報告書番号

V04031

タイトル（和文）

水力発電所におけるトビケラ類付着被害の実状と対策事例

タイトル（英文）

Cases and measures of caddisfly settlement damages at hydroelectric power plants

概要 （図表や脚注は「報告書全文」に掲載しております）

水力発電所導水路におけるトビケラ類付着被害について、文献調査と被害が確認されている発電所に対する聞き取り調査を行った。付着被害をもたらすのはシマトビケラ属のウルマーシマトビケラ、ナカハラシマトビケラの幼虫であった。各発電所の付着被害による出力の低下は10％前後であり、年に１回程度、水路壁面の幼虫を人力で掻き落すことで出力の回復を図っていた。天敵や電撃等を用いた幼虫の駆除、防汚塗料は、対象となる幼虫量や水量が莫大なこと、また施工が困難などの理由から実用には至らなかった。実現可能で効果的な付着対策として、機械化による掻き落し清掃の低コスト化が挙げられた。また、幼虫の付着が少ない時期に清掃すれば清掃直後の発電効率を比較的長期間維持できることから、トビケラ類の付着時期を明らかにした上で、清掃時期の最適化を図れば付着対策を効率化できると推察された。

概要 （英文）

Caddisflies settling on the wall in power plant waterway cause to decrease power generation efficiency. The damage by the caddisfly settlement had been investigated in the 1960's actively. However, few investigations have been reported since 1980's. Ecology of caddisflies in the waterway has not yet been clear, so effective control methods have not been established. Therefore, to develop efficient control methods against caddisfly settlement on the hydroelectric power plant waterway wall, we surveyed documents, and investigated current states and measures of damages at the power plants. Fifty-six documents concerning caddisfly ecology and past damages in hydroelectric power plant were found. Hearings were also done to four hydroelectric power plants in which damage by caddisflies were reported. According to the document published in 1975, 188 power plants in Japan had damaged by caddisfly settlement. Most of them were conduit type power plants, into which caddisfly’s larvae flowed easily from the upstream. Four power plants where we did hearing were also all conduit type, and a decrease of the power generation output has occurred from spring to early autumn. The season coincided with that of hatch and oviposition in the caddisflies. Species of problem caddisflies were in the genus Hydropsyche. These species build nests with net on the waterway wall to capture food in water. It was reported that five species of caddisfly larvae settled to the waterway wall, and H. orientalis and H. setensis were dominant in these. The main method for controlling caddisflies has been physical scrape from the wall. The work has been done usually by human power for a long time, but now, two power plants adopt a scraping machine to reduce the human's work. Introductions of natural enemy for caddisfly lavae, electric shock, and antifouling paint were examined as measures for controlling the caddisfly. But these methods had some problems as follows, the amount of water to exterminate larvae was too enormous, it was difficult to paint the antifoulant on the waterway wall in short period, and it was possible that toxic chemical substances flow out to the river water from the antifouling paint. Here, we propose a plan to investigate settlement season of the problem caddisflies. If a waterway is cleaned when number of inflow and settlement of the larvae decrease after the peak, power generation efficiency will be maintained at high level for a long period. For development of effective control method against sessile caddisflies, it is important to determine the seasonal variation of larval settlement on the waterway wall.

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