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1 <br /> SECTION I <br /> ' SUMMARY <br /> INTRODUCTION <br /> In 1977 the U.S. Army Corps of Engineers (Corps) conducted a hydrology study <br /> ' that included the South Boulder Creek Basin. That study provided the hydrology for <br /> the Urban Drainage and Flood Control District (UDFCD) Flood Hazard Area <br /> Delineation (FHAD) and the Federal Emergency Management Agency (FEMA) Flood <br /> Insurance Study (FIS) and Flood Insurance Rate Maps (FIRMs) for South Boulder <br /> Creek. <br /> In 1996, Love and Associates identified that South Boulder Creek could spill greater <br /> flows than identified in the FHAD and that these spills could travel to the west side <br /> ' of the valley and overtop Highway 36, largely west of Foothills and thus posed a <br /> hazard to the neighborhood north of 36. <br /> Phase I effort reviewed the FHAD and Love's investigation, and identified 100 year <br /> spills on the order of 2700 cfs from South Boulder Creek above Highway 36. The <br /> spill was shown to commingle with local drainage from the Dry Creek Ditch No. 2 <br /> and the Viele watershed. The Phase I effort obtained a copy of the Corps' <br /> hydrology model to identify the timing of the Viele inflows and allow simplified <br /> simulation of its drainage network. Some general problems were noted in the <br /> Corps' model, but our effort focused on the determination of how much of the <br /> South Boulder Creek spill would return via Viele and how much would continue to <br /> the West Valley spill route. Phase I determined that about 1800 cfs would <br /> continue to the West Valley north of Highway 36. <br /> The Urban Drainage and Flood Control District (UDFCD) authorized this Phase II <br /> initial hydrology study to estimate the distribution of flooding in West Valley <br /> downstream of Highway 36 to the area of the Wellman Ditch. For the purposes of <br /> Uthe Phase II study the Corps' hydrology remained unchanged upstream of Highway <br /> 36 other than modifications to better reflect floodplain routing downstream of the <br /> mountains. All new basins and routing elements were inserted for the Viele Basin <br /> U and the area downstream of Highway 36. <br /> UAlso, since questions regarding hydrology had been raised by the local governments <br /> and our work, requests of the Corps were made to obtain background data, basin <br /> mapping, and verification studies. <br /> ' I - 1 <br /> 1 <br />