Abstract
In recent years, extreme rainfalls have occurred and disasters that involve landslides and levee failures have frequently occurred in Japan. A flood analysis model was constructed for the Chitose River basin of the Ishikari River System, a basin that includes Sapporo, the largest economic base of Hokkaido; municipalities surrounding Sapporo; and New Chitose Airport. The model used 1) the storage function method for the basin, 2) one-dimensional unsteady flow for the river channel, and 3) planar two-dimensional unsteady flow for the flood plain. Examination was done for flood forecasting that assumes rainfall of the largest scale. A flood analysis model was constructed that integrated the landside and foreland waters, based on the consideration that the Chitose River flows through a low-lying area and is affected by backflow from the Ishikari River for a distance of more than 30km and based on the consideration that the Chitose receives the influence of the Ishikari's back water in the branches, canals, and drainage canals. For verification of the analysis model, the 1981 flood, which was the largest observed flood in the Ishikari River System, and the 2001 flood, which is the large-scale flood in recent years were reproduced.
