Research teams from Nara Women's University, Hokkaido University, Kumamoto University, Hyogo Prefectural University, Tokushima University, etc. have been working on "soil placement in the downstream area of the dam" (hereinafter "soil reduction") as a measure against sedimentation in the dam lake. It was clarified that it is effective for improving a healthy riverbed environment and biological community.
Sedimentation has become a problem in many dam lakes, while the deterioration of river environment and biological communities caused by sediment shortages has become a problem in the lower reaches of dams.As a countermeasure for sediment in the dam lake, "sediment reduction" is performed by excavating the accumulated sediment, transporting it to the downstream area of the dam, and returning the sediment to the river channel. In recent years, this "sediment reduction" has been carried out under the dam. It has been pointed out that resupplying sediment to the coarse-grained riverbed in the basin may be effective as an environmental mitigation measure.However, the actual effect of "soil reduction" on river organisms has not been clarified.
In this study, a field survey was conducted before and after "soil reduction" in the lower reaches of the Agigawa Dam in Gifu Prefecture, and a detailed comparative study was conducted.As a result, a biotic community with low species diversity was established, in which there was little sediment and the periphyton was thick and thick, and only the net-forming caddisflies that adhered to the giant gravel were remarkably dominant before the sediment reduction. On the other hand, after the sediment reduction, the riverbed material from giant gravel to sediment exists in a well-balanced manner, and not only the reticulated caddisfly but also the classification group with various functions inhabits in a well-balanced manner. We found that it was transforming into a biological community.
This suggests that "soil reduction" may lead to the creation of rivers with high biodiversity.In addition, it is known that if the amount of sediment is too large, the biological community will be poor, so in this study, it is also pointed out that an appropriate amount of sediment is important for improving the deteriorated river ecosystem. doing.
Paper information:[Scientific Reports] Effects of sediment replenishment on riverbed environments and macroinvertebrate assemblages downstream of a dam
