Reservoirs: The Region’s Storage Battery


Photo of wind surfer on a river. Text: #HydroFlowsHere

Just like animals in times of abundance gather and store food for the leaner months, hydropower operators store water during wet months in preparation for drier conditions.

Though squirrels may opt for underground storage, hydropower operators store water behind hydroelectric dams in large pools called reservoirs.

Not all dams have reservoirs, but hydropower system operators work together to make the best use of available storage and release water to meet multiple needs year-round.

Serving Multiple Purposes, Providing Many Benefits

Stored water can be released through turbines to generate electricity. While operations change year to year depending on conditions, reservoirs are generally drawn down in winter and early spring to provide power and make room for heavy spring runoff.

In April through August, as snowpack melts, water is stored to prevent flooding and keep communities safe.

Stored water can be released through spillways rather than turbines to increase river flows and help fish migrate downstream to the ocean.

Reservoirs Enable Reliability

Reservoirs act like giant batteries that provide energy when it is needed.

Hydropower operators use the stored water in the reservoirs behind the dam to adjust the amount of water flowing through the turbines to match electricity use. Power forecasters determine how much electricity will be needed during a given time, and then communicate that to hydropower operators.

Hydro Power Flows HereThe consistent availability of hydropower also helps support other, more variable types of renewable energy sources, such as wind. Dams can quickly ramp up to provide more electricity when the wind drops and can scale back generation when the wind picks up again.

Snowmelt and runoff from upstream mountains in the spring enable reservoirs to be filled. This stored water comes in handy during the drier summer when water can be released to support energy demand and, in some instances, even reduce stream temperatures for the benefit of fish.

Work and Play on a Freshwater Highway

Reservoirs allow barges to move up and down the river, carrying all sorts of materials—from grain to wood chips to garbage. Wheat is brought from Idaho and Washington to Oregon and even overseas. Barges on the Columbia River move almost half of all the wheat from the entire United States.

The reservoirs created behind dams are also popular places for people to fish, swim, boat and windsurf.

Storage, Spill and Salmon

Water stored in reservoirs can help hydropower operators support the seasonal needs of both young and adult salmon.

In the winter and spring, operators help ensure salmon spawning grounds have enough water for spawning and to keep their nests covered. In the spring and summer, extra water is spilled from the dams to help young fish move quickly downstream to the ocean.

Releasing stored water also helps other wildlife, such as lamprey eels, which are an important cultural resource for some Northwest tribes.

Operating the Columbia River hydropower system to support all these needs is quite the balancing act. Having the storage capacity of reservoirs is critical to its success.