HomeMy WebLinkAboutSTEAD (255 S. TAFT HILL RD.) - PDP/FDP - FDP150029 - REPORTS - DRAINAGE REPORTSeptember 24, 2015
FINAL DRAINAGE REPORT FOR
Stead
Fort Collins, Colorado
Prepared for:
Shane Roberts
255 South Taft Hill Road
Fort Collins, Colorado 80521
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: 1130-001
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.
301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com
September 24, 2015
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
STEAD
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage Report for your review. This report
accompanies the Project Development Plan submittal for the proposed Stead project.
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 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.
Danny Weber Nicholas W. Haws, PE
Project Engineer Project Manager
Stead
Final Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 4
A. Location ............................................................................................................................................. 4
B. Description of Property ..................................................................................................................... 4
C. Floodplain.......................................................................................................................................... 6
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 7
A. Major Basin Description .................................................................................................................... 7
B. Sub-Basin Description ....................................................................................................................... 7
III. DRAINAGE DESIGN CRITERIA ................................................................................... 8
A. Regulations........................................................................................................................................ 8
B. Four Step Process .............................................................................................................................. 8
C. Development Criteria Reference and Constraints ............................................................................ 8
D. Hydrological Criteria ......................................................................................................................... 8
E. Hydraulic Criteria .............................................................................................................................. 8
F. Modifications of Criteria ................................................................................................................... 8
IV. DRAINAGE FACILITY DESIGN .................................................................................... 9
A. General Concept ............................................................................................................................... 9
B. Specific Details .................................................................................................................................. 9
V. CONCLUSIONS ........................................................................................................ 9
A. Compliance with Standards .............................................................................................................. 9
B. Drainage Concept ............................................................................................................................ 10
REFERENCES .................................................................................................................. 10
APPENDICES:
APPENDIX A - Hydrologic Computations
LIST OF FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 5
Figure 2 – Proposed Site Plan ............................................................................................... 6
Figure 3 – Existing Floodplains ............................................................................................. 7
MAP POCKET:
Historic Drainage Exhibit
Developed Drainage Exhibit
Stead
Final Drainage Report
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The project site is located in Section 9, 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 north of the intersection of South Taft Hill Road and West
Mulberry Street, and is a flag lot extending to South Taft Hill Road.
4. The project site lies within the Canal Importation Drainage Basin.
5. This is an infill, flag-shaped lot, surrounded entirely by existing development.
6. The project site received no offsite flows from the surrounding areas.
B. Description of Property
1. The development area is roughly 0.68 net acres.
Stead
Final Drainage Report
Figure 1 – Aerial Photograph
2. The subject property is currently undeveloped, with the majority of the site covered
with native grasses while the leg portion of the flag lot is mostly covered with gravel.
Existing ground slopes are mild to moderate (i.e., ±1 - 4%) through the interior of the
property. General topography slopes from northwest to southeast.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey website:
http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx,
the site consists of Nunn Clay Loam, which falls into Hydrologic Soil Group C.
4. The proposed project site plan is composed of the development of a single-family
residential unit, garage, and barn.
PROJECT SITE
Stead
Final Drainage Report
Figure 2– Proposed Site Plan
5. There is a private irrigation ditch in the northwest corner of the site that will not be
disturbed by this development.
6. The proposed land use is a single-family residential unit in the Low Density Mixed-Use
Neighborhood District (L-M-N).
C. Floodplain
7. The project site is not encroached by either a Fort Collins Flood Plain Map of a FEMA
Flood Plain Map (Map #08069C0978G).
Stead
Final Drainage Report
Figure 3 –Area Floodplain Mapping
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The project site lies within the Canal Importation Drainage Basin. Current City of Fort
Collins Stormwater Regulations do not require on-site detention or water quality
measures for single-family developments and are not proposed.
B. Sub-Basin Description
1. The subject property historically drains overland from northwest to southeast. Runoff
from the majority of the site has historically collected at a point near the southeast
corner of the site where it drains onto the adjacent property, then into the South Taft
Hill Road Right-Of-Way, and ultimately onto West Mulberry Street.
2. A summary of the historic runoff rates for each basin is tabularized on the Historic
Drainage Exhibit in the Map Pocket at the end of this report.
Project Site
Stead
Final Drainage Report
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the proposed
project.
B. Four Step Process
The Four Step Process will not be employed as no water quality measures are required
for single-family developments. The permanent site will be either landscaped, roofed, or
hardscaped and, therefore, provides as the water quality measures. No portion of the
developed site shall be non-vegetated.
C. Development Criteria Reference and Constraints
The subject property is surrounded by currently developed properties. Thus, several
constraints have been identified during the course of this analysis that will impact the
proposed drainage system including:
Existing elevations along the property lines will generally be maintained.
As previously mentioned, overall drainage patterns of the existing site will be
maintained.
Elevations of existing downstream facilities that the subject property will release to
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
associated with the proposed 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 RA-7 and RA-8 of the FCSCM. Please see Appendix
A.
3. 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 maintains historic drainage patterns.
2. All drainage facilities proposed with the project are designed in accordance with
criteria outlined in the FCSCM and/or the Urban Drainage and Flood Control District
(UDFCD) Urban Storm Drainage Criteria Manual. Please see Appendix B.
3. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
F. Modifications of Criteria
1. The proposed development is not requesting any modifications to criteria at this time.
Stead
Final Drainage Report
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the project drainage design are to maintain existing drainage
patterns, and to ensure no adverse impacts to any adjacent properties.
2. Drainage patterns anticipated for drainage basins shown in the Drainage Exhibit are
described below.
Basin W
Basins W is largely unmodified with the exception of a proposed barn in the western
half of the site. This basin will follow similar historic patterns sheet draining to the
southeast corner of the site. Due to minor re-grading around the proposed single-
family structure, Basin W has a smaller watershed area than Historic Basin W. This
results in a release rate from proposed Basin W less than Historic Basin W, so no
downstream impacts are expected.
Basin E
Basin E has enlarged as compared to Historic Basin E to encompass the proposed
garage and single-family structure. This basin is graded such that runoff will collect in
a concrete pan surrounding the development and route flows east down the drive-way
to the Taft Hill Rd Right-of-Way through a sidewalk chase. Although the release rate
has increased in comparison to the Historic Basin E, no on-site detention or water
quality measures are required per the City of Fort Collins Stormwater Regulations. The
increased runoff from this basin are considered negligible and no downstream impacts
are expected.
B. Specific Details
1. Summaries of the runoff rates for both the Historic basins and Developed basins are
included on the Drainage Exhibits in the Map Pocket at the end of this report.
2. Proper maintenance of the drainage facilities designed with the proposed development
is a critical component of their ongoing performance and effectiveness.
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the proposed project complies with the City of Fort
Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with this project complies with requirements for the
Canal Importation Drainage Basin.
3. The drainage plan and stormwater management measures proposed with the
proposed development are compliant with all applicable State and Federal regulations
governing stormwater discharge.
Stead
Final Drainage Report
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit any potential
damage associated with its stormwater runoff.
2. The drainage concept for the proposed development is consistent with requirements
for the Canal Importation Drainage Basin.
REFERENCES
1. 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.
2. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
4. 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: Stead
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: D. Weber
Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100 Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90
Gravel ……….…………………….….…………………………..……………………………….0.50 . 40
Roofs …….…….………………..……………….…………………………………………….0.. 95 90
Concrete 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
Concrete
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.
W-Hist 44,845 1.03 0.00 0.00 0.00 0.00 0.00 1.03 0.25 0.25 0.31 0.0
E-Hist 5,474 0.13 0.00 0.01 0.00 0.04 0.00 0.08 0.38 0.38 0.47 18.7
Total 50,319 1.16 0.00 0.01 0.00 0.04 0.00 1.11 0.26 0.26 0.33 2.0
EXISTING 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.
Overland Flow, Time of Concentration:
Project: Stead
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt
= L / 60V
Tc
= Ti
+ 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,
Rational Method Equation: Project: Stead
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
W W-Hist 1.03 12.5 12.5 11.7 0.25 0.25 0.31 2.02 3.45 7.29 0.52 0.89 2.35
E E-Hist 0.13 6.0 6.0 5.3 0.38 0.38 0.47 2.67 4.56 9.95 0.13 0.22 0.59
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
EXISTING RUNOFF COMPUTATIONS
C100
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)
D. Weber
September 24, 2015
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Q = C f ( C )( i )( A )
D:\Projects\1130-001\Drainage\Hydrology\1130-001_Rational-Calcs_Existing.xlsx\Direct-Runoff
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Stead
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: D. Weber
Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100 Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90
Gravel ……….…………………….….…………………………..……………………………….0.50 . 40
Roofs …….…….………………..……………….…………………………………………….0.. 95 90
Concrete 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
Concrete
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.
W 33,781 0.78 0.00 0.00 0.03 0.00 0.00 0.75 0.27 0.27 0.34 3.2
E 16,557 0.38 0.00 0.01 0.06 0.16 0.00 0.15 0.48 0.48 0.61 33.4
Total 50,338 1.16 0.00 0.01 0.09 0.16 0.00 0.90 0.34 0.34 0.43 13.1
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.
Overland Flow, Time of Concentration: The Stead
Project: Stead
42228.0 Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt
= L / 60V
Tc
= Ti
+ 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,
The Stead
Rational Method Equation: Project: Stead
42228Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
W W 0.78 12.5 12.5 11.7 0.27 0.27 0.34 2.02 3.45 7.29 0.43 0.73 1.94
E E 0.38 8.4 8.4 7.1 0.48 0.48 0.61 2.40 4.10 8.80 0.44 0.75 2.03
DEVELOPED RUNOFF COMPUTATIONS
C100
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)
D. Weber
September 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 )
D:\Projects\1130-001\Drainage\Hydrology\1130-001_Rational-Calcs_Proposed.xlsx\Direct-Runoff
MAP POCKET
DR1 – DEVELOPED DRAINAGE EXHIBIT
X X
X X
X
X
X
X
X X X X X X X X
X
X
X
X
X
X X X
X
X
X
X X
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X X
X
X
SS
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SS SS
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SS SS
SS
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SS
SS SS
W
E G
CTV
REC. NO. 99024292
TENTH GREEN, FIRST FILING
9
7 8
10 11
12
W-Hist
E-Hist
These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
200 South College Avenue, Suite 010
Fort Collins, Colorado 80524
N O R T H E RN
PHONE: 970.221.4158 FAX: 970.221.4159
www.northernengineering.com
H1
X X
X X
X X X X X X X
X
X
X X
X
X X X
X
X
X
X
X
X
X
SS
SS
SS SS
SS
SS SS
SS
SS SS
SS
SS SS
SS SS
W
G
E CTV
REC. NO. 99024292
TENTH GREEN, FIRST FILING
9
7 8
10 11
12
W
W
NEW
RESIDENCE
3-CAR
GARAGE
BARN
E
These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
200 South College Avenue, Suite 010
Fort Collins, Colorado 80524
N O R T H E RN
PHONE: 970.221.4158 FAX: 970.221.4159
www.northernengineering.com
DR1
LEGEND:
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
R
NORTH
#
#
1.45 ac
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
DEVELOPED RUNOFF SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C10 C100
2-yr Tc
(min)
10-yr Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
W W 0.78 0.27 0.27 0.34 12.5 12.5 11.7 0.43 0.73 1.94
E E 0.38 0.48 0.48 0.61 8.4 8.4 7.1 0.44 0.75 2.03
LEGEND:
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
R
NORTH
#
#
1.45 ac
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
EXISTING RUNOFF SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C10 C100
2-yr Tc
(min)
10-yr Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
W W-Hist 1.03 0.25 0.25 0.31 12.5 12.5 11.7 0.52 0.89 2.35
E E-Hist 0.13 0.38 0.38 0.47 6.0 6.0 5.3 0.13 0.22 0.59
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
W W No 0.25 0.25 0.31 100 3.0 11.0 11.0 10.2 0 0.0 0.00 N/A 190 2.0 2.12 1.5 12.5 12.5 11.7
E E No 0.50 0.50 0.63 80 4.0 6.3 6.3 5.0 216 0.8 1.73 2.1 0 0.0 0.00 N/A 8.4 8.4 7.1
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
D. Weber
September 24, 2015
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
−
=
D:\Projects\1130-001\Drainage\Hydrology\1130-001_Rational-Calcs_Proposed.xlsx\Tc-2-yr_&_100-yr
10-year Cf
= 1.00
September 24, 2015
D:\Projects\1130-001\Drainage\Hydrology\1130-001_Rational-Calcs_Proposed.xlsx\C-Values
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
W W-Hist No 0.25 0.25 0.31 100 3.0 11.0 11.0 10.2 0 0.0 0.00 N/A 190 2.0 2.12 1.5 12.5 12.5 11.7
E E-Hist No 0.50 0.50 0.63 26 5.0 3.3 3.3 2.6 0 0.0 0.00 N/A 216 0.8 1.34 2.7 6.0 6.0 5.3
EXISTING TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
D. Weber
September 24, 2015
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
−
=
D:\Projects\1130-001\Drainage\Hydrology\1130-001_Rational-Calcs_Existing.xlsx\Tc-2-yr_&_100-yr
10-year Cf
= 1.00
September 24, 2015
D:\Projects\1130-001\Drainage\Hydrology\1130-001_Rational-Calcs_Existing.xlsx\C-Values