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• 17 III. PRESENT-MINING CONDITION RESULTS Using the data presented in the Preliminary Data Base Report and the data • adjustments presented in Chapter II, the water and sediment runoff resulting from the 10-year design storm vas determined for present-mining conditions on the Magpie Creek, Newlin Creek, and Tipple Area watersheds. In addition, the peak runoff resulting from the 25-year design storm was determined for the design of emergenry spillways for the existing and proposed sediment ponds. • The pertinent results for the 25-year design storm are presented in Section • 6.3. The NULTSED physical process model was used for these purposes. The listing of all output results for the 10-year design storm is available upon C request. This information includes hydrographs for all planes, subwatershed~and charuul units, total runoff volume for all units, sediment yield by size frac- tions for ell units, and suspended sediment concentrations during each time r increment for the channel units. The present-mining condition vas evaluated • in order to understand the response of the current system, evaluate the ade- quacy of existing structures, and provide information to design the necessary improvements. 3.1 Magpie Creek Drainage For present-mining conditions, this watershed contains three sediment ponds, two culverts, and two major diversion channels. Locations of these struMures are shown on Hydrology Map 2, Appendix A. Of major concern in the Nagpia Creek • watershed is the adequacy of these structures and channels. The total xater and sediment runoff, peak discharges, peak sediment concentration, and average sedi- ment concentration for the 10-year design storm are listed in Table 4. The average sediment concentration from subwatersheds is determined on the basis of total water and sediment yield for a storm, therefore, peak concentrations are not available. Upstream of the mine site in the undisturbed areas, the peak suspended sediment concentrations average approximately 8400 ppm. Through the mine area, the average suspended sediment concentrations increase notably in CH-15 and CH-17. Channel 15 is referred to as the "No Name" diversion channel and has . average and peak sediment concentrations of 13,130 and 14,150 ppm respectively. • Thcse sezi-e~t concentrations are approximately double that of Ch-7 which is the upstream input to CH-15. The increase in sediment concentration is pri- marily due to the steep slope and small sediment sizes within the channel.