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biases that might result if the substrate was viewed during hand placement. In most cases, turbulence and turbidity precluded the possibility of viewing the river bed. During runoff, as the river receded, measurement sites at a given study location were located progressively lower in the channel to maintain the depth and velocity criteria. At base flow, the river stage stabilized to a large degree and the location of the sampling site remained consistent among sampling dates. In some instances, a riffle would disappear at lower flow stages or current at the 3045 cm depth zone in a run habitat would lose sufficient velocity to meet the criteria. In these cases, base-flow sampling sites were relocated nearby where the appropriate conditions were met. Wolman pebble counts (Wolman 1954) were used to characterize substrate particle size at the locations of the embeddedness measurements. These were done annually at each site. By taking a sufficiently large sample, one can construct a plot of particle size versus frequency in percent. Since each sampled particle represents a portion of the bed surface, the frequency distribution represents the percent of the streambed covered by particles of a certain size, and not the percent by volume or weight. The measurement taken is the particle width or distance across the intermediate axis (Fig. 6), i.e., that axis that would prevent the rock from passing through a sieve of the appropriate size (not the long axis or the thinnest axis, but the breadth or width of the rock). Again, the measurer would look ahead while walking forward to minimize bias. Again, each of the two-member crew would perform half of the measurements at each site. At every second step, the rock beneath the tip of the measurer's shoe was lifted and the width measured with a vernier caliper (to the nearest 1 mm). In most cases, 100 such measurements were made; in some cases when time was limited, only 50 measurements were made. Only rocks with widths greater than 8-10 mm were used. For the sites where embeddedness was measured during runoff, Wolman pebble counts were made after the water receded and rocks were sampled from the exposed bar. Every effort was made to sample the entire area where the previous embeddedness measurements had been made. For the base-flow sites, the sampled substrate never became exposed and the pebble counts were therefore made by wading and pulling up submersed rocks (Fig. 6). If the length of the sampling area was limited, the measurer would sample upstream until reaching the edge of the suitable area and then start over again at the downstream end of the site. Embeddedness measurements were averaged and means were compared among sites and among dates within sites. Particle sizes were also averaged and means compared among sites and between years within sites. The median (D-50) rock size (width) was also calculated as was the D-84 and the D-16; the D-84 is the particle diameter equal to or larger than 84% of the particles (clasts) on the channel bottom. The D-84 and the D-16 are often used to describe the variability of the particle size distribution (MacDonald et al. 1991). We also describe the depth-to-embeddedness in terms of the number of rocks above the embeddedness layer (free rocks or relative DTE). To do so, we divided each of the 20 depth measurements by the median rock width for that site and then took the mean of these. This allowed a measure of variability around the mean number of free rocks. 11