HomeMy WebLinkAboutBROWNS ON HOWES - PDP/FDP - FDP140019 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
Browns on Howes
Fort Collins, Colorado
August 6, 2014
Prepared for:
Maxiimo Development Group
706 S. College Avenue, Suite 201
Fort Collins, CO 8024
Prepared by:
200 South College Avenue, Suite 100
Fort Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 1033-001
3 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.
August 6, 2014
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
Browns on Howes
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies the 05.14.14 Basic Development Review submittal for the
proposed Browns on Howes. Comments from the Conceptual Review Letter dated May 21, 2014
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 Browns on Howes
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
Browns on Howes
Preliminary 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 .................................................................................... 8
A. General Concept .......................................................................................................................... 8
B. Specific Details ............................................................................................................................. 8
V. CONCLUSIONS ........................................................................................................ 9
A. Compliance with Standards .......................................................................................................... 9
B. Drainage Concept ........................................................................................................................ 9
References ....................................................................................................................... 10
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers
B.2 – Inlets
B.3 – Detention Facilities
APPENDIX C – Water Quality Design Computations
APPENDIX D – Erosion Control Report
Browns on Howes
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2– Proposed Site Plan ................................................................................................ 3
Figure 3 – Existing City Floodplains ....................................................................................... 4
MAP POCKET:
C400 - Drainage Exhibit
Browns on Howes
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. Browns on Howes project is located in the southwest quarter of Section 11, 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 at the northeast corner of Shields Street and Mountain
Avenue.
4. Currently the existing lot does not have any stormwater or water quality facilities. The
project primarily consists of an asphalt and concrete fueling area and parking lot. The
remaining area consists of a convenient store and surrounding landscape areas. The
project site is composed of 39% imperviousness. The existing site drains in one
direction from the southwest corner of the property to the northeast corner and into
Howes Street.
5. The project is currently border to the south by a commercial building, west by a public
alley, north by a single-family residence and east by Howes Street.
Browns on Howes
Preliminary Drainage Report 2
B. Description of Property
1. Browns on Howes is approximately 0.436 net acres.
Figure 1 – Aerial Photograph
2. Browns on Howes consists of two properties with one existing structure located in the
northwest corner of the northern lot. The remainder of the lot consists of gravel
parking area for both the residence to the north and the commercial building to the
south. The alley located to the west of the property drains onto the property and this
runoff and all runoff generated from the project site is routed to the northeast corner of
the northern property and discharged directly into Howes 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 Paoli fine
sandy loam, which falls into Hydrologic Soil Groups B.
4. The proposed development will include the demolition of the existing structure and
removal of the existing gravel parking area. The proposed site will include two large
building, each being divided into three single family attached units with an access
drive located to the north composed of both permeable pavers and concrete. The
section of drive constructed of permeable pavers will act as the projects water quality
facility and detention area.
SITE
Browns on Howes
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
5. No irrigation facilities are known to be within the property limits.
6. The project site is within the Downtown (D) Zoning District. The proposed project is
not requesting a change in the land use.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
2. The FEMA Panel 0801010979H, shown below, illustrates the proximity of the
project site to the nearest FEAM delineated regulatory floodplain. It is noted that the
vertical datum utilized for site survey work is the City of Fort Collins Benchmark #1-
13 (Elevation = 4976.58, Fort Collins NVGD 29 – Unadjusted)
Browns on Howes
Preliminary Drainage Report 4
Figure 3 – Existing FEMA Floodplains
Figure 4 – Existing City Floodplains
Browns on Howes
Preliminary Drainage Report 5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Browns on Howes 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 southern lot to the
northeast corner of the northern lot. Stormwater is routed via overland flow across the
existing parking area. Stormwater is discharged directly into Howes street (0.41 cfs
for the 2-year storm and 2.01 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 east, north or south. There is a
public alley that runs along the western boundary and drains to a low point located
north of the property. This alley currently does not include curb and gutter and all the
runoff generated from the western half is routed through sheetflow to the properties to
the east. The amount of runoff is minimal, but is reflected within the historic runoff
calculations.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the Browns on
Howes Project
B. Four Step Process
The overall stormwater management strategy employed with the Browns on Howes 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:
Providing vegetated open areas along the 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 bio-swale 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.
Browns on Howes
Preliminary 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 southerm portion of the building will be
routed through a bio-swale and into a proposed storm collection system. This storm
collection system is proposed to discharge directly into the permeable paver area and
routed through this section to achieve water quality. Stormwater generated from the
northern portion of the building will be routed through planter beds and into a proposed
storm collection system. This storm collection system is proposed to discharge directly
into the detention vault. The stormwater generated from the proposed parking area will be
routed via overland flow to the permeable paver area.
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 Browns on Howes, 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, but the a following site specific source control has been
included:
A localized trash enclosure at the rear of the building for the disposal of office waste.
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 Browns on Howes 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 east and west property lines adjacent to the public
alley and Howes Street will be maintained. Existing elevations along the north and
the south property lines will be maintained.
Existing elevations and vegetation on the east side of the subject property will be
preserved.
As previously mentioned, overall drainage patterns of the existing site will be
maintained.
Browns on Howes
Preliminary 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 the Regency Lakeview 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 Howes Street. The
majority of the site drains stormwater via overland flow.
2. All drainage facilities proposed with the Browns on Howes 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 a FEMA
regulatory floodplain.
4. The Browns on Howes 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
floodplain, and thus are not subject to any floodplain regulations.
G. Modifications of Criteria
1. The proposed Brown on Howes development is not requesting any modifications to
criteria at this time.
Browns on Howes
Preliminary Drainage Report 8
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the Browns on Howes drainage design are to maintain existing
drainage patterns and ensure no adverse impacts to any adjacent properties.
2. The existing site does have off-site flows from the public alley to the west. The
existing routing of this runoff of will remain and pass through the proposed project.
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 Browns on Howes project is composed of one major drainage basin, designated
as Basins A. The project further subdivided Basin A in to two (2) sub-basins,
designated as Basins A1, and A2. The drainage patterns anticipated for Basin A and
associated sub-basins are further described below.
Basin A
Basin A consists of all of the improvements being proposed on-site, as well as all of
the improvements being proposed within the public alley. Basin A1 encompasses the
northern portion of the proposed buildings and the entire drive aisle. Runoff from the
roofs will be discharged via downspouts into designed planter beds with proposed
inlets. The runoff from these planter beds will discharge directly into the underground
detention vault. The runoff generated from the proposed alley improvements will be
routed via curb and gutter into the site. All other runoff from this basin will be routed
over the permeable pavers and intercepted by a combination inlet. This inlet is
designed with an orifice plate to restrict flow to the existing 2-event. The stormwater
intercepted by the combination inlet will back up into the proposed underground
detention vault. Basin A2 encompasses the southern portion of the proposed
buildings and the green belt to the north and east. Runoff from the roofs will be
discharged via downspouts into designed planter beds. Any overflow from these
planter beds and the runoff generated from the proposed concrete areas will discharge
into a bio-swale and be routed to a proposed inlet located at the southeastern corner
of the property. The stormwater intercepted by the proposed inlet or intercepted by
the proposed underdrain within the bio-swale will be discharge directly into the
permeable paver system and ultimately into the underground detention vault.
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 Howes 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 will be routed through a
landscape area.
All improvements generated from the site will be routed through a permeable
paver system.
Browns on Howes
Preliminary Drainage Report 9
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. The total establishes
the overall maximum allowable release rate, 0.41 cfs, from the project site. This
release rate was utilized in the FAA procedure detention storage computations (Refer
to Appendix B for these calculations).
3. The FAA method was used to size the on-site pond for quantity detention.
Calculations for this area, based on the characteristics of basin A and adjusted release
rate, indicated a detention volume of 4523 cu. Ft. This does not include the any
Quality Capture Volume (WQCV), but this it be stored within the proposed permeable
paver system. 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 Paoli fine
sandy loam.
4. The storage volume available within StormTech Vault Structure is 4770 cu. ft. and
the No., open-graded aggregate surrounding the system. This does not include any of
the volume within the permeable paver section.
5. The emergency spillway will be located at the northeastern corner of the street
entrance from Howes Street. In the event that emergency overflows occur, the
drainage will flow to the northeast into Howes Street.
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the Browns on Howes project complies with the
City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with the Browns on Howes 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 Browns on Howes
development.
4. The drainage plan and stormwater management measures proposed with the Browns
on Howes 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. Browns on Howes will detain for the pervious
area converted to impervious areas to release at the 2-year existing rate during the
100-year storm.
2. The proposed Browns on Howes development will not impact the Master Drainage
Plan recommendations for the Old Town major drainage basin
Browns on Howes
Preliminary Drainage Report 10
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: Browns on Howes
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 22408 0.51 0.02 0.01 0.02 0.37 0.09 0.49 0.49 0.61 39%
HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Notes
August 6, 2014
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\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\Hist-C-Values
Overland Flow, Time of Concentration:
Project: Browns on Howes
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: Browns on Howes
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
h1 H1impervious 0.51 20 20 16 0.49 0.49 0.61 1.63 2.78 6.41 0.41 0.70 2.01
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C2 C
10 C100
HISTORIC RUNOFF COMPUTATIONS
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
C. Snowdon
August 6, 2014
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)
Q C f C i A
Page 3 of 10 D:\Projects\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\Hist-Direct-Runoff
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Browns on Howes
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 14895 0.342 0.027 0.087 0.140 0.000 0.045 0.043 0.78 0.78 0.97 68%
A2 7509 0.172 0.000 0.075 0.012 0.000 0.000 0.086 0.55 0.55 0.69 45%
TOTAL 22404 0.514 0.027 0.162 0.152 0.000 0.045 0.173 0.72 0.72 0.89 60%
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
August 6, 2014
Overland Flow, Time of Concentration:
Project: Browns on Howes
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: Browns on Howes
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
a1 A1 0.34 5 5 5 0.78 0.78 0.97 2.85 4.87 9.95 0.8 1.3 3.3
a2 A2 0.17 5 5 5 0.55 0.55 0.69 2.85 4.87 9.95 0.3 0.5 1.2
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)
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
August 6, 2014
Intensity,
i10
(in/hr)
Q C f C i A
Page 6 of 10 D:\Projects\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\Direct-Runoff
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Browns on Howes
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 22404 0.514 0.027 0.162 0.152 0.000 0.045 0.129 0.70 0.70 0.88 60%
COMBINED DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
August 6, 2014
**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
Overland Flow, Time of Concentration:
Project: Browns on Howes
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: Browns on Howes
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
a1 A1-A2 0.51 5 5 5 0.70 0.70 0.88 2.85 4.87 9.95 1.0 1.8 4.5
Intensity,
i100
(in/hr)
COMBINED DEVELOPED RUNOFF COMPUTATIONS
C. Snowdon
August 6, 2014
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)
Q C f C i A
Page 9 of 10 D:\Projects\1033-001\Drainage\Hydrology\1033-001_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 0.342 0.78 0.97 5.0 5.0 0.76 3.31
a2 A2 0.172 0.55 0.69 5.0 5.0 0.27 1.18
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
h1 H1 22408.00 0.49 0.61 19.6 15.7 0.4 2.01
Page 10 of 10 D:\Projects\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\SUMMARY-TABLE
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers (Future Use)
B.2 – Inlets (Future Use)
B.3 – Detention Facilities
APPENDIX B.1
STORM SEWERS (RESERVED FOR FUTURE USE)
APPENDIX B.2
INLETS (RESERVED FOR FUTURE USE)
APPENDIX B.3
DETENTION FACILITIES
Project No. 959-001
Calculations By: CNS
Northern Engineering Services, Inc. Geico Office Building
Pond No :
a1
100-yr
0.89
5.00 min 4523 ft3
0.51 acres 0.10 ac-ft
Max Release Rate = 0.41 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 1366 1.00 0.41 123 1243
10 7.720 2119 0.75 0.31 185 1934
15 6.520 2684 0.67 0.27 246 2438
20 5.600 3074 0.63 0.26 308 2767
25 4.980 3417 0.60 0.25 369 3048
30 4.520 3722 0.58 0.24 431 3291
35 4.080 3920 0.57 0.23 492 3428
40 3.740 4106 0.56 0.23 554 3553
45 3.460 4274 0.56 0.23 615 3659
50 3.230 4433 0.55 0.23 677 3756
55 3.030 4574 0.55 0.22 738 3836
60 2.860 4710 0.54 0.22 800 3911
65 2.720 4853 0.54 0.22 861 3992
70 2.590 4976 0.54 0.22 923 4054
75 2.480 5105 0.53 0.22 984 4121
80 2.380 5226 0.53 0.22 1046 4181
85 2.290 5343 0.53 0.22 1107 4236
90 2.210 5459 0.53 0.22 1169 4291
95 2.130 5554 0.53 0.22 1230 4324
100 2.060 5654 0.53 0.22 1292 4363
105 2.000 5764 0.52 0.21 1353 4411
110 1.940 5857 0.52 0.21 1415 4443
115 1.890 5966 0.52 0.21 1476 4490
120 1.840 6060 0.52 0.21 1538 4523
*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
Project Information:
Project Name: Browns on Howes
Location: Fort Collins, CO
Date: 8/6/2014
Engineer: C. Snowdon
StormTech RPM:
MC-4500 Site Calculator
System Requirements System Sizing
Units Imperial Number of Chambers Required 28 each
Required Storage Volume 4523 CF Number of End Caps Required 2 each
Stone Porosity (Industry Standard = 40%) 40 % Bed Size (including perimeter stone) 1,238 square feet
Stone Above Chambers (12 inch min.) 12 inches Stone Required (including perimeter stone) 278 tons
Stone Foundation Depth (9 inch min.) 9 inches Volume of Excavation 355 cubic yards
Average Cover over Chambers (24 inch min.) 24 inches Non-woven Filter Fabric Required (20% Safety Factor) 564 square yards
Bed size controlled by WIDTH or LENGTH? LENGTH Length of Isolator Row 119.8 feet
Limiting WIDTH or LENGTH dimension 170 feet Woven Isolator Row Fabric (20% Safety Factor) 329 square yards
Storage Volume per Chamber 162.6 CF
Storage Volume per End Cap 108.6 CF Installed Storage Volume 4,770 cubic feet
24
Maximum Length = 170 feet inches
1 row of 28 chambers 12
inches
Maximum Length = 119.8 feet
Maximum Width = 10.3 feet
9
inches
Controlled by Length
60"
(1524 mm)
24"
(610 mm)
MIN.
7.0'
(2.13 m)
MAX.
100" (2540 mm)
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
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 = 100.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 1.000
C) Tributary Watershed Area ATotal
= 4,658 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 1,954 sq ft
(Minimum recommended permeable pavement area = 1553 sq ft)
E) Impervious Tributary Ratio RT
= 1.4
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 155 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
Browns on Howes
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
August 6, 2014
Choose One
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 12.0 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 = 0.40
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 = 716 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
Detention Vault no Underdrain
C) Distance from the Lowest Elevation of the Storage Volume y = 0.3 ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
A) Depth of WQCV in the Reservoir DWQCV
= 2.38 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice
= 0.44 inches
(Use a minimum orifice diameter of 3/8-inches)
Browns on Howes
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
August 6, 2014
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
(Use a minimum orifice diameter of 3/8-inches)
Notes:
1033-001 UD-BMP_v3.02.xls, PPS 8/6/2014, 1:20 PM
APPENDIX D
EROSION CONTROL REPORT
Browns on Howes
Preliminary 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.
Browns on Howes
Preliminary Erosion Control Report
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
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.)
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
1033-001 UD-BMP_v3.02.xls, PPS 8/6/2014, 1:20 PM
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1033-001
Browns on Howes
Project Number :
Project Name :
Underground Detention
Page 1 of 1
1033-001_DetentionVolume_FAAModified Method.xls
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
a1 A1-A2 No 0.78 0.78 0.97 82.00 0.02 4.18 4.18 1.65 45.00 0.01 1.43 0.52 0.00 N/A N/A N/A 5 5 5
COMBINED DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
C. Snowdon
August 6, 2014
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\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\Comb-Tc-10-yr_&_100-yr
Page 7 of 10 D:\Projects\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\Comb-C-Values
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
a1 A1 No 0.78 0.78 0.97 82 2.22% 4.2 4.2 1.7 45 0.51% 1.43 0.5 0 N/A N/A N/A 5 5 5
a2 A2 No 0.55 0.55 0.69 20 8.33% 2.3 2.3 1.7 0 N/A N/A N/A 0 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
August 6, 2014
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
Page 5 of 10 D:\Projects\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr
**Soil Classification of site is Sandy Loam**
C. Snowdon
Page 4 of 10 D:\Projects\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\C-Values
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
h1 H1 No 0.49 0.49 0.61 210 0.60% 19.6 19.6 15.7 N/A N/A N/A N/A N/A N/A 20 20 16
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
C. Snowdon
August 6, 2014
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\1033-001\Drainage\Hydrology\1033-001_Rational-Calcs.xlsx\Hist-Tc-10-yr_&_100-yr