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<br />• <br />(see Map 2.05.4-2) will be restored to its original condition and approximate location as specified by <br />agreement with Montrose County (see Peabody Tab 13, Attachment ~. <br />Postmining Drainage Channels <br />All major drainages in the New Horizon 2 area that are to be disturbed by mining activities will be <br />reclaimed to approximate the premining configuration and to blend with the undisturbed drainage <br />above and below the area to be reclaimed. In the amendment area, no distinct channerls are <br />encountered and none will be restored. The postmining drainage channels will be designed, <br />constructed, and maintained to the following specifications: <br />1. Gentle sloping banks which shall be stabilized by vegetation; <br />2. Prevent additional contributions of suspended solids to streamflow and to runoff <br />outside the permit area; <br />3. Blend with the undisturbed drainage above and below the area to be reclaimed; <br />. 4. Safely pass the runoff from a 10-year, 24-hour precipitation event. <br />The reclaimed drainages are designed to safely pass the 10-year, 24-hour precipitation event and to <br />be stable. The peak flow was determined by using the SEDCAD+ Version 3.0 computer program. A <br />listing of the input parameters for obtaining the peak flows for the reclaimed drainage channels are <br />attached. The peak flow determination assumed the total watershed of the reclaimed channel and was <br />determined at the downstream end of the channel. Most of the reclaimed channel reach will not have <br />to handle that large a peak flow rate. This was done to ensure that the drainage channel capacity will <br />be adequate and conservatively designed. <br />A limiting permissible velocity of 5.0 feet per second (fps) was used to insure that the postmining <br />drainagechannelswould be nonerodibleandstable. The permissible velocity was obtained, Table 3.4, <br />from "Red Book" by Barfield et al., 1981 for a grass mixture vegetated channel. The shape of the <br />reclaimed channel was assumed for design purposesto be trapezoidal with 10h:1 v side slopes as a <br />worst case condition. The side slopes will be no steeper than 10h:1 v. <br />(REVISED 9/99) <br />2.05.4(2)(c) - 7 <br />