EFFECTS OF THE FIRST FLOOD CONTROL PLAN AND RIVER IMPROVEMENTS ON THE ISHIKARI RIVER BASIN

摘要

In 1869 the Meiji Government launched a policy of encouraging migration to Hokkaido and started reclamation of the Ishikari River Basin. In September 1898, when farmland reclamation had started to expand, the Ishikari River was hit by an unprecedented heavy flood that resulted in catastrophic damage and 112 fatalities. This disaster prompted surveys for flood control. Another flood occurred in 1904. Okazaki et al. made detailed investigations and observations on the 1904 flood of the Ishikari River. Based on these investigations, a flood control plan focusing on cutoff works was formulated, and those works were implemented for the half-century from 1910. This study reviews the effects of the 1904 flood, which served as the basis for the flood control plan, on the primeval Ishikari River Basin of the time, utilizing the results of investigations by Okazaki et al. We use two-dimensional flood flow numerical simulation to examine the effects of cutoff works. We also explain how the flood control plan affected the basin development.