Laserfiche WebLink
ditches, and culverts. A copy of the computer program's input and output file information has been <br />included in each sedimentation pond design report. • <br />The input includes precipitation amount linchesl, watershed area lacresl, time of concentration Ihoursl, <br />runoff curve number ICNI, representative particle-size distributions of the soil types in the watershed, <br />sedimentology information, and spillway information, etc. <br />The precipitation amounts for the Seneca II-W Mine for the design storm durations were obtained from <br />the NOAA Precipitation Frequency Atlas Precipitation -Frequency Atlas of the Western States Volume <br />III -Colorado, 1973, and are listed below: <br />10-year, 24-hour- 1.70 inches• <br />25-year, 24-hour- 2.10 inches <br />100-year, 24-hour 2.50 inches <br />•These amounts also include water emanating from snow cover as snowmelt in a limited period of <br />time. <br />The runoff curve number (CNI is a factor relating the amount of rainfall to the amount of runoff for a <br />given area. The soil erodibility factor 1"k" factor) is a factor of a soils susceptibility to erosion and <br />infiltration capacity. These factors are dependent upon the infiltration characteristics of the soil types <br />and the type and amount of vegetation. Tables 13-1 end 13-2 list the values of CN and "k" for • <br />different soils types at the Seneca II-W Mine. <br />The CN and "k" factor for each of the ponds is determined :rs a weighted average. The undisturbed <br />area curve number and "k" factor information is based on the vegetation and soils information found <br />within Tabs 9 and 10, respectively, of the Seneca II-W Mine Permit. <br />The sediment storage is calculated using the Revised Universal Soil Loss Equation or the Modified <br />Universal Soil Equation contained within the SEDCAD+ computer program. The spillways are <br />designed using the spillway routing subroutine program in the SEDCAD+ computer program and <br />applicable engineering procedures as described in the text of each sedimentation pond design report. <br />All sediment ponds are designed and located to capture surface runoff from upstream disturbance areas <br />and to comply with all applicable State and Federal regulations. <br />Design and as-built reports, when applicable, for the followinE~. sedimentation ponds are provided in this <br />tab: <br />• <br />6 Revised 9/98 <br />