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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />the revi sed analysi s i nfi ltrati on losses were modifi ed util i zi ng the <br />guidelines set forth in the USBR's Design of Small Dams. The drainage basin <br />was subdi vi ded into two soi 1 groups. Si xty percent was cons i dered bedrock <br />(C), with an average infiltration rate of 0.12 inches per hour, and 40 percent <br />was classified as glacial till (A-B), with an average rate of 0.32 inches per <br />hour. A wei ghted average of these rates was computed in order to deri ve a <br />constant infi 1 trati on rate of 0.2 inches per hour. Thi s is a more <br />conservati ve val ue than that resulti ng from the Green Ampt model but is <br />considered reasonable as it is based on actual records from the region <br />compiled by the USBR and the SCS. <br /> <br />The revised design flood, based on 75 percent of the PMP produced by the local <br />storm and the new infiltration rates, was used for the feasibility design and <br />had a peak di scharge of 9571 cfs, wi th a vol ume of 1022 acre-feet. The HEC-l <br />computer printout for the design flood is contained in Appendix D. <br /> <br />3.2 Flood Routing <br /> <br />The servi ce spi 11 way at Barnes Meadow Reservoi r consi sts of a 25-foot wi de <br />concrete lined overflow weir at elevation 9087, located in a saddle 200 yards <br />southwest of the main dam. The service spillway is flanked for 100 feet on <br />the 1 eft and 150 feet on the ri ght by a ri prap-l i ned auxil i ary spi 11 way at <br />elevation 9088. In addition, a 180-foot wide riprap-1ined emergency spillway <br />at elevation 9090 is located in the main dam adjacent to the right abutment. <br />Reservoi r routi ngs were performed for the exi sti ng condi ti ons and the three <br />rehabilitation design alternatives considered. All routings began with the <br />reservoir water surface at the service spillway elevation. <br /> <br />The design flood routed through Barnes Meadow Reservoir for the existing <br />conditions resulted in a peak outflow discharge of 9517 cfs, with a maximum <br />water surface of 9091.8 feet. Thus, the design flood comes within 1.4 feet of <br />overtopping the existing earth dam and dike crests, at elevation 9093.2. Even <br />though this meets the SEO's requirement of one foot of freeboard, improvements <br />are proposed to the spillways in all alternatives, as discussed in Section 4 <br />of this chapter. <br /> <br />1231 H <br /> <br />-63- <br />