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Maps of Project Location <br />Figure 1 -1: Lm*d . Map of Tame* Pmervoir <br />Project Description and Alternatives <br />Figure 2: Vicinity Map of Project <br />The proposed modifications to Terrace Reservoir include demolition of the existing spillway, <br />construction to raise the existing saddle dike to the main Terrace Dam crest elevation and <br />construction of a new reinforced concrete labyrinth spillway control structure, chute, and stilling <br />basin. The new structure will be located along an alignment similar to the existing spillway and <br />will narrow from approximately 60 ft. wide at the downstream end of the labyrinth weir, to a 45 <br />— ft. -wide spillway chute. An underdrain system will be installed beneath the spillway chute and <br />stilling basin. In addition, grouted anchors will be installed beneath the labyrinth crest structure <br />slab and the stilling basin slab to resist buoyant and uplift pressures. Estimated Cost of this <br />project is $4,420,445. (See Table 2) <br />Instrumentation proposed for the Terrace Reservoir Dam saddle dike consists to 12 new <br />piezometers installed through the raised saddle dike and in the glacial till slope downstream of <br />the raised saddle dike, and six dam station markers, which will also serve as settlement <br />monuments, installed at 100 -foot centers across the dam crest. A staff gage, mounted to or near <br />the labyrinth crest control structure, will also be included in the design. The staff gauge will be <br />used to measure reservoir storage level. (See Appendix C for final plan drawings.) <br />Several alternatives were considered. <br />Alternative No. 1 — Fuse Gate System — This alternative would still require the removal of the <br />old spillway. Then dependent upon the inflow design flood numbers a determined number of <br />fuse gates would be placed where the existing spillway is located. As more and more water is <br />required to be released through the spillway, the fuse gate would trip one at a time and release <br />water down the river. The draw backs to this alternative are that the fuse gate flows down the <br />river with the water and then has to be retrieved and reset in place. The operation and <br />maintenance of this alternative would have long term recurring expenses. The total cost of this <br />alternative would not be much less than the alternative we selected. The fuse gate system has not <br />been signed off on by the State Division Engineer Office. <br />2 <br />