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• and Post Mining Cross-Sections. An examination of the cross-sections indicates that the post mining <br />conditions are similar to the premine conditions. <br />The above information demonstrates compliance with the requirements of 4.14.2. These post mining <br />slopes approximate the general nature of the pre-mining topography as demonstrated in 2.10.3(1). <br />Post mining Drainaoe Channels <br />All drainages that are to be disturbed by mining activities will be reclaimed to approximate the pre-mining <br />configuration and to blend with the undisturbed drainage above and below the area to be redaimed. The <br />post mining drainage channels will be designed, constructed, and maintained to the following speaficatfons: <br />1. Average stream gradient shall exhibit a concave longitudinal profile to the extent possible; <br />2. Remain in dynamic equilibrium with the drainage basin system without artificial structures; except <br />where necessary to eliminate or reduce erosion; <br />3. Provide separation of flow between adjacent drainages; <br />4. Safely pass the runoff from a 10-year, 24-hour precipitation event; <br />• 5. Designed for long-term stability of the landscape; <br />6. The reconstructed drainage channels will eliminate or reduce the severity of nickpoints to the extent <br />possible. <br />The locations of the postmine channels are shown on Exhibit 20-2, Post~llining Topography, the <br />cross-sections on Exhibit 20-2A, Pre-Mining and Post-Mining CrossSections, and the longitudinal <br />Profiles on Exhibit 20-2B, Post-Mining Channel Profiles (2 sheets} The reclaimed drainage channels <br />are designed to be stable and safely pass the 10-yr./24-hr. precipitation event. The designs are <br />based on peak flows calculated by SEDCAD4 software program. The resulting type of channel (i.e., <br />vegetated or ripraPPed) is based on channel slope and velocity. Tab 13 contains the methodology <br />used in determining peak flows and the input parameters for design. <br />The limiting velocity is estimated from the tables listed in SEDCAD4 based on a vegetated channel <br />using a grass mixture as the vegetation type. The shape of the reclaimed channels aria assumetl to <br />be trapezoidal with 3H:1V side slopes as a worst case condition. Side slopes are no steeper than <br />3H:1V. <br />LJ <br />p12-02 8 Revised 10/05 <br />