The Changes of River Bed and Gravel Exploitation in the Lower Stream of the Fuji River in Shizuoka Prefecture

Abstract

First, the author studied the changes of river bed in the lower stream (0-7Km.) of the Fuji River, considering a) fluctuation in the mean heights of river bed and b) quantity of deposition or scouring in river bed. Then he discussed the relation between the changes of river bed and gravel exploitation in the same stretch. Conclusions are summarized as follows:(1) When the mean heights of river bed in 1963 are compared with those in 1960, it is recognized that the river bed has been considerably lowered excepting at a few gauge stations. The average degradation for all sections is 39.2cm, although values of over 150cm have occurred locally. (2) According to the records of annual amount of deposition and scouring in river bed, there is a huge amount of scouring for every year since 1961, and the total amount of deposition and scouring during recent 3 years (1961-1963) reaches about 2.4×106m3 of scouring.(3) The total quantity of gravel exploitation in the lower stream of the Fuji River during the 3 years (1961-1963) was estimated to be about 6.0×106m3, which was twice as much as the quantity authorized by the prefectural government.(4) Regarding the causes of the degradation of river bed, it can be considered that the effect of gravel exploitation in river bed is far more direct and decisive compared with other causes.