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<br />/"", n ."\. ~., <br />tJJJ, <br /> <br />reservoIr area near the right abutment of the dam. It also appears most of the material <br />could be borrowed below the joint-use pool. <br /> <br />DECEMBER 1977 INSPECTION <br /> <br />Our Inspection of the damsite and vicinIty was made on December 6, 1977. The <br />weather was cold and partly cloudy. A thin mantle of snow was present over the area, <br />but it was lnsufflcient to ObSCW"8 significant detans. The In.spection party consisted of <br />Messrs. C. W. Griffin, N. E. Bennett m. J. M. Walker and G. Rappl for USER, and <br />lndependent consultants Howard A. Coombs, George F ~ Sowers, :md Thomas M. Leps. <br />The party drove to various points of interest on the North and South abutments, ranging <br />from the spillway area on the North to Bijou No. 2 Reservoir on the South. It viewed <br />backhoe e....cavation of a shallow test pit in the proposed core borrow area on the north <br />side of the river. It made a brief aerial reconnalssance of the damsite and nearby reach <br />of the dver, using the USER airplane. The party was unable, because of rep:lrted prob- <br />lems In obtaining ()1.vner approval, to visit the river bottom area along the proposed dam <br /> <br />a.""I:is. <br /> <br />In our judgment, the inspection was adequate to provide us with the follOWing <br />general. lmpressions relative to the design of Narrows Dam. <br />1. The damsite topography 1s gentle and rolling. except for modest bluffs adja- <br />cent to the main river bed. <br />2. The required axis length of the dam is UDcommonly long (over 4 mi.), with <br />the important consequence that exposure to the problems of foundation defects is rela- <br />tively great, and abillty within economic limitations to discover such defects Is rela- <br />tively small. . <br />3. All surficial materials along the dam axis, Including the weathered Pierre <br />slltstone. to the North, and the Bijou E1at nllruium and aeolian sands to the South are <br />highly erodible. <br />4. No evidence of firm, massive Pierre Shale was seen. in outcrops to the North <br />of the river, but samples of such material taken from drill holes at depth were viewed <br />. in the USER laboratory. <br />~J 5. None of the borrow material pointed out to us as potential pervious shell fill <br /> <br />S. <br /> <br />- ..:"\ <br />