CONTROLS ON HYDRAULIC RESISTANCE IN STEP-POOL CHANNELS
Discharge had the largest effect on resistance of all variables tested, and the effect of LWD configuration on roughness tended to be drowned out at high discharges. Debris density, debris orientation, and slope also had highly significant effects on total friction factor, whereas piece length (including presence or absence of rootwads) and arrangement were not significant at a=0.05. In a factorial ANOVA on a subset (n=108) of the runs, significant 3-way interactions at a=0.05 were present for discharge*orientation*slope and discharge*orientation*length, and a significant 2-way interaction was also present for discharge*density. Calculations of resistance partitioning indicated that spill resistance and debris resistance were responsible for the largest components of total resistance, and that grain roughness was a small component of total resistance when steps and/or debris were present. The relative contributions of grain, spill, and debris resistance depended on discharge, with debris resistance dominating at higher discharges, and debris density, with similar contributions from spill and debris components at low debris densities and greater debris roughness at higher debris densities.