HomeMy WebLinkAboutDrainage Reports - 09/12/1991DRAINAGE REPORT
FOR
POUDRE VALLEY HOSPITAL
AMBULANCE CENTER
AT
913 EAST MYRTLE STREET
September 12, 1991
Stewart & Associates, Inc.
214 North Howes Street
Fort Collins, Colorado 80521
STEWART&ASSOCIATES
Consulting Engineers and Surveyors
September 12, 1991
Mr. Glen Schlueter
Storm Water Utility
City of Fort Collins
P.0, Box 580
Fort Collins, Colorado 80522
Dear Glen:
This letter is regarding the storm drainage at 913 East Myrtle Street.
The site is the Southwest corner of the intersection of East Myrtle Street
and Lesser Drive. The Poudre Valley Hospital is proposing to remodel and add
onto the existing building and add some hard surfaced parking area for an
ambulance center.
The additional impervious area is 1277 square feet which would increase
the runoff coefficient from 0.61 to 0..77. ..The ten—year runoff rate would
increase from 0.36 cubic feet per second to 0.52 cubic feet per second.
The site is served by an existing 48" storm drain in Myrtle Street which
runs approximately 700 feet Easterly to the Cache la Poudre River. The inlet
at Lesser Drive and East Myrtle Street and the inlet at East Myrtle Street
and the alley are the last inlets before the storm drain outfalls to the Cache
la Poudre River. Both inlets at the site are grated gutter inlets located
on local streets. The inlets should have been designed to accept the ten—year
frequency storm according to today's standards. The alley inlet has a capacity
of 4.9 c.f.s. and 2.33 c.f.s. entering it in a 10—year storm. The Lesser Drive
inlet has a capacity of 4.9 c.f.s. and has 5.16 c.f.s. entering it in a 10-year
storm. The added runoff from this proposed project does not adversely affect
the two inlets.
We are requesting that no onsite storm water detention be required. The
primary reason is because of the closeness to the Cache la Poudre River. The
time of concentration is low for this site, and it is advantageous that runoff
from this site and this low end of the basin be allowed to outfall before any
upstream runoff flows to this section of the storm drain. A secondary reason
for no detention is the inconvenience that onsite detention would cause the
emergency function of the site. The site is small, and there is no practical
area to create a detention pond.
The increase of runoff is relatively low and will not adversely affect
the storm drainage system. If the variance for no onsite storm water detention
is granted, the raise in ponding level at the alley inlet would be 0.04 feet
and at the Lesser Drive inlet would be 0.01 feet in a 100—year frequency storm.
James H. Stewart
and Associates, Inc.
214 N. Howes Street
P.O. Box 429
Ft. Collins, CO80522
303/482-9331
Mr. Glen Schlueter
September 12, 1991
Page 2
The runoff calculations for the site, the existing site plan, the proposed
site plan and the neighborhood basin plan are enclosed as a part of this report.
- If you have any questions regarding this proposal, please call.
Sincerely,
G Q L 'C'
Richard A. Rutherford, P.E. & L.S.
President
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