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<br />. DEC. -17' 98(THU) 10:32 WRIGHT WATER <br />l' <br /> <br />TEL:303 480 1020 <br /> <br />P.003 <br /> <br />F1l1lldplaln and WeIland study for <br />Verzuh/ McCormick Ranch <br /> <br />statistical methodology used was Log Pearson Type Ille which is the standard method used by <br />FEMA and other agencies to evaluate the magnitude of flood flow events. The results wen: <br />checked against other methods to verify reasonableness of the sIreamflow ~m..t.... The gage has <br />70 square-miles oftnouWy area and has year.; of record spanning from 1940 through 1951 and <br />1994 through 1997. The location ofthc gage is shown on the vicinity map. . , <br />I"^~~t wJ.. w,i~ Cl.oc B ")J"'~7 ~'Jdl,.J' (J) raf't/-) <br />The Log Person Type me lIIIalysi the stream gaging record infonnation indicates that the 100- <br />year flood is approximatel 1,700 bic feet per second. A Jm:vious analysis was perlbnned by the <br />Colorado Water Conservation Board (CWCB) with the ICSuIts pl'CSented in the Tec1mical ManuaJ <br />No. I, entitled ManUQ/ of Estimating Flood Characteristics of Natural Flow Stnams in Colorado <br />dated 1976. This analysis shows the l00-year flood in the Slate River at this location to be 1,390 <br />cubic feet per second. This flow was estimated also using stream gage records; however, the <br />records ended in 1951. The four additional peak annual flows used from 1994 through 1997 <br />include three of the highest annual peaks ever recorded at this stream gage. Thc:n:fote, the results of <br />our analysis indicate that th.e l00-year flood is higher than originally estimated. The results wen: <br />also compared to the regression equations included in the CWCB manual and a Gumbel <br />Distribution analysis, which provide a good verification of the flows being used for the hydraulic <br />study. <br /> <br />Aoodplain Analysis <br /> <br />The floodplain analysis for the Slate River includes seven cross-sections plus an additional two <br />cross-sections on Washington ,Gulch. These cross-sections were field surveyed by Furey <br />Engineering and superimposed on the site base map prepared by Furey Engineering. The <br />topography and cross-sections are all based on USGS datum consistent with the current flood <br />insurance studies for Gunnison County (see the floodplain map for the site benchmark description). <br />The floodplain is shown on Drawing 1. <br /> <br />The hydraulic analysis was pe...fullucd using the U.S. Anny Corps of Engineers HEC-RAS modeL <br />The analysis starts at Section 1 which is located downstream of the property-The starting Water <br />smface elevation is nonna] depth with an energy slope of .002 feet per fcct Manning "n" values in <br /> <br />961-'l05.010 . <br /> <br />wright Water Engineers, inc. <br /> <br />Page 2 <br />