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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 2.10.311). <br />Post mining Drainage Channels <br />All drainages that are to be disturbed by mining activities will be reclaimed to approximate the prrj- <br />mining configuration and to blend with the undisturbed drainage above and below the area to be <br />reclaimed. The post mining drainage channels will be designed, constructed, and maintained to the <br />following specifications: - <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; <br />except 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 <br />extent possible. ~ ~ - <br />The postmining reclaimed drainages in the permit area are located on Exhibit ~20-2, Postmining <br />Topography Map. The average postmining stream gradient will be a concave longitudinal profile which <br />approximates the premining slope. The pre- and postmining drainage areas of the reclaimed channels <br />are very similar in acreage and slope. <br />The reclaimed drainages are designed to safely pass the 10-year, 24-hour precipitation event and to be <br />stable. The peak flow was determined by using the SEDCAD 4 computer model. Tab 13, Facilities, <br />contains the methodology used in determining the input parameters for obtaining the peak flows for <br />the reclaimed drainage channels, The peak flow determination assumed one year of revegetation of <br />the total watershed. The peak flow for the reclaimed drainages were determined at the downstream <br />end of the channel, so most of the reclaimed channel reach will not have to handle the estimated peak <br />flow. This was done to ensure that the reclaimed drainage channel capacity will be adequate and <br />conservatively designed, For channels requiring riprap, the CSU/OSM method was used riprap design <br />For further protection of the channel bed, a layer of Mirafi 700X geotextile fabric will be installed prior <br />to placement of the riprap. <br />TR-25 8 Revised 06/04 <br />