HomeMy WebLinkAboutRIVER DISTRICT BLOCK 8 MIXED-USE DEVELOPMENT (OLD ELK DISTILLERY) - PDP - PDP140016 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTSeptember 24, 2014
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT FOR
Old Elk Distillery
Fort Collins, Colorado
Prepared for:
Blue Ocean Enterprises
401 West Mountain Ave.
Fort Collins, CO 80521
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: 838-013
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 24, 2014
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
Old Elk Distillery
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 Old Elk Distillery 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
Old Elk Distillery
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION .................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 1
C. Floodplain ......................................................................................................................................... 4
II. DRAINAGE BASINS AND SUB-BASINS ........................................................................ 4
A. Major Basin Description .................................................................................................................... 4
B. Sub-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
F. 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 – Detention Computations
APPENDIX C – Water Quality Design Computations
APPENDIX D – Erosion Control Report
APPENDIX E – Reference Material – Selected Portions of the Downtown River District
Improvement Plans (February 2012)
Old Elk Distillery
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
Old Elk Distillery
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The project site is located in the west quarter of Section 12, Township 7 North,
Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado .
3. The proposed development site is situated along the south side of Willow Street, just
southeast of the intersection of Linden Street and Willow Street.
4. The proposed development site is in the City of Fort Collins Old town 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.
5. The project site is located within existing downtown development, and is surrounded
by existing businesses. The existing Ranchway Feeds site is located on the north side
of Willow Street, directly across from the proposed development site.
6. Minimal offsite flows from the west and south are received by the project site.
Existing drainage systems in Linden Street and Willow Street convey the majority of
offsite drainage approaching the site.
B. Description of Property
1. The development area is roughly 1.24 net acres, as identified on the Drainage Exhibit.
Old Elk Distillery
Preliminary Drainage Report 2
Figure 1 – Aerial Photograph
2. The subject property is currently undeveloped ground. The ground cover generally
consists of gravel surfacing. Existing ground slopes are mild to moderate (i.e., 1 -
6±%) through the interior of the property. General topography slopes from southwest
to northeast.
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 Paoli Fine Sandy Loam (Hydrologic Soil Group B).
4. The proposed project site plan is composed of the development of a distillery and
restaurant. 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
the Cache La Poudre River.
Old Elk Distillery
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
5. The Cache La Poudre river is located just north of the proposed development site.
6. The proposed land use is Commerical.
Old Elk Distillery
Preliminary Drainage Report 4
C. Floodplain
Figure 3 –Area Floodplain Mapping
1. No portion of the subject property is encroached by the adjacent FEMA 100-year
floodplain (Cache La Poudre River located just north of the site).
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
2. The proposed development site is in the City of Fort Collins Old Town 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. A historic 2-year
release rate of 1.1 cfs (Please see Appendix A) has been calculated for the overall site
(1.24 acres). Detention and water quality treatment will be provided onsite prior to
discharge into the existing storm system in Willow Street. Per the Downtown River
District Improvement Project Plans (February 2012), the storm system in Willow
Street is to be improved in the near future. It is anticipated that the project site could
at that time tie in to the new storm system.
B. Sub-Basin Description
3. The subject property historically drains overland from southwest to northeast. An
existing area inlet in Willow Street captures runoff within the curb and gutter of
Willow. Stormwater is then conveyed via the existing storm pipe in Willow north to
the Cache La Poudre River. A more detailed description of the project drainage
patterns follows in Section IV.A.4., below.
Old Elk Distillery
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. 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
Old Elk Distillery
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, no portion of the subject property is located in a FEMA regulatory
floodplain or floodway.
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 and water quality treatment will be provided within the four onsite
ponds. The ponds will treat the majority of developed runoff prior to discharge into
Boxelder Creek.
Old Elk Distillery
Preliminary Drainage Report 7
3. The drainage patterns anticipated for proposed drainage basins are described below.
Basin 1
Basins 1 consists of rooftop area and parking/drive area. The entirety of this basin will
be directed to underground detention/water quality holding cells located under the
parking area near the entry point along Willow Street.
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. Detention and water quality treatment in the form of extended detention will
be provided for the proposed development within the proposed underground
detention facility located underneath the parking area near the Willow Street
point of entry. Additionally, LID features will be provided and will be further
detailed at Final Design. Table 1, below outlines preliminary detention, and
extended detention volume requirements. We have assumed the extended
detention volume to be present prior to a 100-year storm event; thus, the total
required volume the underground detention facility is composed of the
detention volume required plus extended detention volume. Further
documentation of treatment volumes will be documented with the Final
Drainage Report prepared during the City FCP process.
TABLE 1 – Preliminary Detention and Water Quality Summary
Pond Detention Vol.
(Ac-Ft)
Extended.Det.
Vol. (Ac-Ft)
Total Req'd.
Vol. (Ac-Ft)
Peak 100-Yr
Release (cfs)
1 0.20 .050 .025 1.1
2. LID features will be further detailed 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
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. Proper maintenance of the drainage facilities designed with the proposed
development is a critical component of their ongoing performance and effectiveness.
The underground detention / water quality facility will be designed at Final to have
good access by maintenance staff.
5. The drainage features associated with the proposed project are all private facilities,
located on private property.
Old Elk Distillery
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 the Old Town 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.
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 Old Town
Master Plan.
Old Elk Distillery
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: 838-013
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.
H1 53806 1.24 0.000 0.000 0.000 1.235 0.000 0.50 0.50 0.63 40%
HISTORIC 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
9/15/2014
Overland Flow, Time of Concentration:
Project: 838-013
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: 838-013
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
H1 H1 1.24 17 17 14 0.50 0.50 0.63 1.78 3.04 6.71 1.1 1.9 5.2
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)
HISTORIC 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
9/15/2014
Q C f C i A
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: 838-013
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 53806 1.24 Note: For preliminary calculations, Composite Runoff Coefficients are 0.95 0.95 1.00 90%
based on an assumed imperviousness of 90% and COFC Storm Drainage
Design Criteria Table 3-3
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
9/15/2014
Overland Flow, Time of Concentration:
Project: 838-013
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: 838-013
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
1 1 1.24 7 7 6 0.95 0.95 1.00 2.60 4.44 9.63 3.0 5.2 11.9
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
9/15/2014
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
40
Table RO-10
Rational Method Minor Storm Runoff Coefficients for Zoning Classifications
Description of Area or Zoning Coefficient
R-F 0.3
U-E 0.3
L-M-In 0.55
R-L, N-C-L 0.6
M-M-N, N-C-M 0.65
N-C-B 0.7
Business:
C-C-N, C-C-R, C-N, N-C, C-S 0.95
R-D-R, C-C, C-L 0.95
D, C 0.95
H-C 0.95
C-S 0.95
Industrial:
E 0.85
I 0.95
Undeveloped:
R-C, T 0.2
P-O-L 0.25
For guidance regarding zoning districts and classifications of such districts please refer to
Article Four of the City Land Use Code, as amended.
41
Table RO-11
Rational Method Runoff Coefficients for Composite Analysis
Character of Surface Runoff Coefficient
Streets, Parking Lots,
Drives:
Asphalt 0.95
Concrete 0.95
Gravel 0.5
Roofs 0.95
Recycled Asphalt 0.8
Lawns, Sandy Soil:
Flat <2% 0.1
Average 2 to 7% 0.15
Steep >7% 0.2
Lawns, Heavy Soil:
Flat <2% 0.2
Average 2 to 7% 0.25
Steep >7% 0.35
(4) A new Section 2.9 is added, to read as follows:
2.9 Composite Runoff Coefficient
Drainage sub-basins are frequently composed of land that has multiple surfaces or zoning
classifications. In such cases a composite runoff coefficient must be calculated for any
given drainage sub-basin.
The composite runoff coefficient is obtained using the following formula:
( )
t
n
i
i i
A
C A
C
∑
= = 1
*
(RO-8)
Where: C = Composite Runoff Coefficient
Ci = Runoff Coefficient for Specific Area (Ai)
Ai = Area of Surface with Runoff Coefficient of Ci, acres or feet2
n = Number of different surfaces to be considered
At = Total Area over which C is applicable, acres or feet2
(5) A new Section 2.10 is added, to read as follows:
42
2.10 Runoff Coefficient Adjustment for Infrequent Storms
The runoff coefficients provided in tables RO-10 and RO-11 are appropriate for use with
the 2-year storm event. For storms with higher intensities, an adjustment of the runoff
coefficient is required due to the lessening amount of infiltration, depression retention,
evapo-transpiration and other losses that have a proportionally smaller effect on storm
runoff. This adjustment is applied to the composite runoff coefficient.
These frequency adjustment factors are found in Table RO-12.
Table RO-12
Rational Method Runoff Coefficients for Composite Analysis
Storm Return Period
(years)
Frequency Factor
Cf
2 to 10
11 to 25
26 to 50
51 to 100
1.00
1.10
1.20
1.25
Note: The product of C times Cf cannot exceed the value of 1, in the cases where it does a value of
1 must be used
(6) Section 3.1 is deleted in its entirety.
(7) Section 3.2 is deleted in its entirety.
(8) Section 3.3 is deleted in its entirety.
(9) A new Section 4.3 is added, to read as follows:
4.3 Computer Modeling Practices
(a) For circumstances requiring computer modeling, the design storm hydrographs must
be determined using the Stormwater Management Model (SWMM). Basin and
conveyance element parameters must be computed based on the physical characteristics
of the site.
(b) Refer to the SWMM Users’ Manual for appropriate modeling methodology, practices
and development. The Users’ Manual can be found on the Environmental Protection
Agency (EPA) website (http://www.epa.gov/ednnrmrl/models/swmm/index.htm).
(c) It is the responsibility of the design engineer to verify that all of the models used in
the design meet all current City criteria and regulations.
4.3.1 Surface Storage, Resistance Factors, and Infiltration
Table RO-13 provides values for surface storage for pervious and impervious surfaces
and the infiltration rates to be used with SWMM. Table RO-13 also lists the appropriate
infiltration decay rate, zero detention depth and resistance factors, or Manning’s “n”
values, for pervious and impervious surfaces to be used for SWMM modeling in the city
of Fort Collins.
33
(11) Section 4.0 is amended to read as follows:
4.0 Intensity-Duration-Frequency Curves for Rational Method:
The one-hour rainfall Intensity-Duration-Frequency tables for use the Rational Method
of runoff analysis are provided in Table RA-7 and in Table RA-8.
Table RA-7 -- City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
for Use with the Rational Method
(5 minutes to 30 minutes)
2-Year 10-Year 100-Year
Duration
(min)
Intensity
(in/hr)
Intensity
(in/hr)
Intensity
(in/hr)
5 2.85 4.87 9.95
6 2.67 4.56 9.31
7 2.52 4.31 8.8
8 2.4 4.1 8.38
9 2.3 3.93 8.03
10 2.21 3.78 7.72
11 2.13 3.63 7.42
12 2.05 3.5 7.16
13 1.98 3.39 6.92
14 1.92 3.29 6.71
15 1.87 3.19 6.52
16 1.81 3.08 6.3
17 1.75 2.99 6.1
18 1.7 2.9 5.92
19 1.65 2.82 5.75
20 1.61 2.74 5.6
21 1.56 2.67 5.46
22 1.53 2.61 5.32
23 1.49 2.55 5.2
24 1.46 2.49 5.09
25 1.43 2.44 4.98
26 1.4 2.39 4.87
27 1.37 2.34 4.78
28 1.34 2.29 4.69
29 1.32 2.25 4.6
30 1.3 2.21 4.52
34
Table RA-8 -- City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
for Use with the Rational Method
(31 minutes to 60 minutes)
2-Year 10-Year 100-Year
Duration
(min)
Intensity
(in/hr)
Intensity
(in/hr)
Intensity
(in/hr)
31 1.27 2.16 4.42
32 1.24 2.12 4.33
33 1.22 2.08 4.24
34 1.19 2.04 4.16
35 1.17 2.0 4.08
36 1.15 1.96 4.01
37 1.16 1.93 3.93
38 1.11 1.89 3.87
39 1.09 1.86 3.8
40 1.07 1.83 3.74
41 1.05 1.8 3.68
42 1.04 1.77 3.62
43 1.02 1.74 3.56
44 1.01 1.72 3.51
45 0.99 1.69 3.46
46 0.98 1.67 3.41
47 0.96 1.64 3.36
48 0.95 1.62 3.31
49 0.94 1.6 3.27
50 0.92 1.58 3.23
51 0.91 1.56 3.18
52 0.9 1.54 3.14
53 0.89 1.52 3.1
54 0.88 1.5 3.07
55 0.87 1.48 3.03
56 0.86 1.47 2.99
57 0.85 1.45 2.96
58 0.84 1.43 2.92
59 0.83 1.42 2.89
60 0.82 1.4 2.86
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
36
RAINFALL INTENSITY-DURATION-FREQUENCY CURVE
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00
STORM DURATION (minutes)
RAINFALL INTENSITY (inches/hour)
2-Year Storm 10-Year Storm 100-Year Storm
Figure RA-16 City of Fort Collins Rainfall Intensity-Duration-Frequency Curves
(13) Section 5.0 is deleted in its entirety.
(14) Section 6.0 is deleted in its entirety.
(15) Section 7.0 is deleted in its entirety.
(16) Section 7.1 is deleted in its entirety.
(17) Section 7.2 is deleted in its entirety.
(18) Section 7.3 is deleted in its entirety.
(19) Section 8.0 is deleted in its entirety.
(20) Table RA-1 is deleted in its entirety.
DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF
Table RO-3—Recommended Percentage Imperviousness Values
Land Use or
Surface Characteristics
Percentage
Imperviousness
Business:
Commercial areas 95
Neighborhood areas 85
Residential:
Single-family *
Multi-unit (detached) 60
Multi-unit (attached) 75
Half-acre lot or larger *
Apartments 80
Industrial:
Light areas 80
Heavy areas 90
Parks, cemeteries 5
Playgrounds 10
Schools 50
Railroad yard areas 15
Undeveloped Areas:
Historic flow analysis 2
Greenbelts, agricultural 2
Off-site flow analysis
(when land use not defined)
45
Streets:
Paved 100
Gravel (packed) 40
Drive and walks 90
Roofs 90
Lawns, sandy soil 0
Lawns, clayey soil 0
* See Figures RO-3 through RO-5 for percentage imperviousness.
C A = K A + ( 1 . 31 i 3 − 1 . 44 i 2 + 1 . 135 i − 0 . 12 ) for CA ≥ 0, otherwise CA = 0 (RO-6)
C CD = K CD + ( 0 . 858 i 3 − 0 . 786 i 2 + 0 . 774 i + 0 . 04 ) (RO-7)
C B = (CA + C CD ) 2
2007-01 RO-9
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF
Table RO-5— Runoff Coefficients, C
Percentage
Imperviousness Type C and D NRCS Hydrologic Soil Groups
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr
0% 0.04 0.15 0.25 0.37 0.44 0.50
5% 0.08 0.18 0.28 0.39 0.46 0.52
10% 0.11 0.21 0.30 0.41 0.47 0.53
15% 0.14 0.24 0.32 0.43 0.49 0.54
20% 0.17 0.26 0.34 0.44 0.50 0.55
25% 0.20 0.28 0.36 0.46 0.51 0.56
30% 0.22 0.30 0.38 0.47 0.52 0.57
35% 0.25 0.33 0.40 0.48 0.53 0.57
40% 0.28 0.35 0.42 0.50 0.54 0.58
45% 0.31 0.37 0.44 0.51 0.55 0.59
50% 0.34 0.40 0.46 0.53 0.57 0.60
55% 0.37 0.43 0.48 0.55 0.58 0.62
60% 0.41 0.46 0.51 0.57 0.60 0.63
65% 0.45 0.49 0.54 0.59 0.62 0.65
70% 0.49 0.53 0.57 0.62 0.65 0.68
75% 0.54 0.58 0.62 0.66 0.68 0.71
80% 0.60 0.63 0.66 0.70 0.72 0.74
85% 0.66 0.68 0.71 0.75 0.77 0.79
90% 0.73 0.75 0.77 0.80 0.82 0.83
95% 0.80 0.82 0.84 0.87 0.88 0.89
100% 0.89 0.90 0.92 0.94 0.95 0.96
TYPE B NRCS HYDROLOGIC SOILS GROUP
0% 0.02 0.08 0.15 0.25 0.30 0.35
5% 0.04 0.10 0.19 0.28 0.33 0.38
10% 0.06 0.14 0.22 0.31 0.36 0.40
15% 0.08 0.17 0.25 0.33 0.38 0.42
20% 0.12 0.20 0.27 0.35 0.40 0.44
25% 0.15 0.22 0.30 0.37 0.41 0.46
30% 0.18 0.25 0.32 0.39 0.43 0.47
35% 0.20 0.27 0.34 0.41 0.44 0.48
40% 0.23 0.30 0.36 0.42 0.46 0.50
45% 0.26 0.32 0.38 0.44 0.48 0.51
50% 0.29 0.35 0.40 0.46 0.49 0.52
55% 0.33 0.38 0.43 0.48 0.51 0.54
60% 0.37 0.41 0.46 0.51 0.54 0.56
65% 0.41 0.45 0.49 0.54 0.57 0.59
70% 0.45 0.49 0.53 0.58 0.60 0.62
75% 0.51 0.54 0.58 0.62 0.64 0.66
80% 0.57 0.59 0.63 0.66 0.68 0.70
85% 0.63 0.66 0.69 0.72 0.73 0.75
90% 0.71 0.73 0.75 0.78 0.80 0.81
95% 0.79 0.81 0.83 0.85 0.87 0.88
100% 0.89 0.90 0.92 0.94 0.95 0.96
2007-01 RO-11
Urban Drainage and Flood Control District
RUNOFF DRAINAGE CRITERIA MANUAL (V. 1)
TABLE RO-5 (Continued)—Runoff Coefficients, C
Percentage
Imperviousness Type A NRCS Hydrologic Soils Group
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr
0% 0.00 0.00 0.05 0.12 0.16 0.20
5% 0.00 0.02 0.10 0.16 0.20 0.24
10% 0.00 0.06 0.14 0.20 0.24 0.28
15% 0.02 0.10 0.17 0.23 0.27 0.30
20% 0.06 0.13 0.20 0.26 0.30 0.33
25% 0.09 0.16 0.23 0.29 0.32 0.35
30% 0.13 0.19 0.25 0.31 0.34 0.37
35% 0.16 0.22 0.28 0.33 0.36 0.39
40% 0.19 0.25 0.30 0.35 0.38 0.41
45% 0.22 0.27 0.33 0.37 0.40 0.43
50% 0.25 0.30 0.35 0.40 0.42 0.45
55% 0.29 0.33 0.38 0.42 0.45 0.47
60% 0.33 0.37 0.41 0.45 0.47 0.50
65% 0.37 0.41 0.45 0.49 0.51 0.53
70% 0.42 0.45 0.49 0.53 0.54 0.56
75% 0.47 0.50 0.54 0.57 0.59 0.61
80% 0.54 0.56 0.60 0.63 0.64 0.66
85% 0.61 0.63 0.66 0.69 0.70 0.72
90% 0.69 0.71 0.73 0.76 0.77 0.79
95% 0.78 0.80 0.82 0.84 0.85 0.86
100% 0.89 0.90 0.92 0.94 0.95 0.96
RO-12 2007-01
Urban Drainage and Flood Control District
APPENDIX B
WATER DETENTION COMPUTATIONS
ATC
Pond No : 1
1
100-yr
1.00
Area (A)= 1.24 acres 8888 ft
3
Max Release Rate = 1.10 cfs 0.20 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 12.34 3701 330.0 3371.4
10 600 7.720 9.57 5744 660.0 5083.7
15 900 6.520 8.08 7276 990.0 6286.3
20 1200 5.600 6.94 8333 1320.0 7012.8
25 1500 4.980 6.18 9263 1650.0 7612.8
30 1800 4.520 5.60 10089 1980.0 8108.6
35 2100 4.080 5.06 10624 2310.0 8314.3
40 2400 3.740 4.64 11130 2640.0 8490.2
45 2700 3.460 4.29 11584 2970.0 8614.1
50 3000 3.230 4.01 12016 3300.0 8715.6
55 3300 3.030 3.76 12399 3630.0 8768.8
60 3600 2.860 3.55 12767 3960.0 8807.0
65 3900 2.720 3.37 13154 4290.0 8863.9
70 4200 2.590 3.21 13489 4620.0 8868.7
75 4500 2.480 3.08 13838 4950.0 8888.4
80 4800 2.380 2.95 14166 5280.0 8885.8
85 5100 2.290 2.84 14482 5610.0 8872.0
90 5400 2.210 2.74 14798 5940.0 8858.2
95 5700 2.130 2.64 15055 6270.0 8784.8
100 6000 2.060 2.55 15326 6600.0 8726.4
105 6300 2.000 2.48 15624 6930.0 8694.0
110 6600 1.940 2.41 15877 7260.0 8617.0
115 6900 1.890 2.34 16171 7590.0 8580.8
120 7200 1.840 2.28 16428 7920.0 8507.5
1.35
Design Point
Design Storm Required Detention Volume
Developed "C" =
Project Location : Fort Collins
Input Variables Results
Calculations By:
DETENTION POND CALCULATION; FAA METHOD
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
EXTENDED DETENTION WATER QUALITY POND DESIGN CALCULATIONS
Pond 1
Project: 838-013
By: ATC
Date: 9-12-14
REQUIRED STORAGE & OUTLET WORKS:
BASIN AREA = 1.240 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 90.00 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.9000 <-- CALCULATED
WQCV (watershed inches) = 0.401 <-- CALCULATED from Figure EDB-2
WQCV (ac-ft) = 0.050 <-- 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 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.
APPENDIX E
REFERENCE MATERIAL – SELECTED PORTIONS OF THE DOWNTOWN RIVER DISTRICT
IMPROVEMENT PLANS (FEBRUARY 2012)
MAP POCKET
DRAINAGE EXHIBITS
Project Number : 838-013
Date : 9-12-14
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
11No0.95 0.95 1.00 80 1.00% 2.5 2.5 1.7 401 0.60% 1.55 4.3 0 0.00% N/A N/A 7 7 6
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
ATC
9/15/2014
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
H1 H1 No 0.50 0.50 0.63 146 1.60% 11.6 11.6 9.2 383 0.40% 1.26 5.0 0 0.00% N/A N/A 17 17 14
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
ATC
9/15/2014
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L