USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Sediment Transport at Gaging Stations near Mount St. Helens, Washington,
1980-90, Data Collection and Analysis
-- Randal L. Dinehart, 1998,
Sediment Transport at Gaging Stations near Mount St. Helens, Washington,
1980-90, Data Collection and Analysis:
U.S. Geological Survey Professional Paper 1573, 111p.
Abstract
River sedimentation caused by the May 18, 1980, eruption of Mount St. helens,
Washington, has been monitored in a continuing program by the U.S.Geological
Survey. In this report, sediment discharge and changes in sediment transport
are summarized from data collected at stream-gaging stations near Mount St.
Helens during the years 1980 through 1990. The objectives of the monitoring
program include collection of data for calculation of total sediment discharge,
computation of daily suspended-sediment discharge, and detailed observations of
unique sediment-laden flows. Over the 11-year period, most sediment data were
collected at gaging stations on seven eruption-affected streams: the Green
River, the North and south Fork Toutle Rivers, the Toutle River, the Cowlitz
River, Clearwater Creek, and the Muddy River.
About 170 million tons of sediment (excluding volcanic debris flows) were
transported in suspension from the Toutle River basin during water years
1980-90. Another 13 million tons were transported past the gaging stations on
Muddy River in the upper Lewis River basin during water years 1982-90.
Long-term reductions in sediment concentration occurred within most ranges of
stream discharge at streams dominated by transport from the debris-avalanche
deposit and at streams in drainage basins with extensive airfall deposits.
Reductions in sediment concentration were less apparent at upper ranges of
discharge in two streams dominated by lahar deposits, the South Fork Toutle
River and the Muddy River.
Bed material, suspended sediment, and bedload were sampled periodically and
analyzed for size distributions. Bed material and bedload coarsened with time
at some stations. Median particle sizes of suspended sediment did not show a
simple relation with time. During water years 1980-84, bed material in the
North Fork Toutle River (downstream from the sediment-retention structure) were
typically coarse gravel.
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12/28/06, Lyn Topinka