報告書番号

N15013

タイトル（和文）

自然の流れを活用した発電所放水口の土砂閉塞防止に関する移動床模型実験

タイトル（英文）

Movable-bed experiments for bed elevation control using water current on outlet of a hydraulic power plant

概要 （図表や脚注は「報告書全文」に掲載しております）

土砂流出の多い山地河川の湾曲内岸に面する水力発電所放水口で，放水口の土砂閉塞を永続的かつ簡便な施工で防止できる現地河床材料を用いた対策工が求められている．本研究では，現地地形を忠実に模擬した縮尺1/50の河川模型と混合粒径を含む複数の河床材料を用いて，非定常流量ハイドロ条件の土砂水理模型実験を実施し，河道内への盛土・置土配置によって自然の流れをコントロールする河床上昇抑制手法を検討した．盛土・置土形状などを変えた複数の実験の結果，放水口上下流の河道線形がストレートになるよう置土を配置した「置土ストレート形状」が複数回のハイドロに対して最も効果的であること，また，置土の側岸は崩壊しやすいので大粒径の礫で侵食を防止する必要があることが分かった．この形状が効果的な理由として，放水口前面の河道幅を狭めることで湾曲内岸の流速低下を極力抑えたことに加え，放水口上流の隅角構造物の局所洗掘が大流量時に放水口まで拡大すること，放水口下流の置土湾曲部が大流量時に河床洗掘されて堆積土砂を引き込みやすいことを確認した．

概要 （英文）

A water outlet of a hydropower plant is located in inner side of a meandering river, and the riverbed aggradation in front of the water outlet needs to be reduced by applying a permanent and practical engineering work. This study experimentally investigated the method for reducing riverbed aggradation by arranging layout of the in-stream earth embankment and controlling river flow associated to sediment transport. In the experiments, a detailed topography of river channel and the water outlet were physically modelled with 1/50 scale, and uniform and non-uniform sands were used as test sediments. Different layouts of in-stream earth embankment were set for each experimental run, and their effects were examined. Experimental results showed that the most effective layout for reducing riverbed aggradation against multiple floods was to arrange the embankment so that straight river channel forms in front of the water outlet. Physical reasons why this layout was the most effective were as follows: (1) decreasing in flow velocity at inside of the meander became considerably small, (2) local scour formed in front of the water outlet during a large flow rate, and (3) riverbed downstream of the water outlet, which degraded during a large flow rate, had ability to catch large amount of sediment, resulting in riverbed degradation around the water inlet. It was also found that the in-stream earth embankment has to be protected against bank erosion by covering the surface of the embankment.

報告者

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