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..~ <br />C <br />Cotter (;or~~oration <br />Mr. George Van Slyke <br />August 26, 1983 <br />Page - 3 - <br />ore. There exists a possibility of high velocity flood flows changing <br />the alignment of the main channel of Ralston Creek. However, due to the <br />short duration of high flow rates for the design storm, the armoring <br />effect of the boulders and cobbles in the alluvial materials, and the <br />distance of the ore loading facilities from the main stream, there is <br />little likelihood of any lateral realignment of a magnitude suffi- <br />cient to significantly affect the loading areas. <br />The following table swrmarizes flow characteristics under improved <br />conditions at selected cross sections shown on the previously submitted <br />drawing: <br />Flow Characteristics under Improved Conditions at <br />Selected Cross Sections <br /> Water Surface Velocity On Approximate <br />Section Elevation Edge of Ore Sorter Area Scour <br />Number ft. ft.jsec. ft. <br /> <br />40+90 6,569.5 4.0 0 <br />40+52 6,567.8 4.0 0 <br />38+11 6,562.1 6.2 0.2 <br />37+70 6,560.6 8.9 0.6 <br />37+30 6,559.0 6.2 0.2 <br />36+57 6,557.4 8.1 0.5 <br />36+34 6,557.1 2.5 0 <br />Recommendations <br />It is recommended that the depth of I-beams or other structures near the <br />ore sorter extend to at least 1.5-feet below grade. This depth includes <br />scour protection plus a factor of safety. This depth is in addition to <br />that required for structural stability. <br />This report has been prepared based on McDermid Engineering Associates, <br />Inc., knowledge of the Ralston Creek watershed and the ore sorter site <br />and in accordance with accepted professional engineering principles <br />and practices. <br />If you have any questions about the forg9inginformation, please contact me. <br />Sincerel , <br />~m ~~v <br />Tim Smith <br />Supervisor of Environmental Activities <br />TS/rg <br />File No. 8111K8620-34-5 <br />attizvpF~n_i~_~ <br />