Bedload was sampled with pressure-difference samplers to estimate bedload-transport rates. Size distributions of the bedload samples were determined by mechanical sieving at regular phi intervals. In 1985, the Helley-Smith sampler (with 3- x 3-in. opening) was used, which excluded coarser gravel and cobbles known to be available for transport. During 1986, the TR-2 sampler (with 6- x 12-in. opening) extended the range of bedload sizes that could be collected (Childers, 1992). Bedload was sampled in the North Fork Toutle River, the Toutle River, and the Muddy River ( table 16 ). Compared with subpavement samples, bedload samples collected at the North Fork Toutle River at Kid Valley in 1986 were more nearly unimodal ( fig. 76 ).
Median bedload sizes were finer at the Toutle River at Tower Road than at the North Fork Toutle River at Kid Valley during water years 1986-87 when similar samplers were used ( fig. 77 ). Bedload samples collected at the North Fork Toutle River at Kid Valley showed larger median particle sizes following the closure of the SRS in November 1987. Bedload samples also showed increasing variability between 1985 and 1989, particularly in the coarse gravel and cobble range.
Bedload was sampled repetitively during storm flow in 1989 and 1990 at the North Fork Toutle River at Kid Valley. Size distribution of bedload approached that of the subpavement following peak stage, and median particle sizes of the bedload coarsened gradually during flow recession (Dinehart, 1992a).
