MOVEMENT OF SURFACE WATER TRANSFERRED TO THE BOTTOM OF THE OGOUCHI RESERVOIR

Abstract

In order to prevent algal blooms in the Ogouchi reservoir, a pump system was deployed to transfer surface water containing phytoplankton and to release it in the bottom of the reservoir. Field measurements were conducted to investigate the movement of the released water. Turbid water was poured into the pump system, and the vertical profiles of temperature, turbidity, and chlorophyll-a around the pump outlet were determined.The released turbid water was not confirmed near the outlet and was not found in upper depth; whereas, chlorophyll-a was distributed horizontally at depths of 7 m and 11 m. Horizontal movement of the reservoir water was estimated from the measured current profile and vertical migration of released water was analyzed using plume theory. Based on the two analyses, we conclude that the peak concentration observed at a depth of 7 m was a natural propagation of phytoplankton, and the phytoplankton contained in the released surface water caused the peak concentration observed at a depth of 11 m.