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alternative which involves increasing the normal pool level would require strengthening and <br />raising the ditch banks and probable relocation of the inlet canal to shorten its length, which <br />would effectively raise the canal invert elevation at the dam. <br />3.1.4 Outlet Works <br />The operator floor level and catwalk on intake tower are set at the elevation of the dam crest, <br />3715.0. The design head for the outlet gates and op:etators is 55 feet, which equals to a <br />water level of 3738. A significant increase in the reservoir storage level would require the <br />raising of the outlet tower platform, extending the- gate operation shafts and possible <br />replacement of the gate operators. The outlet gates would not4equire replacement. Raising <br />of the Dam 4 embankment would require extending the outlet works- conduits downstream, <br />and construction of a new outlet terminal structure. <br />Delivery of water to the wetlands and Little Jumbo Reservoir below Dam 1, and release of <br />storage from new dams constructed downstream from existing dams must also be addressed <br />as part of rehabilitation. <br />3.2 Geotechnical Concerns <br />3.2.1 Seepage <br />Seepage is a known and accepted feature of this reservoir. However, raising of the reservoir <br />from the current level will increase seepage and there would be increased concerns of piping <br />and stability through the embankment and especially through the foundation. The Dam 2 <br />failure in 1910 was due to excessive seepage, and subsequent geotechnical studies indicate <br />the upper portions of the bedrock is pervious and may be subject to piping under the increased <br />storage head. This would indicate that excessive pore pressure build -up in the upper portion <br />of bedrock foundation could be causing erosion and instability. <br />3.2.2 Foundation <br />The depth of the foundation pervious zone is not known, and seems to vary. For the purposes <br />of this study, the upper 5 to 10 feet of the siltstone bedrock is considered to be pervious and <br />Zreports \97- 1- 500.nk <br />