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n LJ a different channel slope. The entire length of the ditch is designed as a triangular shaped, vegetated channel with 2N:lY sideslopes. The design flow to Sections A, B and C is equal to 2.2, 3.6 and 4.8 feet per second, respectively. Therefore, no erosion protection is required. However, rock riprap (D50 ~ 8 inches) will be placed in Section C where it joins with the north collection ditch to prevent erosion at the channel bend. The riprap will be placed to an approximate depth of 18 inches along the channel bottom and sideslopes. Appropriate bedding material will be placed and spread prior to riprap placement. Design details for each channel section are summarized by Figure 3. Design Detail - Refuse Collection Ditches. North Refuse Collection Ditch The north refuse collection ditch extends along the northern toe of the refuse storage pile. This ditch collects all surface drainage flowing • off the north slope of the pile, in addition to flow contributions from the west collection ditch, and conveys it to Sediment Pond 4. The north collection ditch is divided into three (3) sections as shown on figure 1, Refuse Disposal Area Drainage Plan. Each section has the same channel slope but different channel configuration. Section A is designed as a trapezoidal channel with a 5-foot bottom width and 2H: 1V sideslopes. The channel section extends approxi~ately 750 feet at a 3.6 percent slope. The design velocity is 4.8 fps, therefore, no erosion protection is required for this section. Section B is designed as a trapezoidal channel with an 8-foot bottom width and 2N:1Y sideslopes. The channel section extends for approximately 340 feet at a 3.6 percent slope. The design velocity is 5.0 fps, therefore. no erosion protection is required for this section. Section C is designed as a trapezoidal channel with a 2-foot bottom • width and 2H:1V sideslopes. The channel section extends approximately 420 feet at a 3.6 percent slope. The calculated velocity (6.2 fps) -14-