UNFABORABLE GROWTH OF GREEN FILAMENTOUS ALGAE IN GRAVEL-BED RIVER WITH LESS DISTURBANCE

Abstract

In downstream of dams, we often observe unfavorable growth of green filamentous algae and they suppress the attached algae fed for Ayu fish. In order to restore Ayu-fishing activity, several attempts have been tested such as flushing and introducing sand and gravel in a river bed. In this paper, the system how the discharge control by dam changes the bed composition or constitution as growing condition of attached algae is studied. According to the field test, the growth rate can be estimated, while we previously conducted a fundamental research to estimate the detachment rate of algae by impacts caused by colliding sand. In this paper, by coupling these information, we propose a logistic equation model and conduct a simulation algae dynamism responding to flow dynamism. We chose the research field from the Yahagi river for this study, where flow dynamism is strongly controlled by dams and the extraordinary growth of green filamentous algae bother Ayu-fishing activity. This study may provide good information to keep the river-bed condition favorably from the ecological view point.