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In Taiwan, check dam is one of the major structural measures for upstream channel improvement. However, the original river bio-system, especially, on the fish habitat, is seriously affected when the step-form stream channel is created after check dams were filled. With higher attention on natural environment protection, searching for alternatives of Check Dam becomes one of important research topics in this field and re-constructing traditional check dam into Detention Dam is one of the feasible techniques. Check Dam no.3 and no.4 of Gaul-Shane Creek were chosen for this experiment study under hydrology condition of 50 years of return period. With different final dam configurations for these two dams, the model experiments tried to conclude some principles regarding to the deposit slopes of dams, changes in cross sections, dimension of scouring hole, and sediment discharge of observed channel. From the result of this experiment, the average deposit slope, changes in cross sections, scouring hole, and sediment discharge of downstream channel of dam No.4 increased with deeper opening depth of dam No.3. Therefore, the protection of Dam No.4 should be completed to reduce potential damage before re-construction of dam No.3 being proceeded. Besides, the effects on those channel morphologic phenomena were milder when the opening-developing procedures were applied gradually.
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