Abstract
A variety of river improvement works have been put into practice to decrease flooddamages as well as to protect human life and properties, depending on differences ofnatural, historical and social backgrounds inherent to each river system. In particular, the evaluations on whether or not cutoff channel works would succeed vary from river toriver.
The present study addresses the technical background and significance of the Ishikari River cutoff works implemented and their impacts on regional developments in the Ishikari River Watershed and channel regimes of the river.
A hundred and twenty years ago, the extensive plains along the Ishikari River wereentirely covered with large areas of marsh and suffered from flood inundation every year.
These disadvantageous conditions made the plains unsuitable both for human settlementand arable land use. Cutoff channel works were adopted as the main method for loweringboth flood water and groundwater levels, and hence reducing the frequency of inundationdue to floods.
This paper clearly demonstrates that the cutoff works played an important role inaccelerating the degradation of river bed, increasing the discharge capacity and stabilizingthe river channel in the Ishikari River.
