Goichiro TAKAHASHI, Yoshiharu ISHIKAWA, Tatsuo NAKAI and Takehiko OHTA
The central part of a check dam was completely removed for the purpose of the biodiversity restoration in a mountain stream in the Shigekura River of the Tone River system. In the section including the removed dam and the natural stream section in which the dam is not installed, restoration of stream environment was considered by measuring and examining change of logitudinal profile of stream bed and depth of water, and distribution and form of pools. The concavo]convex feature of the stream bed was analyzed by spectral analysis. Comparisons were made between the section affected by the presence of the dam (D]2013) and natural section (U]2013). The pool density and the ratio of the cumulative length of the pools to the section length were found to be smaller in the former compared with those in the latter. In the section affected to the dam, there is almost no peak projected by power]spectrum density. This shows that there is no periodicity in unevenness of a stream bed, and the section accordingly does not have the natural form characteristic of a stream. The ratio of the cumulative length of the pools to the section length in the upper section (D]2013]2), i.e. where the dam was removed, is longer than that in the lower section of the removed dam (D]2013]1).Although the big difference was not seen between the upper and the lower sections of the removed dam about the morphological feature of each pool, unevenness of the stream bed with periodicity was observed in the upper section. In the upper section of the removed dam, stream bed fluctuation becomes active and pool is reviving, the section is accordingly approaching the quality of a natural stream by dam removal.
Key wordsFremoval, check dam, restoration, stream environment, pool, spectral analysis