HomeMy WebLinkAboutOLD TOWN FLATS - FDP - FDP130049 - REPORTS - DRAINAGE REPORTJanuary 22, 2014
FINAL DRAINAGE REPORT
OLD TOWN FLATS
Fort Collins, Colorado
Prepared for:
Brinkman Development, LLC
3003 East Harmony Road, Suite 300
Fort Collins, Colorado 80528
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: 379-039
3This 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.
January 22, 2014
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
Old Town Flats
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage Report for your review.
Comments from the Old Town Flats – Final Development Plan, FDP130049, Round
Number 1 letter dated January 13, 2014 have been addressed. Written responses thereto
can be found in the comprehensive response to comments letter on file with Current
Planning.
This report has been prepared in accordance with the Fort Collins Stormwater Criteria
Manual (FCSCM), and serves to document the stormwater impacts associated with the
proposed Old Town Flats housing project. We understand that review by the City of Fort
Collins 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.
Nicholas W. Haws, PE Andrew Reese
Project Manager Project Engineer
Old Town Flats
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ......................................................... 1
II. DRAINAGE BASINS AND SUB-BASINS ............................................................. 5
III. DRAINAGE DESIGN CRITERIA ......................................................................... 6
IV. DRAINAGE FACILITY DESIGN .......................................................................... 8
V. CONCLUSIONS............................................................................................. 10
References ............................................................................................................. 11
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Hydraulic Computations
B.2 – Detention Facilities
APPENDIX C – Water Quality Design Computations
APPENDIX D – Erosion Control Report
APPENDIX E – Standard Operating Procedures (SOP’s) References
MAP POCKET:
C700 – Drainage Exhibit
EX1 – Existing Drainage Exhibit
Old Town Flats
Page|1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
Figure 1 – Vicinity Map
2. The Old Town Flats project site is located in the Northeast quarter of 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 (refer to Figure 1) is bordered to the north by vacant property; to the
south by Maple Street (100’ ROW); to the east by an existing public alley (20' Right-
of-Way); and to the west by Mason Street (100’ ROW).
4. There are no major drainageways within or adjacent to the site.
Old Town Flats
Page|2
B. Description of Property
1. Old Town Flats is comprised of ±0.87 acres.
2. The site is currently unoccupied, vacant land.
Figure 2 – Aerial Photograph
3. The existing groundcover consists of grasses and gravel. The existing on-site runoff
generally drains from the southwest-to-northeast east across flat grades (e.g.,
<2.00%) into the existing alley. From there it is directed to an existing inlet via a
concrete pan, at which point the drainage continues through an existing storm system
down College Avenue to Willow Street, and on to the Cache La Poudre River. The
existing concrete pan and area inlet are encompassed by an existing 10’ drainage
easement (Rec. #2004-0002334) on Lot 10, Block 23.
4. A soils report (Project No. 1132055 | Date: July 30, 2013) was completed by Earth
Engineering Consultants, LLC. The report contains the results of a complete
geotechnical subsurface exploration as well as pertinent geotechnical
Project Site
Old Town Flats
Page|3
recommendations. According to the summary of findings presented in the
aforementioned report,
"…a surficial layer of gravel, asphaltic concrete, topsoil/landscape material or
concrete was observed through the site at the boring location. An approximate 1-1/2
to 4-foot layout of fill material was encountered immediately beneath the surface
materials. Native cohesive to slightly cohesive sandy lean clay and/or clayey sand
subsoils were encountered at approximate depths of 2 ½ to 4 feet below site grades.”
5. There are no major drainageways within or adjacent to the project site.
6. The proposed Old Town Flats development will consist of a single residential building.
Other proposed improvements include: a new concrete and permeable Modular Block
Paver (MBP) parking area and landscaping.
7. The proposed land use is residential, multi-family dwelling. This is a permitted use in
the Downtown District (D).
Old Town Flats
Page|4
C. Floodplain
1. The subject property is not located in a FEMA regulatory or City of Fort Collins
designated floodplain. In particular, the project site is not located within a FEMA
designated 100-year floodplain per Map Number 08069C0979H (Effective date: May
2, 2012).
Figure 4 – FEMA Firmette (Map Number 08069C0979H)
Project Site
Old Town Flats
Page|5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Old Town Flats is located within the City of Fort Collins Old Town major drainage
basin. Specifically, the project site is situated in the north-central portion of this major
drainage basin. This basin is located in north-central Fort Collins and has a drainage
area of approximately 2,120 acres, including approximately 400 acres of the Colorado
State University campus. The Old Town major drainage basin generally drains from
west to east. It receives some runoff from the Canal Importation Basin directly west of
Old Town. Most of the runoff from the Old Town major drainage basin drains into the
Poudre River.
B. Sub-Basin Description
1. The outfall for the project site is an existing area inlet located just west of College
Avenue between Cherry Street and Maple Street. The existing area inlet is
encompassed by an existing 10’ drainage easement (Rec. #2004-0002334) on Lot
10, Block 23.
2. The existing subject site can be defined with one (1) sub-basin. Refer to the Existing
Drainage Exhibit for additional information.
x Sub-basin EX1 delineates the proposed project site, which was used to
approximate the 2- and 100-year existing runoff.
The existing site runoff generally drains from southwest-to-northeast into the existing
alley along the eastern boundary of the site.
3. The project site does not receive notable runoff from contiguous off-site properties.
Old Town Flats
Page|6
III. DRAINAGE DESIGN CRITERIA
A. There are no optional provisions outside of the FCSCM proposed with Old Town Flats.
B. The overall stormwater management strategy employed with Old Town Flats 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. The first consideration taken in trying to
reduce the stormwater impacts of this development is the site selection itself. By choosing
an already developed site with public storm sewer currently in place, the burden is
significantly less than developing a vacant parcel absent of any infrastructure.
Old Town Flats aims to reduce runoff peaks, volumes and pollutant loads from frequently
occurring storm events (i.e., water quality (i.e., 80th percentile) and 2-year storm events)
by implementing Low Impact Development (LID) strategies. Wherever practical, runoff will
be routed across landscaped areas or Modular Block Pavers (MBPs). This LID practice
reduces the overall amount of impervious area, while at the same time Minimizing Directly
Connected Impervious Areas (MDCIA). The combined LID/MDCIA techniques will be
implemented, where practical, throughout the development, thereby slowing runoff and
increasing opportunities for infiltration.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release. The efforts taken in Step 1 will help to minimize excess runoff from
frequently occurring storm events; however, urban development of this intensity will still
have stormwater runoff leaving the site. The primary water quality treatment will occur in
the Modular Block Paver (MBP) section in sub-basin A.
Step 3 – Stabilize Drainageways. As stated in Section I.B.5, above, there are no major
drainageways in or near the subject site. While this step may not seem applicable to Old
Town Flats, the proposed project indirectly helps achieve stabilized drainageways
nonetheless. Once again, site selection has a positive effect on stream stabilization. By
developing an infill site with existing stormwater infrastructure, combined with LID and
MDCIA strategies, the likelihood of bed and bank erosion is reduced. Furthermore, this
project will pay one-time stormwater development fees, as well as ongoing monthly
stormwater utility fees, both of which help achieve Citywide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs. This step typically
applies to industrial and commercial developments.
C. Development Criteria Reference and Constraints
1. The subject property is not part of any Overall Development Plan (ODP) drainage
study or similar “development/project” drainage master plan.
2. The site plan is constrained on two sides by public streets, as well as by existing
undeveloped and developed sites along the remaining two sides. As previously
mentioned, the drainage outfall for sub-basin A is an existing area inlet located just
west of College Avenue between Cherry Street and Maple Street on Lot 10.
3. Peak runoff from the project site during the 2-year event will remain unchanged and
will decrease during the 100-year storm event. During the 2-year storm event, runoff
Old Town Flats
Page|7
will remain at ±0.82 cfs; and during the 100-year storm event runoff will decrease
from ±3.91 cfs to ±0.82 cfs.
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 Old Town Flats 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. The Rational Formula-based Federal Aviation Administration (FAA) procedure has
utilized for detention storage calculations.
4. Two separate design storms have been utilized to address distinct drainage scenarios.
The first event analyzed is the “Minor,” or “Initial” Storm, which has a 2-year
recurrence interval. The second event considered is the “Major Storm,” which has a
100-year recurrence interval.
E. Hydraulic Criteria
1. The drainage facilities proposed with the Old Town Flats project are designed
in accordance with criteria outlined in the FCSCM and/or the Urban Drainage
and Flood Control District’s (UDFCD) Urban Storm Drainage Criteria Manual.
2. As stated in Section I.C.1, above, the subject property is not located in a
FEMA regulatory or a City of Fort Collins designated floodplain.
F. Floodplain Regulations Compliance
1. As previously mentioned, this project is not subject to any floodplain
regulations.
G. Modifications of Criteria
1. No modifications are requested at this time.
H. Conformance with Low Impact Development (LID)
1. 15,852 sf of paving is proposed with this project, and of the total, 5,275 sf is
proposed to be Modular Block Pavers (MBPs). This means that ± 34% of the
paved areas in the project are pervious, exceeding the minimum requirement
of 25%.
2. The total project area is 38,050 sf. Of that area, 34,884 sf will be treated by
LID techniques, primarily Modular Block Pavers (MBPs). This means that ±
92% of the site will be treated by LID-type technology, exceeding the
minimum requirement of 50%.
Old Town Flats
Page|8
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objective of the Old Town Flats drainage design is to maintain existing
drainage patterns, while not adversely impacting adjacent properties.
2. No notable off-site runoff passes directly through the project site.
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 project site has been divided into four (4) drainage sub-basins, designated as sub-
basins A, B, C, D and OS1. The drainage patterns anticipated for each basin are
further described below.
Sub-Basin A
Sub-basin A encompasses ±90 percent of the total site area. This sub-basin is
comprised of roof area, landscaping and the on-site parking area. This parking area
will be a mix of concrete and Modular Block Pavers (MBPs). Detention will be
provided within in the MBPs (WSEL100-year=4975.6±). This basin will release at an
adjusted 2-year rate of 0.54 cfs through an orifice plate. An outlet orifice cap located
on the east wall of the proposed drain basin will be used to control the flow rate.
Sub-Basin B
Sub-basin B is a relatively small basin (0.02 acre) that is comprised of landscaping.
The developed runoff will follow the historic drainage path north and then east at rates
significantly less than the existing condition. The 100-year developed runoff
(Q100=0.04 cfs), for sub-basin B, was subtracted from the total 2-year existing release
rate (Q100=0.82 cfs).
Sub-Basin C
Sub-basin C encompasses the western edge of the project site along the Mason Street
frontage. It is comprised of public sidewalks and landscaping. The developed runoff
will drain into Mason Street and flow north. The 100-year developed runoff
(Q100=0.12 cfs), for sub-basin C, was subtracted from the total 2-year existing release
rate (Q100=0.82 cfs).
Sub-Basin D
Sub-basin D encompasses the southern edge of the project site along the Maple Street
frontage. It is comprised of public sidewalks and landscaping. The developed runoff
will drain into Maple Street and flow east. The 100-year developed runoff (Q100=0.12
cfs), for sub-basin D, was subtracted from the total 2-year existing release rate
(Q100=0.82 cfs).
Sub-Basin OS1
Sub-basin OS1 is an off-site basing along Mason Street adjacent to the northwest
corner of the project. It is comprised of public sidewalks, public roadway and railroad
tracks. The developed runoff will in Mason Street and will now be intercepted by an
area inlet. From there, stormwater will be conveyed to the existing curb inlet located
Old Town Flats
Page|9
just south of the railroad tracks, at which point the drainage will continue to follow its
historic drainage path to a storm drain on the west side of the railroad tracks and then
north to the Poudre River. The 100-year developed runoff (Q100=0.74 cfs), for sub-
basin OS1, was not subtracted from the total 2-year existing release rate since the
runoff did not originate on-site.
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. The release rate for the undeveloped land (pre-development) was established
by calculating the 2-year peak runoff rate for the entire project area. The total
establishes the overall maximum allowable release rate, 0.82 cfs, from the
project site. The allowable release rate of 0.54 cfs utilized in the FAA
procedure detention storage computations (Refer to Appendix B for these
calculations) and was established by subtracting the total undetained release
of 0.31 cfs (0.04 cfs +0.12 cfs+0.12 cfs) from the overall maximum
allowable release rate.
2. The FAA method was used to size the on-site pond for quantity detention.
Calculations for this area, based on the characteristics of sub-basin A and
adjusted release rate, indicate a detention volume of 6,670 cu. ft. This
includes 849 cu. ft. of Water Quality Capture Volume (WQCV). During water
quality events the water quality capture volume will release over 12-hours.
There is no-infiltration accounted for with this design.
3. The storage volume available within the reservoir area (i.e., No. 57 and No. 2
open-graded aggregate) of the MBP section is ±7213 cu. ft. at WSEL
4975.65. The 100-yr WSEL is 4975.43. The MBP section is designed with
an increased No.2, open-graded aggregate, material depth in order to provide
storage for storm events in excess of the water quality (80th percentile) storm
event.
4. A Drain Basin is located at the downstream end of the landscape island. This
basin will have an orifice cap installed on the east wall that will limit the
release from the site to the maximum allowable release rate (0.54 cfs).
5. All roof drain downspouts will discharge into the MBP section.
6. The emergency spill path will be from the landscaping island into the existing alley,
where flows will proceed along the historic path north along the alley and east to the
existing area inlet.
Old Town Flats
Page|10
V. CONCLUSIONS
A. Compliance with Standards
1. The design elements comply without variation, and meet all LID requirements.
2. The drainage design proposed with Old Town Flats complies with the City of Fort
Collins Master Drainage Plan for the Old Town Basin.
3. There are no regulatory floodplains associated with the Old Town Flats development.
4. The drainage plan and stormwater management measures proposed with the Old
Town Flats project 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 potential damage
associated with its stormwater runoff. Old Town Flats will detain for the pervious area
converted to impervious areas to release at the 2-year existing rate during the 100-
year storm.
2. The proposed Old Town Flats development will not impact the Master Drainage Plan
recommendations for the Old Town major drainage basin.
Old Town Flats
Page|11
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. Subsurface Exploration Report Block 23 – Phase I, July 30, 2013, Earth Engineering
Consultants, LLC (Project No. 1132055).
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.
Page|12
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Old Town Flats
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Reese
Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100 Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90
Gravel ……….…………………….….…………………………..……………………………….0.50 . 40
Roofs …….…….………………..……………….…………………………………………….0..95 90
Concrete Pavers…………………………...………………..…………………………………………….0.40 . 22
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Concrete
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
EX1 38,050 0.87 0.00 0.00 0.00 0.87 0.00 0.00 0.50 0.50 0.63 40.0
EXISTING COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf = 1.00
January 22, 2014
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational Calcs_Existing.xlsx\C-Values
Overland Flow, Time of Concentration:
Project: Old Town Flats
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
T = T + T (Equation RO-2)
EXISTING TIME OF CONCENTRATION COMPUTATIONS
A. Reese
January 22, 2014
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
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)
Rational Method Equation: Project: Old Town Flats
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
EXISTING RUNOFF COMPUTATIONS
A. Reese
January 22, 2014
Q C f C i A
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
EX1 EX1 0.87 15.4 15.4 12.2 0.50 0.50 0.63 1.87 3.19 7.16 0.82 1.39 3.91
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)
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational Calcs_Existing.xlsx\Direct-Runoff
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C10 C100
2-yr Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
EX1 EX1 0.87 0.50 0.50 0.63 15.4 15.4 12.2 0.82 1.39 3.91
EXISTING RUNOFF SUMMARY TABLE
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational Calcs_Existing.xlsx\Summary Table
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Old Town Flats
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Reese
Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100 Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90
Gravel ……….…………………….….…………………………..……………………………….0.50 . 40
Roofs …….…….………………..……………….…………………………………………….0..95 90
Concrete Pavers…………………………...………………..…………………………………………….0.40 . 22
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Concrete
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
A 34,884 0.80 0.00 0.22 0.42 0.00 0.12 0.04 0.83 0.83 1.00 75.2
B 943 0.02 0.00 0.00 0.00 0.00 0.00 0.02 0.15 0.15 0.19 0.0
C 1,402 0.03 0.00 0.01 0.00 0.00 0.00 0.03 0.31 0.31 0.39 17.8
D 821 0.02 0.00 0.01 0.00 0.00 0.00 0.01 0.49 0.49 0.62 38.5
TOTAL ONSITE 38,050 0.87 0.00 0.24 0.42 0.00 0.12 0.10 0.78 0.78 0.98 70.5
OS1 3,248 0.07 0.00 0.07 0.00 0.00 0.00 0.00 0.95 0.95 1.00 90.0
Overland Flow, Time of Concentration:
Project: Old Town Flats
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
A. Reese
January 22, 2014
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
Velocity (Gutter Flow), V = 20·S
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
Rational Method Equation: Project: Old Town Flats
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
DEVELOPED RUNOFF COMPUTATIONS
A. Reese
January 22, 2014
Q C f C i A
Rainfall Intensity:
A A 0.80 5.1 5.1 5.0 0.83 0.83 1.00 2.85 4.87 9.95 1.89 3.23 7.97
B B 0.02 5.0 5.0 5.0 0.15 0.15 0.19 2.85 4.87 9.95 0.01 0.02 0.04
C C 0.03 5.0 5.0 5.0 0.31 0.31 0.39 2.85 4.87 9.95 0.03 0.05 0.12
D D 0.02 5.0 5.0 5.0 0.49 0.49 0.62 2.85 4.87 9.95 0.03 0.05 0.12
OS1 OS1 0.07 5.0 5.0 5.0 0.95 0.95 1.00 2.85 4.87 9.95 0.20 0.34 0.74
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
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)
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational-Calcs_Proposed.xlsx\Direct-Runoff
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C10 C100
2-yr Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
A A 0.80 0.83 0.83 1.00 5.1 5.1 5.0 1.89 3.23 7.97
B B 0.02 0.15 0.15 0.19 5.0 5.0 5.0 0.01 0.02 0.04
C C 0.03 0.31 0.31 0.39 5.0 5.0 5.0 0.03 0.05 0.12
D D 0.02 0.49 0.49 0.62 5.0 5.0 5.0 0.03 0.05 0.12
OS1 OS1 0.07 0.95 0.95 1.00 5.0 5.0 5.0 0.20 0.34 0.74
DEVELOPED RUNOFF SUMMARY TABLE
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational-Calcs_Proposed.xlsx\Summary Table
Page|13
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers
B.2 – Detention
Facilities
Page|14
APPENDIX B.1
STORM SEWERS
Page|15
APPENDIX B.2
DETENTION FACILITIES
Old Town Flats
Old Town Flats
Fort Collins, Colorado
Detention Pond Calculation | FAA Method
Project:
Project Location: Fort Collins, Colorado
A. Reese Date: January 22, 2014
Pond No.: Paver Parking
Project Location:
Calculations By:
Pond No.: Paver Parking
A
Input Variables Results
Design Point A
100-yr
1.00 WQCV 849 ft
3
Design Point
Design Storm Required Detention Volume
Developed "C" = 1.00 WQCV 849 ft
3
Area (A)= 0.80 acres Quantity Detention 6670 ft
3
Max Release Rate = 0.54 cfs Total Volume 6670 ft
3
Developed "C" =
Max Release Rate = 0.54 cfs Total Volume 6670 ft
Total Volume 0.153 ac-ft
Time Time
Ft.Collins
100-yr
Intensity
Q100
Inflow
(Runoff)
Volume
Outflow
(Release) Volume
Storage
Detention
Intensity Volume Volume
(Release) Volume
Volume
(mins) (secs) (in/hr) (cfs) (ft
3
) (ft
3
) (ft
3
)
5 300 9.95 7.9 2379 162 2217
10 600 7.72 6.2 3691 324 3367
15 900 6.52 5.2 4676 486 4190
20 1200 5.60 4.5 5355 648 4707
25 1500 4.98 4.0 5953 810 5143
30 1800 4.52 3.6 6484 972 5512
35 2100 4.08 3.3 6828 1134 5694
40 2400 3.74 3.0 7153 1296 5857
45 2700 3.46 2.8 7445 1458 5987
50 3000 3.23 2.6 7722 1620 6102
Old Town Flats
Old Town Flats
Stage - Storage Calculation
Project Number: Old Town Flats
Fort Collins, Colorado
A. Reese Date:
Project Number:
Project Location:
Calculations By: January 22, 2014
Pond No.: Paver Parking
Required Volume Water Surface Elevation (WSE)
A
WQCV Void Ratio 40%
Design Point
Design Storm
Required Volume Water Surface Elevation (WSE)
WQCV Void Ratio 40%
Required
Material
Design Storm
849 ft3
Material
Volume 16675
Design Storm 100-yr
Require Volume=
Design Storm 100-yr
Required Volume= 6670 ft3 WSEL 4975.43 ft.
Minimum
Contour
Maximum
Contour
Incremental
Volume
Cummulative
Volume Conic
(X-values)
Contour Contour Volume
(X-values)
ft2 ft. ft3
4,971.93 4,972.18 4.96 4.96
4,972.18 4,972.43 94.82 99.78
4,972.43 4,972.68 567.25 667.03
4,972.68 4,972.93 1104.12 1771.15
4,972.93 4,973.18 1407.4 3178.55
4,973.18 4,973.43 1499.37 4677.92
4,973.43 4,973.68 1501.23 6179.15
4,973.68 4,973.93 1502.41 7681.56
4,973.93 4,974.18 1503.58 9185.14
4,974.18 4,974.43 1504.75 10689.89
4,974.43 4,974.68 1505.93 12195.82
4,974.68 4,974.93 1507.1 13702.92
4,974.93 4,975.18 1508.27 15211.19
4,975.18 4,975.43 1509.45 16720.64
4,975.43 4,975.68 1510.62 18231.26
4,975.68 4,975.93 1511.8 19743.06
4,975.93 4,976.18 1512.97 21256.03
4,976.18 4,976.43 1514.14 22770.17
4,976.50
4,976.00
4,976.50
ORIFICE RATING CURVE
Pond Outlet
100-yr Orifice
PROJECT: Old Town Flats
DATE: January 22, 2014
BY: A. Reese
ORIFICE RATING
Orifice Dia (in) 3.2500
Orifice Area (sf) 0.0576
Orifice invert (ft) 4971.91
Orifice Coefficient 0.65
Stage
(FT) Outlet Release (CFS)
4971.91 0.00
4972.00 1.00
4972.10 0.00
4972.20 0.12
4972.30 0.15
4972.40 0.18
4972.50 0.20
4972.60 0.22
4972.70 0.24
4972.80 0.26
4972.90 0.28
4973.00 0.29
4973.10 0.31
4973.20 0.32
4973.30 0.34
4973.40 0.35
4973.50 0.36
4973.60 0.37
4973.70 0.39
4973.80 0.40
4973.90 0.41
4974.00 0.42
4974.10 0.43
4974.20 0.44
4974.30 0.45
4974.40 0.46
4974.50 0.47
4974.60 0.48
4974.70 0.49
4974.80 0.50
4974.90 0.51
4975.00 0.52
4975.10 0.53
4975.20 0.53
4975.30 0.54
4975.40 0.55
4975.50 0.56
4975.60 0.57
4975.70 0.57
4975.80 0.58
4975.90 0.59
4976.00 0.60
4976.10 0.61
4976.20 0.61
4976.30 0.62
4976.40 0.63
Page|16
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
PAVER PARKING AREA
Project: Old Town Flats
By: A. Reese
REQUIRED STORAGE & OUTLET WORKS:
BASIN AREA = 0.800 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 75.91 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.7591 <-- CALCULATED
Drain Time (hrs) 12 <-- INPUT
Drain Time Coefficient 0.8 <-- CALCULATED from Figure Table 3-2
WQCV (watershed inches) = 0.244 <-- CALCULATED from Figure EDB-2
WQCV (ac-ft) = 0.016 <-- CALCULATED from UDFCD DCM V.3 Section 6.5
Adjusted WQCV (ac-ft) = 0.0195 <-- CALCULATED (20% Sedimentation Accumulation)
WQ Depth (ft) = 0.700 <-- INPUT from stage-storage table
AREA REQUIRED PER ROW, a (in
2
) = 0.076 <-- CALCULATED from Figure EDB-3
CIRCULAR PERFORATION SIZING:
dia (in) = 1/3 <-- INPUT from Figure 5
number of rows = 2
t (in) = 0.500 <-- INPUT from Figure 5
number of rows = 1.000 <-- CALCULATED from WQ Depth and row spacing
WATER QUALITY CONTROL STRUCTURE PLATE
January 22, 2014
APPENDIX D
EROSION CONTROL REPORT
Old Town Flats
EROSION CONTROL REPORT
A comprehensive Erosion and Sediment Control Plan (along with associated details) has
been 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 and/or wattles 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 Sheet C001 of the Utility Plans. The
Final Utility Plans will also contain a full-size Erosion Control Plan 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 any existing Development Agreement(s) of record, as well as the Development
Agreement, to be recorded prior to issuance of the Development Construction Permit. Also,
the Site Contractor for this project may 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, before commencing any earth
disturbing 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
STANDARD OPERATING PROCEDURES (SOPs) REFERENCES
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
4,975.50
4,976.00
4,974.50
4,975.00
Contour Elevation
4,974.00
4,974.50
Contour Elevation
4,973.50
4,974.00
Contour Elevation
4,972.50
4,973.00
Contour Elevation
4,972.00
4,972.50
4,971.50
4,972.00
0 5000 10000 15000 20000 25000
Cummulative Volume, cu. ft.
1/22/20147:39 AM D:\Projects\379-039\Drainage\Detention\379-039__Detention Pond.xlsm\Stage_Storage_MBP Volume
55 3300 3.03 2.4 7969 1782 6187
60 3600 2.86 2.3 8205 1944 6261
65 3900 2.72 2.2 8454 2106 6348
70 4200 2.59 2.1 8669 2268 6401
75 4500 2.48 2.0 8894 2430 6464
80 4800 2.38 1.9 9104 2592 6512
85 5100 2.29 1.8 9308 2754 6554
90 5400 2.21 1.8 9511 2916 6595
95 5700 2.13 1.7 9676 3078 6598
100 6000 2.06 1.6 9850 3240 6610
105 6300 2.00 1.6 10042 3402 6640
110 6600 1.94 1.5 10204 3564 6640
115 6900 1.89 1.5 10393 3726 6667
120 7200 1.84 1.5 10558 3888 6670
125 7500 1.79 1.4 10699 4050 6649
130 7800 1.75 1.4 10878 4212 6666
135 8100 1.71 1.4 11039 4374 6665
140 8400 1.67 1.3 11180 4536 6644
145 8700 1.63 1.3 11302 4698 6604
150 9000 1.60 1.3 11476 4860 6616
155 9300 1.57 1.3 11636 5022 6614
160 9600 1.54 1.2 11782 5184 6598
165 9900 1.51 1.2 11914 5346 6568
170 10200 1.48 1.2 12031 5508 6523
175 10500 1.45 1.2 12134 5670 6464
180 10800 1.42 1.1 12222 5832 6390
185 11100 1.40 1.1 12385 5994 6391
190 11400 1.38 1.1 12538 6156 6382
195 11700 1.36 1.1 12681 6318 6363
200 12000 1.34 1.1 12815 6480 6335
205 12300 1.32 1.1 12939 6642 6297
210 12600 1.30 1.0 13054 6804 6250
215 12900 1.28 1.0 13159 6966 6193
220 13200 1.26 1.0 13255 7128 6127
225 13500 1.24 1.0 13341 7290 6051
230 13800 1.22 1.0 13417 7452 5965
235 14100 1.21 1.0 13597 7614 5983
240 14400 1.20 1.0 13771 7776 5995
1/22/2014 7:24 AM D:\Projects\379-039\Drainage\Detention\379-039__Detention Pond.xlsm\FAA_CoFC idf_A
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
A A No 0.95 0.95 1.00 79 25.0 0.9 0.9 0.6 255 0.5 1.41 3.0 113 1.0 1.50 1.3 5.1 5.1 5.0
B B No 0.95 0.95 1.00 10 33.0 0.3 0.3 0.2 0 0.0 0.00 N/A 0 0.0 0.00 N/A 5.0 5.0 5.0
C C No 0.95 0.95 1.00 10 2.0 0.7 0.7 0.5 0 0.0 0.00 N/A 0 0.0 0.00 N/A 5.0 5.0 5.0
D D No 0.95 0.95 1.00 10 2.0 0.7 0.7 0.5 0 0.0 0.00 N/A 0 0.0 0.00 N/A 5.0 5.0 5.0
OS1 OS1 No 0.95 0.95 1.00 36 2.0 1.3 1.3 0.9 0 0.0 0.00 N/A 0 0.0 0.00 N/A 5.0 5.0 5.0
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow Time of Concentration
(Equation RO-4)
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational-Calcs_Proposed.xlsx\Tc-2-yr_&_100-yr
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
January 22, 2014
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational-Calcs_Proposed.xlsx\C-Values
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
EX1 EX1 No 0.50 0.50 0.63 287 1.9 15.4 15.4 12.2 0 0.5 1.41 0.0 0 1.0 1.50 0.0 15.4 15.4 12.2
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow Time of Concentration
(Equation RO-4)
D:\Projects\379-039\Drainage\Hydrology\379-039_Rational Calcs_Existing.xlsx\Tc-2-yr_&_100-yr