2016-09-16_PERMIT FILE - M2016010

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�t - �o' o Transit Mix Concrete Co. of freeboard equal. The typical terrace ditch depth is two feet. A typical cross-section for terrace ditches is shown in Figure G-13. ii. Ditch Designs The designs for clean water ditches, road ditches, and down drain ditches are based on calculated peak flow rates. Ditches have been included along the edges of the overburden and fines stockpile, where a ditch naturally forms or along roads, and at the boundary between native and disturbed areas. Road ditches and clean water ditches are typically trapezoidally-shaped to maintain non-erosive velocities. The ditch side slopes are 3H:1 V, and the gradients are typically less than 10%. Riprap armoring is required in areas where ditches are constructed in unconsolidated materials, for steeper segments, and segments with high flows where the flow velocity exceeds the erosion threshold of five feet per second. Due to the site conditions, the ditches in the upper reaches of the site area and along the access road will be excavated into bedrock. Thus, no riprap will be required for these ditches. Each ditch will be evaluated on-site to determine whether bedrock provides sufficient armoring or if riprap will be required. Table G-4 presents the values assuming that no bedrock were encountered. The down drain ditches will be trapezoidal in shape with at least a 4-ft bottom width and 3HAV side slopes. These ditches typically have high grades (up to 18%) and require riprap armoring. Riprap sizing for channel armoring were determined using a combination of the SEDCAD program to determine the peak flow, the Hydraulic Toolbox program, Version 4.2 from the Federal Highway Administration, to determine the anticipated velocity for the channel, and the USACE EM 1110-2-1601 method for 2% to 20% slopes and the Simons/OSM method in SEDCAD for slopes steeper than 20%. The ditches have been designed to convey runoff from the 100-year, 24-hour storm event with no erosion and a minimum freeboard of 0.5 foot. Table G-4 shows the specifications for each of the ditches. A typical cross-section for ditches is shown in Figure G-13, and the design reports are included in Attachment G-1. Ditch CWD-3 is the by-pass ditch to convey unimpacted drainage from the upstream watershed and convey it through or around the disturbed area. Below sediment detention basin P-DET-1, the flow is conveyed in the channel. Runoff from the south flows in the channel and the runoff from the disturbed area to the east is limited by the outslope berm and the grading of the fines pad toward ditch DD-1. As the pile develops, the outslope of the pile will be contemporaneously reclaimed to minimize the sediment contributed to the by-pass channel. Hitch Rack Ranch Quarry Permit Application M-2016-010 September 15, 2016 G-15