HomeMy WebLinkAboutFOX GROVE - PDP - PDP130029 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTSeptember 4, 2013
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT FOR
FOX GROVE
Fort Collins, Colorado
Prepared for:
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: 335-008
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.
September 4, 2013
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
Fox Grove
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 Fox Grove development.
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
Fox Grove
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION .................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 2
C. Floodplain ......................................................................................................................................... 4
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 ............................................................................ 6
D. Hydrological Criteria ......................................................................................................................... 6
E. Hydraulic Criteria .............................................................................................................................. 6
F. Modifications of Criteria ................................................................................................................... 6
A. General Concept ............................................................................................................................... 7
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 – Stormwater Management Model (SWMM)
APPENDIX D – Erosion Control Report
APPENDIX E – FIRMette
Fox Grove
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph .................................................................................................. 2
Figure 2– Proposed Site Plan .................................................................................................. 3
Figure 3 – Existing Floodplains ............................................................................................... 4
Table 1 – Water Quality Pond Summary .................................................................................. 8
MAP POCKET:
Proposed Drainage Exhibit
Fox Grove
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The project site is located in the northwest quarter of Section 15, Township 7 North,
Range 68 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado .
3. The proposed development site is located southeast of the I-25/Mulberry (State
Highway 14) interchange in Fort Collins, Colorado. The site is situated along the
existing I-25 east frontage road, just south of the existing Interchange Business Park
development.
4. The proposed development site is in the City of Fort Collins Boxelder Creek Basin.
Detention requirements for this basin are to detain the difference between the 100-
year developed inflow rate and the historic 2-year release rate. However, if it can be
shown by basin modeling that undetained flows from the developed site would result
in no increase in peak discharge within Boxelder Creek, the detention requirement
would be waived. No modeling has been done at the present, but may be considered
as this project progresses. The current submittal does show proposed on-site
detention.
Fox Grove
Preliminary Drainage Report 2
5. The existing Interchange Business Park site is located just north of the project site.
Boxelder Creek runs along the west property boundary.
6. Minimal offsite flows from the north are received by the project site. Two offsite
basins to the north of the site have been identified and are shown on the Drainage
Exhibit.
B. Description of Property
1. The development area is roughly 36 net acres.
Figure 1 – Aerial Photograph
2. The subject property is currently leased for farming purposes. The ground cover
generally consists of row crops. Existing ground slopes are mild to moderate (i.e., 1 -
6±%) through the interior of the property. General topography slopes from north to
south.
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 Kim Loam (Hydrologic Soil Group B) and Nunn Clay Loam
(Hydrologic Soil Group C).
4. The proposed project site plan is composed of residential development. Associated
roadways, water and sewer lines will be constructed with the development.
Detention/Water Quality will be placed near the southeast corner of the site and will
treat the majority of developed runoff prior to discharge into the adjacent Boxelder
Creek.
Fox Grove
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
5. Boxelder Creek runs along the west property boundary.
6. The proposed land use is residential.
Fox Grove
Preliminary Drainage Report 4
C. Floodplain
Figure 3 –Area Floodplain Mapping
1. A portion of the subject property is encroached by the FEMA 100-year floodplain
(Boxelder Creek).
2. FEMA FIRM Panel Number 1003 for Larimer County, Dated May 2, 2012 is
referenced in this study. A FIRMette of the area is provided in the appendix.
3. Base (100-year) flood elevations in the vicinity of the proposed project range from
4920.0 to 4919.0 (elevations referenced to the City of Fort Collins NGVD 29).
4. The project is located outside of the 100-year floodplain but a portion of the project is
within the 500-year floodplain.
5. The Boxelder Creek floodway is located near the north and west boundaries of the
property. No fill is proposed within the floodway. Proposed grading will tie-in with
existing grades outside of the floodway boundary.
6. The benchmark for site survey work is listed as “Found 2.5-inch aluminum cap,
stamped LS7839, at the corner of the Northwest Quarter of Section 15, Township 7
North Range 68 West of the 6th P.M.” (Elevation=4922.50, NGVD 29).
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
7. The proposed development site is in the City of Fort Collins Boxelder Creek Basin.
Detention requirements for this basin are to detain the difference between the 100-
year developed inflow rate and the historic 2-year release rate. However, if it can be
shown by basin modeling that undetained flows from the developed site would result
Fox Grove
Preliminary Drainage Report 5
in no increase in peak discharge within Boxelder Creek, the detention requirement
would be waived. No modeling has been done at the present, but may be considered
as this project progresses. The current submittal does show proposed on-site
detention.
B. Sub-Basin Description
8. The subject property historically drains overland from north to south. There is an
existing drainage swale that runs along the southern boundary of the site, which has
historically collected the majority of onsite runoff. This swale then conveys runoff
west, into Boxelder Creek. The proposed site will now direct the majority of runoff
into an onsite Detention/Water Quality pond, which will discharge into Boxelder
Creek. A more detailed description of the project drainage patterns follows in Section
IV.A.4., below.
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. 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,
Fox Grove
Preliminary Drainage Report 6
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
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, portions of the subject property are located in a FEMA regulatory
floodplain and floodway.
Fox Grove
Preliminary Drainage Report 7
4. 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 Detention/Water Quality will be provided at the southwest corner of the site
and will treat the majority of developed runoff prior to discharge into Boxelder Creek.
An intermediate detention pond, noted as Pond 2 on the Drainage Exhibit will provide
detention only and serve to partially detain flows prior to entering Pond 1.
3. The drainage patterns anticipated for proposed drainage basins are described below.
Basins 1-3, 5, 7
Basins 1 through 3 and Basins 7 and 7 consists of residential development. These
basins will drain generally via street curb and gutter to a storm drain system which
will direct developed runoff to a detention/water quality pond, noted as Pond 1.
Basin 4, 6, 8
Basins 4, 6, and 8 consist of the back halves of residential lots and a portion of
proposed roadway. These basins will drain undetained into the existing drainage
swale that runs along the southern boundary of the site, which has historically
collected the majority of onsite runoff. This swale then conveys runoff west, into
Boxelder Creek.
Basins 9
Basin 9 consists of the back halves of residential lots. A portion of this basin will
drain undetained into the existing drainage swale that runs along the southern
boundary of the site, the remainder of the basin drain offsite to the east into existing
open space.
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 will be
provided for the proposed development within the lower stage of Pond 1.
Further documentation of treatment volumes and removal rates of stormwater
BMPs will be documented with the Final Drainage Report prepared during the
City FCP process.
2. LID features will be incorporated at Final Design.
3. Final design details, construction documentation, and Standard Operating
Procedures (SOP) Manual shall be provided to the City of Fort Collins for
Fox Grove
Preliminary Drainage Report 8
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.).
4. Table 1, below, summarizes the water quality information for the proposed water
quality pond.
Table 1 – Water Quality Pond Summary
Water Quality Water Quality Pond Spillway Top of Pond
Capture Volume WSEL Elevation Elevation
(AC-FT) (FT) (FT) (FT)
0.69 4914.0 +/- (prelim.) 4919.0 +/- (prelim.) 4920.0 +/- (prelim.)
5. Proper maintenance of the drainage facilities designed with the proposed
development is a critical component of their ongoing performance and effectiveness.
The water quality pond will be designed at Final to be easily accessed by
maintenance staff via gentle slopes provided to the bottom of the pond.
6. The drainage features associated with the proposed project are all private facilities,
located on private property.
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 the Boxelder Creek
Master Plan.
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.
4. The proposed development will be designed at Final in compliance with Chapter 10 of
City Code.
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 extended
detention.
2. The drainage concept for the proposed development is consistent with the Boxelder
Creek Master Plan.
Fox Grove
Preliminary Drainage Report 9
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: 335-008
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 331412 7.61 Note: For preliminary calculations, Composite Runoff Coefficients are 0.55 0.55 0.69 45%
2 59851 1.37 based on Table RO-10. 0.55 0.55 0.69 45%
3 136222 3.13 Composite % Imperviousness has been estimated based 0.55 0.55 0.69 45%
4 18782 0.43 on UDFCD USDCM, Vol. I, Figures RO-3 and RO-4. 0.55 0.55 0.69 45%
5 168683 3.87 0.55 0.55 0.69 45%
6 33093 0.76 0.55 0.55 0.69 45%
7 202011 4.64 0.55 0.55 0.69 45%
8 9178 0.21 0.55 0.55 0.69 45%
9 52907 1.21 0.55 0.55 0.69 45%
F1 446365 10.25 0.35 0.35 0.44 20%
Overland Flow, Time of Concentration:
Project: 335-008
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: 335-008
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
1 1 7.61 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 10.5 18.0 46.0
2 2 1.37 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 1.9 3.3 8.3
3 3 3.13 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 4.3 7.4 18.9
4 4 0.43 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 0.6 1.0 2.6
5 5 3.87 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 5.4 9.2 23.4
6 6 0.76 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 1.1 1.8 4.6
7 7 4.64 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 6.4 11.0 28.1
8 8 0.21 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 0.3 0.5 1.3
9 9 1.21 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 1.7 2.9 7.3
F1 F1 10.25 7 7 7 0.35 0.35 0.44 2.52 4.31 8.80 9.0 15.5 39.5
OS1 OS1 1.72 7 7 7 0.35 0.35 0.44 2.52 4.31 8.80 1.5 2.6 6.6
OS2 OS2 6.50 7 7 7 0.55 0.55 0.69 2.52 4.31 8.80 9.0 15.4 39.3
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
August 14, 2013
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
APPENDIX B
WATER WAWAWATER QUALITY DESIGN COMPUTATIONS
WATER QUALITY POND DESIGN CALCULATIONS
Pond 1
Project: 335-008
By: ATC
Date: 8/15/13
REQUIRED STORAGE & OUTLET WORKS:
BASIN AREA = 36.000 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 45.00 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.4500 <-- CALCULATED
WQCV (watershed inches) = 0.193 <-- CALCULATED from Figure EDB-2
WQCV (ac-ft) = 0.695 <-- 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
STORMWATER MANAGEMENT MODEL (SWMM)
1
2
out1
out2
mh2
pond1
pond2
FtCollins-100yr
11/21/2012 00:15:00
SWMM 5 Page 1
EPA STORM WATER MANAGEMENT MODEL - VERSION 5.0 (Build 5.0.022)
--------------------------------------------------------------
*********************************************************
NOTE: The summary statistics displayed in this report are
based on results found at every computational time step,
not just on results from each reporting time step.
*********************************************************
****************
Analysis Options
****************
Flow Units ............... CFS
Process Models:
Rainfall/Runoff ........ YES
Snowmelt ............... NO
Groundwater ............ NO
Flow Routing ........... YES
Ponding Allowed ........ NO
Water Quality .......... NO
Infiltration Method ...... HORTON
Flow Routing Method ...... KINWAVE
Starting Date ............ NOV-21-2012 00:00:00
Ending Date .............. NOV-21-2012 06:00:00
Antecedent Dry Days ...... 0.0
Report Time Step ......... 00:15:00
Wet Time Step ............ 00:05:00
Dry Time Step ............ 01:00:00
Routing Time Step ........ 30.00 sec
************************** Volume Depth
Runoff Quantity Continuity acre-feet inches
************************** --------- -------
Total Precipitation ...... 10.090 3.669
Evaporation Loss ......... 0.000 0.000
Infiltration Loss ........ 1.910 0.695
Surface Runoff ........... 8.088 2.941
Final Surface Storage .... 0.153 0.056
Continuity Error (%) ..... -0.601
************************** Volume Volume
Flow Routing Continuity acre-feet 10^6 gal
************************** --------- ---------
Dry Weather Inflow ....... 0.000 0.000
Wet Weather Inflow ....... 8.088 2.635
Groundwater Inflow ....... 0.000 0.000
RDII Inflow .............. 0.000 0.000
External Inflow .......... 0.000 0.000
External Outflow ......... 0.985 0.321
Internal Outflow ......... 0.000 0.000
Storage Losses ........... 0.000 0.000
Initial Stored Volume .... 0.000 0.000
Final Stored Volume ...... 7.103 2.315
Continuity Error (%) ..... -0.003
********************************
SWMM 5 Page 1
Highest Flow Instability Indexes
********************************
All links are stable.
*************************
Routing Time Step Summary
*************************
Minimum Time Step : 30.00 sec
Average Time Step : 30.00 sec
Maximum Time Step : 30.00 sec
Percent in Steady State : 0.00
Average Iterations per Step : 1.00
***************************
Subcatchment Runoff Summary
***************************
--------------------------------------------------------------------------------------------------------
Total Total Total Total Total Total Peak Runoff
Precip Runon Evap Infil Runoff Runoff Runoff Coeff
Subcatchment in in in in in 10^6 gal CFS
--------------------------------------------------------------------------------------------------------
1 3.67 0.00 0.00 0.70 2.93 1.43 122.15 0.800
2 3.67 0.00 0.00 0.69 2.95 1.20 105.52 0.804
******************
Node Depth Summary
******************
---------------------------------------------------------------------
Average Maximum Maximum Time of Max
Depth Depth HGL Occurrence
Node Type Feet Feet Feet days hr:min
---------------------------------------------------------------------
mh2 JUNCTION 0.00 0.00 101.00 0 00:00
pond1 STORAGE 2.65 3.04 108.04 0 02:27
pond2 STORAGE 2.38 2.75 108.75 0 02:19
*******************
Node Inflow Summary
*******************
-------------------------------------------------------------------------------------
Maximum Maximum Lateral Total
Lateral Total Time of Max Inflow Inflow
Inflow Inflow Occurrence Volume Volume
Node Type CFS CFS days hr:min 10^6 gal 10^6 gal
-------------------------------------------------------------------------------------
mh2 JUNCTION 0.00 2.28 0 02:27 0.000 0.321
pond1 STORAGE 122.15 122.91 0 00:40 1.434 1.626
pond2 STORAGE 105.52 105.52 0 00:40 1.201 1.201
**********************
Node Surcharge Summary
**********************
SWMM 5 Page 2
Surcharging occurs when water rises above the top of the highest conduit.
---------------------------------------------------------------------
Max. Height Min. Depth
Hours Above Crown Below Rim
Node Type Surcharged Feet Feet
---------------------------------------------------------------------
mh2 JUNCTION 6.01 0.000 10.000
pond1 STORAGE 6.01 3.045 6.955
pond2 STORAGE 6.01 2.754 7.246
*********************
Node Flooding Summary
*********************
No nodes were flooded.
**********************
Storage Volume Summary
**********************
--------------------------------------------------------------------------------------------
Average Avg E&I Maximum Max Time of Max Maximum
Volume Pcnt Pcnt Volume Pcnt Occurrence Outflow
Storage Unit 1000 ft3 Full Loss 1000 ft3 Full days hr:min CFS
--------------------------------------------------------------------------------------------
pond1 153.143 8 0 185.390 9 0 02:26 2.28
pond2 123.481 6 0 151.701 8 0 02:19 1.38
********************
Link Flow Summary
********************
-----------------------------------------------------------------------------
Maximum Time of Max Maximum Max/ Max/
|Flow| Occurrence |Veloc| Full Full
Link Type CFS days hr:min ft/sec Flow Depth
-----------------------------------------------------------------------------
out1 DUMMY 2.28 0 02:27
out2 DUMMY 1.38 0 02:19
*************************
Conduit Surcharge Summary
*************************
No conduits were surcharged.
Analysis begun on: Wed Sep 04 12:21:42 2013
Analysis ended on: Wed Sep 04 12:21:42 2013
Total elapsed time: < 1 sec
SWMM 5 Page 3
35
(12) A new Section 4.1 is added, to read as follows:
4.1 Intensity-Duration-Frequency Curves for SWMM:
The hyetograph input option must be selected when creating SWMM input files.
Hyetographs for the 2-, 5-, 10-, 25-, 50-, and 100-year City of Fort Collins rainfall events
are provided in Table RA-9.
Table RA-9 – City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
for Use with SWMM
2-Year 5-Year 10-Year 25-Year 50-Year 100-Year
Duration
(min)
Intensity
(in/hr)
Intensity
(in/hr)
Intensity
(in/hr)
Intensity
(in/hr)
Intensity
(in/hr)
Intensity
(in/hr)
5 0.29 0.40 0.49 0.63 0.79 1.00
10 0.33 0.45 0.56 0.72 0.90 1.14
15 0.38 0.53 0.65 0.84 1.05 1.33
20 0.64 0.89 1.09 1.41 1.77 2.23
25 0.81 1.13 1.39 1.80 2.25 2.84
30 1.57 2.19 2.69 3.48 4.36 5.49
35 2.85 3.97 4.87 6.30 7.90 9.95
40 1.18 1.64 2.02 2.61 3.27 4.12
45 0.71 0.99 1.21 1.57 1.97 2.48
50 0.42 0.58 0.71 0.92 1.16 1.46
55 0.35 0.49 0.60 0.77 0.97 1.22
60 0.30 0.42 0.52 0.67 0.84 1.06
65 0.20 0.28 0.39 0.62 0.79 1.00
70 0.19 0.27 0.37 0.59 0.75 0.95
75 0.18 0.25 0.35 0.56 0.72 0.91
80 0.17 0.24 0.34 0.54 0.69 0.87
85 0.17 0.23 0.32 0.52 0.66 0.84
90 0.16 0.22 0.31 0.50 0.64 0.81
95 0.15 0.21 0.30 0.48 0.62 0.78
100 0.15 0.20 0.29 0.47 0.60 0.75
105 0.14 0.19 0.28 0.45 0.58 0.73
110 0.14 0.19 0.27 0.44 0.56 0.71
115 0.13 0.18 0.26 0.42 0.54 0.69
120 0.13 0.18 0.25 0.41 0.53 0.67
43
Table RO-13
SWMM Input Parameters
Depth of Storage on Impervious Areas 0.1 inches
Depth of Storage on Pervious Areas 0.3 inches
Maximum Infiltration Rate 0.51 inches/hour
Minimum Infiltration Rate 0.50 inches/hour
Decay Rate 0.0018 inches/sec
Zero Detention Depth 1%
Manning’s n Value for Pervious Surfaces 0.025
Manning’s n Value for Impervious Surfaces 0.016
4.3.2 Pervious-Impervious Area
Table RO-14 should be used to determine preliminary percentages of impervious land
cover for a given land-use or zoning. The final design must be based on the actual
physical design conditions of the site.
Table RO-14
Percent Imperviousness Relationship to Land Use*
LAND USE OR ZONING
PERCENT IMPERVIOUS
(%)
Business:
T
CCN, CCR, CN
E, RDR, CC, LC
C, NC, I, D, HC, CS
20
70
80
90
Residential:
RF,UE
RL, NCL
LMN,NCM
MMN, NCB
30
45
50
70
Open Space:
Open Space and Parks (POL)
Open Space along foothills ridge
(POL,RF)
RC
10
20
20
*For updated zoning designations and definitions, please refer to Article Four of the City Land
Use Code, as amended
APPENDIX E
FIRMETTE
APPENDIX D
EROSION CONTROL REPORT
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
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
11No0.55 0.55 0.69 140 2.00% 9.7 9.7 7.2 670 1.00% 2.00 5.6 0 0.00% N/A N/A 7 7 7
22No0.55 0.55 0.69 60 2.00% 6.3 6.3 4.7 560 1.00% 2.00 4.7 0 0.00% N/A N/A 7 7 7
33No0.55 0.55 0.69 70 2.00% 6.8 6.8 5.1 720 1.00% 2.00 6.0 0 0.00% N/A N/A 7 7 7
44No0.55 0.55 0.69 55 2.00% 6.1 6.1 4.5 0 0.00% N/A N/A 0 0.00% N/A N/A 7 7 7
55No0.55 0.55 0.69 170 2.00%
10.6 10.6 8.0 520 1.00% 2.00 4.3 0 0.00% N/A N/A 7 7 7
66No0.55 0.55 0.69 55 2.00% 6.1 6.1 4.5 0 1.00% N/A N/A 0 0.00% N/A N/A 7 7 7
77No0.55 0.55 0.69 110 2.00% 8.6 8.6 6.4 690 1.00% 2.00 5.8 0 0.00% N/A N/A 7 7 7
88No0.55 0.55 0.69 30 2.00% 4.5 4.5 3.4 90 1.00% 2.00 0.8 0 0.00% N/A N/A 7 7 7
99No0.55 0.55 0.69 60 2.00% 6.3 6.3 4.7 0 1.00% N/A N/A 0 0.00% N/A N/A 7 7 7
1.00%
F1 F1 N 035 035 044 100 2 00% 11 1 11 1 98 500 1 00% 200 42 0 0 00% N/A N/A 7 7 7
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
ATC
August 14, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
F1 F1 No 0.35 0.35 0.44 100 2.00% 11.1 11.1 9.8 500 1.00% 2.00 4.2 0 0.00% N/A N/A 7 7 7
OS1 OS1 No 0.35 0.35 0.44 352 1.10% 25.5 25.5 22.5 0 1.00% N/A N/A 0 0.00% N/A N/A 7 7 7
OS2 OS2 No 0.55 0.55 0.69 408 0.90% 21.5 21.5 16.1 0 1.00% N/A N/A 0 0.00% N/A N/A 7 7 7
OS1 74794 1.72 0.35 0.35 0.44 20%
OS2 283019 6.50 0.55 0.55 0.69 45%
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 14, 2013