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1 <br /> Mr. Bill DeGroot <br /> March 19, 1997 <br /> ' Page 2 <br /> Ditch which flows east to Dry Creek Ditch No. 2. The Wellman Ditch will convey <br /> t water from Bear Creek and some of the spill flow following Foothills from <br /> Baseline, and would act as a major interceptor for local drainage and South <br /> Boulder Creek spills. At the magnitude of a 100 year flood event flow should <br /> ' overtop the ditch bank on either side of 55th. <br /> We observed several discrepancies in the Corps' model. The more important of <br /> ' these are the tributary area in the model which is significantly less than the actual <br /> watershed area, and the peak one hour rainfall, which is less than that prescribed <br /> ' by local, regional, and National Oceanic and Atmospheric Administration (NOAA) <br /> procedures. Therefore the Corps' model is probably under predicting runoff in the <br /> South Boulder watershed. <br /> We believe the actions should be taken to address the following topics: <br /> 1 . Hydrology Restudy. <br /> 2. Floodplain mapping of the West Valley Overflow of South Boulder Creek <br /> and appropriate hazard notification of the occupants. <br /> 3. Master Plan for South Boulder Creek from the Flatirons Pit to Boulder Creek <br /> including the West Valley area. <br /> The effort involved with investigation of these topics may lead to additional <br /> investigation tasks, hazard management efforts, and physical modification of the <br /> drainage network. <br /> Please let us know if you have further questions. <br /> Sincerely, <br /> TAGGART ENGINEERING ASSOCIATES, INC. <br /> /�0/1 <br /> Peter L. Nelson, P.E. William C. Taggart, P.E. <br /> 1 <br />