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<br />(reestablishment) of the Weat Return Di teh nes compl etnd by the early 1980'5. Table 17-42 <br />presents prams ping and postmini ng stream lengths antl 9radi enta of the West Return Ditch, <br />The reestablishment of the affected West Return Di teh reaul tetl in a postmi ning stream <br />source featurt ng fewor meandars.~ The reeatabiished channel reach Ts apDroxf mately tt <br />percent shorter than bafora mining began. However, the postmi ni ng gradient of the <br />affected reach is .007 ft/ft less steep, Folloning the rmwvat of the 001 pond (after <br />cessation oP mining at the Nycla HS ne), the overall grad Sent oP the West Return Ditch will <br />be only slightly higher than the premining gradient. The design of the reclaimed channel <br />reach of the West Return Oitah, in eombi nail on with the reclamation (topsoil replacement <br />and revegetatTon) of the channel banks, wf 11 largely offset any potential sadfmant load <br />i ncreeses due to the alight increase in channel al ope. Historic mm~i tors ng conducted Sn <br />this channel at Stte SN-N6 has shown no trends toward ~elavated concen troll ono of total <br />suspended solids (see Appendix 7-7). The monitoring conducted at this si to sS nee 1980 <br />iMieates that thfs channel hoe aeabtlized wf Ch regard eo addi ttonal contrS butt ono of <br />suspended sediment. <br />Impacts to the drat nags 6asi ns at both the Nucia Mine and Nucla East mining area include <br />• ~ N~engea fn watershed areas, alsvati ono, slopes, slope lengths and temporary loos of <br />topsoil structure. <br />Tabla 17-23 contains select basin parameters calculated usS ng both the pre- and poafmining <br />topography for tho watershed above the proposed 007 sediment structure in the Nucla East <br />mining area (see £xhi bi is 17-1 and 17-2), It ahwld be noted that the small portion of <br />Lfie Nucla East area that wt 11 be drat nod by the diversion was not included in the <br />cal wlattons. Descriptions of the methods used to determine the basin parameters can be <br />frond in the subsequent section of this Tab {Stied "Effects of Runoff from Roci si mad Areas <br />on Me Quantity of Streamf low^, <br />The data presented to Table 17-23 chow that mining and reel smolt on of the Nucla Eui Brea <br />Hill rasuli in almost a 7 percent increeee in area for the watershed above the 007 pond. <br />Also, the average watershed slope Length M77 increeae by about 27 percent. Average <br />watershed slope nTll be decreased by approximately 18 percent. Time of eoncantrati on, a <br />measure of the time it takes for runoff to travel from the most di slant basin point to the <br />basin outlet, ntll be increased by about 32 percent. As a result of mining, the overall <br />elevation of the Nucla East area will decrease slightly. <br />17-73 Revised 04/ll/88 <br />l/1 <br />l J <br />REVISED MARCH 2006 Attachment 2.05.6(3}2-84 <br />