DESCRIPTION:
Cowlitz River Basin, Mount St. Helens, Washington
Cowlitz River Basin
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Major Hydrologic Features in the Mount St. Helens Region
-- Modified from: Crandell and Mullineaux, 1978, USGS Bulletin
1383-C
From:
Dinehart, 1986, Sediment Data for Streams near Mount St. Helens, Washington --
Volume 2. Water Years 1981-83:
USGS Open-File Report 85-632, 438p.
From:
Dinehart, Ritter, and Knott, 1981,
Sediment Data for Streams near Mount St. Helens, Washington,
Volume 1, 1980 Water-Year Data:
U.S.Geological Survey Open-File Report 81-822, p.27.
The Cowlitz River basin, which includes the
Toutle River,
has an area
of about 2,480 square miles (6,400 square kilometers).
The headwaters of the Cowlitz are on
Mount Rainier.
The flow of the upper Cowlitz River is regulated
by two reservoirs, Riffe Lake, which has a usable capacity of
1,686,300 acre-feet, and Mayfield Reservoir, which has
a usable capacity of 21,380 acre-feet. The eruption spread
volcanic ash on the basin, and the mudflows in the Toutle River affected
the Cowlitz River from the Lewis-Cowlitz County line to the mouth. Most
of the volcanic ash transported by the streams in the upper Cowlitz Basin
was deposited in the downstream reservoirs. Regular sediment sampling
on the Cowlitz River began the day after the eruption.
Mount St. Helens Eruption, 1980
From:
Water Resources Data for Washington, Volume 1, Western Washington,
Water Year 1980:
USGS Water-Data Report WA-80-1, Prepared in cooperation with the State of
Washington and with other agencies, 488p.
On
May 18, 1980, Mount St. Helens violently erupted.
During the eruption, a
massive
debris avalanche,
moving down the north side of Mount St. Helens, was
blasted into the North Fork Toutle River valley,
depositing approximately 3
billion cubic yards of material in the upper 17 miles of the valley. Mudflows
quickly developed in the
South Fork Toutle River and in the Lewis River
tributaries of
Smith Creek,
Muddy River, and
Pine Creek. At least 11,000
acre-ft of water, mud, and debris were deposited in
Swift Reservoir between 9
a.m. and noon on May 18. A massive mudflow originated on the debris pile in the
North Fork Toutle River valley
and caused widespread destruction as it moved
downstream through the Toutle and Cowlitz Rivers. Considerable deposition
occurred in these river channels and in the channel of the
Columbia River, which
was closed to shipping for about 1 week. Channel capacity of the
Cowlitz River
was reduced from 76,000 to 7,300 cubic feet per second (at the flood stage of
23.0 feet). Dredging of the shipping channel in
Columbia River commenced
shortly after May 18, and dredging was started in July in the lower reach of
Toutle River and Cowlitz River.
URL for CVO HomePage is:
<http://vulcan.wr.usgs.gov/home.html>
URL for this page is:
<http://vulcan.wr.usgs.gov/Volcanoes/MSH/Hydrology/Drainages/Cowlitz/description_cowlitz.html>
If you have questions or comments please contact:
<GS-CVO-WEB@usgs.gov>
02/18/99, Lyn Topinka
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