Abstract
The Ogochi reservoir is one of the biggest dams for waterworks in Japan. We have been monitoring its water quality since its establishment. We introduced vertical curtains and some types of equipment in order to suppress algal blooms in the reservoir. The equipment showed suppressive effects against algal bloom expansion by suppressing the increase in surface temperature in the reservoir. An extensive flood in September 2007 induced a marked change in water quality. Because there was no turbidity before the flood, turbid water influx was observed in the depth range of 0-40 m near the dam. In the case of an extensive flood, it is necessary to operate the gates of the dam to form the secondary thermocline at an appropriate depth for discharging turbid water speedily.
