The Columbia River is one of the longest rivers in the United States.

Like any river, it is ecologically inseparable from its watershed and basin. A watershed is the land area that delivers runoff, sediment, and dissolved substances to a river and its tributaries.

The Columbia Basin spans seven states and one Canadian province. The northernmost reach of the basin is found in the high glaciers of the Canadian Rockies. From there, the main body (or stem) of the Columbia River runs over a thousand miles before passing Portland, Oregon and reaching the Pacific. The Columbia River and its tributaries account for about 219,000 square miles of drainage in seven western states, making it almost the size of Texas.

In years with lots of rain or snow, flooding in low lying areas and the lower river, especially near Portland, would be common without flood control. To meet this need, Grand Coulee is one of the dams on the American side of the Columbia River with reservoir capacity sufficient to help prevent flooding. On the Canadian side, additional dams and reservoirs assist with flood control. Via a treaty with Canada and sophisticated interagency planning, up to 39.7 million acre feet of storage space can be made available for flood control. This space is made available by drawing reservoirs down and then capturing spring runoff to refill the reservoirs rather than causing downstream flooding. By making up to 5 million acre feet of space available for flood control, Lake Roosevelt is the system’s primary American storage area.

Forty-eight years of developing this coordinated approach came together as never before in February, 1996. Heavy rains and melting snow pack due to mild temperatures created the worst flooding in over 30 years in the Northwest. Government agencies and non-federal hydro operators worked together to reduce flood damage by an estimated 3.2 billion dollars. Because the Northwest had a flood control plan in place, the evening news did not show downtown Portland six feet deep in water.

In an average year, a year with 100 percent of normal precipitation, Lake Roosevelt is lowered about 50 feet in April and May to insure against downstream flooding of communities and property. The flood control “season” essentially lasts between April and July. The Corps, by federal law and through a formal agreement with the Bureau of Reclamation, sets the elevation of Lake Roosevelt based on daily, weekly and monthly forecasts. Statistical models, weather reports, runoff information and interagency cooperation are all used to create forecasts and manage lake levels for flood control purposes.