The Lewis River Hydroelectric Projects - PacifiCorp

Swift Forest Camp—Interpretive Sign #1 (Hydroelectric Story)
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Swift Forest Camp
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High Water, Low Water
Spend time along the shore of Swift Reservoir and you’ll soon notice that
the lake level is not constant. Over the course of a day, the lake may fall
or rise several inches. Throughout the year, the water may fluctuate many
feet. These constant changes maintain a bare zone around the shoreline—
a bit like a beach at the ocean, where rising and falling reservoir levels
create a unique shoreline landscape.
But unlike tides, the water fluctuations on Swift Reservoir (and
neighboring Yale and Merwin reservoirs) are caused by human actions.
Swift is a reservoir, contained by a hydroelectric dam. Water in the
reservoirs used to turn turbines at the base of the dam, which generate
electricity. When more water is released than flows into the reservoir, the
lake level drops. When more water flows in than is released, the reservoir
rises.
If power generation were the only consideration in determining how
much water to release, PacifiCorp would run all the water that enters
Swift through generators at all three dams, maximizing the total power
output of the river.
However, power generation is not the only factor. Sometimes operators
must release more water than can be run through generators, or must
store water when it could be used to turn the turbines. This is part of the
company’s stewardship of the river and surrounding lands. Ultimately,
the operation of the Lewis River dams is a complex choreography of
water storage, power generation, and water release. The basic needs
driving the system are:
• Electricity generation needs –This includes meeting the needs of the
consumers via the grid, maintaining sufficient water behind the dams
to support spinning reserves, and maximizing profit/minimizing loss
based on fluctuating electricity costs.
• Environmental needs –PacifiCorp is required as part of its FERC license
to maintain at least a minimum flow rate in the Lewis River below
Merwin Dam during all times of the year for fish spawning,
incubation and rearing.
• Recreation needs –PacifiCorp provides recreation sites for the public,
and minimum reservoir heights are required to make these recreation
sites usable.
Appendix 1: panel profiles Lewis River Draft I&E Plan page 48