THE CURRENTS AND THE DISTRIBUTION OF THE TEMPERATURE OF WATER IN MIWA RESERVOIR

Abstract

It has often been pointed out that there is a great difference between the distribution of the temperature of water in the man-made reservoir and that of the natural lake, and this difference is chiefly caused by the greater inflow and outflow in the reservoir. The observation of the current and the temperature of the water in Miwa Reservoir leads us to the conclusion that the horizontal distribution of the temperature of surface water is the result composed of two currents; one is caused by wind, the other by inflow of water. As to the vertical thermal stratification, we can see two thermoclines in the most parts of the reservoir, the upper one may perhaps be the result of the daily change of heat income, and the lower is considered to be that of the influence of the great quantity of inflow at some time before. Comparing two observations on separate dates, it is recognized that the distribution of the temperature of water in the reservoir is much more influenced by the horizontal heat transfer by the inflowing water than the vertical heat transfer. The inflowing water comes into the reservoir forming a density current; a remarkable convergence line collecting floating dusts nearby is seen on the surface of the water. By measuring the temperature and the velocity of that current, the structure of inflow is explained; the depth of the position of the inflowing water depends on the temperature of itself and the thermal stratification of the dead water. It comes into the corresponding layer which has the same temperature with itself. The temperature of it, however, has a tendency to rise after mixing with the hot water of the upper layer, thus the inflowing water makes a complicated motion of water with the wind-drift current of the surface.