EFFECT OF REPLENISHED SEDIMENT ON RIVER ENVIRONMENT IN DOWNSTREAM REACH OF DAM

Abstract

Reservoir sediment replenishment to downstream reach of dam has been conducted in the Nakagawa, Tokushima. However, the effect of replenished sediment on river environment is not clear. In this study, the detachment of attached algae and its influence are studied by field observation and numerical simulation.

The results of field observation and numerical simulation show that the attached algae is almost entirely detached by a flood with the sediment augmentation. On the contrary, over half of attached algae survive in the numerical simulation for the assumed flood without the sediment augmentation. The comparison of longitudinal distribution of δ¹³C and δ¹⁵N in the riverbed sediment between before and after the flood reveals that δ¹⁵N can be a tracer of the detached algae and the deposition of the detached algae could cause secondary pollution in the downstream reach of dam.