FIELD OBSERVATION FOR CONVECTIVE CIRCULATION DUE TO SURFACE COOLING IN THE SIDEARM OF A RESERVOIR

In fall of 2005, CTD measurements were conducted twice in a part of the reservoir from the sidearm to the vicinity of the dam. Bottom water of lower dissolved oxygen was observed in the deepest layer beyond 70 m in the first series of the measurement, it disappeared in the second series after 10 days. A continuous current monitoring in the bottom layer of the sidearm was also conducted to find nocturnal convective circulations as bottom currents. The surface and middle layer temperatures dropped uniformly while only the bottom temperature increased as well as dissolved oxygen. The flux estimation convinced that the initial amount of the oxygen defect is within the order of total oxygen inflow into the bottom layer and the bottom water was replaced by the water from the sidearm.