Abstract
The characteristics of river bed variation at the contraction during the flood are investigated exprimentally. Moreover its characteristics for natural river which have several types of contraction are investigated by the numerical simulation on the basis of one dimensional bed variation method. From the experimental results, it is found the tendency that the bed level approaches to the bed level on equilibrium condition of sediment discharge for flood discharge. As the results, the bed level lowers during rising stage and then phenomenon of bed aggradation during the falling stage occurs at the up-stream end of the contraction. It is found from the numerical simulations that the bed variation of the contraction is influenced by the approach length, length of contraction and duration of the flood.
