HomeMy WebLinkAboutRIGDEN FARM, 9TH FILING, PARKSIDE COMMONS - PDP - 56-98T - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT3.3 Erosion Control
The grading of Rigden Farm — Tract 'U' will be consistent with the approved SDDM criteria;
therefore minimal erosion control efforts will be necessary during the construction of the project.
A concern regarding sediment transport from the site is the existing storm sewer system at the
north and south ends of the site. During construction, this concern will be mitigated primarily by
temporary structural measures of silt fence around the majority of the site. Additional measures
will be used by installing gravel filters over all the inlets and straw bale check dams will be
installed in the swales where required. A vehicle tracking control pad will also be used at the
east entrance of the site to minimize sediment transportation.
Upon completion of the utility work, the roads will be paved and the entire disturbed area of the
site will be reseeded and mulched to provide soil stabilization until build out. Elimination of bare
soils by pavement, riprap, or established vegetation will help eliminate the potential of soil
erosion caused by storm runoff. Since it will take at least one growing season for the
vegetation to establish itself, it will be necessary to leave the structural measures used during
construction in place for some time. The developer will be responsible for periodic maintenance
of the erosion control facilities during construction and the warranty period. At the end of the
warranty period, and with the approval of the city, the developer will be responsible for removing
all of the filters and silt fence. It may also be necessary to flush and remove any sediment that
may have built up in the storm sewers.
The Drainage Plan sheets, located at the end of the report, show the location of the proposed
temporary and permanent erosion control measures. These measures are also shown the
Grading & Erosion Control Plan sheets in the utility plan set. Erosion control performance and
effectiveness calculations have also been performed for the site. The calculations are located
in Appendix D of this report.
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TST, Inc. 11 April 25, 2003
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STORM SEWER NETWORK
Exhibit B
.''(POM
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WO
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ST-1
MANHOLE
MANHOLE
7.00
18
RCP
MANHOLE
MANHOLE
7.00
21
RCP
MANHOLE 3
INLET 1_
7.00
21
RCP
--ST -2
EX. MANHOLE 3
INLET 2A
13.02
24
RCP
I ST-2A
INLET 2A
INLET 2B
5.03
18
RCP
Notes: 1. ST-2 design flow of 13.02 cfs is from JR Engineering design.
2. ST-2A design flow of 5.03 cfs is from JR Engineering design.
TST, INC. 4125/03
CONSULTING 10 040 storm.xls
ENGINEERS
to each inlet, therefore the smaller discharges to the inlets. Differences in the time of
concentration also result in a different discharge. The actual flow -path for routing the storm
water is a longer path than in previous designs. A table created by JR Engineering shows their
designed composite 'c' factors, contributing areas, and discharges. Tables showing TST's
design characteristics are found in Appendix A. The results of the Inlet Analysis and Design
can be found with supporting calculations in Appendix B.
Rigden Farm — Tract 'U' is part of a master plan and runoff from our site has already been
accounted for in this master plan. The design shows runoff from the north half of our site
conveyed east to detention pond 216. Runoff from the south half of our site is conveyed south
to detention pond 218, TST's design of the site provides for no increase in storm runoff than
that of the design by JR Engineering. Therefore, our design is not increasing the volume of
water in either of the two detention ponds used for this development.
3.2.3 Storm Sewer Design
The storm sewer lines were analyzed with Neo UDSEWER. The pipes were sized such that the
hydraulic grade remains below the flow line of the proposed inlets.
Storm Sewer Line ST-1 conveys detained runoff to an existing 30" storm sewer line in Limon
Drive at the south end of the site. A manhole will be formed around the existing 30" line, and
STA will tie into this manhole.
ST-2 and ST-2A convey runoff from Basin D, Kansas Drive, and runoff from the undeveloped
site west of Rigden Farm — Tract'U' via a pair of inlets to the detention pond.
The results of the Storm Sewer Design can be found in Exhibit B with supporting Neo
UDSEWER results presented in Appendix C.
� M 3.2.4 Swale Design
Trickle pans surround the site on all sides and are intended to carry nuisance flows to several
inlets around the site. All grass swales interior to the site are designed to carry nuisance flows
to the trickle pan surrounding the site. Trickle pans are required for slopes less than 2%,
—j therefore all swales interior to the site are designed at 2% or greater to minimize the need for
J trickle pans.
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3.2.1 Street Capacity
Three street sections will be used for the internal streets: 1.) A local residential street section
with 42-foot FL to FL width with vertical curb and gutter and a detached walk, 2.) Private
driveways street section with 28-foot FL to FL width with vertical curb and gutter and attached
walk in some locations, 3.) A local residential street section with 34-foot FL to FL width with
vertical curb and gutter and a detached walk. A worst -case condition was analyzed for the site;
this is the maximum discharge throughout the site flowing at a minimum slope (0.50%).
Street encroachment criteria for the streets was taken from Table 4-1 (minor storm) and Table
4-2 (major storm) of the SDDC. The minor event (2-yr) criteria allows no curb overtopping and
flow may spread to the crown. The major event (100-yr) criteria allows for flow depths of 6
inches over the crown.
All of the streets meet these requirements and will function below the allowable capacities. The
results of the Street Capacity Analysis can be found with supporting calculations in Appendix B.
3.2.2 Inlet Design
CDOT Type "R" curb sump inlets were used to collect the 2-yr and 100-yr. runoff from low
points in the local and private streets. Ponding depths for all inlets in the streets were set such
that flow would not inundate both travel lanes. The inlets are connected to storm sewer
systems that convey the runoff to the detention ponds.
_J Several proposed inlets were designed by JR Engineering, the west and north inlets were part
of JR Engineering's design. With TST's design, there is no increase in storm runoff to those
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inlets. As a result, there is no change in the proposed inlet sizes. JR Engineering proposed a
5' Type 'R' inlet on the west side of the property in Kansas Drive and a 10' Type 'R' inlet on the
north side of the property in the proposed Drake Road. There are also two inlets at the south
end of the property in Limon Drive and one inlet at the east end of the property in Rockford
Drive. Discharges from our site are less than the proposed discharges from JR Engineering's
design; therefore the existing inlets are of sufficient size to collect storm runoff from our site. A
table created by JR Engineering, showing the proposed discharge to the two inlets is found with
this report in Appendix B. Below is a list of TST's proposed storm water runoff to design points
that correspond to JR Engineering's design points.
DP-a5:
TST's Discharge = 5.53cfs
(1.29 ac, C=0.98)
DP-b5:
TST's Discharge = 8.85 cfs
(2.46 ac, C=0.98)
DP-d2:
TST's Discharge = 1.26 cfs
(0.25 ac, C=0.90)
DP-e2:
TST's Discharge = 2.42 cfs
(0.56 ac, C=0.97)
DP-g2:
TST's Discharge = 8.48 cfs
(1.65 ac, C=0.99)
JR Engineering's Discharge = 23.60 cfs
(2.79 ac, C=0.95)
JR Engineering's Discharge = 17.65 cfs
(2.55 ac, C=0.83)
JR Engineering's Discharge = 5.55 cfs
(0.78 ac, C=0.83)
JR Engineering's Discharge = 7.65 cfs
(0.99 ac, C=0.87)
JR Engineering's Discharge = 13.15 cfs
(1.86 ac, C=0.87)
The difference in discharge between JR Engineering's design and TST's design is due to more
contributing area to the inlets. TST's design contributes a portion of the total contributing area
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TST, Inc. 8 April 25, 2003
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HYDROLOGY
Exhibit A
TST. INC.
CONSULTING 7
ENGINEERS
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HYDROLOGY
Exhlbit A
Com osite -tl--
Basin!
Lawns "C"
Gl
rave
Roo0.95 ds
Composite
Sub -basin
Area ac.
0.25
0.50
0.95
2- r "C"
Al
0.17
0.05
0.00
0.12
0.74
A2
0.43
0.09
0.00
0.34
0.81
A3
0.27
0.11
0.00
0.16
0.67
A4
0.18
0.02
0.00
0.16
0.86
A5
0.24
0.04
0.00
0.20
0.83
g1.
0.19
0.10
0.00
0.09
0.57
B2
1.48
0.27
0.00
1.19
0.82
B3-1
0,23
0.09
0,00
0.15
0.69
B32
0.19
O.D6
0.00
0.12
0.72
B4
0.16
0.02
0.00
0.14
0.85
B5
0.23
0.05
0.00
0.19
0.61
Cl
0.49
0.06
0.00
0.44
0.87
C2
0.82
0.16
0.00
0.86
0.81
DI
0.10
0.06
0.00
0.04
0.54
02
0.15
0.02
0.00
0.13
0.84
E1
0.27
0.09
0.00
0.18
0.72
E2
0.29
0.05
0.00
0.24
0.83
F1.
0.36
0,15
0.00-
0.21
0.66
F2
- 0.31
0.05
0.0o
0.25
0.83
GI-1
0.66
0.09
0.00,
0.57
0.85
G1-2
0.11
0.07
0.00
0.04
0.50
G2
0.21
0.06
0.00
0.15
0.75
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Cf2
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TST, INC. 4/25103
CONSULTING 6 040_storm.xis
ENGINEERS
7
then determined by dividing the gutter flow length by the velocity. This procedure for computing
time of concentration allows for overland flow as well as travel time for runoff collected in
streets, gutters, channels, or ditches. After the peak runoff was calculated, attenuated runoff
was calculated. This was done by combining all contributing areas upstream of a given design
point. The time of concentration for the design point was taken as the greatest travel time from
j all of the contributing sub -basins. Spreadsheets showing this process are located in Appendix
w. A with this report.
1 3.2 Drainage Plan Development
The proposed drainage plan consists of a combination of overland flow and gutter flow. The
runoff will sheet flow across common areas and also be routed by grass swales, then
concentrate at proposed and existing streets. Gutter flow in streets will be collected at low
points via curb inlets and then conveyed via a storm sewer system or drainage pans to the
existing inlets on the east and south sides of the site. The existing storm sewer system will
collect the runoff from this site and convey the flows to existing ponds. Storm runoff that enters
the proposed west and north inlets and also the east inlet will be routed to the existing pond
with a designation number 215. Storm runoff that enters the south inlets will be routed to the
existing pond with a designation number 218. A basin delineation plan (JR Engineering)
showing the existing ponds and also the routing path will be provided with this report. Sub
basins for Rigden Farm — Tract 'U' were delineated based on the proposed grading. Final
grading and basin delineation is shown on the Overall Drainage and Erosion Control Plan
�+ Sheet, which can be found in the back of this report.
Basin A encompasses the southwest portion of the site, along Kansas and Limon Drive.
Basin B encompasses the southeast portion of the site, along Rockford and Limon Drive.
Basin C encompasses the center portion of the site.
Basin D encompasses the northwest portion of the site along Kansas Drive.
Basin E encompasses the north portion of the site along Drake Road.
Basin F encompasses the north portion of the site along Drake Road, just east of Basin E.
Basin G encompasses the northeast portion of the site along Drake Road and Rockford Drive.
Runoff from each of the basins will eventually be collected by a storm sewer system and
directed to the two existing detention ponds, located to the south and east of our site. Exhibit A
(next page) shows the Composite 'C' factor and developed conditions hydrology. The exhibit
also shows individual basin hydrology and basin attenuation. All supporting calculations are
found in Appendix A of this report.
TST, Inc. 5 April 25, 2003
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Developed Conditions Plan
3.1 Design Criteria
The drainage system presented in this report has been developed in accordance with the
criteria established by the City of Fort Collins Storm Drainage Design Criteria and Construction
Standards Manual (SDDC) dated May 1984 and revised in January 1997. Where applicable,
design guidelines and information were also obtained from the Denver Regional Council of
Government Urban Storm Drainage Criteria Manual (USDCM).
Developed condition hydrology was evaluated based on the 2-year and 100-year storm
frequencies as dictated by Table 3-1 of the SDDC manual.
Because of the limited size of the sub basins on the site, the Rational Method was selected to
calculate runoff. The Rational Method utilizes the SDDC manual equation:
Q = CCflA
where Q is the flow in cfs, C is the runoff coefficient, Cf is the storm frequency coefficient, I is
the rainfall intensity in inches per hour, and A is the total area of the basin in acres. The runoff
coefficient, C, was calculated from Table 3-3 of the SDDC manual based on the proposed
developed condition land use. A composite runoff coefficient was calculated for each sub -basin
based on the percentage of impervious surface (C = 0.95) and pervious surface (C = 0.25). Cf
was taken from Table 3-4 of the SDDC manual and was determined to be 1.0 for the 2-year
storm and 1.25 for the 100-year storm. The appropriate rainfall intensity was interpolated from
the rainfall intensity duration table in Figure 3-1 of the SDDC manual dated 1999. To obtain the
rainfall intensity, the time of concentration had to be determined. The following equation was
utilized to determine the time of concentration:
tc = t; + tt
where tc is the time of concentration in minutes, t; is the initial or overland flow time in minutes,
and tf is the travel time in the gutter in minutes. The initial or overland flow time was calculated
with the SDDC manual equation:
t, _ [1.87(1.1 - CC&O T(S)oss
where L is the length of overland flow in feet (limited to a maximum of 500 feet), S is the
average basin slope in percent, C is the composite runoff coefficient, and Cf is the storm
_ frequency coefficient. The formula limits the product of CCf to 1.0 and when the product
exceeds this value 1.0 is used in its place. Gutter (or channel) travel times were determined by
1 utilizing Figure 3-3 for the flow velocity within the conveyance element. The travel time was
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TST, Inc. 4 April 25, 2003
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M 2.0
Historic Conditions
The proposed site is currently an undeveloped area located within Rigden Farm II — Filing Eight,
as designated by JR Engineering. JR Engineering previously performed a drainage analysis on
the site (Rigden Farm — Tract 'U'), and a proposed condition was used to calculate runoff to
several proposed and existing inlets surrounding the site. This proposed condition was factored
into TST's final drainage analysis. The site consists of bare ground that sheet -flows from the
center of the site outward. Currently runoff drains to the north, south, and east where there are
three existing inlets and a swale. The swale follows the north end of the site and collects runoff
— from the northern portion of the site. There are two inlets at the southern end of the site and
one at the eastern end of the site; the three inlets collect the remainder of runoff from the site
and convey the storm water to the existing detention ponds discussed earlier. No off -site runoff
enters the Rigden Farm — Tract 'U' site.
JR Engineering's proposed design includes two inlets on the south side of the development,
_ one on the east and west sides, and one inlet on the north side of the development. The two
inlets on the south side of the site and the one inlet on the east side of the site are already
constructed and in place. The inlet on the west side of the development will. be built with the
development of this site. The inlet to the north of the site will be built with the reconstruction of
— Drake Road, before any construction of Rigden Farm — Tract U. Discharges, contributing
area, and composite 'c' values are provided at each design point with JR Engineering's
drainage report. A table showing these characteristics is found in Appendix B of this report.
WO
TST's design provides for no additional runoff contributing to all five inlets designed by JR
Engineering in their proposed drainage plan. A drainage sheet showing basin delineations and
designations is provided with this report for reference.
TST, Inc. 3 April 25, 2003
0953-003
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I. 1.0
Introduction
1.1 Scope and Purpose
This report presents the results of a Final Drainage Evaluation for Rigden Farm — Tract U. In
s accordance with the requirements of the Fort Collins Storm Drainage Design Criteria and
Construction Standards Manual (SDDC), the purpose of this report is to present a storm
drainage plan that identifies peak runoff conditions and provides a means by which to safely
collect and convey runoff across the site. This report will evaluate hydrologic conditions for the
proposed development to determine the location and magnitude of the storm runoff, and will
use that information for hydraulic analysis of the proposed streets and conveyance facilities.
Rigden Farm — Tract 'U' is part of a master plan and runoff from our site has already been
accounted for in this master plan. The design shows runoff from the north half of our site
conveyed east to detention pond 216. Runoff from the south half of our site is conveyed south
to detention pond 218. TST's design of the site provides for no increase in storm runoff than
that of the design by JR Engineering.
1.2 Project Location and Description
W
Rigden Farm — Tract 'U' is a proposed 11 building (6 and 7-plex), 71 multi -family dwelling unit
development located in the Northwest Quarter of Section 29, Township 7 North, Range 68
West of the 6`" P.M., City of Fort Collins, County of Larimer, State of Colorado. The site is
bounded on the north by Drake Road, the south by Limon Drive, the east by Rockford Drive,
and the west by the proposed Kansas Drive. A vicinity map illustrating the project location is
provided in Figure 1.
This project is located entirely within the Ridgen Farm II development. A master drainage plan
was performed by JR Engineering for Rigden Farm — Tract U. All development conforms to
the previously designed drainage plan for Rigden Farm —Tract U.
TST, Inc. 1 April 25, 2003
0953-003
TABLE OF CONTENTS
Page
1.0 Introduction
1.1 Scope and Purpose.............................................................................................1
1.2 Project Location and Description.........................................................................1
2.0 Historic Conditions.......................................................................................................
3
3.0 Developed Conditions Plan..........................................................................................4
3.1 Design Criteria............................................................................................4
3.2 Drainage Plan Development.......................................................................5
3.2.1 Street Capacity................................................................................8
3.2.2 Inlet Design.....................................................................................8
3.2.3 Storm Sewer Design.......................................................................9
3.2.4 Swale Design..................................................................................9
3.3 Erosion Control.........................................................................................11
Exhibits
Exhibit A — Hydrology Tables...................................................................................................6-7
Exhibit B — Storm Sewer Network.............................................................................................10
Technical Aooendices
Appendix A
— Hydrology
Appendix B
— Street Capacity
Appendix C
— Inlet Design
Appendix D
— Storm Sewer Design
Appendix E — Erosion Control
Sheets
MAP POCKET 1 — Overall Drainage and Erosion Control Plan (Sheet 15 of 15)
JR Engineering's Drainage and Erosion Control Plan (Sheet 7 of 20)
April 25, 2003
Mr. Basil Hamden
City of Fort Collins Storm Water Division
P.O. Box 580
Fort Collins, CO 80522
Re: Rigden Farm — Tract 'U'
Project No. 0891-040
Dear Mr. Hamden:
We are pleased to submit to you, this Final Drainage Report for Rigden Farm — Tract
'U'. This report was prepared based on Urban Storm Drainage Criteria and City of Fort
Collins criteria. We believe it satisfies all criteria for a final report. This report also
includes discussion of erosion and sediment control measures that will be utilized during
and after construction.
We look forward to your review and approval and will gladly answer any questions you
may have.
Sincerely,
TST, INC. CONSULTING ENGINEERS
David Huwa
DH/sjk
Enclosures
TST, INC. 748 Whalers Way - Building D
�i Fort Collins, CO 80525
y Consulting Engineers (970) 226-0557
Metro (303) 595-9103
_ Fax (970) 226-0204
Email info@tstinc.com
www.tstine.com
FINAL DRAINAGE REPORT
FOR
RIGDEN FARM - TRACT `U'
Submitted to:
CITY OF FORT COLLINS
April 25, 2003