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<br />73 <br />vegetation for initial restoration; thus, some type of channel and overbank <br />protection will be required. The Magpie Creek drainage is diverted to channel <br />unit PM{}f-10. This channel is undisturbed and will not be disturbed by G.E.C. <br />mining operations. However, by diverting the Magpie Creek drainage to this <br />~ channel, the natural flow through the channel is increased. Ho major work is <br />expected to be required on PM-CH-10. The channel will degrade somewhat initially <br />to reach an equilibrium with the Magpie Creek drainage flows. The magnitude <br />of erosion and change that will take place is not expected to upset the natural <br />hydrologic balance of the system. The channel might require some modifications <br />or added protection due to local effects and should be checked after occurrence <br />of a major runoff event. <br />[~ Channel units PM-CH-13 and PM-CH-11 have already been reclaimed and the <br />basic channel shape already exists. These channels have small peak dischages <br />I of 29 and 43 cfs respectively. The present channel shapes and slope are <br />acceptable. However, based on the hydraulic calculations, some channel protec- <br />' tion is required. <br />• The drainage channel of SW-11 presently has not been disturbed by G.E.C. <br />mining operations. The restoration of this channel is based on the existing <br />channel slope and geometry. The length of channel requiring restoration is <br />not the full length of Sw-11 and only a portion of Sw-11 drainage area contrib- <br />utes to the channel flow. The design discharge vas calculated by taking the <br />ratio of the drainage area rnntributing to the length of channel to be restored <br />to the total SW-11 drainage area, times the peak discharge for Sw-11. This <br />resulted in a 10-year, 28-hour peak dishcarge of 57.4 cfs. The existing slope <br />is 0.072 and the approximate channel geometry is trapezoidal with a base width <br />of five feet and side slopes of 4:1. <br />Channel unit PM-CH-6 is presently in a disturbed condition due to previous <br />mining activities. G.E.C. Minerals, Inc. will do limited mining in this area; <br />however, as part of their reclamation plan, they will reclaim this area. The <br />10-year, 24-hour peak discharge is 89.9 cfs. The natural channel can be ap- <br />proximated using a trapezoidal shape channel with a six-foot base width and <br />3:1 side slopes. The natural gradient through this area is 0.070. <br />Hydraulic calculations for all restored channels were calculated using <br />. Manning's eavation assuming normal deoth. The results of the hydraulic cal- <br />culations are given in Table 20. Included is the riorap size reauized for <br />channel protection. These calculations are based or. the 10-year, 24-hour <br />storm neak discharge. <br />