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Stage Changes during Streambed Fill and Scour

Bed Elevation

Bed elevation was measured with sonar during the rise, crest, and recession of a storm flow in the North Fork Toutle River, Washington, on December 3, 1987. The sonar transducer was held in the flow on a rigid pipe which was suspended from a boom over the channel thalweg.

Sonar detected the superposition of fine-gravel dunes on large bed waves, the depth-limited growth of mean dune heights from 13 to 25 cm, and bedform-related deposition and erosion in the channel thalweg. Bed elevation rose 0.3 m in 2 hours with increasing stream discharge. Dune heights diminished for about an hour before the peak river stage was attained.

Scour of the streambed continued through the peak stage and recession, with 0.7 m of scour over 10 hours. Rapid scour of the streambed produced a falling stage while discharge was still rising. Dune heights grew as flow depth increased after peak stage. Streambed elevation was lowered as large bed waves of fine gravel migrated along the thalweg with successively lower troughs leading each bed wave.

-- adapted from Dinehart, R.L., 1992, Gravel-bed deposition and erosion by bedform migration observed ultrasonically during storm flow, North Fork Toutle River, Washington, Journal of Hydrology, v. 136, pp. 51-71.

Bed Elevation

Bed elevation and river stage at NF Toutle River, December 6-7, 1989

Mean bed elevation, based on the average of all bed-elevation readings in a one-hour recording, rose by 0.5 m in 5 hours, between 22:00 and 03:00 hrs. The thalweg filled by incremental rises in a base level below which dune troughs would not erode. Consecutive rises occurred in increments of 5 to 10 cm.

-- adapted from Dinehart, R.L., 1992, Evolution of coarse-gravel bedforms: Field measurements at flood stage, Water Resources Research, v. 28, n. 10, pp. 2667-2689.

Bed Elevation

Bed elevation and river stage at NF Toutle River, January 10-11, 1990

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