Grand Coulee Dam south, enclosed and created Banks Lake, which covered the northern of the Grand Coulee. Additional dams, such as the Pinto and O'Sullivan Dams, were constructed alongside siphons and canals, creating a vast irrigation supply network called the Columbia Basin Project. Irrigation began between 1951 and 1953 as six of the 12 pumps were installed and Banks Lake was filled. After World War II, the growing demand for electricity sparked interest in constructing another power plant supported by the Grand Coulee Dam. One obstacle to an additional power plant was the great seasonality of the Columbia River's streamflow. Today the flow
Columbia River known as the Grand Coulee. After the floods, the river found its present course, and the Grand Coulee was left dry. The construction of the Grand Coulee Dam in the mid-20th century impounded the river, forming Lake Roosevelt, from which water was pumped into the dry coulee, forming the reservoir of Banks Lake. The river flows past The Gorge Amphitheatre, a prominent concert venue in the Northwest, then through Priest Rapids Dam, and then through the Hanford Nuclear Reservation. Entirely within the reservation is Hanford Reach, the only US stretch of the river that is completely free-flowing, unimpeded by dams