Sediment transport at gaging stations near Mount St. Helens, Washington, 1980-90; data collection and analysis

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1998-06 Excerpt: ...sources can produce a sediment concentration peak nearer to the peak discharge in time. In a storm flow derived from snowmelt in the lower elevations of the Toutle River basin, peak fine concentration coincided with peak discharge on January 23, 1982, at the Toutle River at Highway 99 (fig. 25). In the following two water years, peak fine concentration preceded peak discharge by several hours on December 3, 1982 (fig. 26), and on November 3, 1983 (fig. 27), at the Toutle River at Tower Road. The decrease in sediment lag can be interpreted as a result of decreasing dominance of sediment discharge from the debris-avalanche deposit. Additional factors that influence sediment lag have been described by Williams (1989). Figure 29. Breach in sediment-retention dam N1 on the North Fork Toutle River, near Mount St. Helens, Washington, early March 1982. The north embankment breached during storm flow on February 20, 1982. A storm flow on February 20, 1982, breached the embankment impounding Jackson Lake, which had been formed at Jackson Creek along the southern margin of the debris-avalanche deposit. Outflow from the lake created a flood wave that was sampled at the Toutle River at Highway 99 (fig. 28). Later that day, the north embankment on the temporary sediment-retention dam Nl was breached when the North Fork Toutle River overflowed its existing channel (fig. 29). Sediment from the retention dam was eroded and transported through the breach. At the North Fork Toutle River at Kid Valley and the Toutle River at Tower Road, a small peak of fine concentration lagged the associated increase of discharge by more than 1 hour. As sediment from the Nl breach was transported downstream, the associated sediment peak was diffused and diluted, as shown in samples collect...