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<br />20 <br />^ The total water and sediment runoff, peak discharges, peak sediment con- <br />centrations, and average sediment concentration for the 10-year design storm <br />are listed in Table 5. The average peak sediment concentration for the channels <br />in the Newlin Creek watershed is 31,100 ppm. Channel 2 has the highest sedi- <br />ment concentration and has a peak sediment concentration of 37,960 ppm. Channel <br />2 collects the eater and sediment runoff from the steep, upper part of the - <br />watershed and a high sediment concentration is expected. The sediment concen- ' <br />trations decrease going downstream. The decrease in sediment rnncentrations <br />• is due to the milder slopes in the downstream channels which reduce the ve- <br />locities and, therefore, cause aggradation. A site visit verified that the <br />L lower channels are aggradinq. At the watershed outlet, the average and peak <br />sediment concentrations are 14,630 and 24,090 ppm, respectively. The total <br />eater runoff volume at the watershed outlet is 213.5 acre-feet and the peak <br />discharge is 2325 cfs. The adequacy of the existing culvert at this location <br />is discussed in Section 6.2. <br />• 3.3 Tipple Area Drainage <br />For present-mining conditions, the Tipple Area drainage is represented by <br />Sw-13 and Sediment Pond "T". The total water and sediment runoff for SW-13 is <br />2.3 acre-feet and eight tons, respectively. Due to the compacted soil in this <br />. areas, the 10-year design storm produces an average of 1.15 inches of runoff <br />over the entire area. The average suspended sediment concentration is 2730 ppm. <br />This concentratirn is lower than that found in disturbed areas of the Xagpie <br />Creek watershed and is due to the milder slopes found in the Tipple Area. The <br />peak water discharge at the outlet of Sw-13 is 64 cfs. The adequacy of existing <br />Sediment Pond "T" is discussed in Section 6.3. <br /> <br />