HomeMy WebLinkAboutPROSPECT GREENS PUD - PRELIMINARY - 15-95 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTConclusion and Recommendations:
After reviewing the existing drainage information and site
conditions, the following conclusions can be made.
1. The runoff from proposed development will collect to
backyard or side yard swales and flow to the curb line of
the central street and collect to the far south corner
sump. An area inlet and pipe will convey initial storm
flows to Spring Creek, major storm flows will overtop the
curb and spill into an open channel to Spring Creek.
2. All foundations will be approximately 2.5 to 3.0 feet
above the 100-year surface of Spring Creek, per the FIRM,
1979.
3. No on -site detention will be provided due to the
developed time to peak being approximately two (2) hours
before the Spring Creek peak flows in this reach.
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EROSION CONTROL:
This project is located within an area of moderate wind
erosion and moderate rainfall erosion according to the City of Fort
Collins wind and rainfall erodibility maps.
WIND EROSION:
Wind erosion protection will be provided by silt fencing on
the northern and western perimeter of the project. Asphalt paving
of the parking area and seeding and mulching (or landscaping) of
all disturbed areas will provide final stabilization upon
completion of this project.
WATER EROSION:
As stated above, final stabilization will occur with
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completion of paving and landscaping features. All area disturbed
by grading and fill will receive native grass seed and mulch and
will be graded to establish positive flow as shown on the enclosed
exhibit.
Historic/Developed Drainage conditions:
The historic runoff conditions were calculated for this area
and are available in Appendix A of this report. However, due to
the location of the proposed development adjacent to the Spring
Creek Floodplain and low in the basin, the associated peak runoff
will be released well before the peak flow on Spring Creek.
Developed minor (2-year) and major (100-year) peak runoff
calculations are included in Appendix B of the report. Minor storm
peaks flow calculations show 3.3 cfs from Basin B and 0.3 cfs and
0.2 cfs from Basins C-1 and C-21 respectively.
Major (100-year) flows peak at 15.7 minutes and calculations
show 12.7 cfs. developed flows to Spring Creek. The peak is well
below the 100-year time to peak in this reach as shown in Figure 3.
The peak runoff from proposed developed area would reach maximum
flow almost two hours before the major storm peak on Spring Creek.
Detention storage for this site would have no effect on attenuation
of flows in Spring Creek and on -site detention was not considered
for this development.
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SPRING CREEK
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Southern Railroad
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180
240
300
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31
SPRING
at, Stover St.
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' SPRING CREEK
100yr Hydrograph
at Timberline Road
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0 60 120 IliO 240 300, 360 _ 00 0 60 120 I80 240 360
I TIME (MINUTES) TIME (MINUTES)
ds SPRING CREEP
Lema Ave.
FIGURE 31 SPRING CREEK 100 YEAR HYDROGRAPHS
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Master Drainage:
I The Flood Insurance Rating Mapping (FIRM) are currently under
revision by City personnel and FEMA. The current mapping in force
Ifor the Spring Creek Basin is Dated 1979 and the Zone A and Zone B
floodplain are shown on the enclosed- back pocket exhibit.
Hydrography for Spring Creek was obtained from a "Interim Flood
a Hydrology Report or Spring Creek by RCI. 1977". The Hydrography at
IStover Street, immediately upstream of the proposed development,
gives a 100-year peak flow of 4780 cfs. at around 130 minutes
(Figure 3).
IDesign criteria:
The Rational Method as identified in the "City of Fort Collins
Design Criteria" has been used to calculate runoff from the site.
rThe Rational Method is a widely accepted predictor of flows from
drainage basins less than two hundred (200) acres. All
coefficient, nomegraphs and design values used in this report are
from the Design Criteria or "Urban Storm Drainage Criteria Manual",
Volumes 1 and 2.
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The site frontage on East Prospect Street currently has two
houses, one house is an existing outlot, the other will remain and
be modified to match the character of the proposed development. A
shallow irrigation channel divides the parcel and the area to the
south of the ditch is undeveloped agricultural land for horses and
small livestock. The Spring Creek Floodplain borders the southern
extreme of the site and published flood elevations are shown on the
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drainage exhibit in this reports back pocket. The existing
topography slopes east or southeasterly to the Spring Creek
drainage with the exception of the small area around the existing
I homes that drains to the southern flowline on East Prospect Street.
The proposed development for this site will consist of 17
single family units on approximately 3.73 acres. All public
improvements, as shown on the enclosed back pocket exhibit will be
I constructed with the project.
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PROJ
VICINITY MAP
SCALE: 1 " = 1000'
FIGURE 1
Li
introduction:
This preliminary drainage and erosion control report has been
prepared in conjunction with the preliminary engineering plans to
provide conceptual information for the development of 17 single
family residential lots on E. Prospect Road east of Stover St. (See
Vicinity Map, Figure 1). This report is prepared in conformance
with the City of Fort Collins "Storm Drainage Design Criteria and
Construction Standards and the "Spring Creek Masterplan".
Site Description:
Prospect Greens P.U.D. is a 3.73 acre parcel on the south side
of East Prospect one lot east of the Bauder Elementary School
(Discovery Center), within the Fort Collins City limits.
More specifically the property is located in the East Half of
I the East Half of the Northwest Quarter of the Northwest Quarter of
ISection 24, Township 7 North, Range 69 West of the 6th. Principal
Meridian, County of.Larimer, State of Colorado.
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TABLE OF CONTENTS
INTRODUCTION
SITE DESCRIPTION .....1, 2
MASTER DRAINAGE .....3
DESIGN CRITERIA .....3
HISTORIC/DEVELOPED DRAINAGE CONDITIONS •••••4
EROSION CONTROL .....5
CONCLUSION AND RECOMMENDATIONS .....6
Figure 1
Figure 3
Appendix A
Appendix B
Back Pocket
Vicinity Map
Spring Creek 100 year Hydrographs
Historic Drainage Design Data
Developed Drainage Design Data
E?
PRELIMINARY DRAINAGE & EROSION
CONTROL REPORT
FOR
PROSPECT GREENS P.U.D.
March 16, 1995
PREPARED FOR:
Mr. Larry K. Pedersen
Pedersen Brothers Homes & Development LLC
209 North Link Lane
Fort Collins, CO. 80524
PREPARED BY:
PARSONS & ASSOCIATES, INC.
432 LINK LANE PLAZA
FORT COLLINS, CO. 80524
(303) 221-2400
PROJECT NUMBER 94.09 NLR
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