Diverting the Columbia River

The biggest challenge in building Grand Coulee Dam was diverting the flow of the Columbia. To make this happen, the workers had to build cofferdams, temporary structures that keep the river at bay, allowing workers to dig out the mud and expose the granite bedrock on which the dam would rest. The west side cofferdam was completed on March 23, 1935. Soon after, the water level rose 32 feet.