The Boulder Dam

Abstract

A LECTURE on the remarkable engineering achievement, known as the Boulder Dam, across the Colorado River about thirty miles south-east of Las Vegas, Nevada, where the river forms the boundary between the States of Nevada and Arizona, was delivered to the Institution of Civil Engineers on April 15 by Mr. John Lucian Savage, chief designing engineer, Bureau of Reclamation, United States Department of the Interior. The Dam has already been referred to in NATURE (Feb. 9, 1935) and the leading particulars will be given in one of a series of articles on “Water Power Developments in the United States”, already prepared and awaiting publication. Mr. Savage's lecture was a very detailed account of the engineering features of the undertaking and of the constructional methods employed. It is interesting to note that the four diversion tunnels for the river (which were a necessary provision at the outset of operations) each 56 ft. diameter bore and 4,000 ft. long, were driven through unusually sound monolithic rock, with the result that 1,500,000 cubic yards of excavation in the three miles of tunnel were removed without the use of timbering or roof supports of any sort. “The ideal character of the andesite breccia rock for tunnelling purposes, as evidenced by this record, is one of the marvels of Boulder Dam.” The reservoir behind the dam, called “Mead Lake” in honour of the late Dr. Elwood Mead, has a capacity of 30,500,000 acre-feet, of which 9,500,000 acre-feet has been reserved for flood control. This volume of flood storage, combined with the 520,000 cusecs (cubic feet per second) of flood discharge capacity, provides for an estimated inflow into the reservoir of nearly a million en sees without overtopping the dam. This extraordinary provision for inflow is made in view of the remote contingency of the failure of an upstream dam.