FLOOD09573

• County: Boulder
• Stream Name: South Boulder Creek
• Basin: South Platte
• Title: South Boulder Creek/ Flatirons
• Date: 12/5/1997
• Prepared For: Boulder
• Prepared By: Consultants
• Floodplain - Doc Type: Community File

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Mr, Bill DeGroot
March 19, 1997
Page 2

Ditch which flows east to Dry Creek Ditch No.2. The Wellman Ditch will convey
water from Bear Creek and some of the spill flow following Foothills from
Baseline, and would act as a major interceptor for local drainage and South
Boulder Creek spills, At the magnitude of a 100 year flood event flow should
overtop the ditch bank on either side of 55th,

We observed several discrepancies in the Corps' model. The more important of
these are the tributary area in the model which is significantly less than the actual
watershed area, and the peak one hour rainfall, which is less than that prescribed
by local, regional, and National Oceanic and Atmospheric Administration (NOAA)
procedures, Therefore the Corps' model is probably under predicting runoff in the
South Boulder watershed,

We believe the actions should be taken to address the following topics:

1. Hydrology Restudy.
2. Floodplain mapping of the West Valley Overflow of South Boulder Creek
and appropriate hazard notification of the occupants,
3. Master Plan for South Boulder Creek from the Flatirons Pit to Boulder Creek
including the West Valley area.

The effort involved with investigation of these topics may lead to additional
investigation tasks, hazard management efforts, and physical modification of the
drainage network.

Please let us know if you have further questions.

Sincerely,

TAGGART ENGINEERING ASSOCIATES, INC.

Peter L. Nelson, P.E.

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William C, Taggart, P,E,

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