Historically, the two priorities for coordinated management of the Columbia River system have been electric generation and flood control. Other priorities, such as irrigation, navigation and recreation, are largely carried out within the context of meeting these needs. Most recently, impacts on salmon have resulted in the National Marine Fisheries Services stating that anadromous fish recovery should receive priority over all river uses except flood control.
Understanding the importance of flood control is similar to understanding the importance of insurance. Until you lose something, you do not appreciate how important it is. In 1948, the importance of flood control became a priority after Vanport, Oregon was destroyed by a flood. The Army Corps of Engineers responded by developing a multiple-use reservoir storage plan for the Columbia River Basin.
A treaty with Canada and the evolution of sophisticated planning and interagency cooperation have resulted in up to 39.7 million acre-feet of storage space being available for flood control. That is enough water to cover the Northwest four inches deep in water. For the Columbia River Basin, the need for reservoir space to help reduce the risk of flooding is most important during two seasons of the year: in winter, when there are rain-induced floods, and in the spring and early summer, when there are floods from snowmelt and rain.
By manipulating the amount of water in reservoirs throughout the Basin, system operators are able to create a balance between releasing water to produce hydropower when it is most needed, and reducing the potential for flooding. Looking at average river flows at the Dalles Dam over the course of the year is one way to see the difference between unrestricted water flow and the use of reservoirs to make this flow more constant. Further, reservoir storage is also assisted by a system of levees, flood walls, bank protection, and various types of land use regulation.
Source: Northwest Power Planning Council. Fourth Northwest Power Plan, Portland OR, March 13, 1996, p.4-5
Forty-eight years of developing this coordinated approach came together as never before in February, 1996. Heavy rains and melting snowpack 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. Some of the details of how the flood of 1996 was contained are remarkable. Although nobody expected these types of floods to occur for another several years, floods at the end of 1996 reminded everyone that the importance of flood control is always present.