HomeMy WebLinkAboutDrainage Reports - 06/19/1985FINAL DRAINAGE REPORT
HORSETOOTH ROAD AND LEMAY AVENUE
ROADWAY IMPROVEMENTS
ARIX, Engineers, Architects
By James N. George, P.E.
June 19, 1985
Drainage Analysis - South Lemay Near Ticonderoga
The purpose of this drainage report is to determine the design flows along
the north side of the Golden Meadows II Subdivision. It is necessary to
determine this drainage to properly size and position storm drainage improve-
ments to be implemented by the Lemay Avenue Roadway Project.
Drainage reports on file at the Public Works Department, City of Fort
Collins, show that detention is provided for the majority of development
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bordering Lemay Avenue. The Landings' drains primarily toward the. Harmony
Reservoir located west of South Lemay. 'Golden Meadows' drains easterly
toward a detention basin constructed north of Harmony near the Union Pacific
Railroad. There are four remaining drainage areas that will contribute
runoff to the proposed drainage channel located north of Golden Meadows II.
1. South Lemay Avenue _ The existing roadway on South Lemay drains from
Wheaton Drive down to the northwest corner of Golden Meadows II. The
length of the sub -basin is 2,000'±. Assume a width of 200'± to account
for incidental.runoff adjacent to the curb. Refer to -calculation sheets.
2. Harbor Walk Subdivision —
Q2 (Developed) = 1.8 cfs
Q100 (Developed) = 7.5 cfs
Source: Storm Drainage Report, Exhibit "B"
January 22, 1985
Taranto, Stanton & Tagge
3. South Lemay Avenue - The proposed roadway improvements will drain
southerly from a point 1,000' north of Golden Meadows. Assume a width
of 100' to account for incidental drainage. Refer to calculations sheets.
4. Ronald Bockman property — The remaining seven acre parcel drains from
west to east.and will require some detention facility if developed.
Detention for this parcel is not.addressed in this report and would require
future consideration by the developer. Currently, runoff is very .near
the historic rate.
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Two inlets.are provided to accommodate the flows shown concentrating at
the northwest.corner of Golden Meadows II. This flow will be carried in
earthen channels along the south edge of the Collindale Golf Course. A
crossing of the Warren Lake Ditch will be accomplished via an 18" steel pipe.
The flow will then enter the Golden Meadows drainage system via an'18" R.C.P.
into an inlet. The discharge.from.the A nlet is an existing 15" R.C.P.
The earthen channel capacity is 32 CFS at 4 ft/sec. (Source: Design charts
for Open -Channel Flow, Dept. of Commerce, Chart 17). Since the ditch is
1,400.±/long, the minimum delay is 6 minutes before the water enters the
Golden Meadows system at the north end of Sherman CowEt. The total delay is:
21 (from hydrograph) + 6 = 27 minutes.
The lag time should allow the'peak flow from the subdivision to pass out
the Golden Meadows subdivision. We have contacted M&I to determine: the
hydrologic characteristics of Golden Meadows. Their personnel that
analyzed the subdivision are no longer with the firm - they suggested that
I research City records. The report on file with the City did not have a
hydrograph or detention analysis included since an existing basin was used.
Due to the significant lag time and the minimal flows involved, it is assumed
that the existing basin will handle the additional flows.
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Drainage Analysis - South Lemay & Horsetooth
Analyze flows at intersection of South Lemay & Horsetooth
Reference: Foothills Basin
Drainage Master Plan (1981)
by.Resou me Consultants, Inc.
Basin. Characteristics: Flow is received. from 3 potential sources (refer to
p. 5, ref.)
- overland flow from the southwest and Warren Park
- concentrated flow from the south and the Warren Lake spillway
- concentrated.flow from the southwest and subdivision west of Warren Lake.
Computed Peak'Flows: intersection S. Lemay & Horsetooth
Existing
Q2 - 25 CFS
Q10 - 75
Q25 - 110
Q50 - 140
Q100 -160' j
Recommendations (p..27 ref..):
Fully Developed (P.29 ref.)
26 CFS
72
100
120
160
Install two - 36" culverts from southwest quandrant of intersection to
north side of Horsetooth.
Check: Using Department of Commerce Capacity Charts for Hydraulic Design of
Highway Culverts, p.10-39
Assume: inlet control, groove edge entrance w/4' H.W.D.
capacity - 55 cfs ea. pipe
combined capacity of 2 pipes could handle Q50 fully
developed storm and allow overtopping on more intense storms.
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Installation:
- Southeast and southwest corners of Horsetooth and South Lemay: Future
inlets could possibly service 2000' of Lemay, south of the intersection,
in addition to flows from 1500' west and 500' east of Horsetooth.
Q = CIA
C. = 0.9
I = 3 in/hr -.5 year design storm ( )c = 2000' @ 2 ft/sec = 16 min)
A = (2000 + 1500 + 500) x (60) 43560 = 5.5 acres
Q=0.9x3x5.5=15CFS
* Install 10' wide inlet at each corner using criteria from
Storm Drainage Design Criteria City of Fort Collins Fig. 6 - 11
* Add,4' wide at Horsetooth Road side of southwest quadrant to protect
pedestrians from nuisance flows beginning 1500 ' to the west.
. - Overtopping the inlets would pass flows into Warren Park oe the Collindale
Golf.Course. The minor flooding in either area would be inconsequential.