HomeMy WebLinkAboutCARRIAGE HOUSE APARTMENTS - PDP - PDP120035 - REPORTS - DRAINAGE REPORTFebruary 6, 2013
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
Carriage House Apartments
Fort Collins, Colorado
Prepared for:
Catamount Properties Ltd.
7302 Rozena Drive
Longmont, Colorado 80503
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.
February 6, 2013
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
Carriage House Apartments
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control
Report for your review. Comments from the Carriage House Apartments, PDP120035,
Round Number 1 letter dated January 13, 2013 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 Apartments student 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 Herman H. Feissner, PE
Project Manager Project Engineer
Carriage House Apartments
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:
DR1 – Drainage Exhibit
NOTE: TABLE OF CONTENTS WILL BE UPDATED/CORRECTED WITH SUBSEQUENT
REPORT ISSUANCES.
Carriage House Apartments
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 Apartments 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 (refer to Figure 1) 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 Apartments
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 Apartments 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 consists of grasses and numerous mature trees. The existing
on-site 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 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 sandy lean clay with
occasional small gravels. The natural soil underlying the fill 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."
Project Site
Carriage House Apartments
Preliminary Drainage and Erosion Control Report 3
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.
6. The proposed Carriage House Apartments development will consist of a student
residential complex with five multi-unit buildings. Other proposed improvements
include: a new asphalt and permeable Modular Block Paver (MBP) parking area 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 08069C0978G (Effective date: May
2, 2012).
Figure 4 – FEMA Firmette (Map Number 08069C0978G)
Project Site
Carriage House Apartments
Preliminary Drainage and Erosion Control Report 4
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Carriage House Apartments is located within the City of Fort Collins Old Town major
drainage basin. Specifically, the project site is situated in the southwest corner of the
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 curb inlet located at the southwest corner
of South Shields Street and Springfield Drive.
2. The existing subject site can be defined by three (3) sub-basins (i.e., EX1 through
EX3). Refer to the Existing Conditions Drainage Exhibit.
x Sub-basin EX1 delineates the proposed project site. Approximately twelve feet
of Right-Of-Way (ROW) will be dedicated along South Shields Street with this
project. This area is included in sub-basin EX1, which was used to
approximate the 2- and 100-year existing runoff.
x 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 notable runoff from contiguous off-site properties.
Carriage House Apartments
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
Apartments.
B. The overall stormwater management strategy employed with Carriage House Apartments
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 Apartments 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 through grass-lined swales and
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. The MBP section design will be
more fully developed at Final Design.
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
Carriage House Apartments, the proposed project indirectly helps achieve stabilized
drainageways nonetheless. Once again, site selection has a positive effect on stream
stabilization. By repurposing a developed and underutilized project 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 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 and
fully developed sites along the remaining two sides. As previously mentioned, the
drainage outfall for sub-basin A is an existing curb inlet at the southwest corner of
Carriage House Apartments
Preliminary Drainage and Erosion Control Report 6
Springfield Drive and South Shields Street. Total runoff, from the project site during
the 2- and 100-year storm events will decrease. During the 2-year storm event runoff
decreased negligibly from ±0.91 cfs to ±0.90 cfs; and during the 100-year storm
event runoff decreased from ±4.01 cfs to ±2.01 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 Apartments 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 Apartments 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 Apartments
Preliminary Drainage and Erosion Control Report 7
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objective of the Carriage House Apartments 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 three (3) drainage sub-basins and 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 ±85 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 Modular Block Pavers (MBPs). Detention will be provided
within in the MBPs (WSEL100-year=5030.08). This basin will release at an adjusted 2-
year rate of 0.57 cfs through an orifice plate (to be sized at final design).
Sub-Basin B
Sub-basin B is a relatively small basin (0.02 acre) that is comprised of asphalt (i.e.,
project site drive entrance) and landscaping. The excess developed runoff will drain
into Springfield Drive. The 100-year developed runoff (Q100=0.18 cfs), for sub-basin
B, was subtracted from the total 2-year existing release rate (Q100=2.01cfs).
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=1.26 cfs), for
sub-basin C, was subtracted from the total 2-year existing release rate
(Q100=2.01cfs).
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. 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 (i.e., 1.45cfs and
0.56cfs) establishes the overall maximum allowable release rate, 2.01 cfs,
Carriage House Apartments
Preliminary Drainage and Erosion Control Report 8
from the project site. The allowable release rate of 0.57 cfs utilized in the FAA
procedure detention storage computations (Refer to Appendix B for these
calculations) and was established by subtracting the undetained release of
1.44 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 (existing
or pre-development) rate for the 100-year developed condition.
2. 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 8114 cu. ft. This
includes 713 cu. ft. of Water Quality Capture Volume (WQCV).
3. 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. No-infiltration section because in-situ soils are
USCS Type CL.
4. The storage volume available within the reservoir area (i.e., No. 57 and No. 2
open-graded aggregate) of the MBP section is ±8114 cu. ft. 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. MBPs are a natural choice in lower speed vehicle
areas such as a parking lot. The loading ratio is less than 2:1 (i.e., run-on area
to MBP area).
5. The 100-year emergency spillway are will be more fully developed at final design. The
overflow spillway path, with capacity for passing fully developed 100-year flows in
sub-basin A, will likely occur between Building 3 and Building 4.
Carriage House Apartments
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 Apartments 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 Apartments
development.
4. The drainage plan and stormwater management measures proposed with the Carriage
House Apartments 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 Apartments 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 Carriage House Apartments development will not impact the Master
Drainage Plan recommendations for the Old Town major drainage basin.
Carriage House Apartments
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 Apartments
Project: Carriage House Apartment Homes
Project Site Area 62991 Calculations By:
EX1 62991 Date:
A 54170
B 1439
C 7382
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 6853 Asphalt 100% 6853
A 9142 Pavers 22% 2011
A 5264 Concrete (e.g., walks & parking) 90% 4738
A 12875 Roofs 90% 11588
Impervious Area 25189
% Impervious 47%
B 492 Asphalt 100% 492
B 67 Concrete (e.g., walks & parking) 90% 60
SUMMARY OF EXISTING AND PROPOSED IMPERVIOUS AREA
H. Feissner
February 5, 2013
EXISTING CONDITION
PROPOSED CONDITION
Areas, sq. ft.
B 67 Concrete (e.g., walks & parking) 90% 60
Impervious Area 552
% Impervious 38%
C 684 Concrete (e.g., walks & parking) 90% 616
C 2968 Roofs 90% 2671
Impervious Area 3287
% Impervious 45%
Impervious Area 25742
% Impervious 41%
Area, sq. ft. Area, acre
Total Impervious Area Increase 18051 0.414
SUMMARY
2/5/2013 4:12 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs\Impervious Area
Carriage House Apartments
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 Apartments
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 Apartments
Rational Method Equation: Project: Carriage House Apartment Homes
Calculations By:
Date:
Rainfall Intensity:
n/a EX1Impervious 0.22 15.8 15.8 14.8 0.87 0.87 1.00 1.84 3.14 6.62 0.35 0.59 1.45
n/a EX1Pervious 1.23 15.8 15.8 14.8 0.25 0.25 0.31 1.84 3.14 6.62 0.56 0.96 2.54
EX1 EX1 1.45 15.83 15.83 14.82 0.34 0.34 0.43 1.84 3.14 6.62 0.91 1.56 4.10
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
RUNOFF COMPUTATIONS
H. Feissner
February 1, 2013
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 C100
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Allowable release rate: 1.45
+ 0.56 = 2.01 cfs
Notes
Q C f C i A
2/1/2013 11:30 AM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs\Runoff
Carriage House Apartments
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 1.25 0.16 0.12 0.00 0.30 0.21 Clayey | Average 2% to 7% 0.47 0.60 0.60 0.74 46%
B 0.02 0.01 0.00 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.01 0.67 0.67 0.83 59%
Carriage House Apartments
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 Apartments
Rational Method Equation: Project: Carriage House Apartment Homes
Calculations By:
Date:
Rainfall Intensity:
A A 1.25 5.00 5.00 5.00 0.60 0.60 0.74 2.85 4.87 9.95 2.13 3.64 9.29 Q100 = 0.57 cfs
B B 0.02 5.00 5.00 5.00 0.67 0.67 0.83 2.85 4.87 9.95 0.04 0.07 0.18 Undetained release
C C 0.17 5.00 5.00 5.00 0.60 0.60 0.75 2.85 4.87 9.95 0.29 0.49 1.26 Undetained release
OS1 OS1 0.34 5.00 5.00 5.00 0.89 0.89 1.00 2.85 4.87 9.95 0.86 1.47 3.39
OS2 OS2 0.17 5.00 5.00 5.00 0.82 0.82 1.00 2.85 4.87 9.95 0.40 0.68 1.69
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
RUNOFF COMPUTATIONS
H. Feissner
February 5, 2013
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 C100
Q C f C i A
2/5/2013 4:14 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs\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 Apartments
620-002
Fort Collins, Colorado
Detention Pond Calculation | FAA Method
Project Number:
Project Location: Fort Collins, Colorado
H. Feissner Date: 2/5/2013
Pond No.: Pond A
Project Location:
Calculations By:
Pond No.: Pond A
A
Input Variables Results
Design Point A
100-yr
0.74 WQCV 713 ft
3
Design Point
Design Storm Required Detention Volume
Developed "C" = 0.74 WQCV 713 ft
3
Area (A)= 1.25 acres Quantity Detention 8114 ft
3
Max Release Rate = 0.57 cfs Total Volume 8114 ft
3
Developed "C" =
Max Release Rate = 0.57 cfs Total Volume 8114 ft
Total Volume 0.186 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 9.1 2742 171 2571
10 600 7.72 7.1 4256 342 3914
15 900 6.52 6.0 5391 513 4878
20 1200 5.60 5.1 6174 684 5490
25 1500 4.98 4.6 6863 855 6008
30 1800 4.52 4.2 7475 1026 6449
35 2100 4.08 3.7 7872 1197 6675
40 2400 3.74 3.4 8247 1368 6879
45 2700 3.46 3.2 8583 1539 7044
50 3000 3.23 3.0 8903 1710 7193
Carriage House Apartment Homes
620-002
Stage - Storage Calculation
Project Number: 620-002
Fort Collins, Colorado
H. Feissner Date: 2/6/2013
Project Number:
Project Location:
Calculations By: H. Feissner Date: 2/6/2013
Pond No.: Pond A
Calculations By:
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%
713 ft3 Inclusive ft.
Design Storm
Require Volume=
Design Storm 100-yr
Required Volume= 8114 ft3 5030.08 ft.
Contour
Elevation (Y-
Contour
Depth
Incremental Area Cumulative Volume Incremental Volume
Cummulative
Elevation (Y- Volume Conic (X-
values)
Contour
Area
Depth
Incremental Area
Avg. End
Cumulative Volume
Avg. End
Incremental Volume
Conic
Volume Conic (X-
values)
ft3 ft. ft3 ft3 ft3 ft3
5,027.55 23 0.00 0 0 0 0
5,027.60 357 0.05 9 4 8 3
5,027.80 4146 0.20 450 184 381 156
5,028.00 7746 0.20 1189 660 1171 624
5,028.20 9019 0.20 1677 1330 1675 1294
5,028.40 9037 0.20 1806 2052 1806 2016
5,028.60 9044 0.20 1808 2776 1808 2739
5,028.80 9052 0.20 1810 3500 1810 3463
5,029.00 9059 0.20 1811 4224 1811 4188
5,029.20 9067 0.20 1813 4949 1813 4913
5,029.40 9074 0.20 1814 5675 1814 5638
5,029.60 9082 0.20 1816 6401 1816 6365
5,029.80 9089 0.20 1817 7128 1817 7091
5,030.00 9097 0.20 1819 7855 1819 7819
5,030.10 9101 0.10 910 8219 910 8183
5,030.50
5,030.00
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
= 54,662 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 11,185 sq ft
(Minimum recommended permeable pavement area = 10221 sq ft)
E) Impervious Tributary Ratio RT
= 1.8
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 713 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?
H) Total Volume Needed VTotal
= cu ft
Carriage House Apartments
Fort Collins, Colorado | Sub-Basin A
Design Procedure Form: Permeable Pavement Systems (PPS)
H. Feissner
Northern Engineering
February 5, 2013
Choose One
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 12.0 inches
(Minimum recommended depth is 6 inches)
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
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? CDOT CLASS C FILTER MATERIAL RECOMMENDED
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = 1.0 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.)
A) Depth of WQCV in the Reservoir DWQCV
= 3.71 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice
= 0.71 inches
(Use a minimum orifice diameter of 3/8-inches)
Carriage House Apartment Homes
Design Procedure Form: Permeable Pavement Systems (PPS)
H. Feissner
Northern Engineering
February 5, 2013
Fort Collins, Colorado | Sub-Basin A
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
(Use a minimum orifice diameter of 3/8-inches)
Notes:
UD-BMP_v3.02-Basin A, PPS 2/5/2013, 4:25 PM
APPENDIX D
OPERATIONS AND MAINTENANCE GUIDELINES FOR RAIN GARDENS(reserved for future use)
APPENDIX E
EROSION CONTROL REPORT
Carriage House Apartments
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 CS2 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 Apartments. 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
E) Length Between Lateral Flow Barriers (max = 63.72 ft.) L = 60.0 ft
F) Volume Provided Based on Depth of Base Course V = 3,430 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 = 3
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.)
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 2/5/2013, 4:25 PM
5,030.50
5,030.00
5,029.50
5,029.00
Contour Elevation
5,028.50
Contour Elevation
5,028.00
Contour Elevation
5,027.50
5,028.00
5,027.50
5,027.00
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Cummulative Volume, cu. ft.
2/6/201311:41 AM D:\Projects\620-002\Drainage\Detention\620-002__Detention Pond\Stage_Storage_A
55 3300 3.03 2.8 9187 1881 7306
60 3600 2.86 2.6 9459 2052 7407
65 3900 2.72 2.5 9746 2223 7523
70 4200 2.59 2.4 9994 2394 7600
75 4500 2.48 2.3 10253 2565 7688
80 4800 2.38 2.2 10496 2736 7760
85 5100 2.29 2.1 10730 2907 7823
90 5400 2.21 2.0 10964 3078 7886
95 5700 2.13 2.0 11155 3249 7906
100 6000 2.06 1.9 11356 3420 7936
105 6300 2.00 1.8 11576 3591 7985
110 6600 1.94 1.8 11764 3762 8002
115 6900 1.89 1.7 11981 3933 8048
120 7200 1.84 1.7 12172 4104 8068
125 7500 1.79 1.6 12334 4275 8059
130 7800 1.75 1.6 12541 4446 8095
135 8100 1.71 1.6 12726 4617 8109
140 8400 1.67 1.5 12888 4788 8100
145 8700 1.63 1.5 13029 4959 8070
150 9000 1.60 1.5 13230 5130 8100
155 9300 1.57 1.4 13415 5301 8114
160 9600 1.54 1.4 13583 5472 8111
165 9900 1.51 1.4 13734 5643 8091
170 10200 1.48 1.4 13869 5814 8055
175 10500 1.45 1.3 13988 5985 8003
180 10800 1.42 1.3 14090 6156 7934
185 11100 1.40 1.3 14277 6327 7950
190 11400 1.38 1.3 14454 6498 7956
195 11700 1.36 1.2 14619 6669 7950
200 12000 1.34 1.2 14774 6840 7934
205 12300 1.32 1.2 14917 7011 7906
210 12600 1.30 1.2 15049 7182 7867
215 12900 1.28 1.2 15170 7353 7817
220 13200 1.26 1.2 15281 7524 7757
225 13500 1.24 1.1 15380 7695 7685
230 13800 1.22 1.1 15468 7866 7602
235 14100 1.21 1.1 15675 8037 7638
240 14400 1.20 1.1 15876 8208 7668
2/5/2013 4:25 PM D:\Projects\620-002\Drainage\Detention\620-002__Detention Pond\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 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
February 5, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
2/5/2013 4:13 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs\Tc
C 0.17 0.00 0.02 0.00 0.07 0.00 Clayey | Average 2% to 7% 0.09 0.60 0.60 0.75 45%
OS1 0.34 0.21 0.10 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.03 0.89 0.89 1.00 88%
OS2 0.17 0.09 0.05 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.03 0.82 0.82 1.00 79%
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
February 5, 2013
Composite Runoff Coefficient with Adjustment
2/5/2013 4:13 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs\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 0.31 142 2.60% 13.8 13.8 12.8 282 1.30% 2.28 2.1 0 0.00% N/A N/A 15.83 15.83 14.82
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 2.80% 1.2 1.2 0.8 144 0.80% 1.79 1.3 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
February 1, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
2/1/2013 11:30 AM 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
February 1, 2013
Composite Runoff Coefficient with Adjustment
2/1/2013 11:28 AM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs\Composite Runoff Coefficient