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<br />DRAFT <br /> <br />TABLE 2.8 - CONT. RESULTS OF HEC-l, 24-HOUR STORM MODELING <br /> <br />TRIBUTARY LOCATION AREA PEAK DISCHARGE (cfs) <br />NAME (UNIT .) (SQ.MI.) 2-YR 5-YR 10-YR 25-YR 50-YR 100-YR <br /> <br />Illinois <br />Gulch <br /> <br />CH-7 <br /> <br />3.17 <br /> <br />10. 14. <br /> <br />20. <br /> <br />75.227. <br /> <br />335. <br /> <br />A comparison with FEMA discharges is provided below. The results <br />of the HEC-l modelling show considerable variation from the FEMA <br />values, praticularly at the 10-year level. As previously <br />mentioned, the 10-year events are likely dominated by snowmelt <br />which will be addressed subsequently. At the 100-year level, the <br />French Creek and Illinois Gulch discharge exhibit good agreement <br />between the two methodologies. On Lehman Gulch, the FEMA discharge <br />is nearly double the HEC-l value and on Sawmill Gulch the HEC-l <br />value is nearly double the FEMA value. It is difficult to explain <br />why there is such difference between the FEMA 100-year peak on <br />Sawmill Gulch and the 100-year peak on Lehman Gulch when the two <br />watersheds have similar areas, topography and geology. <br /> <br />TABLE 2.9 - COMPARISON OF HEC-l AND FEMA DISCHARGES <br /> <br />10-YR <br />FEMA HEC-l <br /> <br />DISCHARGE (cfs) <br />50-YR <br />FEMA HEC-l <br /> <br />100-YR <br />FEMA ,HEC-l <br /> <br />TRIBUTARY <br /> <br />Lehman 200 16. 380 73. 580 315. <br />Gulch <br />Sawmill 45 10. 75 l6l. 120 248 <br />Gulch <br />Illinois 130 17. 240 205. 330 30l. <br />Gulch <br />French 280 37. 490. 708 713 <br />Creek* <br /> <br />---------------------------------------------------------------- <br /> <br />* Values from 1975 Leonard Rice Report - "Breckenridge Flood Plain <br />Information" <br /> <br />Final Adopted Flows <br /> <br />Several sets of flows have been developed for <br />tributaries and the Blue River throughout the MPA. <br /> <br />the various <br />The following <br /> <br />16 <br />