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<br />Woodward.CIyde Consultants <br /> <br />r,C1C14 <br />t:.V0 <br /> <br />level will decrease the head difference and reduce the average <br /> <br />gradient. <br /> <br />We believe that consideration should be given to the <br /> <br />following redundant features to minimize risk of unsatisfactory <br /> <br />performance during high reservoir water ~els assuming first <br /> <br />that the relief wells do not operate~~ ~ed and secondly <br /> <br />that there might be "windows" in thO'~~~' or gulleys <br /> <br />in the bedrock, not reaCheable~r ecognizable d~ing the <br /> <br />trench excavation. <br /> <br />(1) We recommend that ~ ~ gr~~'ent in the area of the ynd <br />of the slurry cutdff'b~d?creaSed, by (a) continu- <br />ation of the slurry~ren to reduce the average <br />gradient to 0.1 (wate~~e~b at point of water <br />entrance divided by the a~taqce of travel through <br />prev,ious soi~o~b) place~ent of an impervious <br />blanket of c~~~mpaaa~e~'~beneath the upstream <br />pervious zone OJ\,f~ d,a~tween about Stations 235 <br />and 195, and e ~e~ng the upstream blanket. <br /> <br />(2) We reco~~d CO~~'d~ation of an underdrain system <br />downst7eam ot the ,am where needed. A practical <br />appr9~c ~utd appe to be placement of observat,l'on <br />wel s ~ong t!-h~t~ of tht; dam a!~os<:....~p_a..sJ.!!9,__wjth__ _ . _._ <br />__ _ _ _ _ _ _ _ _ _ jllO t.9r:in.if- c:'ha.r~..::J1eser\70Tr-fi-n lng, then placement <br />-- --- '. of ~~Je'ils or underdrain system at the location <br />wher see~ge problems become evident, if any. <br /> <br />4. Revi.e~l'\\.rr ~nch <br /> <br />) fr ~p~o , an excellent cutoff can be constructed, as <br /> <br />plann ~he ;t~ht abutment utilizing a slurry trench cutoff <br /> <br />below the orm&l cutoff trench as shown on the Bureau drawings, <br />... <br /> <br /> <br /> <br /> <br />extending the slurry trench or an <br /> <br />upstream blanket. Such a cutoff is contingent upon carrying <br /> <br />the slurry trench into competent pierre formation materials, <br /> <br />- 25 - <br /> <br />fI <br />