The Lewis River Hydroelectric Projects - PacifiCorp

Lewis River Interpretive & Education Plan
As operator of the dams of the Lewis River hydroelectric projects, PacifiCorp
has the responsibility to provide flood management (NOT flood control; see
above) 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, meterologists study precipitation patterns and weather forecasts to
create “flow forecasts” to support decisions regarding water levels in the three
reservoirs. Higher flows and energy demand prescribe higher water release rates
through turbines or spillways. When a significantly higher flow is forecasted, the
reservoirs may be drawn down to provide a buffer of space to store the incoming
water.
In addition, as part of their flood management plan, PacifiCorp funds county
agencies whose responsibiliy it is to provide emergency notification to property
owners that may be affected by high water events. PacifiCorp also provides funds
to these agencies 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.
The Christmas Flood of 1933
One dramatic example of the power of flooding on the Lewis is the Christmas
Flood of 1933. At midnight, just three days before Christmas that year,
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 impact of its advance, bowling them over,
piling them in heaps, pushing through roads and railroads, ripping at piers and
bursting dikes, drowning cattle and thousands of chickens, transporting tons of
silt and boulders and trees on its turgid tide.”
The morning before, far up the Lewis, a CCC crew of 200 had been at work
on forest projects when nearby Dry Creek began to rise. Sensing trouble, the
commander had ordered an evacuation. The men toppled a few large trees
across the now-raging torrent and 135 men teetered across to safety as the flood
rose to engulf their makeshift bridge. Within 24 hours Dry Creek had grown to
enormous proportions, and a neighboring stream was flooding as well. Their
combined contributions to the Lewis River would eventually be estimated as six
Sea Reach Ltd • 146 NE yamhill Street • Sheridan, OR draft 3 • November 2008 • page 86