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Introduction <br /> The reclaimed channel design for the Nucla Mine (Area 1) was based on CMLRD regulations <br /> pertaining to diversions and conveyance of overland flow and ephemeral streams draining a <br /> watershed less than one square mile. The location of the reclaimed channel is shown on <br /> Exhibit 20-3 and depicted as profile K-K'. Please refer to Exhibit 20-5 for the profile <br /> of this channel. <br /> The postmining drainage channel is not in the same location as the premining channel. <br /> This situation occurs as a result of taking advantage of the existing pit and ramp <br /> locations. The premining channel slope was 3.3 percent. The postmining channel slope <br /> will be 1.1 percent. <br /> Design <br /> The computer program SEDCAD Version 3.0 was used in the design of the postmining stream <br /> channel. Please refer to the end of this attachment for a complete printout of input and <br /> output. The design was based on the runoff resulting from the 10-year, 24-hour <br /> precipitation event. The peak flow was evaluated just upstream of existing Culvert C-3 <br /> (under Road A-A). The channel downstream from this culvert has already been constructed. <br /> The channel design also considered the possibility that some day the surrounding area <br /> could be irrigated. The channel could potentially have to handle irrigation flow plus the <br /> runoff from the 10-year, 24-hour precipitation event. During the 1989 irrigation season, <br /> the Second Park Irrigation Ditch, which is just upstream of the reclaimed channel, had an <br /> average flow of 8 mgd or approximately 12 cfs. Therefore, 12 cfs was added to the channel <br /> design as a baseflow condition. It should be noted that this is a very conservative <br /> approach due to the fact that the entire flow would have to be diverted to achieve this <br /> condition. The water rights situation would probably preclude this from ever happening. <br /> The following represents the main input parameters for the SEDCAD computer hydrology <br /> model . <br />