Federal agencies operate many Columbia River dams to meet a wide spectrum of needs in the Pacific Northwest. Among the most important are flood risk management, power production, fish and wildlife conservation, navigation, irrigation, recreation and municipal and industrial water supply.
Understanding today's river operations provides valuable context when considering the role of the 14 federal dam and reservoir projects that comprise the federal projects under evaluation in the current Columbia River System Operations NEPA process. See above for a map of the 14-dam system.
The day-to-day and month-to-month variations in river operations may go largely unnoticed to the casual observer. Let's look more closely at how agencies typically operate the Columbia River’s federal dams over the course of one year.
Each new operating year begins in the fall. To prepare, system operators develop overarching guidelines called rule curves that indicate (or “shape”) the timing of water releases from the dams on the river to achieve multiple objectives. Once the basic annual operating plans are set, the operators aim to meet several related, but sometimes conflicting, objectives. These include:
- Providing adequate floodwater storage space in the reservoirs to decrease the downstream flood risk during the winter and spring runoff.
- Accommodating specific seasonal needs for the passage and spawning of a variety of fish species, including providing flows to aid downstream juvenile fish migration.
- Managing water quality.
- Maintaining a high probability that reservoirs will refill at the end of the spring runoff, both to meet recreation needs and to provide water for power, fish operations and irrigation.
- Conserving and enhancing habitat for resident fish (those that do not migrate to the sea).
- Optimizing power generation within the requirements necessary to meet the other objectives.
River managers divide the operations of the Columbia River System for flood risk management, power production, fish and wildlife conservation and other congressionally authorized purposes into three seasons.
September through December
This period is the fixed reservoir drawdown season. During this time, operators lower reservoirs to predetermined levels since it is challenging to forecast with certainty how much storage space will be needed for flood risk management. Monthly water volume forecasts for the upcoming spring are based on the amount of snowpack in the region’s mountains and typically are not available until January.
The goal at this time of year is to ensure that reservoirs reach specific levels by the end of December. Toward the end of this period, operators also begin to manage flows at Bonneville Dam to aid the breeding and rearing of threatened chum salmon immediately downstream. They strive to hold flows from Bonneville Dam at a level that protects nests of chum eggs.
Operators also schedule flows from Grand Coulee Dam at this time to meet the requirements of the Hanford Reach Fall Chinook Protection Program. This is a multi-agency agreement to aid a species of chinook salmon (not listed under the Endangered Species Act) while its eggs incubate and, subsequently, as the young fish emerge from the gravel riverbed in the prolific Vernita Bar area of the Columbia River. Both this and the chum operation extend into the next season and usually conclude in March.
January into April
This is the variable drawdown season when monthly forecasts of runoff volume guide the operation of the reservoirs. These forecasts estimate how much water will flow through the river basin over a given time. This period is the most uncertain regarding the timing and volume of runoff.
System operators lower reservoir levels during the winter and early spring primarily to provide space for water from later snowmelt and rain, helping reduce downstream flooding. The released water also produces electricity and helps maintain flows needed for fish. Operators look ahead and plan operations to hold enough water in storage to be available in early April to aid juvenile salmon and steelhead in their annual downstream migration.
April through August
Spring and summer often see the highest flows of the year due to snowmelt and are the river system’s primary fish passage seasons. During this time, operators manage snowmelt to provide flood risk management benefits. Operators also release water from Columbia Basin reservoirs in support of flow objectives at Lower Granite Dam on the lower Snake River and McNary Dam on the mainstem Columbia River. These flows aid threatened and endangered fish as they migrate. Since flow objectives depend on the amount of water provided by nature, it is not always possible to meet them.
System operators aim to begin July with full reservoirs. This provides water for both summer fish flows and summer recreation. Over this period, operations to manage flood risk continue as needed and power is generated, with some restrictions on the amount of water passing through turbines as opposed to over spillways. Passing water over spillways at mainstem dams benefits migrating fish from April through August.
Putting it all together
As demonstrated above, flood risk management, fish and wildlife conservation and hydropower production all heavily influence the operation of federal Columbia River Basin dams. Other uses of the river also influence management of the system. For example, minimum water levels at several reservoirs ensure irrigation pumps can reach the water. Operators hold reservoir levels steadier at certain times of year to aid tribal fishing. Certain operations that support fish conservation may change briefly to allow shipping traffic to navigate safely past the dams.
Coordinating the delivery of these many regional river system benefits occasionally requires compromise. For the most part, however, system operators successfully meet the diverse requirements of a wide range of stakeholders and river users. This is due in large part to a collaborative Columbia River water management process. While the U.S. Army Corps of Engineers and Bureau of Reclamation have authority over the operation of the federal dams, they work in close alliance with Canada, other federal agencies, states, tribes and regional stakeholders and Canada to best balance the needs of all.