報告書番号

U02035

タイトル（和文）

河川環境向上を目的としたダム試験放流の米国と日本の現状

タイトル（英文）

Domestic and US trends of experimental dam releases conducted for improving riverine environments

概要 （図表や脚注は「報告書全文」に掲載しております）

本報告書では，河川環境変動研究に資するため，ダム下流環境改善を目的とした放流試験に関する文献調査を実施した．文献調査は，日本国内で先駆的事例として度々引用されるものの，実施後の環境改善経過について報告されることの少ない，アメリカ・グレンキャニオンダム制御洪水実験を中心に行った．また，日本国内の環境改善を目的とした試験放流の動向についても取りまとめを行った．その結果，1996年よりグレンキャニオンダムで実施されている制限付き変動放流や制御洪水は，下流河川環境改善に対し，現在のところ，大きな効果をあげていないことが明らかになった．また，国内で実施されている維持流量の増放流やフラッシュ放流は，景観向上や河床堆積物の掃出などの効果が確認されているものの，長期的なモニタリングを通した定量的な評価が不足している等の問題点があることが明らかになった．

概要 （英文）

The concern with riverine environments has been growing for last several years in Japan and experimental dam releases, such as a flushing flow, are conducted for improving downstream environments. However, little is known about the effect of such releases on downstream resources, especially biological resources. In United States, environmental impact studies have been made largely at Glen Canyon Dam and an experimental controlled flood conducted in 1996 is well-known in Japan. This short-duration high release was designed to rebuild high elevation sand bars, deposit nutrients, and partially restore the dynamic nature of the riverine environments. Although the implementation of the controlled flood was reported as an advanced precedent, the result and progress of downstream environmental assessments were not reported in Japan.For the purpose of developing domestic environmental impact studies, a literature search on the experimental dam releases at Glen Canyon Dam was made and the findings are described in this report. In addition, the trend of experimental dam releases conducted for improving riverine environments in Japan was also investigated. As a consequence of the literature search, it was revealed that the modified low fluctuating releases and controlled floods, which had been carrying out as experimental releases at Glen Canyon Dam since 1996, had not brought about the desired effects to downstream physical and biological environments at present.

報告者

キーワード