The Lewis River Hydroelectric Projects - PacifiCorp

Beaver Bay—Interpretive Sign #1 (Hydroelectric Story)
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Beaver Bay
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Cycles of Flow
Rivers are not steady systems. Their flow changes seasonally, and in
response to weather events such as droughts and heavy rains. Here in the
Cascades, floods are a part of natural river cycles of flow. Winter
(November through April) is the time of highest runoff, with frequent
rains, and rain-on-snow events that can cause big surges in the Lewis
River’s flow.
Dams are a means to regulate the flow of a river. But dams can’t change
the rate at which water flows into the system, they can only regulate the
water flowing out of the system. At best, dams can only dampen the
natural oscillations of the river’s flow—and they cannot prevent floods.
As operator of the dams of the Lewis River hydroelectric projects,
PacifiCorp has the responsibility to provide flood management—not
flood control—for the communities below Merwin Dam. Working out the
most efficient pattern of storage, release, and drawdown to control river
flow and buffer water fluctuations, while still generating electricity,
requires a skillful dance of meteorology and hydrology.
To do this, meteorologists study precipitation patterns and weather
forecasts to create “flow forecasts” to help make decisions about water
levels in the three reservoirs. Higher flows and higher energy demands
prescribe higher water release rates through turbines or spillways. When
a significantly higher flow is forecasted, the reservoirs may be drawn
down to provide space to store the incoming water.
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As part of its flood management plan, PacifiCorp funds county agencies
responsible for notifying property owners of sudden high water events.
PacifiCorp also provides funds to the county for the dissemination of
information about water levels in the reservoirs and flow rates at Merwin.
This information is provided in several forms, including weather radio,
Internet, and telephone lines with automated flow information).
At midnight, just three days before Christmas of 1933, inhabitants of the
Lewis River floodplain at Woodland were awakened by the roar of water
as a massive flood swept down the river to Woodland. The following
Sunday’s Oregonian breathlessly trumpeted news of the flood: “The
usually lazy north fork of the Lewis River suddenly became a snarly,
boiling demon of destruction. Rearing four feet above its banks, it
thundered down the broad valley to the fertile farm land above
Woodland, tossing bridges and tractors, barns, sheds and trees before it,
toppling houses, tossing them on its crest, smashing them with the
Appendix 1: panel profiles Lewis River Draft I&E Plan page 44