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1 <br />- B - <br />' A second alternative also shown in Figure 3 is to con- <br />' struct a low berm across the fill as described above but <br />provide a drop inlet and pipe drain. <br /> Drainage Requirements During Later Mining Stages <br /> The facilities described in the preceding section will <br />' adequately protect lower areas as long as the access road to <br /> the south quarry is in place. The quarrying operation is <br />' expected to reach the elevation when the road must be removed <br /> by about the year 1990. <br />' At this point there are two options. The first is to con- <br /> struct a channel diversion around the completed mining area <br /> capable of conveying the 100-year flow of Strain Gulch. A <br /> drop inlet will be constructed near the upper end of the <br /> operating area but below the quarrying area. To get the 100- <br />t year discharge into the drainage system a berm 9 feet high is <br /> required to ensure all of the floodwater gets into the drain- <br />' age inlet. An alternate method is to complete the north area <br /> of the quarry to its final elevation while the access road is <br />' still blocking flow down the canyon. This area would then <br /> serve as a flood detention reservoir and Strain Gulch could be <br />' diverted into it. An open channel outlet or extension of the <br /> pipe drainage system will be provided to the existing under- <br />' ground system as schematically shown in Figure 4. <br /> No change is required at the east end of the operating <br />' area fill. <br /> AFTER MINING <br />' <br /> Gravel mining is expected to extend over a period of 50 <br />' years. It is not possible to identify specific drainage needs <br /> for the area after reclamation until an after use plan has <br /> been firmly established. While some alternative after uses <br />' are included in the Thorne report of 1972, it is assumed at <br />1 <br />~(~ Leonard Rice Cc^s~,~~^~ Watz~ Er; aee•s.!sc "' _ z ~~ - « _ _ <br />