Why are the Columbia River and its tributaries major sources of hydroelectric power in the United States?

The Columbia River and its tributaries serve as a major source of hydroelectric power because the river’s significant elevation drop—nearly 1,290 feet within the United States—has been systematically converted into a series of "stair steps" using 11 main-stem dams and additional structures on its tributaries.1

This development, which began in the 1930s with the construction of the Grand Coulee and Bonneville dams, allows for massive energy generation. To manage the natural variability of the river—where high flows occur during spring snowmelt and low flows occur in winter—the system utilizes upstream storage reservoirs in British Columbia as part of the Columbia River Treaty. These reservoirs, particularly those supporting the Grand Coulee Dam, allow for water storage that can be released to augment power generation during periods of peak demand.12

All power plants in the system are interconnected by high-voltage transmission lines, forming a robust network that supplies the Pacific Northwest and facilitates energy sharing with the American Southwest.1