OCR

1940 Bonneville Dam - As construction at Hoover Dam drew to a close, the focus of dam-building activities shifted to the Columbia River, 40 miles east of Portland, Oregon. Here Bonneville Dam was built for the Army Corps of Engineers by Columbia Construction Company, The powerhouse was built by another association of contractors. Though by no means equal to Hoover in magnitude, Bonneville posed many problems, At the dam site the river is divided into two channels -- the north, or main channel, where the dam was built, and the south channel, which now contains the powerhouse. The broad river, equal in volume to the Colorado at flood, was 60 feet deep, with velocities up to 12 feet a second. Floods swept through the Columbian Valley in the spring and early summer months as melting snow in the hinterlands swelled the river out of its banks. The stream was so swift and deep that some had doubts that dam foundations could be anchored safely. Taming the river to dewater the dam site required an unparalleled coffer- damming operation. The river was diverted by sinking wooden cribs to the bottom, and filling them with river silt by Clamshells mounted on barges. The cribs were then firmly anchored and sealed by sheet piling and the area unwatered with pumps. As the river bed was dried in sections, 6,000,000 cubic yards of earth and rock were removed to make way for the foundations. One of the chief functions of Bonneville is to maintain the desired level of water upstream for the powerhouse supply. Eighteen spillway gates are used to adjust the water level as required, to allow excess water to pass. In addition to diverting water for power production, the dam maintains a steady water level for navigation. Its power plant became the central con- trol point for distribution of electricity generated by all Federal Government plants forming the so-called northwest power pool. Bonneville, a slab-and-butress structure, 197 feet high and 1,450 feet long, was built by Columbia Construction Company, which was a joint venture group composed of Henry J. Kaiser Company (sponsor), Kaiser Company, MacDonald & Kahn, Inc., W. A. Bechtel Company, Morrison-Knudsen and Utah. The approximate cost of the project was $17,000,000. Broadwater-Missouri Dam - Located near the city of Toston on the Missouri River in Montana, this project was completed in 1940. It is a gravity type structure with a height of 40 feet and a crest length of 705 feet. The volume content of the dam is 14,047 cubic yards. The capacity of the reservoir is 42, 000 acre -feet. The purpose of the dam is irrigation. The owner of this project is the Montana Water Company and it was engineered by them also. Approximate cost of this project was $692,000.