HomeMy WebLinkAboutMASON STREET MOTEL - PDP/FDP - 7-98 - REPORTS - DRAINAGE REPORTMr. Basil Hamdan
Page Three
October 30, 2000
Building/
Location
Lowest
Entrance El.
Existing
Freeboard ft
Proposed
Freeboard ft
Salvation Army
5035.12
- 0.72
- 0.98
Raynor Garage Door
5035.44
- 0.40
- 0.66
South Mesa Vet Hospital
5036.55
0.71
0.45
Ramada Inn
5038.67
2.82
2.57
Barnes & Noble
5036.97
1.12
0.87
REI
5037.78
1.94
1.68
Bank on Boardwalk
5039.77
3.93
3.67
Olive Garden
5041.73
5.89
5.63
Storage Unit Office
5034.53
- 1.31
- 1.57
Storage units near Mason St.
5034.20
- 1.64
- 1.90
State Parks Building
5035.73
- 0.11
- 0.37
Movie Theatre
5035.63
- 0.21
- 0.47 71
Floodproofing alternatives were investigated for those buildings within the 100-year water
surface. Due to their entrance configurations, several of the buildings would be difficult to
floodproof and the costs prohibitive. The only item identified that would benefit property owners
along Mason Street would be to construct regional basin improvements west of the railroad
tracks, which might reduce spills into this area.
The SWMM model was also run for existing and proposed conditions assuming that spills over
the railroad track would be eliminated by future basin -wide improvements. The resulting 100-
year water surface elevation of 5035.16 would inundate only the Salvation Army and Storage
Unit area. Building the Motel 6 would raise the 100-year water surface elevation to 5035.51.
Only the Salvation Army, Storage Units, and Raynor Garage Door buildings would be inundated
under proposed conditions and with basin -wide improvements. Obviously, basin -wide
improvements have a significant benefit to the Mason Street area.
We hope this provides the information you require at this time. If you have any questions or
comments, please feel free to call.
Sincerely,
Owen Ayres & Associates, Inn
Chris Carlson, P.E.
Project Manager
CC:sp
Enclosure
HAMM OLT.DOC
34-0754.00
' Mr. Basil Hamdan
' Page Two
October 30, 2000
I Our investigation examined only the 100-year storm event and included the spill hydrograph
over the Burlington Northern railroad tracks, which came from the "Burlington Northern Santa Fe
Track Raising Study" by MK Centennial (July 2, 1998). The following table indicates the results
for each development condition:
Condition
Basin
Area
%
Impervious
100-Yr. Q
cfs
Pond
Volume
ac-ft
WSEL w/
0 cfs out
WSEL w/ 10
cfs out
Historic
31.41 ac
54.2
218.80
13.14
5034.10
--
Existing
33.49 ac
81.8
280.45
14.79
5035.84
5035.76
Proposed
33.49 ac
1 83.6
1 283.34
1 14.85
1 5036.10
5035.86
Exist. w/o Track Spill
33.49 ac
81.8
257.25
9.30
5035.51
--
Prop. w/o Track Spill
33.49 ac
83.6
260.12
9.36
5035.24
Water surface elevations were evaluated assuming no release from the basin as most
conservative and assuming a 10 cfs release through the existing storm sewer. Although the
actual storm sewer capacity and hydraulics were not evaluated as part of our investigation, it is
evident from.the results that the storm sewer has very little benefit for the 100-year storm event.
Changes from the historic and existing conditions are also included in the following table:
Condition
Impervious Area
change)
100-yr Q
% Chan e
Pond Volume
% change)
WSEL
Chan e ft
Existing -
Increase
51%
28%
13%
1.74
from historic
Proposed -
Increase
2%
1 %
<1 %
0.26
from existing
Previous development in the area increased the 100-year water surface elevation 1.74 feet
above the historic conditions. Several buildings were built below this flooding level as a result.
Based on the 100-year water surface elevation, the neighboring buildings were investigated for
possible flooding. The details are shown on the following page:
The west entrance elevation to the Colorado State Parks building is very close (within 0.1 foot)
to the 100-year water surface elevation under existing conditions. Since the SWMM model is
limited to the accuracy of the available topographic data, this building may or may not be
currently flooded. If it isn't flooded, then minimal freeboard exists.
As shown above, the proposed Motel 6 site development will increase the 100-year water
surface elevation 0.26 feet. With the exception of possibly the State Parks Building, no building
that isn't already being inundated will be effected by the development.
HAMDI0LT.DOC
34-0754.00
AIRES
ASSOCIATES
October 30, 2000.
Mr. Basil Hamdan
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
Re: Mason Street/Motel 6 Drainage
Dear Basil,
This letter summarizes Ayres Associates investigation to determine the regional drainage
effects of the proposed Motel 6 site, which is on the west side of Mason Street just north of the
Mason Street and Boardwalk Drive intersection. This letter also addresses the City's comments
made on June 30, 2000. Written responses to those comments are included in the Appendix.
The area south of Horsetooth Road and north of Troutman Parkway along Mason Street is a
closed basin with no appreciable outlet. It is also bordered by the Burlington Northern railroad
tracks on the west and College Avenue on the east.
Historically, the area has acted as a very large detention pond surrounded by undeveloped
parcels. Mason Street was constructed directly through the historic ponding area then
commercial construction proceeded on a lot by lot basis until the majority of the pond was filled
in. The basin currently exists as a developed and highly impervious closed basin with the
exception of the storm sewer in Mason Street. There are a couple remaining open lots,
including the proposed Motel 6 lot, which is at the current low point for ponding.
The purpose of our investigation was to determine the regional drainage effects of constructing
a motel on the previously mentioned lot. This work included determining the expected rise in
water surface elevation, loss of available pond volume, effects on adjacent properties, and
whether mitigation would be possible. Unfortunately for the property owner, they are the last
property to develop on the west side of Mason Street and thereby have a proportionately higher
impact on flood elevations than had they been first.
We surveyed what was reasonably available and use aerial ortho-photo maps .to provide the
remaining topographic information. Entrance elevations were also taken at neighboring
buildings. The analysis was performed using UDSWMM and was completed in accordance with
the City of Fort Collins Storm Drainage Design Criteria as revised in January 1997. Five
development conditions were investigated:
• Historic conditions (before development of the area)
• Existing conditions
• Proposed conditions (existing conditions plus the proposed Motel 6)
• Existing conditions without track spill
• Proposed conditions without track spill
Owen Ayres & Associates, Inc.
Engineers/Scientists/Surveyors
3665 JFK Parkway, Building 2, Suite 200, P.O. Box 270460, Fort Collins, CO 80527 HAMD10LT.DOC
(970) 223-5556, Denver Metro (303) 572-1806, FAX (970) 223-5578 34-0754.00
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