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Section 2 <br />Drainage Contra/Design <br />CDM used the UDFCD Drainage Criteria (UDFCD 2005) to calculate flow velocity to <br />determine the appropriate channel lining for the diversion channel. UDFCD (2005) <br />recommends flow velocity be less than 5 ft/sec for grass-lined channels and less than <br />12 ft/sec for riprap channels. Based on these recommendations, a Manning's n value <br />of 0.035 was selected for design calculations to check the capacity of grass-lined <br />channels. <br />The calculated channel depth and velocity of the diversion channel are shown in <br />Table 2-3. CDM recommends adding 2 feet of freeboard to the calculated flow depth <br />to account for potential channel overtopping. 'T'herefore, a design depth of 3.5 feet is <br />recommended for the diversion channel. Based on UDFCD criteria, CDM <br />recommends grass-lined channel for the diversion channel since the flow velocity is <br />less than 5 ft/ sec. <br />As noted on Exhibits A and B, a roadside channel exists along the north side of <br />County Road DD19. CDM recommends that Denison complete a field inspection to <br />confirm that the current channel configuration satisfies the minimum design criteria <br />(e.g., channel depth is greater than or equal to 3.5 feet and the side slope is milder <br />than or equal to 3H:1V). If the dimensions of the existing channel do not meet these <br />criteria, Denison will modify the channel to satisfy the channel configuration as <br />illustrated in Exhibit A. <br />Table 2-3 Calculation Summa for Diversion Channel <br />h Freeboard Design Depth V <br />N ft ft ft/sec <br />1.29 2 3.29 3.71 <br />2.4.2 Berm Design <br />CDM designed earthen berms to capture and retain surface water runoff from Basins <br />2 and 3. Runoff in Basin 2 will be captured by a berm along the crest of the DRA. <br />Runoff in Basin 3 will be captured by a berm along the toe of the DRA (refer to <br />Exhibits A and B). The berms were designed to contain runoff from the 100-year, <br />24-hour storm event. The point precipitation frequency estimate for the 100-year, <br />24-hour storm, obtained from NOAA Atlas 2, Volume 3 for Colorado (NOAA 1973) is <br />3.0 inches (refer to Appendix B). CDM used the SCS runoff equation to estimate <br />runoff from the 3.0 inches of rainfall. The SCS runoff equation is: <br />(P - 0.2SY <br />Q- (P+0.sS) <br />where: <br />Q = runoff (in) <br />P = rainfall (in) <br />S = potential maximum retention after runoff begins (in) <br />2-3 <br />am <br />7:(84986-Denison Mines%Task Order 1 - Sunday Mines Drainage StuCMVan 4 Mine Drainage Study\ReporttVan4 Mine Drainage Report_ inal.d-x