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<br />POPULATION AT RISK <br /> <br /> <br />Population characteristics of those residing in the study area were <br /> <br />extracted from the appropriate census tracts in the 1980 Census of Population and <br /> <br /> <br />Housing. Population estimates were estimated for two different times of day, <br /> <br />nighttime and daytime. Nighttime hours for this study were estimated to be <br /> <br />between the hours of 10 p.m. and 6 a.m. and daytime hours were estimated between <br /> <br />6 a.m. and 10 p.m. The probable nighttime PAR affected by dam failure of <br /> <br />existing conditions is approximately 100,000 downstream of Cherry Creek Dam and <br /> <br />4,200 along Sand and Toll Gate. The probable daytime PAR is considerably greater <br /> <br />than the probable nighttime PAR due to the central business district being in the <br /> <br />Cherry Creek flood plain. DownstreaDI of Cherry Creek, probable daytime PAR <br /> <br />affected by dam failure under existing conditions is approximately 138,000. <br /> <br /> <br />Probable daytime PAR along Sand and Toll Gate Creeks that would be at risk if dam <br /> <br /> <br />failure occurred under existing conditions is 5,800. <br /> <br />WARNING TIME <br /> <br /> <br />A key variable in estimating LOL is the amount of time individuals in the <br /> <br />flood plain have to evacuate the flood plain from the time a warning is first <br /> <br />issued. The analysis in this document is based on the assumption that the <br /> <br />warning time begins when the pool reaches the top of the flood control pool (5596 <br /> <br />feet m.s.l.). The warning time is defined as the period of time from when water <br /> <br /> <br />is at the top of the flood control pool until the time it spills out of the <br /> <br /> <br />channel. The warning times at different cross sections vary depending on channel <br /> <br /> <br />capacity at that location. Arrival time, which was referred to. earlier in the <br /> <br />text, is a term that could be used interchangeably with warning time in this <br /> <br /> <br />particular document. <br /> <br />WARNING AND EVACUATION <br /> <br /> <br />For the Cherry Creek Lake project, the project manager, area engineer, or <br /> <br />his representative have the authority to commit the Government for whatever <br /> <br /> <br />resources are necessary to prevent failure and to minimize the loss of life and <br /> <br /> <br />property, The current project warning and evacuation plan is contained in the <br /> <br />"Contingency Plan for Emergencies," Appendix E of the proj ect Operation and <br /> <br /> <br />Maintenance Manual, revised 1984. <br /> <br />36 <br />