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<br />5.0 <br /> <br />INTERPRETATION OF TillS REPORT <br /> <br />6.0 <br /> <br />5.1 <br /> <br />Hvdrologic Findings <br /> <br />1. <br /> <br />The results of the hydrologic analysis for the Gunnison River are considered accurate. They are <br />based in part on existing approved data from detailed studies at the upstream and downstream <br />limits of the study reach: The existing data demonstrate a linear relationship of peak flow versus <br />drainage area for the study reach. <br /> <br />2. <br /> <br />3. <br /> <br />5.2 <br /> <br />Hvdraulic Findings <br /> <br />The hydraulic methods used for this study are the same used in more detailed studies and much <br />more detailed than the typical approximate studies. The 100-year flood depths range from 11.6 <br />feet in a medium reach of the river to 17.3 feet near the downstream limit of the study. The <br />flood depths are generally consistent throughout the study reach with differences of only a few <br />feet (12-17 feet for the 100-year flow depths). <br /> <br />4. <br /> <br />5. <br /> <br />5.3 <br /> <br />Floodolain Delineations <br /> <br />6. <br /> <br />The primary difficulty in presenting precise delineation of the 50-year and 100-year floodplains <br />was the limited quality of the available base mapping for the lower Gunnison River. Using <br />USGS topographic quadrangle maps at contour intervals of 20 or 40 feet to portray flood lines <br />in unsurveyed areas provides limited information. The margin for interpretation is very great, <br />especially in medium to wide reaches of the river where contours are widely spaced. More <br />detailed techniques will be necessary in areas of interest. <br /> <br />7. <br /> <br />8. <br /> <br />9. <br /> <br />This study can be utilized to prepare more detailed floodplain delineations in such areas of <br />specific interest. Those who are interested in greater detail have three choices for using this <br />study: <br /> <br />1) They can refer to the detailed study information for the upstream stream reach near Delta; <br />2) They can rely on the hydrologic determinations and use other topographic information and <br />hydraulic models; or <br />3) They can use the depth calculations with other topographic information from field surveys <br />or other maps. <br /> <br />20 <br /> <br />REFERENCES . <br /> <br />Federal Emerflencv Manaflement Al!encv. Flood Insurance Study and Flood Insurance <br />Rate Map dated August, 1991; City of Delta, Colorado. <br /> <br />Federal Emerflencv Manal!ement Aflencv. Flood Insurance Study and Flood Insurance <br />Rate Map dated August, 1991; unincorporated Delta County, Colorado. <br /> <br />Federal Emerl!encv Manaflement Al!encv. Flood Insurance Studies and Flood Insurance <br />Rate Map dated July, 1992; City of Grand Junction. <br /> <br />Federal Emerl!encv Manaflement Aflencv, Flood Insurance Studies and Flood Insurance <br />Rate Map dated July, 1992; unincorporated Mesa County. <br /> <br />US Armv COrDS of Enflineers: Flood Hazard Information, Grand Junction, Colorado, dated <br />November 1976 <br /> <br />United States Geolol!ical Survev: Water-Data Report, Water Resources Data, Colorado, <br />Water Year 1993. <br /> <br />Curve fit Prof!f'am: A public domain computer program, version 1.0 by T~ S. Cox. <br /> <br />Chow. Ven Te: Open Channel Hydraulics, 1959 <br /> <br />OANY; An in-house hydraulics computer program (not for public domain) <br /> <br />21 <br />