Construction

Low dam

On July 16, 1933, a crowd of 3,000 watched the driving of the first stake at the low dam site, and excavation soon began. Core drilling commenced that September while the Bureau of Reclamation accelerated its studies and designs for the dam.^[22] It would still help control floods and provide for irrigation and hydroelectricity, though at a reduced capacity. Most importantly, it would not raise its reservoir high enough to irrigate the plateau around the Grand Coulee. However, the dam's design provided for future raising and upgrading.^[18]

The east-side cofferdam after the west base was complete

Before and during construction, workers and engineers experienced problems. Contracts for companies to construct the various parts of the dam were difficult to award as few companies were sizable enough to fill them. This forced companies to consolidate. In addition, Native American graves had to be relocated and temporary fish ladders had to be constructed. During construction additional problems included landslides and the need to protect newly poured concrete from freezing.^[17] Construction on the downstream Grand Coulee Bridge began in May 1934 and more considerable earth-moving began in August. Excavation for the dam's foundation required the removal of 22,000,000 cu yd (17,000,000 m³) of dirt and stone.^[23] To reduce the amount of trucking required in the excavation, a conveyor belt nearly 2 mi (3.2 km) long was built.^[24] To further secure the foundation, workers drilled 660–880 ft (200–270 m) holes into the granite and filled any fissures with grout, creating a grout curtain.^[25] At times, excavated areas collapsed from overburden. In order to secure these areas from further movement and continue excavation, 3-inch (76 mm) diameter pipes were inserted into the mass and chilled with cold liquid from a refrigeration plant. This froze the earth and secured it so construction could continue.^[26]
Final contract bidding for the dam began June 18, 1934, in Spokane, and four bids were submitted. One bid was from a lawyer with no financial backing; another was from actress Mae West which consisted of nothing more than a poem and promise to divert the river.^[27] Of the two serious bids, the lowest bid was from a consortium of three companies: Silas Mason Co. from Louisville, Kentucky, Walsh Construction Co. of Davenport, Iowa and New York and Atkinson-Kier Company of San Francisco and San Diego. The consortium was known as MWAK and their bid was $29,339,301, almost 15% lower than the $34.5 million option submitted by the next bidder, Six Companies, Inc., which was building Hoover Dam at the time.^[28]

Cofferdams

Two large cofferdams were constructed for the dam, but they were parallel to the river rather than straddling its width, so drilling into the canyon walls was not required. By the end of 1935 about 1,200 workers completed the west and east cofferdams. The west cofferdam was 2,000 ft (610 m) long, 50 ft (15 m) thick and was constructed 110 ft (34 m) above the bedrock.^[29] The cofferdams allowed workers to dry portions of the riverbed and begin constructing the dam, while water continued to flow down the center of the riverbed.^[30] In August 1936, once the west foundation was complete, portions of the west cofferdam were dismantled, allowing water to flow through part of the dam's new foundation. In February 1936, MWAK had begun constructing cofferdams above and below the channel between the east and west cofferdams. By December, the entire Columbia River was diverted over the foundations constructed within the east and west cofferdams. On December 15, 1936, the Wenatchee Daily World announced that the river was diverted and by early the next year, people were arriving in large numbers to see the riverbed.^[31]