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<br />PREFACE <br /> <br />In 1983. the Governor of Colorado signed into law House Bill 1416 directing <br />the state engineer. Jeris A. Danielson. to prepare a floodplain inundation map <br />for each of the 238 high-hazard dams in the State. Each map was to show the <br />extent of flooding which would occur in the event of failure. downstream to a <br />point where the dam-failure flood would be contained within the lOO-year <br />floodplain. The legislation allowed only four months for completion of the <br />project and required that every political entity (city, town. county) receive <br />a copy of the floodplain map for each dam failure which would affect <br />properties within thetr jurisdiction. Certain political entities were <br />impacted by as many as 30 separate dam failure floodplain maps. The project <br />represented a major challenge because of time and resource constraints. <br /> <br />TO complete the project. the state engineer's office developed a procedure <br />which combined the use of an empirical dam breach algorithm. a recognized <br />flood routing teChnique. and an approximate mapping method. The dam breach <br />algorithm had been used by the state engineer earlier to establish hazard <br />classifications. Desk top calculators and ;.5 minute U.S.G.S. topographic <br />maps provided the necessary tools at minimal expense. <br /> <br />In spite of the approximate methods used. it was found that the procedure <br />later predicted. with reasonable accuracy. the limits of flooding which <br />actually occurred fOllowing the failure of two dams in Colorado. Flood depths <br />and aerial flood extent were determined to be relatively insensitive to <br />changes in peak failure discharge at the dam site. Therefore. this procedure <br />is of value to emergency planners and government agencies as a quick and <br />inexpensive way to estimate inundation areas and flood travel times in the <br />event of a dam failure. <br /> <br />ii <br />