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Area since the original channel will be covered with fill material cut from <br />bench areas above the bottom of the Gulch. Three loose rock check dams will be ,~,~ <br />installed downstream of the project before construction begins. (Page IV-73 of ~ 0 <br />the permit application). The culvert dimensions have been described in Section <br />B, Description of Applicant's Proposal, of this TEA. Although the diversion is <br />anticipated only for the life of the mine, it has been designed to carry flow <br />from a 100 year-24 hour precipitation event as derived from methodology pre- <br />sented in Chapter 21, Section 4 of the SCS National Engineering Handbook and <br />TP149. These figures were checked with data presented in Colorado Water Con- <br />servation Board Technical Manual No. 1 and were found to be acceptable. The <br />three lateral diversions contribute 351 cfs, resulting in flow at the outlet of <br />854 cfs. <br />Diversion sizing was accomplished by utilizing Bernoulli's equation to con- <br />struct backwater curves along the culvert, and peak flows from the main channel <br />and laterals were assumed to reach the primary culvert simultaneously which was <br />a conservative assumption (page V-24 of the permit application). Illustration <br />9 of the permit application details design calculations. Although the illu- <br />stration included erroneous diameters for two of the laterals, a calculation <br />check was made using the diameters of 72 and 42 inches given on Map 31 instead <br />of 84 and 48 inches. Headwater depths were slightly higher than originally <br />calculated, but were still acceptable. Headwater depth at the primary culvert <br />inlet will be approximately 9.6 feet above the inlet invert. At this depth, <br />the concrete headwall, which extends four feet above the crown of the pipe, <br />will protect the fill from erosion. Furthermore, the Scullion Gulch channel <br />should not be excessively inundated nor will the haul road embankment be <br />overtopped (See Map 29 of the permit application). <br />The inlet of the diversion will be provided with a trash rack and a riprap <br />apron will be installed at the outlet. Anti-seep collars will be provided <br />along the length of the culvert to prevent seepage beneath the D-Portal sedi- <br />mentation pond (page Y-20 of the permit application). / <br />Restoration of the Scullion Gulch channel and its tributaries will recreate the <br />approximate original channel slope and meander pattern. (See Maps 48 through <br />51 of the permit application). A series of 13 loose rock check dams will be <br />16 <br />