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• Channel Designs The surface water diversion dimensions were determined using Mannings Equation for open channel flow. All channels will be either gravel- or vegetated-lined channels. If flow velocities exceed 6 feet per second, the channels will be lined with riprap or erosion will be controlled with the use of rock check dams. Channels will be designed with a 0.3 foot freeboard. For channels where rock check dams or straw bales are installed, a 7 foot freeboard was added to the design depth. The Elk Creek postmine channel will also be designed with a 1 foot freeboard. Riprap sizes were deteanined using Pader, OSM or limiting velocity methods. Given the uncenainry in determining riprap sizes for steep grades, a factor of safety of 3 inches was added to the riprap Ds~, designed using the Pader method. The limiting velocities were determined from the "Erosion and Sediment Pollution Control Program Manual", Bureau of Land and Water Conservation, Pennsylvania. The limiting velocities are shown in the channel design section. The Elk Creek channel was designed using the Simons/OSM method which includes abuilt-in factor-of-safety. Riprap will consist of durable rock, resistant to weathering, with a uniform gradation. This section contains design calculations for the following ditches: • Elk Creek Mine. D-Seam Portal. and Coal Refuse Facilir~Ditches Yard Ditches 1 and 2 Berm Ditch Refuse Ditches Haul Road Ditch Conveyor lA Ditch East Clean Water Ditch West Refuse Pile Diversion West Refuse Ditch East Refuse Ditch Elk Creek Mine Ditches Dl, D2, D3 Upper, D3 Lower, D4, DS Upper, DS Middle, DS Lower, D6, D7, DS Upper & D8 Lower. IIW-2, IIW HR Upper, IIW HR Lower, IIW Clean Water Diversion, Bench Channel In addition, this section contains the design calculation for the following postmine temporary and permanent ditches and channels: • Substation 3 Channels SS-], SS-2, SS-3, & SS-4 TR-43 Revised September ?003