Sediment Flushing from Sabo Dams and its Environmental Impact on River

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The habitat of fishes and aquatic insects must deteriorate by passing of turbidity water and sediment when the deposit in sabo dams is released all at once to the river where the sediment transport becomes not active. ln this research, we have investigated the riverbed variation by a series of sabo dams and studied how they influence the habitat. Moreover, the impact that the artificial sediment flushing from sabo dams gives to the habitat in mountain streams is investigated from some field experiments and numerical simulations. The following results were obtained :1.Riverbed variation by a series of sabo dams(1)The effect of a series of sabo dams cannot be estimated by the addition of the effect of a single sabo dam.(2)Because much sediment would be flushed from slit sabo dams when the water discharge decreases at floods, the impact to the habitat might be severe.2.Movement of the sediment artificially flushed from sabo dams(1)The calculation program for analyzing the movement of the bed load was presented. The program could explain the deposition and erosion process in pools.3.Influence of sediment movement on the environment in habitat of fishes(1)The indices such as turbidity, dissolved oxygen, sediment storage capacity of pools, the space scale between gravels and cobbles, sediment deposition depth on riverbed, plane shape of streams are important in evaluation of the influence of sediment flushing.(2)The above-mentioned program was applicable to the evaluation of impacts by sediment flushing and recovering to the original riverbed.(3)The relation between the influence level and the stress index for char was experimentally clarified, and the sediment flushing condition with a little influence was presented.