フラッシュ放流による河床環境改善効果と放流波形の重要性

抄録

Owing to regulation of river flow, there have been gradual but drastic changes in the biotic and abiotic environment of rivers. These changes may have led to lowering of the quality of ecosystem services provided by the affected rivers. In this study, a flush discharge release conducted on March 25, 2009 was observed to estimate the impact of the flush discharge on the river environments of an upstream reach of the Jyouge River, which flows through the northern part of Hiroshima, Japan. The river reach assessed in this study is 8 km in length and is located just downstream of the Haiduka dam, which released a maximum flush discharge of 100 m³/s. Water stage hydrographs were recorded at 21 stations using the hygrometers. At two stations, water sampling had been conducted to quantify suspended sediment (SS) and chlorophyll a (chl.a.) Two-dimensional flow simulation was performed to represent the time-dependent flow and material transport processes. Using the observed and simulated results, transport of chl.a, transport distance of chl.a and its relation to the flood duration are discussed.