Yuhei TODO
Long term changes of the river bed shape in the Ookouzu flood control channel and evaluation of countermeasure against erosion
Tokuzou HOSOYAMADA
People in echigo plain had been suffering from flood disasters of the shinano river for long time from Edo era.The ookouzu flood control channel is an artificial river constructed to short cut and redirect the Shinano river to Japansea for the purpose of flood prevention in Niigata plain.
Because it is artificial river and which has constrain of civil engineering of construction works of that age, the shape of the river is far from natural and equilibrium state between erosion and accumulation of sediment. The channel has getting narrow and steep for the downstream direction.Therefore, in flood time, velocity is remarkably high and river bed is eroded considerably.
In this study, long term data analysis for hydrographical data ( water level, flow rate, suspended solid:SS) in the Ookozu channel and the Shinano river, and one-dimensional numerical simulation of sediment transport with long term boundary condition of flow rate have been carried out.
By temporal integration of multiplication of SS and river flow rate, total amount of sediment trapped by SS monitoring system is about 400,000m3/year, which corresponds to 50% of total amount of sediment as estimated conventionally.
Numerical results show that river bottom shear stress and sediment flux takes comparatively high value around the riverbed sill.
Long-term periodical survey of river shape, which continues for more than 60 years show rapid erosion just downstream side of the sill. That agree with numerical results.
In near future, it is necessary to take maintenance of the countermeasures for riverbed erosion and degradation in the direct of down stream part of the river bed sill
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