Laserfiche WebLink
lVurrinhri l9'1; C')'CC-.SeJinrenl ))eld Ddnnmvn'ulirnr - dArnc 3 ; <br />• 2.0 METHODOLOGY AND ASSUMPTIONS <br />The required hydrology, scdimenrology, and hydraulic calculations for Mine 3, Blocks North and South, and the <br />comparable adjacent pastureland areas were performed utilizing the SEDCAD+ computer model developed by <br />Civil Sofhvare Design. SEDCAD+ is a third generation hydrologic and hydraulic calculation model designed <br />for use un IBM-compatible computers. <br />2.1 HYDROLOGY <br />The SEDCAD+ model calculates runoff and peak Flow via a numerical modeling technique based on user inputs <br />of runoff basin information and design storm. Design storm inputs include rainfall amount and duration, <br />selection of a rainfall distribution, and convolution increment. Hydrographs are developed on a subwatershed <br />basis wi[b [he inputs of area, time of concentration, SCS curve number, and selection of one of three <br />dimensionless double triangle unit hydrograph ~itapes. This information is further discussed in the SEDCAD+ <br />Users Manual (Schwab and Warner, 1987) and in the SEDCAD+ Inputs discussion that follows. Routing of <br />hydrographs as appropriate is accomplished by Muskingum's methods. <br />Specific Hydrologic output values calculated by the SEDCAD+ model are as follows: <br />• Peak Flows (cfs) <br />• Stonn Runoff (inches) <br />• Runoff volume (acre-feet) <br />• Total Storm Hydrograph <br />• Inputs to the hydrology component of die SEDCAD+ computer model include: <br />• Precipitation Distribution <br />• Storm Duration <br />• Return Period/Precipitation <br />• Hydrograph Response Shape <br />• Time of Concentration <br />• Curve Number <br />Precipitation Distribution. A precipitation distribution is input to model the runoff hydrograph. SEDCAD+ <br />allows the user to choose between [he SCS Type I or Type ^ storms. The SCS Type 11 storm distribution was <br />selected for this demonstration. <br />Storm Duration. A storm duration of 24 hours was used for comparison purposes. <br />Return Period/Precipitation. A precipitation amount is required for the appropriate return period. For the <br />CYCC Mine 3 areas, the following precipitation value was used: <br />10-year, 24-hour event: I.8 inches <br />The precipitation value was obtained from the Precipitation Frequency Atlas of the Western United States, <br />• Volume 3, Colorado (NOAH, 1973). <br />i abondrenminc3lsedlsedmine3.doc <br />