| In the vicinity of Asahikawa City of the Ishikari River, the zone of exposed bedrock has been increased due to the degradation of alluvium. We surveyed the fall habitat of tribolodon sachalinensis and stone loach (Barbatula barbatula) in both bedrock and alluvial beds. Based on survey results, we made the SI(Suitability Index) concerning with flow depth, velocity and substrate, and compared the WUA(Weighted Usable Area) before and after the bedrock is exposed. The planar distribution of water depth and flow velocity required for the evaluation of the WUA was calculated by 2D numerical simulations. The analysis results showed that the WUA of tribolodon sachalinensis has been reduced 66%, and the WUA of stone loach has been reduced 81% by bedrock exposing. The analysis results also suggested that the change in water depth and flow velocity due to the narrow inner channel formed by bedrock incision has a great influence on the WUA. |
