HomeMy WebLinkAboutBLEVINS SUBDIVISION LOT 9 PUD PRELIMINARY - 42 91A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE & EROSION CONTROL REPORT
FOR
LOT 9, BLEVINS COURT, P.U.D.
.FORT COLLINS, COLORADO
SEPTEMBER 27, 1991
(REVISED JANUARY 6, 1992)
PREPARED FOR:
KENT GLOVER
PREPARED BY: .
PARSONS & ASSOCIATES
CONSULTING ENGINEERS
--43-2-LINK-LANE_P_LAZA
FORT COLLINS, COLORADO. 80524
(303) 221-2400
PROJECT NUMBER: 91.15 GLV
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PRELIMINARY DRAINAGE & EROSION CONTROL REPORT
FOR
LOT 9, BLEVINS COURT, P.U.D.
INTRODUCTION
This drainage investigation has been prepared along with
preliminary plans for the development of a tri-plea on Lot 9 of the
Blevins Subdivision. This study was prepared in accordance with
the City of Fort Collins "Storm Drainage Design Criteria and
Construction Standards."
SITE DESCRIPTION
This project is to be constructed on Lot 9 of the Blevins
Subdivision which is located at the southwest corner of the Blevins
Court cul de sac in the Southeast Quarter of the Southwest Quarter
of Section 14, Township 7 North, Range 69 West of the 6th Principal
Meridian, Larimer County, Colorado (see figure 1) Lot 9 includes
11,846 square feet and was platted as part of the Blevins
Subdivision in 1958. Lot 9 remains the only vacant lot in this
area. Adjacent structures appear to be single family residences
converted to
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PROJECT SITE
FIGURE 1
rental property due to their proximity to the Colorado State
University Campus. These units are typically raised one to two
feet above curb level with individual yards draining into
side yards and then into street curbs.
This site slopes from west to east at about a 1.5% slope and
is covered by natural grasses. It appears that no drainage
facilities were constructed as part of the Blevins Subdivision and
runoff is conveyed via streets in this area towards Spring Creek.
All other utilities (including sewer and water) were located along
back property lines and extend from south Whitcomb Road.
CRITERIA
The Rational Formula as identified in the City of Fort Collins
"Storm Drainage Design Criteria and Construction Standards" has
been used to develop runoff flows from this site. The Rational
Formula is an excellent predictor of flows from drainage basins
with areas less than 200 acres.
HISTORIC DRAINAGE
Runoff in this area is primarily from residential buildings
that sheet flows towards local streets. Water runs from west to
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east on Lot 9 before spilling into Blevins Court. It is intended
that this development will maintain this pattern.
PROPOSED DRAINAGE
OFF -SITE FLOWS
Water from the north and east will be conveyed by a drainage
swale along the north property line to Blevins Court. This will
allow flows (primarily from the west) to continue through the site.
Areas east and south of this site continue to flow away from the
proposed improvements. There appears to be a small low lying area
at the southeast corner of the site. These flows will be brought
into the parking lot and conveyed along the easterly edge of the
site. This area is less than .01 acres.
ON -SITE FLOWS
Runoff from the majority of the site including roof drainage,
sidewalks and open space will be directed to the parking lot at the
east edge of the site (see figure 2). These flows will be detained
in the parking lot and metered through a curb opening at the
northeast corner of the parking lot. A sidewalk culvert will allow
these flows to discharge into Blevins Court at their historic rate.
These flows are as follows:
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Historic
Q2 = .17 cfs
Q100 = .63 cfs
Developed
Q2 = .48 cfs
Q10o = 1.63 cfs
Calculations for these flows are attached.
EROSION CONTROL
This site will be completely stripped during construction.
Due to the small size of this project all of the structures will be
built at one time. Water erosion control will be accomplished by
the placement of a sediment trap at the location of the proposed
detention pond. Wind erosion control will be accomplished by
existing trees and the placement of the furthest west structure
which will provide a barrier along 60% of the west property line.
Detailed Erosion Control calculations will be submitted along with
final plans as required.
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CONCLUSION
The development of a tri-plex on this site will increase
runoff onto adjacent streets. To mitigate this increased flow;
runoff will be directed to the parking area of the east edge of the
site which will act as a detention pond. A weir will control the
discharge from the parking lot into a sidewalk culvert which will
direct the water to Blevins Court. These improvements will insure
that drainage from the site will remain at existing levels.
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