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I I I I I I I I I I I I I I I I I I I structural or construction considerations. The main details of the rehabllltatlon of the dam and saddle dam are shown on Figures V-2, V-3, V-4, and V-5. The alternatives considered and shown on these drawings are discussed In Chapter 6 and In the following sections. The dam Itself wlll change very little as the alternatives primarily deal with options for the spillway and outlet works. Cost and stability analyses for flatter sections were not developed as a flatter section was not deemed necessary as IndIcated above. For the studies conducted, a small clay filled core trench approxImately ten (10) foot deep, placed along the upstream toe wIth an upstream clay blanket coverIng the entire upstream dam face, was considered to cut off any possIble seepage between the exIsting embankment flll and the foundation solis. An Inspection trench of thIs nature Is required for the main dam only. The water height against the saddle dam Is only 5 feet at normal pool and a cutoff Is not necessary. For the maIn dam, an alternative to a shallow Inspection trench was consIdered to cut off the sand layer that lies beneath the deepest portion of the dam. ThIs trench would extend from about Station 20+00 to Station 32+00 and would be approximately 45 feet deep. Due to the requIred depth, thIs cutoff would be a slurry trench excavated near the upstream toe of the dam through the sand layer located beneath the central portion of the dam. The trench would be excavated wIth a bentonIte slurry and backfilled wIth a select sand fill. ThIs cutoff Is not requIred but would reduce the seepage loss from the reservoir and would add some degree to the overall safety of the dam. This alternative will be feasIble only If adequate select fill materials can be located on site. The Investigations conducted by Chen do not IndIcate any borrow sources contaInIng materIals usable for slurry trench fIll. The cost of Imported materIals may eliminate this alternative as a vIable one. 2. Toe DraIns. A toe draIn Is recommended along the downstream toe of the maIn dam and along a portion of the outlet channel. The toe drain Is recom- mended In the area of the outlet due to the seepage whIch has historically emerged from the outlet channel slope. This seepage may be due to the sand layer In the dam foundation located below the central portion of the dam or may be due to seepage along the dam fill to foundation contact. As good practice for a modern dam, we recommended the drain be extended along the maJority of the main dam from Station 20+00 to Station 31 +00 to ensure any underseepage Is controlled. A toe draIn Is a relatively Inexpensive way to ensure stability of the downstream toe and It also satisfIes the State EngIneer's requIrement that the seepage be controlled. AddItional draInage protection Is recommended at the outlet channel due to the seepage expected If the sand layer located beneath the dam Is not cut off. A l2-lnch sand blanket placed against the natural solis wIth a 12-lnch gravel blanket covered by the rlprap and beddIng Is recommended In the outlet channel to Intercept the underseepage and resIst the potential for pIpIng. FIgure V-2 shows the blanket details proposed In the outlet channel. PAGE 10 Chlpter V - No. 6 l'eulbUlty