Channel bed steps and pool shapes along Soda Creek, Three Sisters Wilderness, Oregon

Field study of bedrock step–pool systems along the upper reaches of Soda Creek in the Three Sisters Wilderness of Oregon shows strong correlation between several form variables (shape) and channel slope. Although step height and step length showed no regular spacing and variable correlation with channel slope, length to height ratios demonstrated strong negative correlations: steep slopes (20% to 80%) featured greater step height and shorter pool lengths than did flatter channel slopes. Correlations between step height to length ratios and channel slope varied between three lithologies. Explained variations ranged from 0.984 for the oldest channel steps developed in basalt, to 0.982 for steps of intermediate age developed in andesite, to 0.964 for the youngest steps developed in dacite. Sample size was 57, 40, and 33, respectively. The frequency of pool shape classes did not vary by lithology, but specific shape classes developed under differing slope conditions by rock type. All pool classes have adjusted (developed) their form to maximize resistance to flow H/L/S, and they have done so in remarkably uniform fashion.