00 2.85 4.87 9.95 3.9 6.6 16.1
c1 C1 & C2 0.16 5 5 5 0.53 0.53 0.66 2.85 4.87 9.95 0.2 0.4 1.0
COMBINED DEVELOPED RUNOFF COMPUTATIONS
C. Snowdon
September 19, 2016
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C2 C10 C100
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Q = C f ( C )( i )( A )
Page 9 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Comb-Direct-Runoff
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
a1 A1 0.145 0.24 0.30 6.0 5.6 0.10 0.43
a2 A2 0.177 0.95 1.00 5.0 5.0 0.48 1.76
b1 B1 0.449 0.61 0.76 5.2 5.0 0.78 3.39
b2 B2 0.422 0.95 1.00 5.0 5.0 1.14 4.20
b3 B3 0.188 0.80 1.00 5.0 5.0 0.43 1.87
b4 B4 0.557 0.95 1.00 5.0 5.0 1.51 5.54
c1 C1 0.109 0.32 0.40 5.0 5.0 0.10 0.43
c2 C2 0.051 0.88 1.00 5.0 5.0 0.13 0.51
d1 D1 0.136 0.76 0.96 5.0 5.0 0.30 1.29
os1 OS1 0.154 0.24 0.29 5.0 5.0 0.10 0.45
os2 OS2 0.024 0.58 0.73 5.0 5.0 0.04 0.17
os3 OS3 0.039 0.15 0.19 5.0 5.0 0.02 0.07
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
h1 H1 2.451 0.38 0.47 14.5 13.0 1.75 8.15
Page 10 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\SUMMARY-TABLE
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers
B.2 – Inlets
B.3 – Detention Facilities
APPENDIX B.1
STORM SEWERS (FOR FUTURE USE)
APPENDIX B.2
INLETS (FOR FUTURE USE)
APPENDIX B.3
DETENTION FACILITIES
Pond No :
a1
100-yr
0.79
6.00 min 2015 ft3
0.32 acres 0.046 ac-ft
Max Release Rate = 0.36 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 760 1.00 0.36 108 652
10 7.720 1180 0.80 0.29 173 1007
15 6.520 1495 0.70 0.25 227 1268
20 5.600 1712 0.65 0.23 281 1431
25 4.980 1903 0.62 0.22 335 1568
30 4.520 2072 0.60 0.22 389 1684
35 4.080 2182 0.59 0.21 443 1740
40 3.740 2286 0.58 0.21 497 1790
45 3.460 2380 0.57 0.20 551 1829
50 3.230 2468 0.56 0.20 605 1863
55 3.030 2547 0.55 0.20 659 1888
60 2.860 2623 0.55 0.20 713 1910
65 2.720 2702 0.55 0.20 767 1935
70 2.590 2771 0.54 0.20 821 1950
75 2.480 2843 0.54 0.19 875 1968
80 2.380 2910 0.54 0.19 929 1981
85 2.290 2975 0.54 0.19 983 1992
90 2.210 3040 0.53 0.19 1037 2003
95 2.130 3093 0.53 0.19 1091 2002
100 2.060 3148 0.53 0.19 1145 2004
105 2.000 3209 0.53 0.19 1199 2011
110 1.940 3261 0.53 0.19 1253 2009
115 1.890 3322 0.53 0.19 1307 2015
120 1.840 3375 0.53 0.19 1361 2014
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Invert Elevation
Water Quality Volume
100-yr Detention Volume
Total Pond Volume
Min Sc
D = Depth between contours (ft.)
A1 = Surface Area lower contour (ft2) t
A2 = Surface Area upper contour (ft2) Area/Row
No. of Rows
5026.80 0.18 0.00 0.00 0.00 0.0000
5027.00 76.37 0.20 5.35 5.35 0.0001
5027.20 238.22 0.20 29.96 35.32 0.0008
5027.40 439.08 0.20 66.71 102.03 0.0023
5027.80 1128.04 0.40 302.79 404.82 0.0093 WQCV
5028.00 1558.80 0.20 267.53 672.34 0.0154
5028.20 1943.94 0.20 349.57 1021.91 0.0235
5028.40 2290.48 0.20 422.97 1444.88 0.0332
5028.60 2606.17 0.20 489.33 1934.20 0.0444
5028.80 2911.56 0.20 551.49 2485.69 0.0571 Total Vol
Elevation Depth Volume
WQCV 5027.60 0.80 0.0058
100-yr Detention 5028.63 1.83 0.0463
Overall Detention 5028.72 1.92 0.0521
Total Outlet
Area 0.10 sq. in.
Detention Pond A Volume
Elevation
(ft)
Surface
Area (ft2)
Incremental
Depth (ft)
Incremental
Vol. (ft3)
Total Vol.
(ft3)
Total Vol.
(ac-ft)
n
1/4
0.05
Required Area
Per Row 0.031 sq-in
2
Detention Pond A
5026.80 ft
0.0058 ac-ft
0.0463 ac-ft Circular Perforation Sizing
1
0.0521 ac-ft Dia (in.)
Student Housing CSU, LLC
Lake Street Apartments September 19, 2016
1232-001 C. Snowdon
( )
3
V D * A 1 A 2 A 1 * A 2
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = 0.34 cfs
C = 0.65
Q = Release Rate (cfs) Eh = 5028.72 ft
C = Discharge Coefficients (unitless) Ei = 5026.80 ft
Aa = Area Allowed of Opening (ft2) Ec = 5026.92 ft Circular
g = Gravity (32.2 ft/s2) Ec = 5026.89 ft Rectangular
Eh = High Water Surface Elevation (ft)
Ei = Elevation of Outlet Invert (ft) 0.047020725 ft2
Ec = Elevation of Outlet Centroid (ft) 6.770984 in2
Orifice Size (in.) 2 -15/16 in.
Area (in2) 6.72 sq-in
Q 0.33 cfs
Orifice Height (in.) 2 - 1/4 in.
Orifice Width (in.) 3 in.
Area (in2) 6.72 sq-in
Q 0.33 cfs
September 19, 2016
1232-001 C. Snowdon
Student Housing CSU, LLC
Detention Pond A
Aa =
Circular Orifice
100-Year Orifice
Rectangular Orifice
100-Year Orifice
Lake Street Apartments
Detention Pond A 0.006 5027.60 0.0463 0.0521 5028.72 5028.80
Required Water
Quality Storage (ac-
ft)
Water Quality
Surface
Pond ID Elevation (ft)
High Water
Surface Elevation
(ft)
Top of Pond
Elevation (ft)
Total Detention
Volume (ac-ft)
Required 100-year
Detention Volume
(ac-ft)
Pond No :
b1
100-yr
1.00
5.00 min 20281 ft3
1.62 acres 0.466 ac-ft
Max Release Rate = 0.30 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 4823 1.00 0.30 90 4733
10 7.720 7484 0.75 0.23 135 7349
15 6.520 9481 0.67 0.20 180 9301
20 5.600 10858 0.63 0.19 225 10633
25 4.980 12070 0.60 0.18 270 11800
30 4.520 13146 0.58 0.18 315 12831
35 4.080 13844 0.57 0.17 360 13484
40 3.740 14503 0.56 0.17 405 14098
45 3.460 15095 0.56 0.17 450 14645
50 3.230 15657 0.55 0.17 495 15162
55 3.030 16156 0.55 0.16 540 15616
60 2.860 16636 0.54 0.16 585 16051
65 2.720 17140 0.54 0.16 630 16510
70 2.590 17576 0.54 0.16 675 16901
75 2.480 18032 0.53 0.16 720 17312
80 2.380 18459 0.53 0.16 765 17694
85 2.290 18871 0.53 0.16 810 18061
90 2.210 19283 0.53 0.16 855 18428
95 2.130 19617 0.53 0.16 900 18717
100 2.060 19971 0.53 0.16 945 19026
105 2.000 20359 0.52 0.16 990 19369
110 1.940 20688 0.52 0.16 1035 19653
115 1.890 21071 0.52 0.16 1080 19991
120 1.840 21406 0.52 0.16 1125 20281
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1232-001
Lake Street Apartments
Project Number :
Project Name :
Pond B
A =
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = 0.30 cfs
C = 0.65
Q = Release Rate (cfs) Eh = 5028.99 ft
C = Discharge Coefficients (unitless) Ei = 5025.49 ft
Aa = Area Allowed of Opening (ft2) Ec = 5025.59 ft Circular
g = Gravity (32.2 ft/s2) Ec = 5025.62 ft Rectangular
Eh = High Water Surface Elevation (ft)
Ei = Elevation of Outlet Invert (ft) 0.030741917 ft2
Ec = Elevation of Outlet Centroid (ft) 4.426836 in2
Orifice Size (in.) 2 - 3/8 in.
Area (in2) 4.43 sq-in
Q 0.30 cfs
Orifice Height (in.) 3 in.
Orifice Width (in.) 1 - 4/8 in.
Area (in2) 4.43 sq-in
Q 0.29 cfs
September 19, 2016
Lake Street Apartments C. Snowdon
Student Housing CSU, LLC
Pond B - Outlet Structure
Aa =
Circular Orifice
100-Year Orifice
Rectangular Orifice
100-Year Orifice
1232-001
Project:
By:
Units: Imperial Point of Contact
Date:
Required Storage Volume 20,281 CF
Select Stormtech Chamber System SC-740
Stone Porosity (Industry Standard = 40%) 40%
Stone Foundation Depth 6 Inches
Storage Volume Per Chamber 74.90 CF
Avg Cover over Chambers (18 in min. & 96 in max.) 18 Inches 30 in (762 mm)
Number of Chambers Required - 271 6 in (150 mm)
Approximate Bed Size Required 9,656 SF
Tons of Stone Required 1,107 Tons
Volume of Excavation 1,609 CY
Area of Filter Fabric 2,708 SY
# of End Caps Required 18 Each
Length of ISOLATOR ROW 220.72 FT
ISOLATOR FABRIC 123 SY
Is the limiting dimension for the bed the width or length? width
Width 45 FT Length 45 FT
# of Chambers Long 31 EA # of Chambers long - EA
# of Rows 9 EA # of Rows - EA
Actual Length 224.32 FT Actual Length - FT
Actual Width 44.25 FT Actual Width - FT
8 of the chambers rows will contain only 30 chambers
Please call StormTech @ 888-892-2694 for conceptual cost estimates.
To use this sheet: Please enter data into the blue and green cells. If switching between Imperial and Metric units please check the
correct units and data is input in the green cells.
System Requirements
Lake Street Apartments - Detention Pond B
Northern Engineering
C. Snowdon
9.19.16
Material Estimate
Controlled by Width (Rows) Controlled by Length
6" (150 mm) MIN.
6" MIN. 12" MIN. TYP.
PAVEMENT 18" (460 mm)
MIN.
96" (2440 mm)
MAX.
FOR UNPAVED INSTALLATION WHERE RUTTING FROM
VEHICLES MAY OCCUR, INCREAST COVER TO 24" MINIMUM.
www.stormtech.com│20 Beaver Road│Suite 104│Wethersfield│Connecticut│06109│888.892.2694│fax 866.328.8401
Project:
Chamber Model - SC-740
Units - Imperial
100
Number of chambers - 271
Voids in the stone (porosity) - 40 %
Base of STONE Elevation - 5025.49 ft
Amount of Stone Above Chambers - 6 in
Amount of Stone Below Chambers - 6 in
Height of
System
Incremental Single
Chamber
Incremental
Total Chamber
Incremental
Stone
Incremental Ch
& St
Cumulative
Chamber Elevation
(inches) (cubic feet) (cubic feet) (cubic feet) (cubic feet) (cubic feet) (feet)
42 0.00 0.00 305.36 305.36 20296.91 5028.99
41 0.00 0.00 305.36 305.36 19991.54 5028.91
40 0.00 0.00 305.36 305.36 19686.18 5028.82
39 0.00 0.00 305.36 305.36 19380.81 5028.74
38 0.00 0.00 305.36 305.36 19075.45 5028.66
37 0.00 0.00 305.36 305.36 18770.09 5028.57
36 0.05 14.90 299.40 314.31 18464.72 5028.49
35 0.16 44.15 287.70 331.86 18150.42 5028.41
34 0.28 76.41 274.80 351.21 17818.56 5028.32
33 0.60 163.67 239.89 403.57 17467.35 5028.24
32 0.80 217.26 218.46 435.72 17063.78 5028.16
31 0.95 257.63 202.31 459.94 16628.06 5028.07
30 1.07 291.19 188.89 480.08 16168.12 5027.99
29 1.18 319.91 177.40 497.31 15688.04 5027.91
28 1.27 342.99 168.17 511.16 15190.72 5027.82
27 1.36 367.21 158.48 525.69 14679.56 5027.74
26 1.45 394.06 147.74 541.80 14153.88 5027.66
25 1.52 413.20 140.08 553.28 13612.07 5027.57
24 1.58 428.81 133.84 562.65 13058.79 5027.49
23 1.64 445.06 127.34 572.40 12496.14 5027.41
22 1.70 460.57 121.14 581.71 11923.74 5027.32
21 1.75 475.04 115.35 590.39 11342.03 5027.24
20 1.80 488.56 109.94 598.50 10751.64 5027.16
19 1.85 502.70 104.28 606.99 10153.14 5027.07
18 1.89 513.03 100.15 613.18 9546.16 5026.99
17 1.93 524.12 95.72 619.83 8932.97 5026.91
16 1.97 535.22 91.27 626.50 8313.14 5026.82
15 2.01 544.69 87.49 632.18 7686.64 5026.74
14 2.04 554.19 83.69 637.88 7054.46 5026.66
13 2.07 562.31 80.44 642.75 6416.58 5026.57
12 2.10 570.43 77.19 647.62 5773.83 5026.49
11 2.13 577.72 74.28 651.99 5126.21 5026.41
10 2.15 583.69 71.89 655.58 4474.21 5026.32
9 2.18 589.98 69.37 659.35 3818.63 5026.24
8 2.20 595.75 67.06 662.82 3159.28 5026.16
7 2.21 598.19 66.09 664.28 2496.46 5026.07
6 0.00 0.00 305.36 305.36 1832.19 5025.99
5 0.00 0.00 305.36 305.36 1526.82 5025.91
Pond No :
c1
100-yr
0.66
5.00 min 697 ft3
0.16 acres 0.016 ac-ft
Max Release Rate = 0.20 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 314 1.00 0.20 60 254
10 7.720 488 0.75 0.15 90 398
15 6.520 618 0.67 0.13 120 498
20 5.600 707 0.63 0.13 150 557
25 4.980 786 0.60 0.12 180 606
30 4.520 856 0.58 0.12 210 646
35 4.080 902 0.57 0.11 240 662
40 3.740 945 0.56 0.11 270 675
45 3.460 983 0.56 0.11 300 683
50 3.230 1020 0.55 0.11 330 690
55 3.030 1052 0.55 0.11 360 692
60 2.860 1084 0.54 0.11 390 694
65 2.720 1117 0.54 0.11 420 697
70 2.590 1145 0.54 0.11 450 695
75 2.480 1175 0.53 0.11 480 695
80 2.380 1202 0.53 0.11 510 692
85 2.290 1229 0.53 0.11 540 689
90 2.210 1256 0.53 0.11 570 686
95 2.130 1278 0.53 0.11 600 678
100 2.060 1301 0.53 0.11 630 671
105 2.000 1326 0.52 0.10 660 666
110 1.940 1348 0.52 0.10 690 658
115 1.890 1373 0.52 0.10 720 653
120 1.840 1394 0.52 0.10 750 644
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Invert Elevation
Water Quality Volume
100-yr Detention Volume
Total Pond Volume
Min Sc
D = Depth between contours (ft.)
A1 = Surface Area lower contour (ft2) t
A2 = Surface Area upper contour (ft2) Area/Row
No. of Rows
5025.40 27.16 0.00 0.00 0.00 0.0000
5025.60 373.07 0.20 33.39 33.39 0.0008
5025.80 663.64 0.20 102.29 135.68 0.0031 WQCV
5026.00 1113.21 0.20 175.76 311.44 0.0071
5026.20 1744.81 0.20 283.45 594.88 0.0137
5026.40 2151.73 0.20 388.94 983.83 0.0226 Total Vol
WQCV Elevation Depth Volume
WQCV 5025.78 0.38 0.0029
100-yr Detention 5026.25 0.85 0.0160
Overall Detention 5026.32 0.92 0.0189
Total Outlet
Area 0.05 sq. in.
Pond C Volume
Elevation
(ft)
Surface
Area (ft2)
Incremental
Depth (ft)
Incremental
Vol. (ft3)
Total Vol.
(ft3)
Total Vol.
(ac-ft)
n
1/4
0.05
Required Area
Per Row 0.021 sq-in
1
Pond C
5025.40 ft
0.0029 ac-ft
0.0160 ac-ft Circular Perforation Sizing
1
0.0189 ac-ft Dia (in.)
Student Housing CSU, LLC
Lake Street Apartments September 19, 2016
1232-001 C. Snowdon
( )
3
V D * A 1 A 2 A 1 * A 2
= + +
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = 0.20 cfs
C = 0.65
Q = Release Rate (cfs) Eh = 5026.34 ft
C = Discharge Coefficients (unitless) Ei = 5025.40 ft
Aa = Area Allowed of Opening (ft2) Ec = 5025.51 ft Circular
g = Gravity (32.2 ft/s2) Ec = 5025.52 ft Rectangular
Eh = High Water Surface Elevation (ft)
Ei = Elevation of Outlet Invert (ft) 0.039535711 ft2
Ec = Elevation of Outlet Centroid (ft) 5.693142 in2
Orifice Size (in.) 2 -11/16 in.
Area (in2) 5.69 sq-in
Q 0.19 cfs
Orifice Height (in.) 2 - 7/8 in.
Orifice Width (in.) 2 in.
Area (in2) 5.69 sq-in
Q 0.19 cfs
Circular Orifice
100-Year Orifice
Rectangular Orifice
100-Year Orifice
Lake Street Apartments September 19, 2016
1232-001 C. Snowdon
Student Housing CSU, LLC
Pond C
Aa =
Pond C 0.00291 5025.83 0.0160 0.0189 5026.34 5026.40
Required Water
Quality Storage
(ac-ft)
Water Quality
Surface
Pond ID Elevation (ft)
High Water
Surface Elevation
(ft)
Top of Pond
Elevation (ft)
Total Detention
Volume
(ac-ft)
Required 100-year
Detention Volume
(ac-ft)
Pond No :
d1
100-yr
0.96
5.00 min 991 ft3
0.14 acres 0.023 ac-ft
Max Release Rate = 0.20 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 390 1.00 0.20 60 330
10 7.720 606 0.75 0.15 90 516
15 6.520 768 0.67 0.13 120 648
20 5.600 879 0.63 0.13 150 729
25 4.980 977 0.60 0.12 180 797
30 4.520 1064 0.58 0.12 210 854
35 4.080 1121 0.57 0.11 240 881
40 3.740 1174 0.56 0.11 270 904
45 3.460 1222 0.56 0.11 300 922
50 3.230 1267 0.55 0.11 330 937
55 3.030 1308 0.55 0.11 360 948
60 2.860 1347 0.54 0.11 390 957
65 2.720 1388 0.54 0.11 420 968
70 2.590 1423 0.54 0.11 450 973
75 2.480 1460 0.53 0.11 480 980
80 2.380 1494 0.53 0.11 510 984
85 2.290 1528 0.53 0.11 540 988
90 2.210 1561 0.53 0.11 570 991
95 2.130 1588 0.53 0.11 600 988
100 2.060 1617 0.53 0.11 630 987
105 2.000 1648 0.52 0.10 660 988
110 1.940 1675 0.52 0.10 690 985
115 1.890 1706 0.52 0.10 720 986
120 1.840 1733 0.52 0.10 750 983
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1232-001
Lake Street Apartments
Project Number :
Project Name :
Pond D
A =
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = 0.20 cfs
C = 0.65
Q = Release Rate (cfs) Eh = 5028.04 ft
C = Discharge Coefficients (unitless) Ei = 5025.71 ft
Aa = Area Allowed of Opening (ft2) Ec = 5025.80 ft Circular
g = Gravity (32.2 ft/s2) Ec = 5025.84 ft Rectangular
Eh = High Water Surface Elevation (ft)
Ei = Elevation of Outlet Invert (ft) 0.025118618 ft2
Ec = Elevation of Outlet Centroid (ft) 3.617081 in2
Orifice Size (in.) 2 - 1/8 in.
Area (in2) 3.62 sq-in
Q 0.20 cfs
Orifice Height (in.) 3 in.
Orifice Width (in.) 1 - 1/4 in.
Area (in2) 3.62 sq-in
Q 0.19 cfs
September 19, 2016
Lake Street Apartments C. Snowdon
Student Housing CSU, LLC
Pond D
Aa =
Circular Orifice
100-Year Orifice
Rectangular Orifice
100-Year Orifice
1232-001
Project:
By:
Units: Imperial Point of Contact
Date:
Required Storage Volume 991 CF
Select Stormtech Chamber System SC-310
Stone Porosity (Industry Standard = 40%) 40%
Stone Foundation Depth 6 Inches
Storage Volume Per Chamber 31.00 CF
Avg Cover over Chambers (18 in min. & 96 in max.) 18 Inches 16 in (406 mm)
Number of Chambers Required - 32 6 in (150 mm)
Approximate Bed Size Required 952 SF
Tons of Stone Required 91 Tons
Volume of Excavation 118 CY
Area of Filter Fabric 285 SY
# of End Caps Required 26 Each
Length of ISOLATOR ROW 21.36 FT
ISOLATOR FABRIC 9 SY
Is the limiting dimension for the bed the width or length? width
Width 45 FT Length 45 FT
# of Chambers Long 3 EA # of Chambers long - EA
# of Rows 13 EA # of Rows - EA
Actual Length 24.96 FT Actual Length - FT
Actual Width 44.79 FT Actual Width - FT
7 of the chambers rows will contain only 2 chambers
Please call StormTech @ 888-892-2694 for conceptual cost estimates.
To use this sheet: Please enter data into the blue and green cells. If switching between Imperial and Metric units please check the
correct units and data is input in the green cells.
System Requirements
Lake Street Apartments - Detention Pond D
Northern Engineering
C. Snowdon
9.19.16
Material Estimate
Controlled by Width (Rows) Controlled by Length
6" (150 mm) MIN.
6" MIN. 12" MIN. TYP.
PAVEMENT 18" (460 mm)
MIN.
96" (2440 mm)
MAX.
FOR UNPAVED INSTALLATION WHERE RUTTING FROM
VEHICLES MAY OCCUR, INCREAST COVER TO 24" MINIMUM.
www.stormtech.com│20 Beaver Road│Suite 104│Wethersfield│Connecticut│06109│888.892.2694│fax 866.328.8401
Project:
Chamber Model - SC-310
Units - Imperial
100
Number of chambers - 32
Voids in the stone (porosity) - 40 %
Base of STONE Elevation - 5025.71 ft
Amount of Stone Above Chambers - 6 in
Amount of Stone Below Chambers - 6 in
Height of
System
Incremental Single
Chamber
Incremental
Total Chamber
Incremental
Stone
Incremental Ch
& St
Cumulative
Chamber Elevation
(inches) (cubic feet) (cubic feet) (cubic feet) (cubic feet) (cubic feet) (feet)
28 0.00 0.00 25.30 25.30 991.90 5028.04
27 0.00 0.00 25.30 25.30 966.59 5027.96
26 0.00 0.00 25.30 25.30 941.29 5027.88
25 0.00 0.00 25.30 25.30 915.99 5027.79
24 0.00 0.00 25.30 25.30 890.68 5027.71
23 0.00 0.00 25.30 25.30 865.38 5027.63
22 0.06 1.88 24.55 26.43 840.08 5027.54
21 0.15 4.95 23.32 28.27 813.64 5027.46
20 0.27 8.51 21.90 30.41 785.37 5027.38
19 0.54 17.43 18.33 35.76 754.96 5027.29
18 0.70 22.53 16.29 38.82 719.20 5027.21
17 0.82 26.38 14.75 41.13 680.38 5027.13
16 0.92 29.59 13.47 43.06 639.24 5027.04
15 1.01 32.48 12.31 44.79 596.19 5026.96
14 1.09 35.03 11.29 46.32 551.39 5026.88
13 1.15 36.94 10.53 47.47 505.07 5026.79
12 1.21 38.88 9.75 48.63 457.61 5026.71
11 1.27 40.80 8.99 49.78 408.98 5026.63
10 1.32 42.39 8.35 50.74 359.20 5026.54
9 1.36 43.68 7.83 51.51 308.46 5026.46
8 1.40 44.96 7.32 52.28 256.95 5026.38
7 1.43 45.91 6.94 52.85 204.67 5026.29
6 0.00 0.00 25.30 25.30 151.82 5026.21
5 0.00 0.00 25.30 25.30 126.52 5026.13
4 0.00 0.00 25.30 25.30 101.21 5026.04
3 0.00 0.00 25.30 25.30 75.91 5025.96
2 0.00 0.00 25.30 25.30 50.61 5025.88
1 0.00 0.00 25.30 25.30 25.30 5025.79
StormTech SC-310 Cumulative Storage Volumes
Lake Street Apartments - Pond D
Include Perimeter Stone in Calculations
Click Here for Metric
Pond ID
Required Water
Quality Volume
(ac-ft)
Water Quality Surface
Elevation
(ft)
Required 100-year
Detention Volume
(ac-ft)
Total Detention
Volume
(ac-ft)
High Water Surface
Elevation (ft)
Top of Pond
Elevation
(ft)
Pond A (EDB) 0.006 5027.60 0.0480 0.0538 5028.75 5028.80
Pond B (UG) 0.0355 N/A 0.4656 0.4656 5028.99 N/A
Pond C (EDB) 0.0029 5025.83 0.0160 0.0189 5026.34 5026.40
Pond D (UG) 0.0029 N/A 0.0160 0.0160 5028.04 N/A
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
1
WQCV = Watershed inches of Runoff (inches) 54.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.217 in
A = 0.32 ac
V = 0.0058 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
255 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
Lake Street Apartments September 19, 2016
1232-001 C. Snowdon
Student Housing CSU, LLC
Detention Pond A
0.217
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
ø
1008
Project Title Date:
Project Number Calcs By:
Client
Basins
0.8
WQCV = Watershed inches of Runoff (inches) 73.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.231 in
A = 0.87 ac
V = 0.0168 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
1232-001 September 19, 2016
Lake Street Apartments C. Snowdon
Student Housing CSU, LLC
WQ Basins B1 & B2
732 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
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
WQ
0.77
5.00 min 543 ft3
0.87 acres 0.01 ac-ft
Max Release Rate = 0.24 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 287 1.00 0.24 71 216
10 1.105 445 1.00 0.24 142 303
15 0.935 564 0.67 0.16 142 423
20 0.805 648 0.63 0.15 177 471
25 0.715 719 0.60 0.14 212 507
30 0.650 785 0.58 0.14 248 537
35 0.585 824 0.57 0.13 283 541
40 0.535 861 0.56 0.13 318 543
45 0.495 896 0.56 0.13 354 542
50 0.460 925 0.55 0.13 389 536
55 0.435 963 0.55 0.13 425 538
60 0.410 990 0.54 0.13 460 530
65 0.385 1007 0.54 0.13 495 512
70 0.365 1028 0.54 0.13 531 497
75 0.345 1041 0.53 0.13 566 475
80 0.330 1062 0.53 0.13 601 461
85 0.315 1077 0.53 0.12 637 441
90 0.305 1105 0.53 0.12 672 432
95 0.290 1109 0.53 0.12 708 401
100 0.280 1127 0.53 0.12 743 384
105 0.270 1141 0.52 0.12 778 362
110 0.260 1151 0.52 0.12 814 337
115 0.255 1180 0.52 0.12 849 331
120 0.245 1183 0.52 0.12 884 299
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
Lake Street Apartments
1232-001
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Client
Basins
Project Number
Project Title
WQ Basins B1 & B2
Student Housing CSU, LLC
1008
Project Title Date:
Project Number Calcs By:
Client
Basins
0.8
WQCV = Watershed inches of Runoff (inches) 87.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.302 in
A = 0.74 ac
V = 0.0187 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
816 cu. ft.
Drain Time
a =
i =
WQCV =
1232-001 September 19, 2016
Lake Street Apartments C. Snowdon
Student Housing CSU, LLC
WQ Basins B3 & B4
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
WQ
0.94
5.00 min 549 ft3
0.74 acres 0.01 ac-ft
Max Release Rate = 0.26 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 299 1.00 0.26 78 221
10 1.105 464 1.00 0.26 156 309
15 0.935 589 0.67 0.17 156 434
20 0.805 676 0.63 0.16 195 482
25 0.715 751 0.60 0.16 233 517
30 0.650 819 0.58 0.15 272 547
35 0.585 860 0.57 0.15 311 549
40 0.535 899 0.56 0.15 350 549
45 0.495 936 0.56 0.14 389 547
50 0.460 966 0.55 0.14 428 538
55 0.435 1005 0.55 0.14 467 538
60 0.410 1033 0.54 0.14 506 527
65 0.385 1051 0.54 0.14 545 506
70 0.365 1073 0.54 0.14 584 490
75 0.345 1087 0.53 0.14 623 464
80 0.330 1109 0.53 0.14 662 447
85 0.315 1125 0.53 0.14 700 424
90 0.305 1153 0.53 0.14 739 414
95 0.290 1157 0.53 0.14 778 379
100 0.280 1176 0.53 0.14 817 359
105 0.270 1191 0.52 0.14 856 335
110 0.260 1201 0.52 0.14 895 306
115 0.255 1232 0.52 0.14 934 298
120 0.245 1235 0.52 0.14 973 262
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
Basins WQ Basins B1 & B2
Input Variables Results
Design Point
Design Storm Required Detention Volume
WQ Basins B3 & B4
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title 1232-001
Project Number Lake Street Apartments
Vault ID
Total
Required
WQ Volume
(cf)
Flow,
WQ
(cfs)
Chamber
Type
Chamber Release
Ratea
(cfs)
Chamber
Volumeb
(cf)
Installed Camber
w/ Aggregatec
(cf)
Mimimum
No. of
Chambersd
Total Release
Ratee
(cfs)
Required
Storage
Volume by
FAA Method
(cf)
Mimimum
No. of
Chambersf
Storage
Provided
within the
Chambersg
(cf)
Total
Installed
System
Volumeh
(cf)
WQ Basins B1 & B2 732 0.95 SC-740 0.024 45.90 74.90 10 0.24 543 12 551 899
WQ Basins B3 & B4 816 1.00 SC-740 0.024 45.90 74.90 11 0.26 549 12 551 899
SC-740
a. Release rate per chamber, limited by flow through geotextile with accumulated sediment.
b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.
c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.
d. Number of chambers required to provide full WQCV within total installed system, including aggregate.
e. Release rate per chamber times number of chambers.
f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage).
g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume.
e. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV.
Chamber Configuration Summary
D:\Projects\1232-001\Drainage\Detention\1232-002 Pond B Pond_Orifice Calc.xls
Chamber Dimensions SC-160 SC-310 SC-740
Width (in) 25.0 34.0 51.0
Length (in) 84.4 85.4 85.4
Height (in) 12.0 16.0 30.0
Floor Area (sf) 14.7 20.2 30.2
Chamber Volume (cf) 6.9 14.7 45.9
Chamber/Aggregate Volume (cf) 15.0 29.3 74.9
Flow Rate* 0.35 gpm/sf
1 cf = 7.48052 gal
1 gallon = 0.133681 cf
1 GPM = 0.002228 cfs
*Flow rate based on 1/2 of Nov 07 QMAX in Figure 17 of UNH Testing Report
SC-160 SC-310 SC-740
Flow Rate/chamber (cfs) 0.011426 0.015724 0.023586
StormTech Chamber Data
Chamber Flow Rate
Chamber Flow Rate Conversion (gpm/sf to cfs)
D:\Projects\1232-001\Drainage\Detention\1232-002 Pond B Pond_Orifice Calc.xls
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
1
WQCV = Watershed inches of Runoff (inches) 41.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.182 in
A = 0.16 ac
V = 0.0029 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
1.2 = 20% Additional Volume (Sediment Accumulation)
127 cu. ft.
Lake Street Apartments September 19, 2016
1232-001 C. Snowdon
Student Housing CSU, LLC
Pond C
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
0.182
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
* * 1 . 2
12
V WQCV A
÷
1008
Project Title Date:
Project Number Calcs By:
Client
Basins
0.8
WQCV = Watershed inches of Runoff (inches) 76.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.244 in
A = 0.14 ac
V = 0.0028 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
121 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
1232-001 September 19, 2016
Lake Street Apartments C. Snowdon
Student Housing CSU, LLC
Pond D
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 - 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
÷
Pond D
WQ
0.76
5.00 min 41 ft3
0.14 acres 0.00 ac-ft
Max Release Rate = 0.08 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 44 1.00 0.08 24 21
10 1.105 69 1.00 0.08 47 21
15 0.935 87 0.67 0.05 47 40
20 0.805 100 0.63 0.05 59 41
25 0.715 111 0.60 0.05 71 40
30 0.650 121 0.58 0.05 83 39
35 0.585 127 0.57 0.04 94 33
40 0.535 133 0.56 0.04 106 27
45 0.495 138 0.56 0.04 118 20
50 0.460 143 0.55 0.04 130 13
55 0.435 149 0.55 0.04 142 7
60 0.410 153 0.54 0.04 153 0
65 0.385 155 0.54 0.04 165 -10
70 0.365 159 0.54 0.04 177 -18
75 0.345 161 0.53 0.04 189 -28
80 0.330 164 0.53 0.04 200 -36
85 0.315 166 0.53 0.04 212 -46
90 0.305 171 0.53 0.04 224 -54
95 0.290 171 0.53 0.04 236 -65
100 0.280 174 0.53 0.04 248 -74
105 0.270 176 0.52 0.04 259 -83
110 0.260 178 0.52 0.04 271 -94
115 0.255 182 0.52 0.04 283 -101
120 0.245 183 0.52 0.04 295 -112
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
Pond D
Student Housing CSU, LLC
A =
Tc =
Design Point
C =
Design Storm
Lake Street Apartments
1232-001
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Vault ID
Total
Required
WQ Volume
(cf)
Flow,
WQ
(cfs)
Chamber
Type
Chamber Release
Ratea
(cfs)
Chamber
Volumeb
(cf)
Installed Camber
w/ Aggregatec
(cf)
Mimimum
No. of
Chambersd
Total Release
Ratee
(cfs)
Required
Storage
Volume by
FAA Method
(cf)
Mimimum
No. of
Chambersf
Storage
Provided
within the
Chambersg
(cf)
Total
Installed
System
Volumeh
(cf)
Pond D 121 0.13 SC-310 0.016 14.70 29.30 5 0.08 41 3 44 147
SC-740
a. Release rate per chamber, limited by flow through geotextile with accumulated sediment.
b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.
c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.
d. Number of chambers required to provide full WQCV within total installed system, including aggregate.
e. Release rate per chamber times number of chambers.
f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage).
g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume.
e. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV.
Chamber Configuration Summary
D:\Projects\1232-001\Drainage\Detention\1232-002 Pond D Pond_Orifice Calc.xls
Chamber Dimensions SC-160 SC-310 SC-740
Width (in) 25.0 34.0 51.0
Length (in) 84.4 85.4 85.4
Height (in) 12.0 16.0 30.0
Floor Area (sf) 14.7 20.2 30.2
Chamber Volume (cf) 6.9 14.7 45.9
Chamber/Aggregate Volume (cf) 15.0 29.3 74.9
Flow Rate* 0.35 gpm/sf
1 cf = 7.48052 gal
1 gallon = 0.133681 cf
1 GPM = 0.002228 cfs
*Flow rate based on 1/2 of Nov 07 QMAX in Figure 17 of UNH Testing Report
SC-160 SC-310 SC-740
Flow Rate/chamber (cfs) 0.011426 0.015724 0.023586
StormTech Chamber Data
Chamber Flow Rate
Chamber Flow Rate Conversion (gpm/sf to cfs)
D:\Projects\1232-001\Drainage\Detention\1232-002 Pond D Pond_Orifice Calc.xls
APPENDIX D
EROSION CONTROL REPORT
Lake Avenue Apartments
Final Erosion Control Report
A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included
with the final construction drawings. It should be noted, however, that any such Erosion and
Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of
the BMPs depicted, and additional or different BMPs from those included may be necessary during
construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented
during construction, as well as permanent erosion control protection. Best Management Practices
from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are
not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways
and inlet protection at proposed storm inlets. Vehicle tracking control pads, spill containment and
clean-up procedures, designated concrete washout areas, dumpsters, and job site restrooms shall
also be provided by the Contractor.
Grading and Erosion Control Notes can be found on Sheet CS2 of the Utility Plans. The Utility
Plans at final design will also contain a full-size Erosion Control Plan as well as a separate sheet
dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets, the
Contractor shall be aware of, and adhere to, the applicable requirements outlined in any existing
Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior
to issuance of the Development Construction Permit. Also, the Site Contractor for this project will
be required to secure a Stormwater Construction General Permit from the Colorado Department of
Public Health and Environment (CDPHE), Water Quality Control Division – Stormwater Program,
before commencing any earth disturbing activities. Prior to securing said permit, the Site Contractor
shall develop a comprehensive StormWater Management Plan (SWMP) pursuant to CDPHE
requirements and guidelines. The SWMP will further describe and document the ongoing activities,
inspections, and maintenance of construction BMPs.
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
Input Variables Results
Required Detention Volume
Client
Basins
Project Number
Project Title
Page 2 of 5
1232-002 Pond D Pond_Orifice Calc.xls
ø
ö
ç
è
= æ
12 hr
ø
ö
ç
è
= æ
40 hr
Client Student Housing CSU, LLC
Page 4 of 7
1232-002 Pond B Pond_Orifice Calc.xls
ø
ö
ç
è
= æ
12 hr
A =
Tc =
Design Point
C =
Design Storm
WQ Basins B1 & B2
Page 2 of 7
1232-002 Pond B Pond_Orifice Calc.xls
ø
ö
ç
è
= æ
12 hr
ö
ç
è
= æ
40 hr
Tc =
Project Location :
Design Point
C =
Design Storm
Page 1 of 1
1232-001_Pond D_DetentionVolume_FAAModified Method.xls
1232-001
Lake Street Apartments
Project Number :
Project Name :
Pond C
Page 1 of 1
1232-001_Pond C_DetentionVolume_FAAModified Method.xls
4 0.00 0.00 305.36 305.36 1221.46 5025.82
3 0.00 0.00 305.36 305.36 916.09 5025.74
2 0.00 0.00 305.36 305.36 610.73 5025.66
1 0.00 0.00 305.36 305.36 305.36 5025.57
StormTech SC-740 Cumulative Storage Volumes
Lake Street Apartments - Pond B
Include Perimeter Stone in Calculations
Click Here for Metric
Tc =
Project Location :
Design Point
C =
Design Storm
Page 1 of 1
1232-001_Pond B_DetentionVolume_FAAModified Method.xls
= + +
1232-001
Lake Street Apartments
Project Number :
Project Name :
Pond A
Page 1 of 1
1232-001_Pond A_DetentionVolume_FAAModified Method.xls
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
a1 A1-A2 No 0.24 0.24 0.30 20 2.00 5.69 5.69 5.29 N/A N/A N/A 187 0.5 10.61 0.3 6 6 6
b1 B1-B2 No 0.95 0.95 1.00 N/A N/A N/A N/A 100 1.00% 2.00 0.8 N/A N/A N/A 5 5 5
b3 B3-B4 No 0.61 0.61 0.76 N/A N/A N/A N/A 325 1.00% 2.00 2.7 N/A N/A N/A 5 5 5
b1 B1-B4 No 0.61 0.61 0.76 N/A N/A N/A N/A 165 1.00% 2.00 1.4 N/A N/A N/A 5 5 5
c1 C1 & C2 No 0.95 0.95 1.00 20 14.40% 0.5 0.5 0.3 N/A N/A N/A N/A N/A N/A 5 5 5
COMBINED DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
C. Snowdon
September 19, 2016
Design
Point
Basin IDs
Overland Flow Pipe/Internal Building Flow Swale Flow Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
Page 8 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Comb-Tc-10-yr_&_100-yr
**Soil Classification of site is Sandy Loam**
10-year Cf = 1.00
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
C. Snowdon
Page 7 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Comb-C-Values
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
a1 A1 No 0.24 0.24 0.30 20 2.00% 5.7 5.7 5.3 N/A N/A N/A 187 0.5 10.61 0.3 6 6 6
a2 A2 No 0.95 0.95 1.00 N/A N/A N/A N/A 100 1.00% 2.00 0.8 N/A N/A N/A 5 5 5
b1 B1 No 0.61 0.61 0.76 25 3.00% 3.2 3.2 2.2 235 1.00% 2.00 2.0 N/A N/A N/A 5 5 5
b2 B2 No 0.95 0.95 1.00 N/A N/A N/A N/A 100 1.00% 2.00 0.8 N/A N/A N/A 5 5 5
b3 B3 No 0.80 0.80 1.00 74 3.11% 3.3 3.3 1.1 64 0.50% 1.41 0.8 N/A N/A N/A 5 5 5
b4 B4 No 0.95 0.95 1.00 N/A N/A N/A N/A 293 1.00% 2.00 2.4 N/A N/A N/A 5 5 5
c1 C1 No 0.32 0.32 0.40 20 14.40% 2.7 2.7 2.4 N/A N/A N/A 165 0.5 10.61 0.3 5 5 5
c2 C2 No 0.88 0.88 1.00 N/A N/A N/A N/A 67 0.54% 1.47 0.8 N/A N/A N/A 5 5 5
d1 D1 No 0.76 0.76 0.96 13 5.00% 1.3 1.3 0.6 156 0.87% 1.87 1.4 N/A N/A N/A 5 5 5
os1 OS1 No 0.24 0.24 0.29 35 15.00% 3.9 3.9 3.6 0 N/A N/A N/A N/A N/A N/A 5 5 5
os2 OS2 No 0.58 0.58 0.73 10 2.00% 2.4 2.4 1.7 52 4.50% 4.24 0.2 N/A N/A N/A 5 5 5
os3 OS3 No 0.15 0.15 0.19 21 25.00% 2.8 2.8 2.7 N/A N/A N/A N/A N/A N/A 5 5 5
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter/Internal Building Flow Swale Flow
Design
Point
Basin
Overland Flow
C. Snowdon
September 19, 2016
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
Page 5 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr
C2 2217 0.051 0.029 0.017 0.000 0.000 0.000 0.004 0.88 0.88 1.00 88%
D1 5935 0.136 0.091 0.014 0.000 0.000 0.000 0.032 0.76 0.76 0.96 76%
OS1 6696 0.154 0.000 0.016 0.000 0.000 0.000 0.137 0.24 0.24 0.29 10%
OS2 1052 0.024 0.009 0.004 0.000 0.000 0.000 0.011 0.58 0.58 0.73 52%
OS3 1691 0.039 0.000 0.000 0.000 0.000 0.000 0.039 0.15 0.15 0.19 0%
TOTAL 106749 2.45 0.481 0.326 0.979 0.000 0.000 0.665 0.73 0.73 0.92 68%
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf = 1.00
September 19, 2016
**Soil Classification of site is Sandy Loam**
C. Snowdon
Page 4 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\C-Values
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
h1 H1 No 0.38 0.38 0.47 146 2.74% 11.7 11.7 10.1 N/A N/A N/A 241 0.88% 1.41 2.9 15 15 13
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
C. Snowdon
September 19, 2016
Design
Point
Basin
Overland Flow Gutter Flow Swale Flow Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
Page 2 of 10 D:\Projects\1232-001\Drainage\Hydrology\1232-001_Rational-Calcs.xlsx\Hist-Tc-10-yr_&_100-yr