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<br />DEC. -17' 98 (THUI 10:32 WRIGHT WATER <br /> <br />TEL:303 480 1020 <br /> <br />r. UU4 <br /> <br />'" <br /> <br />'-. <br /> <br />- -. --- <br /> <br />Floodplain and WeII8nd ~ for <br />Ven.uN McCormick Ranch <br /> <br />the analysis include 0.04 in the ...h~nn"'l and 0.07 fur the over-banks. Calculations illdi..JO~ that <br />overtopping occurs on the Slate River at Sections I, 2, and 3. However, to establish base flood <br />e1evatiollS, flow was contained by utilizing the ineffective flow option and setting stations at the <br />gtade break of the overtopping flows. Delineations of the l00-year floodplain are based on th.ese <br />base flood elevations. / f Qf'J >-e) J~MJ.. I~ <br /> <br /> <br />A second hydraulic analysis was conducted in which the caplcity oft1Je overtoppin <br />detemUned in order to establish the amount of flow lost out of UU: Slate Ri . The lost flow <br />analysis was conducted as follows: First, the bydraulic analysis was co for the existing <br />/ <br />conditions. The existing conditions I1lOdel was then evaluated to identifY v4lich sections appear to <br />.--<- "-----.., <br />have flow depths higher than the highest point of ground within thez~~JlIain of ~ The <br />model was then rerun with reduced flows at that section until the water surt'alieIeWtion matched <br />this high point. This procedure is conducted from upstream to downstream until the rMlI"'ed flows <br />remain fUlly contained. The results of this analysis indi""tes that then: is appro,w,.AtAly 130 cfs lost <br />out of Section 8 on Washington Gulch. 645 cfs lost from the Slate River Station 3, 215 cfs lost <br />from the Slate River Station 2, and 10 cfs lost from the Slate River Station 1. Most of the <br />overtopping flows are recollected in a ditch located east of the Slate River. This ditch has its <br />confluence with the Slate River immediately dowostream of Section 1. A second floodplain was <br />d~lin""t..d in the ditch which reflects'the amount ofiost flow from the Slate River. The depth of <br />flow between th.e two floodplains (Slate River and the ditch) is estimated to be less than one foot <br />This area is labeled "shallow flooding. n <br /> <br />Proposed Conditions <br /> <br />Crested Butte's cunent floodplain regulations require that no development be pemritted within the <br />100-year floodplain. In addition, the town requires a 20-foot buffer beyond the floodplain. <br />Exceptions to the regulations include access and bridge crossings. <br /> <br />Because proposed CODditiOllS will not encroach on or alter the floodplain, an additional run was not <br />necessary. Development will include improvements to the existing bridge, but will be placed at or <br />above the elevation of the existing bridge with abutment<: that are at least equal to the width. of the <br /> <br />961-005.010 <br /> <br />Wight Waler Engineers, hie. <br /> <br />Page 3 <br />