HomeMy WebLinkAboutCARRIAGE HOUSE APARTMENTS - PDP - PDP120035 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTDecember 19, 2012
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
Carriage House Apartment Homes
Fort Collins, Colorado
Prepared for:
Epsilon Theta Corporation
200 South Avenue, Suite 10
Fort Collins, Colorado 80524
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: 620-002
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.
December 19, 2012
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
Carriage House Apartment Homes
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control
Report for your review. Comments from the Conceptual Review letter dated 10.24.12 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 Carriage House Apartment Homes student housing 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.
Nicholas W. Haws, PE Herman H. Feissner, PE
Project Manager Project Engineer
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ......................................................... 1
II. DRAINAGE BASINS AND SUB-BASINS ............................................................. 4
III. DRAINAGE DESIGN CRITERIA ......................................................................... 5
IV. DRAINAGE FACILITY DESIGN .......................................................................... 7
V. CONCLUSIONS............................................................................................... 9
References ............................................................................................................. 10
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers (reserved for future use)
B.2 – Street Flow (reserved for future use)
B.3 – Inlets (reserved for future use)
B.4 – Detention Facilities
APPENDIX C – Water Quality Design Computations
APPENDIX D – Operations and Maintenance Guidelines for Rain Gardens
(reserved for future use)
APPENDIX E – Erosion Control Report
LIST OF TABLES AND FIGURES:
MAP POCKET:
C4.00 – Drainage Exhibit
NOTE: TABLE OF CONTENTS WILL BE UPDATED/CORRECTED WITH SUBSEQUENT
REPORT ISSUANCES.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
Figure 1 – Vicinity Map
2. The Carriage House Apartment Homes project site is located in the Southeast quarter
of Section 15, Township 7 North, Range 69 West of the 6th Principal Meridian, City of
Fort Collins, County of Larimer, State of Colorado.
3. The project site is bordered to the north by Springfield Drive (60' Right-of-Way); to the
south by Bennett Road Bungalows, a detention pond and single-family residential; to
the east by South Shields Street (proposed 100' Right-of-Way); and to the west by
single-family residential.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 2
4. There are no major drainageways within or adjacent to the site.
B. Description of Property
1. Carriage House Apartment Homes is comprised of ±1.45 acres.
2. The site is currently occupied by three single-family residences and associated
improvements.
Figure 2 – Aerial Photograph
3. The existing groundcover currently consists of grasses and numerous mature trees. The
existing on-site excess runoff generally drains west-to-east across flat grades (e.g.,
<2.00%) into Springfield Drive and South Shields Street.
4. A soils report (Project No. 12-1-5-517 | Date: December 12, 2012) was completed
by Kumar and Associates, Inc. The report contains the results of a complete
geotechnical subsurface exploration as well as pertinent geotechnical
recommendations. According to the summary of findings presented in the
aforementioned report, the "The borings encountered 4 to 6 inches of topsoil overlying
nil to 5 feet of man-placed fill. The fill was composed of fine to coarse-grained
material consisted of fine-grained sandy lean clay with occasional zones of lean clay.
In the deeper foundation borings, fine to coarse-grained clayey sand was encountered
below the clayey soil and continued to the overburden soil/bedrock interface. The
natural overburden clay soils were slightly moist to moist, and generally very stiff to
hard. The natural clayey sands were slightly moist to wet below ground water, and
medium dense to dense."
The boring logs show that USCS soil group CL is predominant on-site. These soils are
inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays and
lean clays.
5. There are no major drainageways within or adjacent to the project site.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 3
6. The proposed Carriage House Apartment Homes development will consist of a student
residential complex with five multi-unit buildings. Other proposed improvements
include: a new asphalt and porous Modular Block Paver (MBP) parking and
landscaping.
7. The proposed land use is residential, multi-family dwellings. This is a permitted use in
the Neighborhood Community - Buffer District (NCB).
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 08069C0978G)
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 4
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Carriage House Apartment Homes is located within the City of Fort Collins Old Town
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.
Street flooding is a common occurrence in Old Town. Several capital projects such as
the Howes Street, Locust Street and Oak Street Outfall projects have addressed the
problem and improved drainage in the area.
B. Sub-Basin Description
1. The outfall for the project site is an existing inlet at the southwest corner of South
Shields Street and Springfield Drive.
2. The subject site can be historically defined by three (3) sub-basins (i.e., EX1 thru
EX3). Sub-basin EX1 delineates the proposed project site. It was used to approximate
the 2- and 100-year historic runoff rates. Sub-basins EX2 and EX3 delineate the
existing Springfield Drive and South Shields Street right-of-way areas contiguous with
the project site, respectively.
The existing site runoff generally drains from west to east into Springfield Drive and
South Shields Street.
3. The project site does not receive any notable runoff from off-site properties.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 5
III. DRAINAGE DESIGN CRITERIA
A. There are no optional provisions outside of the FCSCM proposed with Carriage House
Apartment Homes.
B. The overall stormwater management strategy employed with Carriage House Apartment
Homes 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.
Carriage House Apartment Homes aims to reduce runoff peaks, volumes and pollutant
loads from frequently occurring storm events (i.e., water quality (80th percentile) and 2-
year storm events) by implementing Low Impact Development (LID) strategies. Wherever
practical, runoff will be routed across landscaped areas or through grass-lined swales and
Modular Block Pavers (MBPs). This LID practice reduces the overall amount of impervious
area, while Minimizing Directly Connected Impervious Areas (MDCIA) at the same time.
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 will occur in a Modular
Block Paver (MBP) section in sub-basin A. The MBP section design will be more fully
developed at Final Design.
Step 3 – Stabilize Drainageways. As stated in Section I.B.4, above, there are no major
drainageways in or near the subject site. While this step may not seem applicable to
Carriage House Apartment Homes, the proposed project indirectly helps achieve stabilized
drainageways nonetheless. Once again, site selection has a positive effect on stream
stabilization. By repurposing an already developed, under-utilized site with existing
stormwater infrastructure, combined with LID and MDCIA strategies, the likelihood of bed
and bank erosion is greatly 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 drainage study or
similar “development/project” drainage master plan.
2. The site plan will be constrained on two sides by public streets and by existing and
fully developed sites along the remaining two sides. As previously mentioned, the
drainage outfall for sub-basin A is an existing inlet at the southwest corner of
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 6
Springfield Drive and South Shields Street. The proposed design matches the existing
historic release rate (i.e., 1.86 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 Carriage House Apartment Homes 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 Carriage House Apartment Homes
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.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 7
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objective of the Carriage House Apartment Homes drainage design is to
maintain existing drainage patterns, while not adversely impacting adjacent properties.
2. No notable off-site runoff flows 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 three (3) drainage sub-basins, designated as
sub-basins A, B, and C. The drainage patterns anticipated for each basin are further
described below.
Sub-Basin A
Sub-basin A encompasses nearly 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 asphalt and MBPs. This basin releases at the adjusted 2-year historic
rate of 0.84 cfs.
Sub-Basin B
Sub-basin B is a relatively small basin that is comprised of asphalt (i.e., site drive
entrance) and landscaping. The excess developed runoff will drain into Springfield
Drive. The 100-year developed runoff (Q100=0.25 cfs), for sub-basin B, was
subtracted from the total 2-year historic release rate.
Sub-Basin C
Sub-basin C encompasses the northeast corner of the project site. It is comprised of
roof area and landscaping. The excess developed runoff will drain into Springfield
Drive and South Shields Street. The 100-year developed runoff (Q100=0.77 cfs), for
sub-basin C, was subtracted from the total 2-year historic release rate.
A full-size copy of the Drainage Exhibit (sheet DR1) can be found in the Map Pocket
at the end of this report.
B. Specific Details
1. The FAA method was used to size the on-site pond for quantity detention.
Preliminary calculations for this area, based on the characteristics of sub-basin
A and adjusted release rate, indicate a required volume of 7808 cu. ft. This
includes 727 cu. ft. of storage for the water quality capture volume.
2. During Final Design, computations will be more fully developed for the proposed
Modular Block Pavers (MBPs) in sub-basin A by utilizing the UDFCD’s UD-BMP
Version 3.02 “Permeable Paver Systems (PPS)” Design Procedure Form. During water
quality events the water quality capture volume will release over 12-hours.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 8
3. A hybrid approach was utilized to compute the maximum allowable release rate
associated with the FAA detention sizing calculations. The 100-year peak runoff rate
was calculated for the pre-development impervious areas. This essentially
“grandfathers” the existing impervious areas by allowing the respective 100-year
peak discharge to be added to the maximum allowable release rate. The release rate
for the remaining undeveloped land (pre-development pervious areas) was
established by calculating the 2-year peak runoff rate for these areas. The total of
these two discharges establishes the overall maximum allowable release rate, 1.86
cfs, from the project site. The allowable release rate, 0.84 cfs, utilized in the FAA
procedure detention storage computations (Refer to Appendix B for these
calculations) was established by subtracting undetained releases, 1.02 cfs, from the
overall maximum allowable release rate. This hybrid approach ensures that all
increased impervious areas, not just those greater than 5,000 sq-ft, are over-
detained down to the 2-year undeveloped (historic or pre-development) rate for the
100-year developed condition.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 9
V. CONCLUSIONS
A. Compliance with Standards
1. The design elements comply without variation.
2. The drainage design proposed with Carriage House Apartment Homes complies with
the City of Fort Collins Master Drainage Plan for the Old Town Basin.
3. There are no regulatory floodplains associated with the Carriage House Apartment
Homes development.
4. The drainage plan and stormwater management measures proposed with the Carriage
House Apartment Homes student housing 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. Carriage House Apartment Homes will detain for
the pervious area converted to impervious areas to release at the 2-year historic rate
during the 100-year storm.
2. The proposed Carriage House Apartment Homes development will not impact the
Master Drainage Plan recommendations for the Old Town Basin.
Carriage House Apartment Homes
Preliminary Drainage and Erosion Control Report 10
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. Geotechnical Engineering Study and Pavement Thickness Design Proposed Student
Apartment Development 1305 and 1319 South Shields Avenue Fort Collins, Colorado,
December 13, 2012, Kumar and Associates, Inc. (Project No. 12-1-517).
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
Carriage House Apartment Homes
Project: Carriage House Apartment Homes
Project Site Area 62991 Calculations By:
EX1 62991 Date:
A 52676
B 1925
C 8391
Basin Area, sq. ft. Surface Description % Impervious Area, sq. ft. Notes
EX1 0 Asphalt 100% 0
EX1 2864 Concrete (e.g., walks & parking) 90% 2578
EX1 1773 Gravel 40% 709
EX1 4893 Roofs 90% 4404
Impervious Area 7691
% Impervious 12%
Total Impervious Area 7691
% Impervious 12%
Basin Area, sq. ft. Surface Description % Impervious Area, sq. ft. Notes
A 16905 Asphalt 100% 16905
A 4366.00 Concrete (e.g., walks & parking) 90% 3929
A 12894.00 Roofs 90% 11605
SUMMARY OF EXISTING AND PROPOSED IMPERVIOUS AREA
H. Feissner
December 19, 2012
EXISTING CONDITION
PROPOSED CONDITION
Areas, sq. ft.
A 12894.00 Roofs 90% 11605
Impervious Area 32439
% Impervious 62%
B 478 Asphalt 100% 478
B 99 Concrete (e.g., walks & parking) 90% 89
Impervious Area 567
% Impervious 29%
C 598 Concrete (e.g., walks & parking) 90% 538
C 2968 Roofs 90% 2671
Impervious Area 3209
% Impervious 38%
Impervious Area 33006
% Impervious 52%
Area, sq. ft. Area, acre
Total Impervious Area Increase 25316 0.581
SUMMARY
12/19/2012 1:18 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs\Impervious Area
Carriage House Apartment Homes
CHARACTER OF SURFACE1:
Runoff
Coefficient
Percentage
Impervious Project: Carriage House Apartment Homes
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: H. Feissner
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
Flat <2% ……………………………………………………………………………………………………………… 0.10 0%
Average 2% to 7% ………………………………………………………………………………………………….0.15 0% .
Steep >7% …………………………………………………………………………………………………………… 0.20 0%
Clayey Soil
Flat <2% ……………………………………………………………………………………………………………… 0.20 0%
Average 2% to 7% ………………………………………………………………………………………………….0.25 0% .
Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25
Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11
Basin ID
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Gravel
(ac)
Area of
Roofs
(ac)
Area of
Pavers
(ac)
Soil Type and Average
Slope
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Carriage House Apartment Homes
Overland Flow, Time of Concentration:
Project: Carriage House Apartment Homes
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = T
i + Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
Carriage House Apartment Homes
Rational Method Equation: Project: Carriage House Apartment Homes
Calculations By:
Date:
Rainfall Intensity:
n/a EX1Impervious 0.22 18.2 18.2 17.0 0.87 0.87 1.00 1.70 2.90 6.10 0.32 0.55 1.33
n/a EX1Pervious 1.23 18.2 18.2 17.0 0.25 0.25 0.31 1.70 2.90 6.10 0.52 0.89 2.34
EX1 EX1 1.45 18.24 18.24 17.02 0.34 0.34 0.43 1.70 2.90 6.10 0.84 1.44 3.78
EX2 EX2 0.34 5.00 5.00 5.00 0.82 0.82 1.00 2.85 4.87 9.95 0.80 1.36 3.39
EX3 EX3 0.17 5.00 5.00 5.00 0.80 0.80 1.00 2.85 4.87 9.95 0.39 0.66 1.69
C100
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Allowable release rate: 1.33
+ 0.52 = 1.86 cfs
Notes
RUNOFF COMPUTATIONS
H. Feissner
December 19, 2012
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C2 C10
Q C f C i A
12/19/2012 1:15 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs\Runoff
Carriage House Apartment Homes
CHARACTER OF SURFACE1:
Runoff
Coefficient
Percentage
Impervious Project: Carriage House Apartment Homes
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: H. Feissner
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
Flat <2% ……………………………………………………………………………………………………………… 0.10 0%
Average 2% to 7% ………………………………………………………………………………………………….0.15 0% .
Steep >7% …………………………………………………………………………………………………………… 0.20 0%
Clayey Soil
Flat <2% ……………………………………………………………………………………………………………… 0.20 0%
Average 2% to 7% ………………………………………………………………………………………………….0.25 0% .
Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25
Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11
Basin ID
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Gravel
(ac)
Area of
Roofs
(ac)
Area of
Pavers
(ac)
Soil Type and Average
Slope
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite Runoff
Coefficient
Composite
% Imperv.
A 1.28 0.23 0.10 0.00 0.30 0.16 Clayey | Average 2% to 7% 0.50 0.61 0.61 0.76 46%
B 0.04 0.01 0.00 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.03 0.46 0.46 0.57 29%
Carriage House Apartment Homes
Overland Flow, Time of Concentration:
Project: Carriage House Apartment Homes
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = T
i + Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
Carriage House Apartment Homes
Rational Method Equation: Project: Carriage House Apartment Homes
Calculations By:
Date:
Rainfall Intensity:
A A 1.28 5.00 5.00 5.00 0.61 0.61 0.76 2.85 4.87 9.95 2.23 3.80 9.71
B B 0.04 5.00 5.00 5.00 0.46 0.46 0.57 2.85 4.87 9.95 0.06 0.10 0.25 Undetained release
C C 0.12 5.00 5.00 5.00 0.51 0.51 0.64 2.85 4.87 9.95 0.18 0.30 0.77 Undetained release
OS1 OS1 0.34 5.00 5.00 5.00 0.85 0.85 1.00 2.85 4.87 9.95 0.83 1.41 3.39
OS2 OS2 0.17 5.00 5.00 5.00 0.79 0.79 0.99 2.85 4.87 9.95 0.38 0.66 1.68
C100
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
RUNOFF COMPUTATIONS
H. Feissner
December 19, 2012
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C2 C10
Q C f C i A
12/19/2012 2:40 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs_Alt\Runoff
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers (reserved for future use)
B.2 – Street Flow (reserved for future use)
B.3 – Inlets (reserved for future use)
B.4 – Detention Facilities
APPENDIX B.1
STORM SEWERS (reserved for future use)
APPENDIX B.2
STREET FLOW (reserved for future use)
APPENDIX B.3
INLETS (reserved for future use)
APPENDIX B.4
DETENTION FACILITIES
Carriage House Apartment Homes
620-002
Detention Pond Calculation | FAA Method
Project Number: 620-002
Fort Collins, Colorado
H. Feissner Date: 12/19/2012
Project Number:
Project Location:
Calculations By: H. Feissner Date: 12/19/2012
Pond No.: Pond A
Calculations By:
A
Input Variables Results
Design Point A
100-yr
0.76 WQCV 727 ft3
Design Point
Design Storm Required Detention Volume
Developed "C" = 0.76 WQCV 727 ft3
Area (A)= 1.28 acres Quantity Detention 7081 ft3
Developed "C" =
Area (A)= 1.28 acres Quantity Detention 7081 ft
Max Release Rate = 0.84 cfs Total Volume 7808 ft3
Total Volume 0.179 ac-ft
Ft.Collins Inflow Storage
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) (ft3) ft ) (ft3) ft ) (ft3) ft )
5 300 9.95 9.7 2904 252 2652
10 600 7.72 7.5 4506 504 4002
15 900 6.52 6.3 5708 756 4952
20 1200 5.60 5.4 6537 1008 5529
25 1500 4.98 4.8 7267 1260 6007
30 1800 4.52 4.4 7915 1512 6403
35 2100 4.08 4.0 8335 1764 6571
40 2400 3.74 3.6 8732 2016 6716
45 2700 3.46 3.4 9088 2268 6820
50 3000 3.23 3.1 9426 2520 6906
55 3300 3.03 2.9 9727 2772 6955
60 3600 2.86 2.8 10016 3024 6992
65 3900 2.72 2.6 10319 3276 7043
70 4200 2.59 2.5 10582 3528 7054
75 4500 2.48 2.4 10856 3780 7076
80 4800 2.38 2.3 11113 4032 7081
85 5100 2.29 2.2 11361 4284 7077
90 5400 2.21 2.1 11609 4536 7073
95 5700 2.13 2.1 11811 4788 7023
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia
Ia
= 46.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia
/ 100) i = 0.460
C) Tributary Watershed Area ATotal
= 55,792 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 14,915 sq ft
(Minimum recommended permeable pavement area = 10433 sq ft)
E) Impervious Tributary Ratio RT
= 1.3
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 727 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
Provide overflow to carry runoff directly
Carriage House Apartment Homes
Fort Collins, Colorado | Basin A
Design Procedure Form: Permeable Pavement Systems (PPS)
H. Feissner
Northern Engineering
December 19, 2012
Choose One
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
Provide overflow to carry runoff directly
into the reservoir layer to ensure use
of flood control volume regardless
H) Total Volume Needed VTotal
= 7,808 cu ft of infiltration rates.
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 18.0 inches
(Minimum recommended depth is 6 inches)
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = 1.5 ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
Fort Collins, Colorado | Basin A
Carriage House Apartment Homes
Design Procedure Form: Permeable Pavement Systems (PPS)
H. Feissner
Northern Engineering
December 19, 2012
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
A) Depth of WQCV in the Reservoir DWQCV
= 2.66 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice
= 0.66 inches
(Use a minimum orifice diameter of 3/8-inches)
Notes:
UD-BMP_v3.02-Basin A, PPS 12/19/2012, 2:32 PM
APPENDIX D
OPERATIONS AND MAINTENANCE GUIDELINES FOR RAIN GARDENS(reserved for future use)
APPENDIX E
EROSION CONTROL REPORT
Carriage House Apartment Homes
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 Best Management Practices (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 Sheet C.?? of the Utility Plans. The Final Plans
will contain a full-size Erosion Controlsheet 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 Carriage
House Apartment Homes. 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.
Carriage House Apartment Homes
Preliminary Erosion Control Report
MAP POCKET
C4.00 – DRAINAGE EXHIBIT
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.40
D) Slope of the Base Course/Subgrade Interface S = 0.005 ft / ft
E) Length Between Lateral Flow Barriers (max = 48.77 ft.) L = 40.0 ft
F) Volume Provided Based on Depth of Base Course V = 7,855 cu ft
Flat or Stepped: V = P * ((Dmin-1
)/12) * Area
Sloped: V = P * [(Dmin -
(Dmin
- 6*SL-1)) / 12] * Area Volume assumes uniform slope & lateral flow barrier spacing.
Calculate the volume of each cell individually when this varies.
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells = 1
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
UD-BMP_v3.02-Basin A, PPS 12/19/2012, 2:32 PM
100 6000 2.06 2.0 12024 5040 6984
105 6300 2.00 1.9 12257 5292 6965
110 6600 1.94 1.9 12456 5544 6912
115 6900 1.89 1.8 12686 5796 6890
120 7200 1.84 1.8 12888 6048 6840
12/19/2012 2:42 PM D:\Projects\620-002\Drainage\Detention\620-002__Detention Pond.xlsm\FAA_Current idf_A
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
A A No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
B B No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
C C No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
OS1 OS1 No 0.95 0.95 1.00 20 3.10% 0.9 0.9 0.6 429 0.90% 1.90 3.8 0 0.00% N/A N/A 5.00 5.00 5.00
OS2 OS2 No 0.95 0.95 1.00 34 1.90% 1.3 1.3 0.9 144 1.00% 2.00 1.2 0 0.00% N/A N/A 5.00 5.00 5.00
TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
H. Feissner
December 19, 2012
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
12/19/2012 2:39 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs_Alt\Tc
C 0.12 0.00 0.01 0.00 0.03 0.00 Clayey | Average 2% to 7% 0.08 0.51 0.51 0.64 34%
OS1 0.34 0.21 0.08 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.05 0.85 0.85 1.00 83%
OS2 0.17 0.09 0.04 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.04 0.79 0.79 0.99 75%
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
December 19, 2012
Composite Runoff Coefficient with Adjustment
12/19/2012 2:39 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs_Alt\Composite Runoff Coefficient
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
EX1 EX1 No 0.25 0.25 0.31 185 2.20% 16.6 16.6 15.4 224 1.30% 2.28 1.6 0 0.00% N/A N/A 18.24 18.24 17.02
EX2 EX2 No 0.95 0.95 1.00 20 3.10% 0.9 0.9 0.6 429 0.90% 1.90 3.8 0 0.00% N/A N/A 5.00 5.00 5.00
EX3 EX3 No 0.95 0.95 1.00 34 1.90% 1.3 1.3 0.9 144 1.00% 2.00 1.2 0 0.00% N/A N/A 5.00 5.00 5.00
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
H. Feissner
December 19, 2012
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
12/19/2012 1:16 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs\Tc
EX1Impervious 0.22 0.00 0.07 0.04 0.11 0.000 Clayey | Average 2% to 7% 0.00 0.87 0.87 1.00 81%
EX1Pervious 1.23 0.00 0.00 0.00 0.00 0.000 Clayey | Average 2% to 7% 1.23 0.25 0.25 0.31 0%
EX1 1.45 0.00 0.07 0.04 0.11 0.000 Clayey | Average 2% to 7% 1.23 0.34 0.34 0.43 12%
EX2 0.34 0.22 0.06 0.00 0.00 0.000 Clayey | Average 2% to 7% 0.06 0.82 0.82 1.00 80%
EX3 0.17 0.09 0.04 0.00 0.00 0.000 Clayey | Average 2% to 7% 0.04 0.80 0.80 1.00 76%
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
December 19, 2012
Composite Runoff Coefficient with Adjustment
12/19/2012 1:15 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs\Composite Runoff Coefficient