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The aforementioned calculated changes in basin parameters that will result from mining the <br /> Nucla East area are likely expressed in reclaimed areas at the Nucla Mine. However, due <br /> to the lack of premining (before 1960's) topographic mapping at a suitable scale (1 inch = <br /> 400 feet), meaningful estimates of the premining basin parameters for the Nucla Mine <br />cannot be determined. <br />A final impact to drainage basins in both areas is the temporary loss of topsoil <br />structure. This could potentially reduce the infiltration capacity of the soil and <br />increase overland runoff. <br />In summary, impacts from mining on the local geomorphology will be long term, but appear <br />to be of minimal significance. The reestablished reach of the West Return Ditch will <br />result in a shorter, slightly steeper stream channel. The potential for increased <br />sediment loads in the West Return Ditch (once the 001 sediment pond is removed) should be <br />offset by the stable banksides and the relatively small change in overall gradient. The <br />increased runoff and consequent erosion potential on disturbed basins in either mining <br />area due to the temporary loss of topsoil structure should be of minimal significance. <br />Contour ripping, mulching and revegetation have been demonstrated to minimize soil erosion <br />• and will be used to mitigate the increased runoff potential until the topsoil structure is <br />developed. <br />Effects of Sediment Ponds on Channel Characteristics and Downstream Users. During the <br />permit period of both the Nucla Mine and the Nucla East mining areas, seven sediment ponds <br />will be utilized to impound the runoff from disturbed areas and provide for sufficient <br />detention time before any water is discharged from the ponds. Six of these ponds have <br />already been constructed at the Nucla Mine (Ponds 001, 002, 003, 004, 005 and 006, see <br />Exhibit 13-4, Tab 13). The seventh pond, 007, will be constructed near the southern <br />boundary of the Nucla East mining area (see Exhibit 13-5). Impacts to the channels as a <br />result of these ponds are expected as follows. <br />The ponds that collect flow from larger drainages dominated by irrigation tailwater (001, <br />006 and 007) wt 11 eventually reach an equilibrium with water gains (inflow) and losses <br />(seepage, evaporation and discharge). Channel reaches immediately below these ponds will <br />become incised with smaller, actively meandering channels whose geometries will be a <br />• function of reduced runoff potential, channel gradients and sediment load particle size <br />ranges. Vegetation will begin encroaching on the edges of the new active channels as <br />there will be insufficient runoff to remove it. <br />17-76 Revised 04/11/88 <br />