FLOOD00385

• County: Boulder
• Community: Boulder
• Stream Name: Boulder Creek
• Title: South Boulder Creek Interim Hydrology Study
• Date: 7/1/2000
• Prepared For: Boulder County
• Prepared By: Taggart Engineering Associates, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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DISCHARGE PROFILES

The discharge profiles for South Boulder Creek and the West Valley Overflow are
presented in Figures 1-1 and 1-2, respectively. Stationing along South Boulder Creek
begins at the confluence with Boulder Creek and increases going upstream. The
significant spill from South Boulder Creek to the West Valley Overflow begins
approximately at Station 359 + 50 on South Boulder Creek.

The Figure 1-1 South Boulder Creek discharge profile shows four major spills to the
West Valley Overflow: two upstream of Highway 93, one upstream of Highway 36,
and one downstream of the Wellman to the golf course. Two major inflows occur:
one from the West Valley Overflow in the area of the middle levee on CU's
property, about 1500 to 2000 feet upstream of Highway 36, and the
Viele/Anderson Ditch inflow which carries some of the West Valley Overflow
discharge back to South Boulder Creek. There are also several tributary basin
inflows, such as David's Draw and the areas along South Boulder Creek.

The Figure 1-2 discharge profiles show the spills from South Boulder Creek above
Highway 93 and Highway 36, and the flows returning to South Boulder Creek nes.r
the CU middle levee and the Viele channel and Anderson Ditch. At Baseline the
West Valley Overflow spills seven different ways, three of which can send portions
of their discharges to Bear Canyon Creek. Some of this flow, and flood discharges
following other routes, discharge to the Wellman Ditch, with a portion of the total
flow going north to Boulder Creek through neighborhoods midway between 55th
and Foothills. From Foothills and Baseline, the West Valley Overflow discharge
only reflects the estimated portion of the West Valley Overflow following the
Crossover Ditch and Dry Creek Ditch No.2. The discharge drops to nil (30 cfs) for
the flow crossing under the Wellman. Thus, of all the flow arriving in the West
Valley Overflow to Foothills and Baseline, most spills to Bear Canyon Creek or the
Wellman Ditch, with portions of the Wellman overflow going north to Boulder
Creek. Downstream of the Wellman the route along Dry Creek Ditch No.2
increases as the Wellman spills just upstream and downstream of 55th, and
increases again midway across the golf course due to the South Boulder Creek spill.

MODEL REASONABLENESS AND REFINEMENT

Detailed model verification and reasonableness evaluations are presented in
Section V for individual basins, comparative Colorado Unit Hydrograph Procedure
(CUHPj modeling for representative tributaries, for regional relations developed by
CWCB, and other unit discharge (ets/acre) comparison. It appears the results are
reasonable for the tributary watersheds.