Design change

Base of the dam in 1938

On August 4, 1934, President Franklin D. Roosevelt visited the construction site and was impressed by the project and its purpose.^[32] He gave a speech to workers and spectators, closing with this statement: "I leave here today with the feeling that this work is well undertaken; that we are going ahead with a useful project, and we are going to see it through for the benefit of our country."^[33] Soon after his visit, Reclamation was allowed to proceed with the high dam plan but faced the problems of transitioning the design and negotiating an altered contract with MWAK. In June 1935, for an additional $7 million, MWAK and Six Companies, Inc. agreed to join together as Consolidated Builders Inc. and construct the high dam. Six Companies had just finished the Hoover Dam and was nearing completion of Parker Dam. The new design, chosen and approved by the Reclamation office in Denver, included several improvements, one of which was the irrigation pumping plant.^[32]
Roosevelt envisioned the dam would fit into his New Deal under the Public Works Administration; it would create jobs, farming opportunities and would pay for itself. In addition, as part of a larger public effort, Roosevelt wanted to keep electricity prices low by limiting private ownership of utility companies, which could charge high prices for energy.^[18] Many opposed a federal takeover of the project, including its most prominent supporters, but Washington State lacked the resources to fully realize the project.^[34][35] In August 1935, with the help of Roosevelt and a Supreme Court decision allowing the acquisition of public land and Indian Reservations, Congress authorized funding for the upgraded high dam under the 1935 River and Harbors Act.^[36] The most significant legislative hurdle for the dam was over.^[37]

That for the purpose of controlling floods, improving navigation, regulating the flow of the streams of the United States, providing for storage and for the delivery of the stored waters thereof, for the reclamation of public lands and Indian reservations, and other beneficial uses, and for the generation of electric energy as a means of financially aiding and assisting such undertakings the projects known as "Parker Dam" on the Colorado River and "Grand Coulee Dam" on the Columbia River are hereby authorized and adopted. —1935 Rivers and Harbors Act SEC 2, August 30, 1935, [H.R. 6250] [Public, No. 409]^[37]

First concrete pour and completion

The dam after completion and water over-topping the spillway

On December 6, 1935, Governor Clarence Martin presided over the ceremonial first concrete pour.^[38] During construction, bulk concrete was delivered on site by rail-cars where it was further processed by eight large mixers before being placed in form. Concrete was poured into 50 sq ft (4.6 m²) columns by crane-lifted buckets, each supporting eight tons of concrete.^[39] To cool the concrete and facilitate curing, about 2,000 mi (3,200 km) of piping was placed throughout the hardening mass. Cold water from the river was pumped into the pipes, reducing the temperature within the forms from 105 °F (41 °C) to 45 °F (7 °C). This caused the dam to contract about eight inches in length; the resulting gaps were filled with grout.^[30]
Until the project began, the stretch of the Columbia River where the dam was to rise was as yet unbridged, making it difficult to move men and materials.^[40] In January 1936, the Grand Coulee Bridge (a permanent highway bridge) was opened after major delays caused by high water; three additional and temporary bridges downstream had moved vehicles and workers along with sand and gravel for cement mixing.^[26][41] In March 1938, MWAK completed the lower dam and Consolidated Builders Inc. began constructing the high dam. The west power house was completed in December 1939 and about 5,500 workers were on site that year. Between 1940 and 1941, the dam's eleven floodgates were installed on the spillway and the dam's first generator went into operation in January 1941. The reservoir was full and the first water flowed over the dam's spillway on June 1, 1942, while work was officially complete on January 31, 1943.^[42][43] The last of the original 18 generators was not operational until 1950.^[2]