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<br />Dm~ = 0.9 feet <br />D50 = 0.75 feet <br />D1o 0.25 feet <br />Riprap must be well graded, angular in shape, and of excellent <br />durability. The installation must be keyed in at the top and the <br />bottom of the channel. Rip-rap installation at the upper end of <br />Section B must extend a minimum of 15 feet along the native <br />channel. The junction between Sections B, C and D should provide <br />riprap to length of 15 feet along Channel C. Section E should be <br />riprapped such that rip-rap extends into the Magpie Channel and <br />upstream along the Magpie Channel for distances of 15 feet. The <br />channel junction angle between the major diversion and the natural <br />stream channel shall be no larger than 45 to 55 degrees (Figure 7). <br />A filter layer of gravel shall be installed beneath the riprap <br />layer. The layer should be a minimum of nine inches (9~~) deep and <br />a thickness of 10 to 12 inches. The filter layer gradation should <br />be as follows: <br />Dm~ = 3 inches <br />D20_90= 3/4 inch <br />DZO = ~4 mesh <br />Total channel dimensions given above are those dimensions at the <br />rock surface. The rip-rap must be installed over the entire cross <br />section. Please see Figure 8 for ditch profile. All junctions <br />must be properly keyed in place 3 feet deep, for a 5 foot long key <br />length. <br />No additional disturbance shall occur beyond the existing <br />disturbance in the natural drainage. The existing portion of the <br />lower diverted natural drainage shall be backfilled with the <br />adjacent stockpiled material and blend in with the existing <br />topography. The embankment from the outfall of the ditch shall be <br />cut to a 2H:1V slope. All regraded slopes shall be revegetated in <br />accordance with Task 7. <br />m:\coal\esc\gec\fd1AA <br />