HomeMy WebLinkAboutTHE GREENS AT COLLINDALE PUD - FINAL - 8-96A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTwhere ti is the initial time of concentration, D is the length of the overland flow in feet, S is the average
3 basin overland slope in percent. This procedure for computing time of concentration allows for
' overland flow as well as travel time for runoff collected in streets, gutters, channels, pipes, or ditches.
The times of concentration calculated assumed only about 100 feet overland flow of the total travel
length. The remainder of the flow was considered as channel flow (in street gutters).
3.2 Drainagg Plan Development
IThe proposed drainage plan consists of overland flow across lots which will be collected in the streets,
then directed to a detention pond(please note: there are two ponds connected by a pipe of sufficient
size to assume easy transference of flow and thus acting as one pond). The detention pond will then
release the storm runoff at the existing 2-year rate of 2.73 cfs (per Table 1, Existing Hydrologic
Calculation Worksheet) as called for in the Fox Meadows Drainage Master Plan. Gutter flow in streets
will be collected at low points via curb inlets and then piped to the detention ponds. Subbasins were
delineated based on the final grading plan. The results of the hydrologic analysis can be found in Table
2 with supporting calculations shown in Appendix A(Table 3 depicts the attenuated flows for this site).
Table 4 depicts the estimated detention requirements based on the weighted runoff rate. Supporting
information for the detention requirements can be found in Appendix B.
An analysis of street capacities to determine if curb inlets and storm sewers will be necessary at points
further upstream than the low points was performed. Curb inlets, channels, culverts, and detention
facilities will be sized to intercept and convey runoff from the 100-year storm. Channels, roadside
ditches, and detention facilities will be designed to incorporate a minimum of V of freeboard and will
have velocities that do not promote erosion.
' 3.3 Erosion Control Plan
Erosion Control Calculations were performed and by utilizing revegetation and silt fencing during
fconstruction, our effectiveness levels were very good. After Final Construction when vegetation is in
place and well established, our effectiveness levels are also very good. We plan on using an inlet filter
at our only street inlet. We are also planning on installing a silt fence to run along the North and East
property lines. Please refer to Table 6 for the effectiveness calculations.
TST, Inc.
10-842-000 5
3.0
Developed Conditions Plan
3.1 Design Criteria
IThe drainage system presented in this report has been developed in accordance with the guidelines
established by the Fort Collins Storm Drainage Design Criteria and Construction Standards
(S.D.D.C.), and the Denver Regional Council of Government Urban Storm Drainage Criteria Manual
(USDCM).
Developed condition stonn facilities were evaluated based on the 100-year stone frequency. Since a
Drainage Master Plan for the area has been completed, we followed the Master Plan's guidelines,
which limits our 100-year developed discharge to the existing two-year discharge.
' Due to the limited size of the site, the Rational Method was selected to calculate runoff for street
capacity analysis. The Rational Method utilizes the S.D.D.C. Manual Equation:
Q=CfCIA
' where Q is the flow in CFS, A is the total Area of the basin in acres, Cf is the storm frequency
adjustment factor, C is the runoff coefficient, and I is the rainfall intensity in inches per hour. The
runoff coefficient, C. was selected to be 0.45 as taken from the S.D.D.C. Manual for RLP zoning. The
frequency adjustment factor, Cr, is given on pages 3-5, Table 3-4 of the S.D.D.C. Manual and is 1.25
for the 100-year storm and 1.00 for the 2-year storm. The intensity (1) was taken from the City of Fort
i Collins rainfall intensity duration curve in the S.D.D.C. Manual. To obtain the rainfall intensity, the
time of concentration had to be determined. The following equation was utilized to determine the time
of concentration:
tcrti+tt
where t� is the time of concentration in minutes, ti is the initial or overland flow time in minutes, and t, is
I the concentrated flow time (ditch, channel, or gutter) in minutes. The initial or overland flow time was
calculated using the equation on pages 3-5, section 3.1.7 in the S.D.D.C. Manual:
ti=IIHLI-CCt)D�'
50.33
TST, Lic.
10-842-000 4
2. o
Historic Conditions
The existing site, which is currently a farm field, runoff sheet flows to the east and onto the golf course
and eventually into the existing swale along the south property line of the golf course. The runoff
discharges into the drainage collection system in Golden Meadows and eventually discharges into
Fossil Creek Reservoir Inlet Ditch (FCRID). There are no offsite flows which pass through the site.
Street runoff from Lemay Avenue remains in the street until it reaches the inlets located near the south
end of our site. The street flow then is routed in the same manner as our parcel's existing flow.
TST, Inc.
10-842-000 3
FIGURE 1
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1.0
Introduction
1.1 Scone and Put -nose
This report presents the results of a Final Drainage Evaluation for The Greens at Collindale
Subdivision. A hydrologic analysis of the proposed development plan was completed to determine the
location and magnitude of the storm runoff. An evaluation of required detention storage was
conducted to determine the required size of the detention facility.
The purpose of this report is to evaluate the development and prepare a stormwater management plan
that will address: (1) overall storm drainage planning and management, (2) detention of flows
exceeding allowable release rates, and (3) erosion control.
1.2 Proiect Location and Description
The Greens at Collindale Subdivision is a proposed residential site located in the northwest quarter of
Section 31, Township 7 north, Range 68 west, of the 6th Principal Meridian, in Larimer County,
Colorado. The site is roughly bounded by Lemay Avenue to the west, Collindale Golf Course on the
north and east, and Golden Meadows Filing Two to the South. See Figure 1. The proposed site falls
within the Fox Meadows Drainage Basin.
The Greens at Collindale Subdivision consists of approximately 6.43 acres and is within an RLP (Low
Density Residential) Zoning District within the City of Fort Collins, Colorado. The development will
have approximately 33 lots. All of the roadways within the development will be private streets
designed as close as possible to the City of Fort Collins' classification of local streets.
1.3 Previous Studies
The "Fox Meadows Basin (Basin I) Drainage Master Plan" (Resource Consultants, Inc., February 25,
1981) was reviewed prior to commencement of this report.
TST, Inc.
10-842-000
TABLE OF CONTENTS
1.0 Introduction
Page
1.1 Scope and Purpose..............................................................................1
1.2 Project Location and Description.............................................................1
1.3 Previous Studies.................................................................................
1
2.0
Historic Conditions......................................................................................3
3.0 Developed Conditions Plan
3.1
Design Criteria..................................................................................
4
3.2
Drainage Plan Development..................................................................
5
3.3
Erosion Control Plan ...........................................................................
5
Figures
Figure1 - Vicinity Map.......................................................................................... 2
Tables
Table 1 - Existing Hydrologic Calculations Worksheet
Table 2 - Proposed Hydrologic Calculations Worksheet
Table 3 - Summary of Attenuated Runoff
Table 4 - Required Detention Calculations
Table 5 - Rainfall Performance Standard Evaluation
Table 6 - Effectiveness Calculations
Table 7 - Construction Sequence
Table 8 - Summary of Storm Sewer Design
1 Appendices
Appendix A - Rational Method Analysis
y Appendix B - Preliminary Detention Analysis
f Appendix C - Street Capacity Analysis
Appendix D - Inlet Capacity Analysis
Appendix E - Erosion Control Calculations
Appendix F - Storm Sewer Analysis
Sheets
Existing Drainage Sheet............................................................................. Sheet 1 of 1
FinalDrainage Plan .................................................................................. Sheet 1 of 1
TST, Inc. t
10-842-000
August 26, 1996
Mr. Basil Hamdan
City of Fort Collins
Stormwater Utility Department
235 Mathews Street
Fort Collins, CO 80524
Re: The Greens at Collindale P. U.D.
Project No. 1 a842-002
Dear Mr. Schlueter:
We are pleased to submit this Final Drainage and Erosion Control Report for The Greens at
Collindale, P.U.D. This report was prepared based on City of Fort Collins criteria and we believe
satisfies all criteria for a final report. As you are aware from our earlier conversations, this report
does not include any of the existing Lemay runoff models. Also, we did not model the storm pipe
on our South property line per my discussion with you and the fact that we are matching to the
existing 15" pipe to the East.
We look forward to your review and comments and will gladly answer any questions you may
have.
Sincerely,
TST, INC. CONSULTING ENGINEERS
Michael B. Reeve, P.E.
Enclosure
TSTINC. 748 Whalers Way — Building D 102 lnverness Terrace Fast
! Fort Collins, CO 80525 Suite 105
Consulting Engineers (970) 226-0557 Englewood, CO 80112
Metro Denver (303) 595-9103 (303)792-0557 AMR
Fax (970) 226-0204 Fax (303) 792-9489�K
FINAL
DRAINAGE REPORT
FOR
FfHE GREENS AT COLLINDALE
P.U.D.
SUMMED TO
CITY OF FORT COLLINS
AUGUST 26, 1996
TST, INC.
CONSULTONG
ENGO EERS