This 1941 cover image shows workers on top of the drum gates of the mile-long Grand Coulee Dam in Washington State.

During the 1920s there was a bitter debate over whether to build a 290-ft tall “low dam” which would generate electricity without supplying irrigation, or a 550-ft tall “high dam” which would provide sufficient electricity to pump water into the Columbia basin for irrigation.

In 1933 the U.S. Bureau of Reclamation and a consortium of three companies called MWAK (Mason-Walsh-Atkinson Kier Co.) began construction on a high dam, although they had only received approval for a low dam.

Finally, in 1934, with construction underway, President Franklin D. Roosevelt visited the site and approved the high dam design. That led to the Bureau of Reclamation deciding to add the Six Companies, the successful group that had recently finished building Hoover Dam, to the contracting consortium, since the project had become exponentially larger.

Fabricated and installed by American Bridge Co., the 11 drum gates, each measuring 135 ft x 28 ft, provide a movable spillway crest 1,485 ft long.

When fully lowered they have an outlet capacity of 1 million cu ft per second, and when raised can increase the reservoir’s capacity 2.4 million acre-ft, or 32%.

Completed in 1942, the dam’s electric power generation capacity of 6,809 MW makes it the nation’s leading power plant of any type.