| Abstract: | Experiments were conducted and field investigations were performed to study the development of step-pool sequence and its effects on resistance to the flow and stream bed stability. Step-pool sequence develops in incised channels as a result of streambed erosion, which is compared with sand dunes and armor layer of the role in resistance and streambed protection. The tight interlocking of particles in steps gives them an inherent stability which only extreme floods are likely to disturb. That stability suggests that step-pools are a valid equilibrium form, especially when coupled with their apparent regularity form and their role in satisfying the extreme condition of resistance maximization. The development degree of step-pools, SP, is proportional to the streambed slope. If the incoming sediment load is equal to or more than the sediment-carrying capacity of the flow, there is no bed erosion and thence there are no step-pools. If the flow depth increases and is over the step-height the resistance caused by the step-pool sequence will be greatly reduced. The rate of energy dissipation by step-pools is a function of SP. The higher is SP, the larger is the rate of energy dissipation. The step-pool sequence increases the resistance and flow depth, reduces the shear stress of the flow and protects the streambed from erosion. Moreover, step-pool sequence provides ecologically sound habitats for aquatic bio-community as well. |
