渡良瀬川山地部における生息場としての河床構造と流域・河道特性の関係性

抄録

The riverbed structure is often focused in terms of habitat for the benthic animals in previous studies, however the mechanism how such kind of riverbed is formed, or what basin/channel characteristics affect the structure is yet to be clarified. By conducting field surveys at the mountainous regions of the Watarase River, this study clarifies the relationship between riverbed and basin/channel characteristics, and evaluates the riverbed in terms of habitat for benthic animals. First of all, it was found that the representative diameter of the bed material corresponds to the critical diameter for the mean annual maximum discharge. This is due to the existence of large boulders. The shape of size distribution curve is almost same among all sites because of the harmonious size distribution from boulder to gravel. In milder reach with alternate bars, riverbed material on flat riffle is diverse, but it was monotonous in steeper reach with step-pool structure due to the sorting process. Size distribution of fine gravel and sand, however, should be coarse and uniform in order to create soft riverbed.