Current and vertical mixing in a shallow lake

Summary

Some limnological surveys were carried out in Lake Kasumigaura, which is a typical shallow lake in Japan, in order to understand the current structure and the mixing properties. First, hourly variation of vertical distribution for lake current and water temperature were measured. Second, several times of surveys were pursued to get the continuous record of lake current and wind for several days. Statistical analysis of observed data might decompose the lake current into wind-induced current, seiche current, and flow induced by river influent, though the last is quite small in general. The mean component of wind-induced current is related to wind to a slight degree, while turbulent intensity follows the change of wind speed in short time. The seiche current is supercomposed on the wind-induced current. The rate of energy dissipation seems to be several per cents of the rate of wind energy supply averagely given to unit body of lake water. Furthermore, some phenomena which concern total energy balance in lake current are discussed.