天竜川における濁質成分の流程変化に基づく砂州地形の濾過機能推定

Abstract

Sediment transport from upstream and sediment deposition in dams reduces storage capacity poses long-term persistence of turbid water in dam downstream. Along the leading edges of lateral sandbars, turbid surface water downwells into the sediments where it spends varying periods of time as groundwater before emerging in upwelling zones at the downstream end of the bar. We evaluated the filtering efficiency of sandbar geomorphology based on the longitudinal changes in turbid water component in the Tenryu river. In the whole survey river section, sandbar area variation was mainly erosion tendency, and area variation in alternate bars was lower than double row bars. The relationship between filtering efficiency based on turbidity and area variation is approximated to a quadratic curve, and filtering efficiency is highest when the area variation is intermediate values. This result suggests that the filtering efficiency of sandbar could be evaluated by the turbidity variation.