Abstract
The movement of lake waters has been considered as one of the basic field of limnology. However an accurate and satisfactory observation of the movements could not be easily taken due to the non-steadiness of lake currents as well as indistinctness of the movements.
The movements can be classified as waves and lake currents and the latter is the main concern of this paper. The research was carried out by the following methods:
1. Measurements of lake currents by special floats.
2. Measurements of lake currents by lake sediments.
What should be noted here is the type float that the author used for the measurement. It could be used at the any depth of the lake unlike ordinary ones. The following points have been concluded:
1. A certain amount of water movements can be seen around the lower part of thermo cline where no current was ordinarily thought to exist so far.
2. During the stagnation period of thermal stratification in summer, turbulent flow exsists down to the depth of 2 meters from the surface and beyond that depth laminar flow can be seen. These results led to the conclusion that diffusion phenomena of substance should not be thought to be active except near the surface layer.
3. In autumn, the depth of the layer of turbulent flow becomes around 10 meters. This shows that substance diffusion by turbulence plays an important role during the cooling stage from summer to autumn. Eddy diff usivity calculated from temperature changes was obtained to be several decuple as large compared with molecular diffusivity.
4. In the summer stagnation period water circulation as well as substance diffusion are horizontal while they are vertical in the autumn partial circulation period.
