Columbia Basin Project were built at the north and south ends of Grand Coulee, the dry canyon south of Grand Coulee Dam, allowing the coulee to be filled with water pumped up from the Columbia River. The resulting reservoir, called Banks Lake, is about long. Banks Lake serves as the CBP's initial storage reservoir. Additional canals, siphons, and reservoirs were built south of Bank Lake, reaching over . Water is lifted from Lake Roosevelt to feed the massive network. The total amount of the Columbia flow that is diverted into the CBP at Grand Coulee varies a little from year to year, and
Grand Coulee Dam interest in irrigation projects. The Bureau of Reclamation, desirous of a major project that would bolster its reputation, was focusing on the Boulder Canyon Project that resulted in the Hoover Dam. Reclamation was authorized to conduct a study in 1923, but the project's cost made federal officials reluctant. The Washington state proposals received little support from those further east, who feared the irrigation would result in more crops, depressing prices. With President Coolidge opposed to the project, bills to appropriate money for surveys of the Grand Coulee site failed. In 1925, Congress authorized a U.S. Army Corps of Engineers study