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<br />Box Elder Creek Hydrology <br /> <br />h <br /> <br />Judging the Validity ofCUHP Results <br />As noted above, all parties having an interest in this hydrologic analysis of the Box Elder <br />Creek watershed have agreed that the published regression equations (USGS, 1976) <br />overestimate discharges for most drainageways in eastern Colorado. In response to the <br />lack of an accepted published regional regression equation, FEMA developed a new set <br />of regression equations utilizing data from 42 sites from Colorado and five nearby states. <br />As also noted above, the District, Brian Hyde with CWCB and Bob Jarrett with the <br />USGS agree that drainageways on the eastern plains of Colorado are not hydrologically <br />homogeneous, need additional explanatory variables, and additional flood data; and <br />therefore the FEMA regression equations do not adequately estimate flood-frequency <br />relations. Absent regression equations that the various parties can agree to, other means <br />of judging the validity ofthe CUHP analysis can be used, as described in the following <br />paragraphs. <br /> <br />~1 <br /> <br />I.... <br />'J <br />,I <br />i <br />I <br />I <br />I <br /> <br />. <br />, <br />," <br />f~'J <br />~:.' <br />~J <br />" <br />I <br />"i <br /> <br />In order to compare discharges from several different sources of information, the <br />common border of Adams and Arapahoe Counties will be used. Discharges from these <br />various studies are tabulated in the accompanying table. <br /> <br />~ <br /> <br />Existing Conditions 100- Year discharges At 1-70 <br />(Adams County/Arapahoe County Border) From Various Sources <br />Study and Date Discharge (cfs) <br />Adams County FIS (1989) 26,500" <br />Arapahoe County FIS (1993) 26,500 <br />Corps of Engineers (1989) 8900 <br />District (1995) 8820 <br />FEMA revised regression 16,800 <br />"FIS published discharge of 13,900 is a lypcgraphic error <br /> <br />~~ i <br />1 <br /> <br />The observed flood of record for Box Elder Creek has been estimated by CWCB at a <br />peak discharge of approximately 6000 cfs at Bootleg Reservoir in May, 1973. Bootleg <br /> <br />CTC8.dcc <br /> <br />7 <br />