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The time of concentration was calculated using the SCS upland method (a sub- <br />routine built into the SEDCAD model). The hydraulic lengths, drainage heights <br />and slopes were measured directly from the mine permit watershed maps. The <br />calculated T~ value for each structure is found in the SEDCAD demonstration. <br />Muskingum Routing Parameters: The Muskingum routing parameters, K and X, were <br />also calculated using the SCS upland method. The hydraulic lengths, drainage <br />heights and slopes were measured directly from the mine permit watershed maps. <br />The calculated routing values are also found in the SEDCAD demonstration. <br />Curve Number: Curve numbers (CN) were approximated based on the hydrologic <br />soil type, as well as the amount of ground cover. Approved curve numbers for <br />postmine land conditions are presented in Attachment 13-5B, Table 1, Seneca <br />II-W Curve Numbers. The values in this table were agreed upon by <br />representatives of CDRMS and SCC in conjunction with Permit Revision No. 2. <br />The following table summarizes as-built hydrology for Pond 005. <br />...,- <br />' ~ As-Built Hydrology.5ummary <br />Parameter 10-Year, 24-Hour 25-Year, 24-Hour 100-Year, 24-Hour <br />Precipitation Depth 1.7 2.1 2.4 <br />(inches) <br /> <br />Inflow Runoff Volume 1.9 4.1 6.3 <br />(acre-feet) <br />Peak Inflow Rate 14.0 36.4 57.1 <br />(cubic feet per second) <br /> <br />Pond Volume at Peak Stage 8.5 10.6 11.0 <br />(acre-feet) <br />Peak Stage Elevation 6,872.5 6,874.6 6,674.9 <br />(feet) <br /> <br />Peak Discharge Rate 3.2 12.1 20.7 <br />(cubic feet per second) <br />• <br />Sedimentology: The sedimentology sub-routine in SEDCAD was used to calculate <br />the sediment yield to Pond 005. SCC revised the as-built SEDCAD demonstration <br />to recalculate the volume of allowable sediment storage in Pond 005. With the <br />cessation of mining operations in the watershed and subsequent revegetation of <br />disturbed areas, the annual sediment yield to the pond will decrease <br />significantly. Consequently it is not necessary to maintain the excessive <br />sediment storage capacity which was used to capture the large volumes of <br />sediment generated from the disturbed and barren areas during coal resource <br />TR-59 13-3C-4 Revised 08/07 <br />removal operations. <br />