HomeMy WebLinkAboutSTEAD (255 S. TAFT HILL RD.) - PDP/FDP - FDP150029 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTAugust 12, 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
August 12, 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 ......................................................................................................................... 9
E. Hydraulic Criteria .............................................................................................................................. 9
F. Modifications of Criteria ................................................................................................................... 9
IV. DRAINAGE FACILITY DESIGN .................................................................................... 9
A. General Concept ............................................................................................................................... 9
B. Specific Details ................................................................................................................................ 10
V. CONCLUSIONS ...................................................................................................... 11
A. Compliance with Standards ............................................................................................................ 11
B. Drainage Concept ............................................................................................................................ 11
REFERENCES .................................................................................................................. 11
APPENDICES:
APPENDIX A - Hydrologic Computations
APPENDIX B - Hydraulic Computations
B.1 - Detention Facilities
LIST OF FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 5
Figure 2 – Proposed Site Plan ............................................................................................... 6
Figure 3 – Existing Floodplains ............................................................................................. 7
MAP POCKET:
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. Detention is
required between the developed 100-year inflow rate and 2-year historic release rate.
However, due to the site constraints of the flag-shaped, infill development and the
feasible of a detention pond outfall location, an on-site retention pond is proposed, as
suggested as an alternative by City Staff. Additionally, the leg portion of the flag lot
cannot be graded to be retained on-site but sees very little to no increase in runoff
caused by the development.
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 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 overall stormwater management strategy employed with the proposed 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:
Conserving existing amenities in the site including the existing vegetated areas.
Providing vegetated open areas throughout the site to reduce the overall impervious
area and to minimize directly connected impervious areas (MDCIA).
Routing flows, to the extent feasible, through vegetated swales to increase time of
concentration, promote infiltration and provide initial water quality.
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, urban
development of this intensity will still generate stormwater runoff that will require
additional BMPs and water quality. The majority of stormwater runoff from the site will
ultimately be intercepted and treated using a retention pond.
Step 3 – Stabilize Drainageways
There are no major drainageways within the subject property. While this step may not
seem applicable to proposed development, the project indirectly helps achieve stabilized
drainageways nonetheless. By providing water quality treatment, where none previously
existed, sediment with erosion potential is removed from downstream drainageway
systems. Furthermore, this project will pay one-time stormwater development fees, as
well as ongoing monthly stormwater utility fees, both of which help achieve City-wide
drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs.
The proposed project will improve upon site specific source controls compared to historic
conditions:
The proposed development will provide LID and water quality treatment; thus,
eliminating sources of potential pollution previously left exposed to weathering and
runoff processes.
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
Stead
Final Drainage Report
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. The Rational Formula-based FAA procedure has been employed to compute the
required storage volume of the retention pond.
3. 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.
4. 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.
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. Onsite water quality treatment will be provided, as well as other LID features, which
are discussed further below.
3. Drainage patterns anticipated for drainage basins shown in the Drainage Exhibit are
described below.
Stead
Final Drainage Report
Basin W
Basins W will drain via overland flow to the retention pond located at the southeast
corner of the site. This basin was considered as the gross area of improved surfaces
as to properly size the retention pond and not retain the historic flows from the entire
watershed basin. More specific information regarding the retention pond is included
below. Please see further discussion of water quality and LID features in Section IV.B,
below.
Basin E
Basin E will sheet drain to the southeast before entering the South Taft Hill Road
Right-Of-Way. Due to the constraints of the surrounding existing developments, little
to no re-grading of this area can be performed and, therefore, cannot be detained or
retained.
B. Specific Details
1. The retention pond has been sized to retain the volume of two times the 100-
yr, 2-hour event with an effective High Water Service Elevation of 5074.05,
leaving 0.20’ for additional freeboard. An overflow weir will be located along
the east side at the natural low point, discharging away from any structures. A
summary of the developed runoff information is tabularized on the Drainage
Exhibit included in the Map Pocket at the end of this report.
2. The following table summarizes LID features and overall percentage of the basin being
treated by the proposed LID features.
Table 2 – LID Summary
Basin
Basin
Area
Portion of Basin
Captured
(sq.ft.)
Treatment
Type
W 7540 7540 Retention Pond
E 5474 0 None
Total 13014 7540
Total Percentage
Treated:
57.94%
3. Standard Operating Procedures (SOP) Manual shall be provided to the City of
Fort Collins for review prior to Final Development Plan approval. A final copy
of the approved SOP manual shall be provided to City and must be maintained
on-site by the entity responsible for the facility maintenance. Annual reports
must also be prepared and submitted to the City discussing the results of the
maintenance program (i.e. inspection dates, inspection frequency, volume loss
due to sedimentation, corrective actions taken, etc.).
Stead
Final Drainage Report
4. 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.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit any potential
damage associated with its stormwater runoff by providing detention and water
quality mitigation features.
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: The 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 7,540 0.17 0.00 0.00 0.00 0.00 0.00 0.17 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 13,014 0.30 0.00 0.01 0.00 0.04 0.00 0.25 0.30 0.30 0.38 7.8
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: The 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: The Stead
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
W W-Hist 0.17 15.5 15.5 14.3 0.25 0.25 0.31 1.87 3.19 6.71 0.08 0.14 0.36
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
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)
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
August 12, 2015
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: The 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 7,540 0.17 0.00 0.00 0.11 0.06 0.00 0.00 0.79 0.79 0.98 71.7
E 5,474 0.13 0.00 0.00 0.00 0.09 0.00 0.03 0.44 0.44 0.55 29.8
Total 13,014 0.30 0.00 0.00 0.11 0.16 0.00 0.03 0.64 0.64 0.80 54.1
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: The 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: The Stead
42228Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
W W 0.17 9.7 9.7 9.0 0.79 0.79 0.98 2.26 3.86 8.03 0.31 0.52 1.36
E E 0.13 5.7 5.7 5.0 0.44 0.44 0.55 2.76 4.72 9.95 0.15 0.26 0.68
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
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
August 12, 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_Proposed.xlsx\Direct-Runoff
APPENDIX B
HYDRAULIC COMPUTATIONS
APPENDIX B.1
DETENTION FACILITIES
D. Weber
Pond No : Retention
W
100-yr
0.98
Area (A)= 0.17 acres 4414 ft
3
Max Release Rate = 0.00 cfs 0.10 ac-ft
Time Time
100-yr
Intensity
Q100
Inflow
(Runoff)
Volume
Outflow
(Release)
Volume
Storage
Detention
Volume
(mins) (secs) (in/hr) (cfs) (ft
3
) (ft
3
) (ft
3
)
5 300 9.950 1.66 497 0.0 497.3
10 600 7.720 1.29 772 0.0 771.7
15 900 6.520 1.09 978 0.0 977.6
20 1200 5.600 0.93 1120 0.0 1119.6
25 1500 4.980 0.83 1245 0.0 1244.5
30 1800 4.520 0.75 1355 0.0 1355.5
35 2100 4.080 0.68 1427 0.0 1427.4
40 2400 3.740 0.62 1495 0.0 1495.4
45 2700 3.460 0.58 1556 0.0 1556.4
50 3000 3.230 0.54 1614 0.0 1614.4
55 3300 3.030 0.50 1666 0.0 1665.8
60 3600 2.860 0.48 1715 0.0 1715.3
65 3900 2.720 0.45 1767 0.0 1767.3
70 4200 2.590 0.43 1812 0.0 1812.3
75 4500 2.480 0.41 1859 0.0 1859.3
80 4800 2.380 0.40 1903 0.0 1903.2
85 5100 2.290 0.38 1946 0.0 1945.7
90 5400 2.210 0.37 1988 0.0 1988.2
95 5700 2.130 0.35 2023 0.0 2022.7
100 6000 2.060 0.34 2059 0.0 2059.2
105 6300 2.000 0.33 2099 0.0 2099.2
110 6600 1.940 0.32 2133 0.0 2133.1
115 6900 1.890 0.31 2173 0.0 2172.6
120 7200 1.840 0.31 2207 0.0 2207.1
Design Point
Design Storm
Developed "C" =
Project Location : Fort Collins, CO
Input Variables Results
Calculations By:
Required Retention Volume
(2xDetention Vol)
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
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 E
NEW
RESIDENCE
3-CAR
GARAGE
BARN
RETENTION
POND
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
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 0.17 0.25 0.25 0.31 15.5 15.5 14.3 0.08 0.14 0.36
E E-Hist 0.13 0.38 0.38 0.47 6.0 6.0 5.3 0.13 0.22 0.59
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 0.17 0.79 0.79 0.98 9.7 9.7 9.0 0.31 0.52 1.36
E E 0.13 0.44 0.44 0.55 5.7 5.7 5.0 0.15 0.26 0.68
RETENTION POND CALCULATION; FAA METHOD
Project Number : 1130-001
Date : August 12, 2015
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 30 1.0 8.7 8.7 8.1 0 0.0 0.00 N/A 150 3.0 2.60 1.0 9.7 9.7 9.0
E E No 0.50 0.50 0.63 26 5.0 3.3 3.3 2.6 0 0.0 0.00 N/A 215 1.0 1.50 2.4 5.7 5.7 5.0
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
D. Weber
August 12, 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
August 12, 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 0.31 150 2.0 15.5 15.5 14.3 0 0.0 0.00 N/A 0 0.0 0.00 N/A 15.5 15.5 14.3
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
August 12, 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
August 12, 2015
D:\Projects\1130-001\Drainage\Hydrology\1130-001_Rational-Calcs_Existing.xlsx\C-Values