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<br />Routt County Commissioners <br />June 4, 2001 <br />Page 3 of 8 <br />in the channel is less than modeled (i.e., depth of channel or width of channel is less than shown in <br />the HEC-RAS results), the Base Flood Elevation (BFE) will be higher and encroachment onto the <br />project site will be greater than stated in Applicant's Flood Delineation report. <br />Hydrology <br />The hydrology used in the Applicant's Flood Delineation report is based on the following: <br />~ Yampa River flow data recorded at USGS Gage 09244410 <br />• Fish Creek flow data recorded at USGS Gage 09244100 <br />The Applicant's report accurately stated that Trout Creek is the name of the tributary abutting the <br />south and west boundaries of the project site. However, the report is in error as to identifying and <br />correctly developing the appropriate hydrology for the Trout Creek basin. On page 3 of 7 of the <br />report it is stated "On Trout Creek the USGS operated a gaging station on the subject property <br />beginning in 1955. This was operated for the next ] 8 years." There is a serious error in this statement <br />and with the subsequent engineering assumptions and flood modehng results. The errors associated <br />with this statement are as follows: <br />1. USGS Gage 09244100 is not located on the subject property, nor is it located on Trout <br />Creek. The gage is located on Fish Creek in the upper reaches of the Fish Creek Basin. <br />2. The Fish Creek basin encompasses approxi~~~ately 90 square miles. The Fish Creek Gage <br />09244100 records flows for only 34.5 square miles of the basin, or approximately one- <br />third of the Fish Creek basin. <br />3. Fish Creek is a smaller tributary to the larger Trout Creek Basin. The Trout Creek basin <br />encompasses more than 165 square miles. Therefore, the Fish Creek gage (Gage <br />09244100) accounts for only 20 percent of the total Trout Creek Basin drainage. <br />4. The assumption that 272 cfs represents peak flood flow on Trout Creek, as appazently <br />gleamed from the Fish Creek gage (Gage 09244100), completely underestimates peak <br />flood nmoff. Based on basin-area ratios (i.e., Elk River gage) peak flood flows on Trout <br />Creek could be expected in the range of 2,000 cfs. <br />Identified in Figure 1 are the Trout Creek and Fish Creek drainage basins and the relative location <br />of the subject property. Also provided in Appendix A of this response are the USGS Peak Flow <br />