矢作川古鼡の中州の発達過程とその侵食を促進する事業の効果

Abstract

We surveyed the evolution of a mid-channel bar from 1960 to 2009 using aerial photographs and cross sections of river channel, and assessed the effect of vegetation and soil stripping from the bar in 2007 upon the erosion of the bar, in the Yahagi River, central Honshu, Japan. The stripping was also aimed to mitigate armouring of the extremely stable river-bed by supplying eroded sediment from the bar to the river-bed. The aerial photographs and cross sections of the channel show that the mid-channel bar grew in height from 1960’s to 2007 in parallel to the development of vegetation. After the vegetation and soil stripping in 2007 until 2009, the upstream part of the bar tended to be eroded whereas deposition was dominant on the downstream part of the bar. As a whole of the bar, the deposition slightly exceeded the erosion. Vegetation survey in the spring, summer and autumn of 2009 suggests that recovered vegetation would tend to assist the deposition. Accordingly, the vegetation and soil stripping in 2007 hardly assisted the erosion of the mid-channel bar, and probably did not have an apparent effect upon mitigating the armouring.