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TABLI? t. <br />- ~ DMG APPROVED SCS CURVE NUN113ERS . <br />COVER COVER TYPE HYDROLOGI PERCENT HYDROLOGIC CURVE <br /> C ~ COVER SOIL GROUP NUMBER <br /> CONDITION <br />Undisturbed Mountain Good 85 C 41 <br /> Shrub <br /> Oak-Aspen Good 85 C 41 <br /> Sagebrush Good 85 C 47 <br /> Sagebrush Fair 50 C 63 <br />Disturbed Topsoil Bare N/A C 91 <br /> Stripped <br />Reclaimed Topsoiled and Bare N/A B 86 <br /> Seeded <br /> 1 to 2 Year Fair -Good 85 B 61 - 58 <br /> Growth <br /> 3+ Yaar Fair -Good 85 B 56 - 48 <br /> Growth <br />Sources: SCS TR-55 Urban Hydrology for Small Watersheds June, 1986 <br />SEDCAD+ Version 3.1 Users Manual <br />Agreement between DMG and Colowyo Hydrologists <br />1.9 BASE FLOW <br />Abase flow of 0.]5 cfs was used for the Streeter Pond design. Abase flow of 0.03 cfs was used for the <br />West Pit Pond design. Base flows were not used in any other pond design calculations. Discharge of <br />collected water from the open pits, as a result of pumping, will not be permitted during a storm event equal <br />to or greater than the 10-year, 24hour storm event. <br />2.0 SEDIMENTATION CALCULATIONS <br />The sedimentation calculations for each pond on the Colowyo Mine were performed using the SEDCAD4 <br />Computer Modeling Program developed by CivIl Software Design. The SEDCAD4 Computer model is <br />based on the Revised Universal Soil Loss Equation (RUBLE). The input parameters used in the <br />sedimentation analyses are presented in the following sections. <br />2.1 RAINFALL FACTOR, R <br />A rainfall factor of 19 was used for the Colowyo mine site. This factor is consistent with other recent <br />erosion analyses performed for the Colowyo Coal Company. <br />Exhibit 7 3 Revision Date 10/23/03 <br />Revision No. TR-56 <br />