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<br />percentage o} each soil type that will be stripped end radi st ri bated (or reestablishing <br />irrigated pasture and rangeland. <br />Natershed slope (S) and slope length (L) i+ere averaged for both conditions by measurf ng at <br />least ten slopes and slope lengths on both the pre- and postmi Wing 1:400 scale maps. 7ha <br />average Watershed al ope and length for premi ni ng conditions acre calculated to be 8.2 <br />portent antl 250,6 feat, racDacti vol y, For poctmini ng condi tiona, an average alapa oP 6,7 <br />percenE and an avarape slope length of 318.2 feet ware calcul atad. <br />Once all fnDUt Da rametera Here determined for both pre- and postni ni ng condi tt ons, Mo <br />computer files (batch input) Here constructed and run using SF~IH07 11. Appandlx 17-1 <br />conta7ns both fnDUt fil as used to e~aluata Cho effects of pre- and pastmi Wing condi ti ens <br />in the Watershed area above the proposed 007 pond on runoff and eedtmant. Table 77-28 <br />presents the results of both SIiD IMOT 11 runs using the two batch input files. Reaul to <br />include peak discharge (efs), runoff volume (acre-feat), peak sediment coneentrati on <br />(mq/7) and sediment yield (tons). <br />Poatmi of ng condi tt one reaultad in reductions Of all runoff end sediment parameters <br />• predicted by SEDIMOT 11. Peak tli echarge and runoff vol use ware reduced by 64 and 47 <br />percent. reapeeti valy. Sedimont eoncentratton was reduced by 38 percent, and a 66 percent <br />dacreeae Sn sediment yield was pretli Cted for poatmt nS ng Condtti ons. <br />The predicted decreases to ru:roff are largely due to the increased time of eoncentratton <br />resulting from laver slopes within the disturbance lima is and a slight increase to the <br />hydraulic length of the watershed raDresentative of the postmi ni rag topoy raphy. Also, the <br />lower curve number selected for postmS ping conditions roflecra the proposed reclematS on of <br />the di sturhed area, including raplacasant of adequate depths of suitable topsoil maeeri al <br />and a successful stand oP reeatabli shed vegetation. <br />predicted redueti ons in aedimenL concentration end yt old era largely due to ai gnif leantly <br />7 owar alapea (8) under postni nt ng condf ti ova. Although the alape lengths will increase, <br />reduced runoff free the lower al opss Hill result in lower sediment production. <br />Rurwff from postlaw reclaimed era es in the Nuols Hine 1Skely axhi bit similarly reduced <br />runoff and sedtmenC as predicted by SEDIMOT II for the Nucla Ease mining area. Although <br />reeatabl7 shad vegetation at the Nuela Mine is largely characterized as rangeland, the <br />17-e6 Ravt sod 04/11/88 <br />• <br />REVISED MARCH 2006 Attachment 2.05.6(3)-2-98 <br />