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<br />n~2157 <br /> <br />3. Outlet and Penstock Structures <br /> <br />A 10-foot diameter penstock and 36-inch diameter bypass outlet will be <br /> <br /> <br />encased in a reinforced concrete structure under the dam embankment as shown in <br /> <br /> <br />figure 5. The intake for the outlet pipes will consist of a tower and four gated <br /> <br /> <br />openings. The gates will provide for emergency closure to enable inspection and <br /> <br /> <br />maintenance of the conduits. The bypass outlet will be utilized to maintain <br /> <br /> <br />downstream irrigation releases if the power plant were to be shut down. <br /> <br />4. Material Sources <br /> <br />Three major sources will be used to provide embankment materials. River <br /> <br /> <br />deposits from both upstream and downstream of the dam will be used. Through <br /> <br /> <br />selective borrowing, it is anticipated the river alluvium can provide materials <br /> <br /> <br />with properties suitable for use as core and shell zones and possibly transition <br /> <br /> <br />or filter zones. Initial permeability testing indicated, with proper selection <br /> <br /> <br />and density control, a ratio of the permeability of the sands to that of the <br /> <br /> <br />silts on the order of 10:1 could readily be achieved. The sandy gravels found <br /> <br /> <br />below the silts and sands will provide good drainage characteristics when <br /> <br /> <br />incorporated into the shell of the embankment. <br /> <br />Gravelly terrace deposits from within the reservoir basin on the north <br /> <br /> <br />side of the river and just upstream from the dam will be used for shell zones <br /> <br /> <br />and processed materials for drains and transition zones. Additional terrace <br /> <br /> <br />deposits just south of the dam and above the reservoir in Sec. 17, TIOS, R24E, <br /> <br /> <br />may be needed. The amount of borrow that might be needed from the terrace deposits <br /> <br /> <br />has not been quantified at this stage of the investigation. <br /> <br /> <br />The rock generated by excavation for the spillway, access road, outlet <br /> <br />works and power house will be incorporated into the embankment as rockfill and <br /> <br /> <br />riprap. Due to the nature of this rock, it is anticipated it will be necessary <br /> <br /> <br />to place it in compacted lifts. The permeabilities resulting from the compacted <br /> <br /> <br />rockfill are yet to be determined and will affect the design of drains in this <br /> <br /> <br />area. It is anticipated that as much as 250,000 cubic yards of rockfill will be <br /> <br /> <br />generated due to the excavation of the above-mentioned features. The remaining <br /> <br /> <br />1,300,OOO cubic yards of embankment fill will be compacted earth from the borrow <br /> <br /> <br />areas discussed above. <br /> <br />- 15 - <br /> <br />