Page 85


Page 85
Colorado River problem
Is Part Of,8
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390 DAVIS ON THE COLORADO RIVER PROBLEM A further comparison may be made by omitting the dam near Williams from Table 28. This produces the exhibit shown in Table 29. TABLE 29.—-Comparison of Plans—Williams Reservoir Omitted. Head, in feet. Surface area, in acres. Capacity, in acres. Davis' plan__ Author's plan. 1,290 1,310 174,000 220,000 83,100,000 25,800,000 By this comparison over the same stretch of the river, the author's plan develops about 1 1/2% more head, but owing to better regulation, higher on the stream, the speaker's plan would develop far more power. The latter would expose 46,000 less acres to evaporation, in a region where the rate of evaporation would be less, and afford more than 7,000,000 additional acre-feet of storage capacity, and, hence, would last 70 years longer; and it would not submerge the fertile Mohave Valley. It is clear, therefore, that the plan proposed by the author does not conform to the best development of the river and that it violates each of the maxims enunciated. For irrigation and flood control, the Mohave site has no advantages over the Boulder site, as there are no tributary streams between, but the Boulder Reser-voir would protect the Mohave Valley from floods, provide it with irrigation storage, and facilitate its reclamation, while a dam in Mohave Canyon would submerge and destroy that valley forever. Storage in Boulder Reservoir would be beneficial for power development at Boulder Canyon, Bulls Head, and Williams, a total fall of 820 ft., while that at Mohave could be of no benefit for power except at its own site, which is so unfavorable that none of the power companies has applied for it. Storage at Mohave, therefore, would require duplication somewhere above, for power development. Poor Rock in Glen Canyon.—The author expresses disagreement with the Consulting Board that examined the dam site above Lees Ferry in Glen Canyon and advised limiting the pressure on the rock to 20 tons per sq. ft. on account of its soft, friable character. This Board included four experienced engineers all of whom have borne the responsibilities of designing and building some of the world's greatest dams, including the Don Pedro, Arrowrock, and Roosevelt Dams, and an eminent geologist, who made a very careful examination of the site and the material. It seems rather bold for one who has made no such examination to overrule them summarily on the strength of three samples of drill cores. Any one experienced in diamond drilling knows the persistent tendency of the core fragments to grind each other to powder in the rapidly revolving core-barrel, so that the soft parts are washed out and only the hardest survive. So great is this tendency, that the recovery of 100% of core even in the hardest rock is rare.

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