HomeMy WebLinkAboutCITY OF FORT COLLINS UTILITIES CUSTOMER SERVICES BUILDING - PDP - PDP140005 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTMay 7, 2014
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT FOR
CITY OF FORT COLLINS UTILITIES CUSTOMER
SERVICE BUILDING
Fort Collins, Colorado
Prepared for:
City of Fort Collins
Prepared by:
200 South College Avenue, Suite 10
Fort Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 940-002
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.
May 7, 2014
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
CITY OF FORT COLLINS UTILITIES CUSTOMER SERVICE BUILDING
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report
for your review. This report accompanies the Project Development Plan submittal for the
proposed City of Fort Collins Utilities Customer Service Building.
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.
Aaron Cvar, PE
Project Engineer
Utilities Customer Service Building
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 ........................................................................ 4
A. Major Basin Description .................................................................................................................... 4
III. DRAINAGE DESIGN CRITERIA .................................................................................... 5
A. Regulations ........................................................................................................................................ 5
B. Four Step Process .............................................................................................................................. 5
C. Development Criteria Reference and Constraints ............................................................................ 5
D. Hydrological Criteria ......................................................................................................................... 6
E. Hydraulic Criteria .............................................................................................................................. 6
G. Modifications of Criteria ................................................................................................................... 6
IV. DRAINAGE FACILITY DESIGN ..................................................................................... 6
A. General Concept ............................................................................................................................... 6
B. Specific Details .................................................................................................................................. 7
V. CONCLUSIONS .......................................................................................................... 8
A. Compliance with Standards .............................................................................................................. 8
B. Drainage Concept .............................................................................................................................. 8
References ........................................................................................................................... 9
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B - Water Quality Design Computations
APPENDIX C – Erosion Control Report
Utilities Customer Service Building
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2– Proposed Site Plan ................................................................................................ 3
Figure 3 – Existing Floodplains ............................................................................................. 4
MAP POCKET:
Proposed Drainage Exhibit
Utilities Customer Service Building
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The project site is located in 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 just northeast of the intersection of Laporte Avenue and
Howes.
4. The project site lies within the Old Town Basin. Due to the site’s proximity to the
Howes Street outfall, there are no detention requirements for the site. However, the
site still must provide water quality treatment. Several water quality treatment
methods are proposed for the site, and are described in further detail below.
5. As this is an infill site, the area surrounding the site is fully developed.
6. No offsite flows enter the site from the south, west, or east. A small area to the north
of the site sheet flows onto the site.
Utilities Customer Service Building
Preliminary Drainage Report 2
B. Description of Property
1. The development area is roughly 1.17 net acres.
Figure 1 – Aerial Photograph
2. The subject property is currently composed of existing buildings, and landscaped
areas. Existing ground slopes are mild to moderate (i.e., 1 - 6±%) 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 City customer
service building. Associated roadways, water and sewer lines will be constructed with
the development. Onsite water quality treatment is proposed within the subgrade of a
permeable paver system. The proposed paver system is to be located within the
south common area as shown on the Drainage Exhibit. This paver system is
anticipated to meet or exceed the current City LID requirements. In addition to the
paver system, a bio-swale, and small extended detention basin is proposed on the
north side of the site, as shown on the Drainage Exhibit. These water quality features
are further described below.
Utilities Customer Service Building
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
5. There are no known irrigation laterals crossing the site.
6. The proposed land use is a City customer service building.
C. Floodplain
1. The project site is encroached by a City designated 100-year floodplain. The City of
Fort Collins Stormwater Utility has identified a 100-year floodplain and floodway in
Laporte Avenue, as well as a shallow flooding area through the project site. The
proposed building footprint has been located outside of the flood fringe and floodway
identified along Laporte Avenue.
Utilities Customer Service Building
Preliminary Drainage Report 4
Figure 3 –Area Floodplain Mapping
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
2. The project site lies within the Old Town Basin. Detention requirements are to detain
the difference between the 100-year developed inflow rate and the historic 2-year
release rate. However, the site is adjacent to the Howes Street Outfall, and all runoff
will be directed into this outfall. Therefore, detention is not required for this particular
site. Water quality treatment is required and will be provided.
B. Sub-Basin Description
1. The subject property historically drains overland from northwest to southeast. Runoff
from the majority of the site has historically been collected in the existing Laporte
Avenue storm system running along the southern boundary of the site.
2. A more detailed description of the project drainage patterns follows in Section IV.A.4.,
below.
Utilities Customer Service Building
Preliminary Drainage Report 5
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 extended detention methods prior to exiting the
site.
Step 3 – Stabilize Drainageways
There are no major drainageways within the subject property (the Lincoln Channel is
located outside of the property boundary). While this step may not seem applicable to
proposed development, the project indirectly helps achieve stabilized drainageways
nonetheless. By providing water quality where none previously existed, sediment with
erosion potential is removed from the 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:
Trash, waste products, etc. that were previously left exposed with the historic trailer
park will no longer be allowed to exposure to runoff and transport to receiving
drainageways. The proposed development will eliminate these sources of potential
pollution.
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
Utilities Customer Service Building
Preliminary Drainage Report 6
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 RO-11 and RO-12 of the FCSCM.
3. 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.
4. 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.
3. As stated above, the subject property is located in a City designated floodplain.
The proposed project does not propose to modify any natural drainageways.
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 within the subgrade of the proposed
permeable pavement systems. Additionally, water quality capture volume for the
purpose of water quality treatment conforming to extended detention criteria will be
provided in a small extended detention basin in the north portion of the site. Water
quality release rates for the subgrade system will be controlled through sub-surface
Utilities Customer Service Building
Preliminary Drainage Report 7
control structures.
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 drainage patterns anticipated for proposed drainage basins are described below.
Basins 1 and 2
Basins 1 and 2 will generally drain via overland flow and curb and gutter flow into the
proposed water quality facilities. A series of permeable paver systems will be designed
to both capture direct runoff as well as runoff directed via curb and gutter flow. The
permeable paver sub-grade material will be utilized for water quality capture volume.
Runoff along the north side of the site will be directed in a bio-swale to a small
extended detention basin, which will provide 40-hour water extended detention
treatment. Please see further discussion of water quality and detention requirements
in Section IV.B, below.
Basin OS1 and OS2
Basin OS-1 consists portions of the site which physically cannot be directed into the
proposed water quality facilities. Runoff from these basins will be directed via sheet
flow into adjacent Right of Way, where it will be conveyed via curb and gutter into
existing storm line systems. We do not anticipate any issues arising from the free
release of these basins into adjacent Right of Way, as there is no significant change
from historic drainage conditions.
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. Standard water quality treatment in the form of extended detention is being is
proposed within the permeable paver sub-grade material. A series of sub-
grade detention release structures will be designed at Final in order to provide
the required water quality capture volume and to maintain the required site
release rate.
2. A small extended detention basin is proposed in the north portion of the site.
This basin will provide standard 40-hour extended detention treatment.
3. A bio-swale will be provided in the north portion of the site, conveying onsite
runoff to the proposed extended detention basin.
4. Final design details, construction documentation, and 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.).
5. Proper maintenance of the drainage facilities designed with the proposed
development is a critical component of their ongoing performance and
effectiveness.
Utilities Customer Service Building
Preliminary Drainage Report 8
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 Old
Town 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 Old Town Basin.
Utilities Customer Service Building
Preliminary Drainage Report 9
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: 940-002
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: ATC
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.
1 17405 0.40 Note: For preliminary calculations, Composite Runoff Coefficients are 0.60 0.60 0.75 55%
2 25166 0.58 based on Table RO-10. 0.95 0.95 1.00 90%
OS1 3049 0.07 Composite % Imperviousness has been estimated based 0.95 0.95 1.00 90%
OS2 5145 0.12 on UDFCD USDCM, Vol. I, Figures RO-3 and RO-4. 0.95 0.95 1.00 90%
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
May 1, 2014
Overland Flow, Time of Concentration:
Project: 940-002
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: 940-002
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
1 1 0.40 5 5 5 0.60 0.60 0.75 2.85 4.87 9.95 0.7 1.2 3.0
2 2 0.58 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.6 2.7 5.7
OS1 OS1 0.07 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.2 0.3 0.7
OS2 OS2 0.12 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.3 0.5 1.2
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)
ATC
May 1, 2014
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
APPENDIX B
WATER WAWAWATER QUALITY DESIGN COMPUTATIONS
WATER QUALITY DESIGN CALCULATIONS
Total Req'd Water Quality Capture Volume
Project: 940-002
By: ATC
Date: 5/1/14
REQUIRED STORAGE & OUTLET WORKS:
BASIN AREA = 0.980 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 76.00 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.7600 <-- CALCULATED
WQCV (watershed inches) = 0.305 <-- CALCULATED from Figure EDB-2
WQCV (ac-ft) = 0.025 <-- CALCULATED from UDFCD DCM V.3 Section 6.5
WQ Depth (ft) = ** <-- INPUT from stage-storage table
AREA REQUIRED PER ROW, a (in
2
) = ** <-- CALCULATED from Figure EDB-3
CIRCULAR PERFORATION SIZING:
dia (in) = ** <-- INPUT from Figure 5
n = ** <-- INPUT from Figure 5
t (in) = ** <-- INPUT from Figure 5
number of rows = ** <-- CALCULATED from WQ Depth and row spacing
**To be completed at final design
APPENDIX C
EROSION CONTROL REPORT
Utilities Customer Service Building
Preliminary Erosion Control Report
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 existing and 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 the Utility Plans. The Final Plans will contain a
full-size Erosion Control sheet 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 the Development Agreement for the development. 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, prior to any earth disturbance 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
DRAINAGE EXHIBITS
ST ST
ST
ST
ST
ST
UD
UD
UD
UD UD UD UD
UD
UD
UD
UD
UD
UD
UD
UD
EXISTING STORM
INLETS (TYP.)
LAPORTE AVENUE
(100' ROW)
HOWES STREET
(100' ROW)
EXISTING
215 N. MASON BUILDING
EXISTING 25' WIDE ALLEY
PROPOSED CUSTOMER
SERVICE BUILDING
FF = 4985.50
EXISTING
214 N. HOWES BUILDING
EXISTING
BUTTERFLY
BLDG
EX FF = 4983.53
PROPOSED PERMEABLE
PAVER TERRACE
APPROXIMATE LOCATION
OF 16' WIDE x5' HIGH
PROPOSED PERMEABLE CONCRETE BOX CULVERT
PAVER TERRACE
PROPOSED PERMEABLE
PAVER TERRACE
EXISTING
RIGHT-OF-WAY
EXISTING
RIGHT-OF-WAY
EXISTING
RIGHT-OF-WAY
EXISTING 100-YR
CITY FLOODPLAIN
EXISTING 100-YR
CITY FLOODWAY
4984.1 100-YR FLOOD ELEVATION
(FT.COLLINS NGVD29)
1
2
OS2
1
2
OS1 OS2
EXISTING RIGHT-OF-WAY
FLOWLINE OF PROPOSED
BIOSWALE AT 0.4% SLOPE
PROPOSED UNDERDRAIN
PROPOSED WATER QUALITY
OUTLET STRUCTURE
WATER QUALITY
CONTROL POND
OS1
NORTH
Monday, April 14, 2014 10:17 AM
D:\Projects\940-002\Dwg\Drng\940-002_DRNG.dwg
Wegert Provencio
C500
DRAINAGE PLAN
CITY OF FORT COLLINS
222 Laporte Avenue
Fort Collins, CO 80524
UTILITIES CUSTOMER
SERVICE BUILDING
PROJECT DEVELOPMENT PLAN
1050 17th STREET,
SUITE A200
DENVER, CO 80265
303 295 1717 t
303 292 0845 f
DRAWN BY: CHECKED BY:
A
B
C
D
E
F
G
H
I
J
A
B
C
D
E
F
G
H
I
J
1 2 3 4 5 6 7 8 9 10 11 12 13 14
14 13 12 11 10 9 8 7 6 5 4 3 2 1
15
15
K K
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
2 Project Development Plan 05/07/14
ST
NOTES:
LEGEND:
A
B2
1.45 ac
UD
NOT FOR CONSTRUCTION
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
11No0.55 0.60 0.75 20 2.00% 3.7 3.3 2.3 143 0.75% 1.73 1.4 0 0.00% N/A N/A 5 5 5
22No0.55 0.95 1.00 20 2.00% 3.7 1.0 0.7 101 0.75% 1.73 1.0 0 0.00% N/A N/A 5 5 5
OS1 OS1 No 0.55 0.95 1.00 20 2.00% 3.7 1.0 0.7 94 0.75% 1.73 0.9 0 0.00% N/A N/A 5 5 5
OS2 OS2 No 0.55 0.95 1.00 20 2.00% 3.7 1.0 0.7 154 0.75% 1.73 1.5 0 0.00% N/A N/A 5 5 5
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
ATC
May 1, 2014
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L