Summary
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 included 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 lower Toutle River
was medium to coarse sand. During the same
period, bed material in the North Fork Toutle River
was coarse sand and fine gravel. By 1990, bedload
samples collected in the North Fork Toutle River
(downstream from the sediment-retention structure)
were typically coarse gravel.
|
- Readme HTM (5 KB)
This file contains links to 25 individual Sediment Data files covering Daily Mean Discharge, Daily Sediment Discharge, Daily Mean Concentration, Instantaneous Sediment Concentration, and Bed Material statistics
-
Print versions of this publication available at the USGS Store: 13738
Part or all of this report is presented in Portable Document Format (PDF). For best results viewing and printing PDF documents, it is recommended that you download the documents to your computer and open them with Adobe Reader. PDF documents opened from your browser may not display or print as intended. Download the latest version of Adobe Reader, free of charge.
|