EFFECT OF ADDITIONAL DAMS ON FLOOD CONTROL AT YATTAJIMA, THE TONE RIVER, JAPAN

This study estimated the safety degree of flood control at Yattajima, the Tone River, Japan to verify effects of additional dams. Rainfall events considered are Catherine Typhoon in 1947, Ise Bay Typhoon in 1959, the Typhoon No. 15 in 1981, and the Typhoon No. 5 in 1998. The storage function method was used for runoff analysis, which showed good agreement between observed and computed discharges. Using the spatiotemporal rainfall pattern of Catherine Typhoon, this study simulated rainfall-runoff at each time stage; 1959 with two dams, 1981 with five dams, and 1998 with six dams (the same as present situation), and evaluated the effect of these added dams on flood control in terms of the decrease of peak discharge at Yattajima. The decreases estimated were 513-1, 253 m3/s for the 1959 situation; 2, 025-2, 765 m3/s for 1981; and 2, 233-2, 973 m3/s for 1998. It is also verified that the present situation with six dams can cope with 200-year floods, which is significant improvement because the past situation without dams could cope with 100-year floods.