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<br />• <br />FLOOD ROUTING <br />The flood routing assumed an initial water surface at the <br />required sedimentation level. This is the elevation of the <br />dewatering hole(s) in the riser pipe. Rule 4.05.6(b) requires <br />periodic sediment removal, but after the first significant <br />inflow, a permanent maximum pool elevation equal to the <br />required sedimentation level will develop. <br />The Type 3 riser limits the outflow rate to such an extent <br />that the entire 10-year inflow volume was assumed to be <br />stored for the purpose of setting the top of riser elevation. <br />To test this assumption, an actual flood routing was computed <br />for the 10-year, 24-hour flood for Pond A. <br />INTERCEPTOR DITCHES <br />Interceptor ditches were used to modify the natural tributary <br />areas to various ponds in order to maximize the use of <br />favorable ponding loctions. The ditches are located in plan <br />view on the Energy Mine No. 3 Surface Water Hydrology (Energy <br />Fuels Map 8). They are identified with letters which <br />correspond to the pond identification letters. LRCWE Plate I <br />shows the typical ditch section and a schedule of information <br />for the ditches. The design frequency for the ditches is <br />either 10-years or 100-years depending on whether ditch <br />overflow would cause significant problems for downstream <br />ponds. The ditches were sized to handle the peak rate of <br />runoff for the desired frequency for the tributary area to <br />the ditch. Peak flow rates were determined in accordance with <br />the SCS publication titled Procedure for Determining Peak <br />Flow in Colorado, (1977). The ditches were designed in <br />• accordance with a document titled Design Charts for Open <br />Channel Flow, published in 1979 by the U.S. Bureau of Public <br />Leonard Rice Consulting Water Engineers. Inc. <br />