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<br />'. <br />. <br />I <br />I <br />I <br />I <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />I <br /> <br />Mr. Bill DeGroot <br />March 19, 1997 <br />Page 2 <br /> <br />Ditch which flows east to Dry Creek Ditch No.2. The Wellman Ditch will convey <br />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 /> <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 /> <br />We believe the actions should be taken to address the following topics: <br /> <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 /> <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 /> <br />Please let us know if you have further questions. <br /> <br />Sincerely, <br /> <br />TAGGART ENGINEERING ASSOCIATES, INC. <br /> <br />p~cJ,~ <br /> <br />I{I~~ <br /> <br />William C. Taggart, P.E. <br /> <br />Peter L. Nelson, P.E. <br />