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.. M <::> M :;HAPTER II DESIGNS AND ESTIiIfATr1: -..J at the reservoir outlet pipe. When used for diversion during constructioL, the tunnel could discharge l,OOO second-feet. For diversion a coffer dam would be built to elevation ,,875 feet, Spillwa~. An uncontrolled side channel spillway, shOwn in the drawing on the preceding page, would be located on the left abutment of the dam. The spillway would be a concrete-lined structure, 7~0 feet long. The upstream portion would have a base width of 20 feet and side slopes of l/2 to 1, The channel width would gradually increase to 60 feet and side slopes would reach a vertical position at the stilling basin. Under 8 feet of head, the spillWaY cculd discharge l2,aOO seoond-feet. A stilling basin, lOa feet long, would receive discharges from both spill- way and outlet structures. :Cavie Ditch Davie ditch as reconstructed fOr project development would have an initial capacity of 18 second-feet. The canal, about 6 miles in length, would include 30,700 feet of earth section, two tunnels with a total length of 340 feet, a concrete flume 86 feet long, and a siphon nearly 700 feet long. The earth section of the main ditch would have a base width of 4 feet and side slopes of .It to 1. Normal water depth would be 1.6 feet, but 2 additional feet of depth would be allowed for free- board. The first mile of ditch would require heavy rock excavation but the remainder would require common excavation. The tunnels, only existing canal structures that would be used, would be cleaned and lined. A third short tunnel would be replaced by an open cut. CUlverts, waste- ways, turnouts, and bridges would be provided as required. Water would be delivered to Davie ditch at elevation 5,900, l8 feet above the reservoir dead storage level, through a riser pipe connected to the outlet works. Energy required for p1.llnping during low reservoir stages would be provided by a direct-connected turbine. The turbine would be motivated by 30 to 4~ second-feet of water released to lower Rifle Creek lanC.sunder a 57-foot elevation head. Near its terminal Davie ditch wculd be divided into two branches, each with a capacity of 10 second-feet. Small distribution lat erals also wculd be proVided. ',! Grass Valley Canal The present Grass Valley Canal would be utilized, but considerable rehabili tati on and new construction would be required. The canal would have a capacity of ,0 second-feet from its head at East Rifle Creek to its terminus at Harvey Gap Reservoir. To prevent ercsion of the earth section now experienced, drops or checks would be provided to reduce the velocity of flow in places of excessive slope. , ., 14