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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />1 <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I, <br />I <br />I <br /> <br />C.2 Formed Concrete vs. Roller Compacted Concrete <br />The dimensions of Plan C-3 are used for a basis of comparison between a formed concrete <br />spillway (Plan C-3a) and a stepped RCC spillway (Plan C-3b). Hydraulic calculations show that <br />velocities on a 2.25: I formed concrete chute, using n=0.008 (Design of Small Dams, pg. 384), <br />would be approximately 52.6 feet per second, for a discharge of 7,625 cfs and width of 95 feet <br />converging to 70 feet (Plan C-3a). The depth of flow entering the stilling basin would be <br />approximately 1.9 feet and the Froude number would be approximately 6.7 The conjugate depth <br />for determining the depth of the stilling basin would be 17.2 feet and the stilling basin (assuming <br />USBR Type II Basin) would be 72 feet in length. The longest basin which will fit within the <br />property is about 55 feet. The physical restriction imposed by the Company's property on the size <br />of the stilling basin makes the use of formed concrete less desirable. Dam safety could still be <br />adequately provided with the shorter stilling basin, but downstream hydraulics would not be <br />optimal. Before dismissing this option because of the stilling basin length requirement a cost <br />estimate was made. If the cost is favorable compared to other alternatives a formed concrete <br />spillway could be feasible. Table V-I shows that Plan C-3a using formed concrete would require <br />a budget of approximately $594,500. <br /> <br />For the same flow on a stepped RCC spillway the velocity (using n=0.033 per the USBR <br />McClure Dam modeling results) would be 42.5 feet per second, the depth entering the stilling basin <br />would be 2.4 feet, the Froude number would be 4.88, the conjugate depth would be 15 feet, and the <br />Type II stilling basin length would be 58.5 feet, much closer to the space available. The hydraulic <br />characteristics of the RCC spillway make it more technically feasible for this site than the formed <br />concrete spillway. As will be discussed in a later section the cost of Plan C-3b using roller <br />compacted concrete is also less than the same configuration constructed of conventional formed <br />concrete. For these reasons roller compacted concrete construction is more feasible than <br />conventional formed concrete construction for this alternative. <br /> <br />28 <br />