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r � I <br /> This section describes the sediment control structures necessary to meet the water <br /> management design criteria during reclamation and includes two types of channels: terrace <br /> ditches and down drain ditches. The ditches have been designed to collect runoff from <br /> reclaimed areas and convey it to existing drainages. Runoff from native areas between the <br /> drainages and the reclaimed areas will collect in the down drain ditches and is included in the <br /> runoff calculations. Runon from drainages west of the quarry is also considered in the <br /> calculations. The designs for each of the ditches are based on calculated peak flow rates. Figure <br /> G-1 shows the drainage plan for the final re-sloped surface and includes the network of ditches. <br /> Terrace ditches will intercept runoff from reclaimed areas, minimizing local erosion and assisting <br /> the shedding of water off the surface. The terrace ditches have been spaced to limit slope <br /> lengths to approximately 225 feet (100 feet in elevation). This slope length is typical for the <br /> mining industry and will help reduce the sediment volume that erodes from these areas. The <br /> terraces will be built onto the slope as benches. The terrace ditches will be triangularly shaped <br /> with 2.25H:1 V and 1 OH:1 V side slopes. These ditches have gradients of approximately 2% and <br /> do not require armoring. Terrace ditches have been designed to convey runoff from the 100- <br /> year, 24-hour storm with a minimum of one-foot of freeboard. The typical terrace ditch depth is <br /> two feet. The design for the longest terrace ditch was included in the hydrologic model included <br /> in Attachment G-1. A typical cross-section for terrace ditches is shown in Figure G-2. <br /> The terrace ditches discharge to downdrain ditches. Down drain ditches have been included <br /> along the edges of the backfill slope, where a ditch naturally forms. The North Channel will <br /> convey water from the northern drainages west of the quarry and from the northern half of the <br /> reclaimed slope. The South Channel will convey water from the southernmost drainage west of <br /> the quarry and from the southern half of the reclaimed slope. The two channels combine to form <br /> the Lower Channel, which will convey runoff from the entire quarry into existing drainages <br /> downstream from the quarry. Details on the channels are included in Figure G-2. The ditches <br /> will be trapezoidal in shape with at least a 4-foot bottom width and 3H:1 V side slopes. The <br /> steep channel gradients require riprap armoring. <br /> Riprap sizing for channel armoring was determined using a combination of the SEDCAD <br /> program to determine the peak flow, the Hydraulic Toolbox program, Version 4.2 from the <br /> Federal Highway Administration, to determine the anticipated velocity for the channel, and the <br /> USACE EM 1110-2-1601 method for 2% to 20% slopes and the Simons/OSM method in <br /> SEDCAD for slopes steeper than 20%. The ditches have been designed to convey runoff from <br /> the 100-year, 24-hour storm event with no erosion and a minimum freeboard of 0.5 foot. Table <br /> G-3 shows the specifications for each of the ditches. A typical cross-section for ditches is shown <br /> in Figure G-2, and the design reports are included in Attachment G-1. <br /> Pikeview Quarry Amendment 4 <br /> 2019 <br /> G-6 <br />