The river water flowing into a lake is considered to mix gradually with the lake water and may diffuse in that lake. The mechanism of mixing and diffusion in such cases are so complicated that any definite theoretical investigation has not yet appeared.
In any flood, when the river water is turbid owing to much suspension and solvents in the water, its density will be higher than that either of the river water in an ordinary state or of the lake water. After the flood, if we can detect the density distribution of the lake water near the mouth of the river, the diffusion process of the inlet water in the lake will be found.
On such assumption we tried to measure the density distribution of the water of Lake Biwa off the mouth of the River Ado ; the results obtained are shown in Table 2 and are graphically represented in Figs. 2, 3, 4 and 5.
The density measurements were carried on in the laboratory of the Geophysical Institute, Kyoto University, by using a specially designed equipment for density measurement. Its accuracy is±2×10
-6 gr/cm
3. Δρ, the tabulated values (Table 2) indicate the density difference between the sampling water and the distilled water at 0°C ; i.e., Δρ
s0-Δρ
d0.
It is very interesting that there likely exists a water mass of high density,
Δρ=70, floating in the surface layer at about 1500m off the mouth of the river.Another water mass, Δρ=5060, sinks to the bottom at about the same position. Moreover, a small water mass occurs in the layer of 1020 m in depth 500 m off the mouth. These water masses of high density are certainly brought into from the river at any previous flood, because the proper density of the lake water seems to be about Δρ=3040.
We attempted to analyse the water masses as in the case of the sea water, in taking the density and B. C. P. alkalinity, instead of the water temperature and salinity for the sea water. It is easily seen in Fig. 7 that the river water in the ordinary stage is in the lower left corner, the lake water proper nearly in the central region, and the inlet water at flood is scattered in the upper region. Such a configuration may prove to hold the key to solve the mechanism in mixing and diffusion of the inlet river water in the lake water. We intend to discuss this problem in the future when additional data are obtained.
In conclusion, it is worthy of notice that the inlet river water and the lake water cannot easily mix, because the water masses of high density maintain their properties in the lake for such a long time.
抄録全体を表示