HomeMy WebLinkAboutLAKE STREET APARTMENTS - PDP - PDP160007 - REPORTS - DRAINAGE REPORTFINAL DRAINAGE REPORT
Lake Street Apartments
Fort Collins, Colorado
March 30, 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.
March 30, 2016
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
Lake Street 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 Lake Street Apartments. Comments from the Preliminary Development Review Letter
dated March 16, 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 Lake Street
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
Lake Street 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 .................................................................................................................... 6
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
Lake Street Apartments
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
Lake Street Apartments
Final Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. Lake Street 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.
Lake Street Apartments
Final Drainage Report 2
B. Description of Property
1. Lake Street Apartments is approximately 2.45 net acres.
Figure 1 – Aerial Photograph
2. Lake Street 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 permeable pavers
and asphalt paving. The section of drive constructed of permeable pavers 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.
Lake Street Apartments
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)
Lake Street Apartments
Final Drainage Report 4
Figure 3 – Existing FEMA Floodplains
Figure 4 – Existing City Floodplains
Lake Street Apartments
Final Drainage Report 5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Lake Street 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 Lake Street
Apartments project.
B. Four Step Process
The overall stormwater management strategy employed with the Lake Street 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 paver section
or the underground detention section to increase time of concentration, promote
infiltration and provide initial water quality.
Providing permeable paver areas with underground detention area to increase time of
concentration promote infiltration and provide water quality.
Routing runoff from the proposed roofs into individual drain rock to promote
infiltration, biological uptake, and evapotranspiration.
Lake Street Apartments
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 the drain rock located in the underground detention section surrounding the detention
chambers. Stormwater generated from the southern portion of the parking area will be
routed via overland flow across permeable pavers with any additional capture volume held
within the proposed rain garden located along the southern property line. Stormwater
generated from the northern portion of the parking area will be routed via overland flow
across permeable pavers. Stormwater generated from the area to the north of the building
will be routed through an extended detention pond for water quality.
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 Lake Street 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 Lake Street 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.
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
Lake Street Apartments
Final Drainage Report 7
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 Lake Street 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 Lake Street 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 Lake Street Apartments development is not requesting any modification
at this time.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the Lake Street 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.
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.
Lake Street Apartments
Final Drainage Report 8
4. The Lake Street 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, but predominantly hardscape.
Stormwater generated from this sub-basin is routed via overland and gutter flow and
discharges through curb cuts directly into Sub-Basin B4. Sub-Basin B4 composed
primarily of the landscaping south of the southern parking area and consists entirely of
landscape area. Stormwater generated from this sub-basin is routed via overland flow
and discharges directly into the rain garden located along the southern property line.
The major storm events are captured by an area inlet located within the rain garden
and discharge directly into the Underground Pond B. Sub-basin B2 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 B3 is composed entirely of the building
roofs and consists entirely of roof surface and internal roof leaders. Stormwater
generated from this sub-basin is routed internal to the building through pipe flow and
discharged directly into the drain rock surrounding the detention chambers and then
into 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.
Lake Street Apartments
Final Drainage Report 9
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.
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
(Basin B1, B2 and D1) will be routed through a permeable paver system. The
remaining runoff (Basin C2) will be routed to an extended detention pond.
All runoff generated from the interal courtyard and landscape areas surround the
southeast corner of the building (Basins A1 & A2) will be routed to an extended
detention pond.
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 1.04 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).
Lake Street Apartments
Final Drainage Report 10
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 0.44 cfs, indicate a detention volume of 1435 cu. ft. This does not
included any Water Quality Capture Volume (WQCV) of 159 cu. ft., resulting in an
overall detention volume of 1594 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 20,204 cu. ft. This does not
included any Water Quality Capture Volume (WQCV). During the water quality
events, the water quality capture volume will release into and through either the
permeable paver section or drain rock surrounding the detention chambers over 12-
hours. There is additional water quality volume within the proposed rain garden.
These sections are considered infiltration sections because the in-situ soils in this
area are Altvan-Satanta loam. The rain garden located along the southern property
line can account for additional water quality.
Pond C
Calculations for Pond C, based on the characteristics of Basin C and an adjusted
release rate of 0.10 cfs, indicate a detention volume of 727 cu. ft. This does not
included any Water Quality Capture Volume (WQCV) of 145 cu. ft., resulting in an
overall detention volume of 872 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 867 cu. ft. This does not
included any Water Quality Capture Volume (WQCV). During the water quality
events, the water quality capture volume will release into and through the permeable
paver section over 12-hours. This section is considered an infiltration section
because the in-situ soils in this area are Altvan-Satanta loam.
4. Detention Pond Results
Pond A
The total storage available within Pond A is 2130 cu. ft at a top of pond elevation of
5028.8 feet. The WQCV is achieved at a water surface elevation of 5027.59 feet,
the 100-year detention volume is achieved at a water surface elevation of 5028.49
feet and the overall detention volume is achieved at a high water surface elevation of
5028.57 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
20,204 cu. ft. This also does not include any of the volume within the permeable
paver section. The overall required water quality for Sub-Basins B1-B4 is 1376 cu.
ft. Accounting only for the volume within the permeable paver section and the rain
garden, 1627 cu. ft. for water quality is being provided, resulting in an overall
volume of 21,942 cu. ft.
Lake Street Apartments
Final Drainage Report 11
Pond C
The total storage available within Pond C is 1118 cu. ft at a top of pond elevation of
5026.4 feet. The WQCV is achieved at a water surface elevation of 5025.81 feet,
the 100-year detention volume is achieved at a water surface elevation of 5026.22
feet and the overall detention volume is achieved at a high water surface elevation of
5026.29 feet.
Pond D
The storage volume available within StormTech Vault Structure within Pond D is 867
cu. ft. This also does not include any of the volume within the permeable paver
section. The overall required water quality for Sub-Basin D1 is 93 cu. ft.
Accounting only for the volume within the permeable paver section, 308 cu. ft. for
water quality is being provided, resulting in an overall volume of 1,175 cu. ft.
5. To minimize the potential for increased flow to leave the site in the event the
permeable pavers cannot infiltrate fast enough, a combination of curb inlets and an
area inlet have been provided to capture and direct excess runoff into the underground
detention vaults. All inlets will have a sumped bottom to capture sediment and
prevent the vault or surrounding drainage rock from siltation. Additionally, all runoff
generated from the water quality event will be routed through an isolator row to
collect any additional sedimentation. The water quality volume within the isolator
row was not included in the overall water quality quantities.
6. 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.
Lake Street Apartments
Final Drainage Report 12
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the Lake Street Apartments project complies with
the City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with the Lake Street 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 Lake Street Apartments
development.
4. The drainage plan and stormwater management measures proposed with the Lake
Street 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. Lake Street 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 Lake Street Apartments development will not impact the Master
Drainage Plan recommendations for the Old Town major drainage basin.
Lake Street Apartments
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
February 24, 2015
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
February 24, 2015
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 6149 0.141 0.000 0.012 0.000 0.000 0.000 0.130 0.22 0.22 0.27 7%
A2 8101 0.186 0.151 0.000 0.000 0.000 0.000 0.035 0.80 0.80 1.00 81%
B1 13884 0.319 0.166 0.027 0.000 0.000 0.064 0.061 0.69 0.69 0.86 60%
B2 8223 0.189 0.098 0.021 0.000 0.000 0.039 0.031 0.71 0.71 0.88 62%
B3 42425 0.974 0.000 0.000 0.974 0.000 0.000 0.000 0.95 0.95 1.00 90%
B4 5619 0.129 0.000 0.000 0.000 0.000 0.000 0.129 0.15 0.15 0.19 0%
C1 4869 0.112 0.000 0.013 0.000 0.000 0.000 0.098 0.25 0.25 0.31 11%
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 0.14 9 9 8 0.22 0.22 0.27 2.35 4.02 8.38 0.07 0.12 0.32
a2 A2 0.19 5 5 5 0.80 0.80 1.00 2.85 4.87 9.95 0.42 0.72 1.85
b1 B1 0.32 5 5 5 0.69 0.69 0.86 2.85 4.87 9.95 0.62 1.06 2.72
b2 B2 0.19 5 5 5 0.71 0.71 0.88 2.85 4.87 9.95 0.38 0.65 1.66
b3 B3 0.97 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 2.64 4.51 9.69
b4 B4 0.13 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.06 0.09 0.24
c1 C1 0.11 5 5 5 0.25 0.25 0.31 2.85 4.87 9.95 0.08 0.13 0.34
c2 C2 0.05 5 5 5 0.80 0.80 1.00 2.85 4.87 9.95 0.12 0.20 0.52
d1 D1 0.14 5 5 5 0.69 0.69 0.86 2.85 4.87 9.95 0.27 0.46 1.16
os1 OS1 0.15 5 5 5 0.23 0.23 0.29 2.85 4.87 9.95 0.10 0.17 0.43
os2 OS2 0.02 5 5 5 0.69 0.69 0.86 2.85 4.87 9.95 0.05 0.08 0.21
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
February 24, 2015
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 14250 0.327 0.151 0.012 0.000 0.000 0.000 0.164 0.55 0.55 0.68 49%
b1 B1-B4 70151 1.610 0.264 0.048 0.974 0.000 0.103 0.222 0.80 0.80 1.00 74%
c1 C1 & C2 7145 0.164 0.030 0.026 0.000 0.000 0.000 0.227 0.53 0.53 0.67 33%
COMBINED DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
February 24, 2015
**Soil Classification of site is Sandy Loam**
10-year Cf = 1.00
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 0.33 9 9 8 0.55 0.55 0.68 2.35 4.02 8.38 0.4 0.7 1.9
b1 B1-B4 1.61 5 5 5 0.80 0.80 1.00 2.85 4.87 9.95 3.7 6.3 16.0
c1 C1 & C2 0.16 5 5 5 0.53 0.53 0.67 2.85 4.87 9.95 0.2 0.4 1.1
C100
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
COMBINED DEVELOPED RUNOFF COMPUTATIONS
C. Snowdon
February 24, 2015
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
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 0.141 0.22 0.27 8.8 8.5 0.07 0.32
a2 A2 0.186 0.80 1.00 5.0 5.0 0.42 1.85
b1 B1 0.319 0.69 0.86 5.0 5.0 0.62 2.72
b2 B2 0.189 0.71 0.88 5.0 5.0 0.38 1.66
b3 B3 0.974 0.95 1.00 5.0 5.0 2.64 9.69
b4 B4 0.129 0.15 0.19 5.0 5.0 0.06 0.24
c1 C1 0.112 0.25 0.31 5.0 5.0 0.08 0.34
c2 C2 0.052 0.80 1.00 5.0 5.0 0.12 0.52
d1 D1 0.136 0.69 0.86 5.0 5.0 0.27 1.16
os1 OS1 0.150 0.23 0.29 5.0 5.0 0.10 0.43
os2 OS2 0.024 0.69 0.86 5.0 5.0 0.05 0.21
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
0.68
5.00 min 1435 ft3
0.33 acres 0.033 ac-ft
Max Release Rate = 0.44 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 9.950 664 1.00 0.44 132 532
10 7.720 1030 0.75 0.33 198 832
15 6.520 1305 0.67 0.29 264 1041
20 5.600 1494 0.63 0.28 330 1164
25 4.980 1661 0.60 0.26 396 1265
30 4.520 1809 0.58 0.26 462 1347
35 4.080 1905 0.57 0.25 528 1377
40 3.740 1996 0.56 0.25 594 1402
45 3.460 2077 0.56 0.24 660 1417
50 3.230 2155 0.55 0.24 726 1429
55 3.030 2223 0.55 0.24 792 1431
60 2.860 2289 0.54 0.24 858 1431
65 2.720 2359 0.54 0.24 924 1435
70 2.590 2419 0.54 0.24 990 1429
75 2.480 2482 0.53 0.23 1056 1426
80 2.380 2540 0.53 0.23 1122 1418
85 2.290 2597 0.53 0.23 1188 1409
90 2.210 2654 0.53 0.23 1254 1400
95 2.130 2700 0.53 0.23 1320 1380
100 2.060 2748 0.53 0.23 1386 1362
105 2.000 2802 0.52 0.23 1452 1350
110 1.940 2847 0.52 0.23 1518 1329
115 1.890 2900 0.52 0.23 1584 1316
120 1.840 2946 0.52 0.23 1650 1296
*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 A
A =
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 0.07 0.00 0.00 0.00 0.0000
5027.00 34.65 0.20 2.42 2.42 0.0001
5027.20 145.83 0.20 16.77 19.19 0.0004
5027.40 357.54 0.20 48.78 67.97 0.0016
5027.60 602.02 0.20 94.90 162.87 0.0037 WQCV
5027.80 1037.87 0.20 162.02 324.89 0.0075
5028.00 1377.47 0.20 240.73 565.63 0.0130
5028.20 1702.24 0.20 307.40 873.03 0.0200
5028.40 1979.04 0.20 367.78 1240.81 0.0285
5028.60 2226.76 0.20 420.34 1661.14 0.0381 Total Vol
5028.80 2472.06 0.20 469.67 2130.81 0.0489
Elevation Depth Volume
WQCV 5027.59 0.79 0.0036
100-yr Detention 5028.49 1.69 0.0329
Overall Detention 5028.57 1.77 0.0366
Lake Street Apartments February 25, 2016
1232-001 C. Snowdon
Detention Pond A
5026.80 ft
0.0036 ac-ft
0.0329 ac-ft Circular Perforation Sizing
1
0.0366 ac-ft
Dia (in.)
n
1/4
0.05
Required Area
Per Row
0.020 sq-in
2
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)
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = 0.44 cfs
C = 0.65
Q = Release Rate (cfs) Eh = 5028.57 ft
C = Discharge Coefficients (unitless) Ei = 5026.80 ft
Aa = Area Allowed of Opening (ft2) Ec = 5026.94 ft Circular
g = Gravity (32.2 ft/s2) Ec = 5026.93 ft Rectangular
Eh = High Water Surface Elevation (ft)
Ei = Elevation of Outlet Invert (ft) 0.063442 ft2
Ec = Elevation of Outlet Centroid (ft) 9.135648 in2
Orifice Size (in.) 3 - 7/16 in.
Area (in2) 9.26 sq-in
Q 0.43 cfs
Orifice Height (in.) 3 - 1/8 in.
Orifice Width (in.) 3 in.
Area (in2) 9.26 sq-in
Q 0.43 cfs
Circular Orifice
100-Year Orifice
Rectangular Orifice
100-Year Orifice
Lake Street Apartments February 25, 2016
1232-001 C. Snowdon
0
Detention Pond A
Aa =
Detention Pond A 0.004 5027.59 0.0329 0.0366 5028.57 5029.34
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 20204 ft3
1.61 acres 0.464 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 4806 1.00 0.30 90 4716
10 7.720 7458 0.75 0.23 135 7323
15 6.520 9447 0.67 0.20 180 9267
20 5.600 10819 0.63 0.19 225 10594
25 4.980 12027 0.60 0.18 270 11757
30 4.520 13099 0.58 0.18 315 12784
35 4.080 13794 0.57 0.17 360 13434
40 3.740 14451 0.56 0.17 405 14046
45 3.460 15041 0.56 0.17 450 14591
50 3.230 15601 0.55 0.17 495 15106
55 3.030 16098 0.55 0.16 540 15558
60 2.860 16577 0.54 0.16 585 15992
65 2.720 17079 0.54 0.16 630 16449
70 2.590 17514 0.54 0.16 675 16839
75 2.480 17968 0.53 0.16 720 17248
80 2.380 18393 0.53 0.16 765 17628
85 2.290 18803 0.53 0.16 810 17993
90 2.210 19214 0.53 0.16 855 18359
95 2.130 19547 0.53 0.16 900 18647
100 2.060 19900 0.53 0.16 945 18955
105 2.000 20286 0.52 0.16 990 19296
110 1.940 20614 0.52 0.16 1035 19579
115 1.890 20996 0.52 0.16 1080 19916
120 1.840 21329 0.52 0.16 1125 20204
*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:
By:
Units: Imperial Point of Contact
Date:
Required Storage Volume 20,204 CF
Select Stormtech Chamber System SC-740
Stone Porosity (Industry Standard = 40%) 30%
Stone Foundation Depth 6 Inches
Storage Volume Per Chamber 67.60 CF
Avg Cover over Chambers (18 in min. & 96 in max.) 18 Inches 30 in (762 mm)
Number of Chambers Required - 299 6 in (150 mm)
Approximate Bed Size Required 10,635 SF
Tons of Stone Required 1,218 Tons
Volume of Excavation 1,772 CY
Area of Filter Fabric 2,977 SY
# of End Caps Required 18 Each
Length of ISOLATOR ROW 242.08 FT
ISOLATOR FABRIC 134 SY
Is the limiting dimension for the bed the width or length? width
Width 45 FT Length 45 FT
# of Chambers Long 34 EA # of Chambers long - EA
# of Rows 9 EA # of Rows - EA
Actual Length 245.68 FT Actual Length - FT
Actual Width 44.25 FT Actual Width - FT
7 of the chambers rows will contain only 33 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
02.22.16
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
Pond ID
Required Water
Quality Storage
Water Quality Volume
Provided within
Pavers
Water Quality Volume
Provided within
Rain Garden
Total Water Quality
Volume
Provided
100-year Detention
Volume Required
100-year Volume
Provided within
Chamber Sytem
Total Volume
Provided
Pond B 1376 cu. ft. 1008 cu. ft. 619 cu. ft. 1627 cu. ft. 20204 cu. ft. 20204 cu. ft. 21831 cu. ft.
Pond No :
c1
100-yr
0.52
5.00 min 727 ft3
0.16 acres 0.017 ac-ft
Max Release Rate = 0.10 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 9.950 248 1.00 0.10 30 218
10 7.720 385 0.75 0.08 45 340
15 6.520 488 0.67 0.07 60 428
20 5.600 559 0.63 0.06 75 484
25 4.980 622 0.60 0.06 90 532
30 4.520 677 0.58 0.06 105 572
35 4.080 713 0.57 0.06 120 593
40 3.740 747 0.56 0.06 135 612
45 3.460 777 0.56 0.06 150 627
50 3.230 806 0.55 0.06 165 641
55 3.030 832 0.55 0.05 180 652
60 2.860 857 0.54 0.05 195 662
65 2.720 883 0.54 0.05 210 673
70 2.590 905 0.54 0.05 225 680
75 2.480 929 0.53 0.05 240 689
80 2.380 950 0.53 0.05 255 695
85 2.290 972 0.53 0.05 270 702
90 2.210 993 0.53 0.05 285 708
95 2.130 1010 0.53 0.05 300 710
100 2.060 1028 0.53 0.05 315 713
105 2.000 1048 0.52 0.05 330 718
110 1.940 1065 0.52 0.05 345 720
115 1.890 1085 0.52 0.05 360 725
120 1.840 1102 0.52 0.05 375 727
*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 62.55 0.00 0.00 0.00 0.0000
5025.60 318.97 0.20 34.85 34.85 0.0008
5025.80 732.74 0.20 102.34 137.20 0.0031
5026.00 1344.25 0.20 204.63 341.83 0.0078 WQCV
5026.20 2026.55 0.20 334.75 676.58 0.0155
5026.40 2391.20 0.20 441.27 1117.85 0.0257 Total Vol
100-yr Detention Elevation Depth Volume
WQCV 5025.81 0.41 0.0033
100-yr Detention 5026.22 0.82 0.0167
Overall Detention 5026.29 0.89 0.0200
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
0.025 sq-in
1
Pond C
5025.40 ft
0.0033 ac-ft
0.0167 ac-ft Circular Perforation Sizing
1
0.0200 ac-ft
Dia (in.)
Lake Street Apartments February 25, 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 = 5026.29 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) 0.040670781 ft2
Ec = Elevation of Outlet Centroid (ft) 5.856592 in2
Orifice Size (in.) 2 -23/32 in.
Area (in2) 5.86 sq-in
Q 0.19 cfs
Orifice Height (in.) 2 - 7/8 in.
Orifice Width (in.) 2 in.
Area (in2) 5.86 sq-in
Q 0.19 cfs
February 25, 2016
1232-001 C. Snowdon
0
Pond C
Aa =
Circular Orifice
100-Year Orifice
Rectangular Orifice
100-Year Orifice
Lake Street Apartments
Pond C 0.003 5025.808 0.02 0.02 5026.29 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
0.86
5.00 min 867 ft3
0.14 acres 0.020 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 9.950 359 1.00 0.20 60 299
10 7.720 558 0.75 0.15 90 468
15 6.520 707 0.67 0.13 120 587
20 5.600 809 0.63 0.13 150 659
25 4.980 899 0.60 0.12 180 719
30 4.520 980 0.58 0.12 210 770
35 4.080 1032 0.57 0.11 240 792
40 3.740 1081 0.56 0.11 270 811
45 3.460 1125 0.56 0.11 300 825
50 3.230 1167 0.55 0.11 330 837
55 3.030 1204 0.55 0.11 360 844
60 2.860 1240 0.54 0.11 390 850
65 2.720 1277 0.54 0.11 420 857
70 2.590 1310 0.54 0.11 450 860
75 2.480 1344 0.53 0.11 480 864
80 2.380 1375 0.53 0.11 510 865
85 2.290 1406 0.53 0.11 540 866
90 2.210 1437 0.53 0.11 570 867
95 2.130 1462 0.53 0.11 600 862
100 2.060 1488 0.53 0.11 630 858
105 2.000 1517 0.52 0.10 660 857
110 1.940 1542 0.52 0.10 690 852
115 1.890 1570 0.52 0.10 720 850
120 1.840 1595 0.52 0.10 750 845
*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:
By:
Units: Imperial Point of Contact
Date:
Required Storage Volume 867 CF
Select Stormtech Chamber System SC-310
Stone Porosity (Industry Standard = 40%) 30%
Stone Foundation Depth 6 Inches
Storage Volume Per Chamber 26.90 CF
Avg Cover over Chambers (18 in min. & 96 in max.) 18 Inches 16 in (406 mm)
Number of Chambers Required - 33 6 in (150 mm)
Approximate Bed Size Required 976 SF
Tons of Stone Required 93 Tons
Volume of Excavation 120 CY
Area of Filter Fabric 291 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
6 of the chambers rows will contain only 2 chambers
Lake Street Apartments - Detention Pond D
Northern Engineering
C. Snowdon
02.22.16
Material Estimate
Controlled by Width (Rows) Controlled by Length
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
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
Pond ID
Required Water
Quality Storage
Water Quality Volume
Provided within
Pavers
Water Quality Volume
Provided within
Rain Garden
Total Water Quality
Volume
Provided
100-year Detention
Volume Required
100-year Volume
Provided within
Chamber Sytem
Total Volume
Provided
Pond D 93 cu. ft. 277 cu. ft. 0 cu. ft. 277 cu. ft. 867 cu. ft. 867 cu. ft. 1144 cu. ft.
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
1
WQCV = Watershed inches of Runoff (inches) 68.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.266 in
A = 0.16 ac
V = 0.0036 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
Lake Street Apartments February 25, 2016
1232-001 C. Snowdon
Detention Pond A
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
0.266
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
ö
ç
Project Title Date:
Project Number Calcs By:
Client
Basins
0.8
WQCV = Watershed inches of Runoff (inches) 74.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.235 in
A = 1.61 ac
V = 0.0316 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
1376 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
Lake Street Apartments March 28, 2016
1232-001 C. Snowdon
Basins B1 - B4
0.235
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
ö
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia I
a = 60.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 0.600
C) Tributary Watershed Area ATotal
= 13,884 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 2,794 sq ft
(Minimum recommended permeable pavement area = 3204 sq ft)
E) Impervious Tributary Ratio RT
= 2.4 IMPERVIOUS TRIBUTARY RATIO EXCEEDS 2.0
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 219 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal
= cu ft
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 10.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.30
D) Slope of the Base Course/Subgrade Interface S = ft / ft
E) Length Between Lateral Flow Barriers L = ft
F) Volume Provided Based on Depth of Base Course V = 629 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sloped: V = P * [(Dmin - (D
min - 6*SL-1)) / 12] * Area
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells = 1
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
Lake Street Apartments
Basin B1
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
March 29, 2016
Choose One
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia I
a = 62.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 0.620
C) Tributary Watershed Area ATotal
= 8,223 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 1,684 sq ft
(Minimum recommended permeable pavement area = 1946 sq ft)
E) Impervious Tributary Ratio RT
= 2.4 IMPERVIOUS TRIBUTARY RATIO EXCEEDS 2.0
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 133 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal
= cu ft
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 10.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.30
D) Slope of the Base Course/Subgrade Interface S = ft / ft
E) Length Between Lateral Flow Barriers L = ft
F) Volume Provided Based on Depth of Base Course V = 379 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sloped: V = P * [(Dmin - (D
min - 6*SL-1)) / 12] * Area
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells = 1
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
Lake Street Apartments
Basin B2
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
March 29, 2016
Choose One
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Invert Elevation
Water Quality Volume
100-yr Detention Volume
Total Pond Volume
D = Depth between contours (ft.)
A1 = Surface Area lower contour (ft2)
A2 = Surface Area upper contour (ft2)
5030.00 6.82 0.20 0.45 0.45 0.0000
5030.20 730.97 0.20 53.89 54.35 0.0012
5030.40 1551.82 0.20 223.19 277.54 0.0064
5030.60 1878.27 0.20 342.49 620.03 0.0142 WQCV
Elevation Depth Volume
Rain Garden WQCV 5030.60 0.80 0.0142
100-yr Detention NA NA NA
Overall Detention NA NA NA
Rain Garden Volume
Elevation
(ft)
Surface
Area (ft2)
Incremental
Depth (ft)
Incremental
Vol. (ft3)
Total Vol.
(ft3)
Total Vol.
(ac-ft)
Rain Garden
5029.80 ft
0.0142 ac-ft
NA
NA
Lake Street Apartments March 30, 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
1
WQCV = Watershed inches of Runoff (inches) 49.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.204 in
A = 0.16 ac
V = 0.0033 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)
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
Lake Street Apartments February 25, 2016
1232-001 C. Snowdon
Pond C
0.204
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
÷
ø
ö
Project Title Date:
Project Number Calcs By:
Client
Pond ID
0.8
WQCV = Watershed inches of Runoff (inches) 60.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100) 0.189 in
A = 0.14 ac
V = 0.0021 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
Lake Street Apartments March 28, 2016
1232-001 C. Snowdon
Pond D
93.2700 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
0.189
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
ö
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia I
a = 60.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 0.600
C) Tributary Watershed Area ATotal
= 5,917 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 1,232 sq ft
(Minimum recommended permeable pavement area = 1365 sq ft)
E) Impervious Tributary Ratio RT
= 2.3 IMPERVIOUS TRIBUTARY RATIO EXCEEDS 2.0
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 93 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal
= cu ft
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 10.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.30
D) Slope of the Base Course/Subgrade Interface S = ft / ft
E) Length Between Lateral Flow Barriers L = ft
F) Volume Provided Based on Depth of Base Course V = 277 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sloped: V = P * [(Dmin - (D
min - 6*SL-1)) / 12] * Area
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells = 1
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
Lake Street Apartments
Pond D
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
March 29, 2016
Choose One
Design
Point
Basin ID Basin Area Treatment Type
LID
System
Area Treated
by LID
System
Percent of Site
Treated by LID
System
Area of
Pavers
Area of
Aphalt
Parking
Percent
Pavers
a1 A1 & A2 0.327 ac. Extended Detention No 0.000 ac. 0.000 ac. N/A
b1 B1 0.319 ac. Paver System Yes 0.319 ac. 18.25% 0.064 ac. 0.193 ac. 33.16%
b2 B2 0.189 ac. Paver System Yes 0.189 ac. 10.81% 0.039 ac. 0.119 ac. 32.77%
b3 B3 0.974 ac. Paver System Yes 0.974 ac. 55.77% 0.000 ac. 0.000 ac. N/A
b4 B4 0.129 ac. Rain Garden Yes 0.129 ac. 7.39% 0.000 ac. 0.000 ac. N/A
c1 C1 & C2 0.164 ac. Extended Detention No 0.000 ac. 0.000 ac. N/A
d1 D1 0.136 ac. Paver System Yes 0.136 ac. 7.78% 0.028 ac. 0.069 ac. 40.58%
os1 OS1 0.150 ac. Grass Buffer No 0.000 ac. 0.000 ac. N/A
os2 OS2 0.024 ac. None No 0.000 ac. 0.016 ac. N/A
os3 OS3 0.039 ac. Grass Buffer No 0.000 ac. 0.000 ac. N/A
Total 2.451 ac. 1.746 ac. 71% 0.131 ac. 0.397 ac. 33.00%
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
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
1232-001 Basin D1 UD-BMP_v3.02.xls, PPS 3/29/2016, 4:04 PM
ç
è
= æ
12 hr
ç
è
= æ
40 hr
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
1232-001 Basin B2 UD-BMP_v3.02.xls, PPS 3/29/2016, 3:57 PM
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
1232-001 Basin B1 UD-BMP_v3.02.xls, PPS 3/29/2016, 3:55 PM
ç
è
= æ
12 hr
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
Tc =
Project Location :
Design Point
C =
Design Storm
Page 1 of 1
1232-001_Pond B_DetentionVolume_FAAModified Method.xls
( )
3
V D * A 1 A 2 A 1 * A 2
= + +
Tc =
Project Location :
Design Point
C =
Design Storm
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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 0.22 0.22 0.27 0.02 5.87 5.87 5.51 N/A N/A N/A 0.01 1.06 2.94 9 9 8
b1 B1-B4 No 0.69 0.69 0.86 0.03 2.69 2.69 1.58 0.01 2.00 1.96 N/A N/A N/A 5 5 5
c1 C1 & C2 No 0.80 0.80 1.00 N/A N/A N/A N/A 0.01 1.41 1.18 N/A N/A N/A 5 5 5
COMBINED DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
C. Snowdon
February 24, 2015
Design
Point
Basin IDs
Overland Flow Pipe 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
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 0.22 0.22 0.27 20 2.00% 5.9 5.9 5.5 N/A N/A N/A 187 0.50% 1.06 2.9 9 9 8
a2 A2 No 0.80 0.80 1.00 N/A N/A N/A N/A 100 0.50% 1.41 1.2 N/A N/A N/A 5 5 5
b1 B1 No 0.69 0.69 0.86 25 3.00% 2.7 2.7 1.6 235 1.00% 2.00 2.0 N/A N/A N/A 5 5 5
b2 B2 No 0.71 0.71 0.88 16 2.00% 2.3 2.3 1.3 100 1.36% 2.33 0.7 N/A N/A N/A 5 5 5
b3 B3 No 0.95 0.95 1.00 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 5 5 5
b4 B4 No 0.15 0.15 0.19 20 11.10% 3.6 3.6 3.4 N/A N/A N/A 61 0.50% 1.06 1.0 5 5 5
c1 C1 No 0.25 0.25 0.31 N/A N/A N/A N/A N/A N/A N/A 188 0.27% 0.77 4.1 5 5 5
c2 C2 No 0.80 0.80 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 0.69 0.69 0.86 13 5.00% 1.6 1.6 0.9 156 0.87% 1.87 1.4 N/A N/A N/A 5 5 5
os1 OS1 No 0.23 0.23 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 0.69 0.69 0.86 10 2.00% 1.9 1.9 1.1 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 Flow Swale Flow
Design
Point
Basin
Overland Flow
C. Snowdon
February 24, 2015
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 2276 0.052 0.030 0.012 0.000 0.000 0.000 0.010 0.80 0.80 1.00 79%
D1 5917 0.136 0.069 0.014 0.000 0.000 0.028 0.025 0.69 0.69 0.86 60%
OS1 6544 0.150 0.000 0.015 0.000 0.000 0.000 0.135 0.23 0.23 0.29 9%
OS2 1052 0.024 0.010 0.006 0.000 0.000 0.000 0.008 0.69 0.69 0.86 65%
OS3 1691 0.039 0.000 0.000 0.000 0.000 0.000 0.039 0.15 0.15 0.19 0%
TOTAL 106750 2.45 0.524 0.120 0.974 0.000 0.131 0.963 0.71 0.71 0.88 62%
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
February 24, 2015
**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
February 24, 2015
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