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DITCH HYDRAULICS AND DESIGN <br /> Diversion ditches have been designed and will be constructed to modify <br /> natural drainage boundaries for various ponds in order to make use of <br />• favorable pond locations. The followi ng proposed ditches are located in <br /> plain view on the Mine Area Surface water Hydrology Map (Map 16A) and the <br /> Kerr Mine Area Postmining Topography Map (Map 37A): <br /> • B-3 <br /> • C-1 <br /> • C-2 <br /> • Revised F-1 <br /> • G-2 <br /> • H-lA, 1B, 1C, and 1D <br /> • I-1, 2, 3A, 3B, 4, SA, SB, and 6 <br /> • J-1 <br /> • L-1, 2, 3A, 3B <br /> • Light-Use Road Ditches 1, 4, and 5 <br /> • Clean Water Diversion <br /> • Permanent Diversion No. 1 (PD-1) <br /> • Permanent Diversion No. 2 (PD-2) <br /> • Permanent Diversion No. 3 (PD-3) <br /> • Permanent Diversion No. 4 (PD-4) <br />The majority of the ditches are designed as triangular ditches, with <br />trapezoidal ditches being used where design flow volumes or erosion <br />protection requirements dictate. All proposed ditches except the <br />Permanent Diversions are designed using either the 2-year, 24-hour or 10- <br />year, 24-hour storm. The Permanent Diversions are designed using the 10- <br />year, 24-hour storm. The Clean Water Diversion is designed using the <br />100-year, 24-hour storm. The ditches are sized to handle the peak runoff <br />from the appropriate storm maintaining 0.30 feet of freeboard. The <br />ditches will be stabilized with grass lining and design velocities are <br />kept under five (5) feet per second to prevent erosion. Riprap or <br />synthetic erosion control materials will be utilized in ditch sections <br />where velocities exceed 5-0 feet per second. <br />Manning's equation for open channel flow was utilized to design the <br />ditches as follows: <br />Q = 1,436 AR'C'S ~~' <br />• n <br />23-151-R Revised - December 1995 <br />TR -~ ~~ <br />