Open-Channel Flow Control by Vegetation and Artificial Roughness and Hydraulic Design of Multi-Function Channels

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Recently, river improvement should be planned to refine various functional aspects of rivers such as flood control, more efficient water resources utilization, recreational or leisure usage of rivers, well-conserved ecological situation, aquatic habitat and so on. And to achieve such multi-functions, the flow and river morphology should be more skillfully managed or controlled based on hydraulics and mechanics of sediment transport.In this study, control of cellular motion by oblique arrangements of strip roughness and promotion of lateral diffusion by arrangement of vegetation zone have been focused. Cellular motion helps straight navigation of boat and canoe, or removed snow lumps by secondary flow motion, or it gathers floating garbage to remove them by side overflow. Furthermore, it even changes the primary velocity profile. Stream-type fish way is an example of the latter. While, the promoted lateral diffusion works to decrease the turbidity of the main channel by trapping it to the vegetation zone.In this study, various types of approaches have been employed : laboratory experiments, field measurements and numerical analysis as well as simplified hydraulic understanding of the phenomena. The mechanism of formation of cellular motion by obliquely arranged strip roughness on bed and/or side walls and promotion of lateral diffusion by vegetation zone have been understood at several levels. The experiment has provided empirical relations and they have been supported by numerical analysis. And, they must be useful for hydraulic design of multi-functional streams.