RESEARCH ON THE COMPREHENSIVE METHOD FOR ANALYZING THE DAMAGE MITIGATION EFFECTS OF FLOOD CONTROL FACILITIES FOR FLOODS EXCEEDING THE DESIGN LEVEL

本研究は，超過洪水によって発生する氾濫被害を最小化できるような施設運用について分析できる手法の開発を目的とする．具体的には，遊水地群，排水機場，樋門といった施設運用を勘案し，内水・外水を一体化した氾濫解析が行えるような手法を提案する．研究対象とした千歳川は石狩川の支川の一つであり，その背水影響を30km以上にわたり受ける河川で，流域の主要部分が地盤の低い低平地を流れるため，氾濫リスクが高い．ここで整備が進められている治水施設の操作を勘案した氾濫解析をおこない，(1)観測史上最大の昭和56年洪水の再現計算，(2)計画を上回る大雨に対する分析をおこなった．検討結果より，治水施設の効果が総合的に分析でき，今後の気候変動で懸念される超過洪水への適応策を検討するうえで有効な手法を提案することができた．This research aims to develop a method for analyzing the operation of flood control facilities towards minimizing damage from floods that exceed the design flood. Specifically, we propose a method in which the operations of complete sets of flood control facilities, such as flood control basins, pumping stations and sluiceways, are taken into account in comprehensive flood analysis for inland water and bank overflow. We studied the Chitose River, which is a tributary of the Ishikari River. The Chitose River is affected by backwater from the Ishikari River on a roughly 30km reach. Because most of the Chitose River basin is flat, low lying land, the flooding risk is high. Using our method, we performed flood analyses that incorporate the operations of flood control facilities being developed in the basin. The analyses reproduced the following: 1) record flooding of 1981 and 2) assumed flooding that exceeds the design water level. The study indicates that our proposed method is able to comprehensively analyze flood control facilities and is useful for examining countermeasures against floods exceeding the design water level, which are expected to increase due to ongoing climate change