板櫃川で実施された多自然川づくりの魚類生息環境からみた評価

摘要

多自然型川づくりは1990年に始まって以来，日本全国 において実践されてきたが,中には魚巣プロックの乱 用や中·下,に溪流域の様相を呈する巨岩の配置など, 生態系ゃ景観に配慮したとは言い難いものも散見された. そこで，2006年に「多自然川づくり基本方针」が新たに 定められ，抜本的見直しが行われたところであるが， 多自然川づくりは現場の±木技術者によってまだまだ経 験的に進められているのが現状である. これは，魚類等 の生息環境の保全に関する工学的知見の拡充と技術の確 立がまだまだ不十分なためといえよう.%In the midstream area on the Itabitsu River which flows through Kyushu northern part, a nature-friendly river work was done in 2005 by about 3 times of width of a river expansion compared with the upper and lower style, by the non-fixation of the waterside and by the existing of megaliths in the fairway.rnThe purpose of this research is to evaluate the repairing method by the fish habitat. We investigated the fish distribution and the physical property in 2005, 2008, 2009 in 3 or 4 sections repaired by different methods. There were many kinds of fish in section B in 2005 just after repairing by the nature-friendly method. The number of kinds was same with the natural section D which was repaired about 50 years ago, and with the section C which was repaired 2 years ago by the fixation of the waterside by deleted megaliths in the fairway. But, after that, the number of individuals of fish in the section B decreased substantially like the section D. We clarified that the number of megaliths was correlated with the number of individuals of fish by analyzing the physical elements statistically. In the stream, the number of megaliths was positively correlated with the average water depth and the percentage of granule on the riverbed. Therefore, we supposed that the number of megaliths raised the value of the fish habitat.