Laserfiche WebLink
Section 5 <br />Carnation Mine <br />CDM used the UDFCD Drainage Criteria manual and calculated flow velocities to <br />determine the appropriate channel lining for Channels 1. UDFCD recommends flow <br />velocity be less than 5 ft/ sec for grass-lined channels and less than 12 ft/ sec for riprap <br />channels (UDFCD 2005). A Manning's n value of 0.035 was selected for design <br />calculations, based UDFCD recommendations, to check the capacity of grass-lined <br />channels. Based on these criteria, CDM recommends a grass-lined channel for <br />Channel 1 since the flow velocity is less than 5 ft/ sec. <br />5.4.2 Berm Design <br />CDM designed earth berms to capture surface water runoff from Basins 2 and 3. <br />Runoff in Basin 2 will be captured by a berm along the crest of the WRA. Runoff from <br />Basin 3 will be routed to and captured in the existing sediment pond (refer to Exhibit . <br />D-1). The berms and pond were designed to contain runoff from the 100-year, 24-hour <br />storm event. <br />The point precipitation frequency estimate for the 100-year, 24-hour storm, obtained <br />from NOAA Atlas 14, Volume 1 for Colorado (NOAA 1973) is 3.0 inches. CDM used <br />the SCS runoff equation to estimate runoff from the 3.0 inches of rainfall. The SCS <br />Q= (P - 0.2S)2 <br />(P + 0.8s) <br />runoff equation is: <br />where: <br />Q = runoff (in) <br />P = rainfall (in) <br />S = potential maximum retention after runoff begins (in) <br />S is related to the soil and cover conditions of the watershed through the Curve <br />Number (CN). CN has a range of 0 to 100, and S is related to CN by: <br />S = 1000 _ 10 <br />CN <br />According to the US Department of Agriculture (USDA) TR 55 report (USDA 1986), <br />the CN for bare soil of hydrologic soil group of "D" is 94. For P equal to 3.0 inches <br />and CN equal to 94, S equals 0.64 and Q equals 2.35 inches. Therefore, CDM used 2.35 <br />inches as the design runoff for the berm design calculation. <br />The total runoff volume was divided by available catchment area within the surface <br />facilities area to calculate the minimum required berm elevation of Basin 2. The <br />calculated minimum berm elevation is 1.5 feet, which includes 1-foot of freeboard. An <br />existing berm encloses Basin 2. However, CDM recommends increasing the height of <br />the existing berm, where it is less than 1.5-feet high, to the calculated minimum <br /> <br />5-3 <br />OAS4988- Denison\Task Order 1 - Sunday Mines Drainage StudMeporKFinal Report\Final Sunday Mines Drainage Report _052208.doc