河川の横断測量データに基づく水面比高分布を用いた生息場評価法

抄録

Frequency distribution of bed relative elevation (relative to normal water level) determines the potential habitat availability of sediment bars for various biotic communities in rivers. We developed a method to examine the frequency distribution in the past and present by using data of cross-sectional bed profiles, which have been routinely measured for several decades by river managers.

In 0-24kp reaches of the Kizu River, where channel has been degraded since 1960’s, cross-sectional shape of bars changed from concave-type in 1960’s to convex-type in recent decades. Accordingly, the frequency of low relative elevation (0-0.5m) decreased, while that of high elevation (>2.5m) increased. The frequency of a middle elevation (0.7-1.5m), which maximize the habitat suitability of "tamari (floodplain ponds)", showed a unimodal change with a peak in 70’s to early 90’s. Thus, in case of using tamari as an index of ecosystem health, the sediment conditions in 70’s to early 90’s are suggested to be preferable for the Kizu River ecosystem.