d4PDFを用いた日本全国の主要河川流域におけるダム治水効果の将来変化分析

Abstract

全国一級水系で構築した分布型降雨流出モデルとd4PDFから得られる年最大降水量を用いて59一級水系でダムがある場合とない場合の降雨流出計算を行い, ダムの治水効果の全国的な将来変化を分析した. 基準地点の洪水ピーク流量の比率(ダムあり/ダムなし)は一定規模以上の洪水で増加する水系と増加しない水系があることがわかった. 前者は降雨規模が大きく貯水容量が小さい九州や太平洋側, 後者は瀬戸内海や日本海側に分布した. 計画規模に相当する洪水強度は4度上昇シナリオのもとで全国的に増大し, 両者の違いは現在の治水容量によって決まることがわかった. また, 4度上昇シナリオ下での異常洪水時防災操作に入る回数も治水容量によって決まることがわかった.

Future changes of flood control effect (FCE) by major existing dams were analyzed for 59 river systems all over Japan using d4PDF rainfall data and the rainfall-runoff model 1K-DHM. The rate of flood peak discharge with/without dams increased for floods over a particular magnitude (FCE was reduced) for some river systems near the Pacific Ocean and not (FCE was remained) for ones near the Seto Inland and Japan Seas. The former has smaller dam capacity despite receiving heavier rainfall, where larger future changes of extreme discharge are projected but its impact was not significant. Similarly, the frequency of emergency operation is also related to the flood storage, indicating that flexible dam operation such as preliminary release will make a significant contribution to flood control in a changing climate in Japan.