かつら沢貯留水池における密度躍層の季節的変化

Abstract

The seasonal variation of water temperature and suspended solid concentration (SS) were measured in Katsurazawa Reservoir in a period from May, 1978 to April, 1979, Measurements were carried out at a station 50-100m from the dam site.In early spring the reservoir was filled with water of low temperature and high SS which was caused by the melting snow. The inflow water formed the transitional SS layer at the same depth as thermocline in spring and early summer, In the circulation period after summer, both the thermocline and the SS transitional layer descended toward the bottom. In November and December, the latter remained at a depth of about 30m after the former had disappeared, showing that the thickness of the surface mixing layer could not be adequately estimated only by the apparent thermocline. Concentration of SS increases exponentially with depth in each of the surface and the bottom layers. The vertical gradients change under the influence of seasonal climate condition. In the heating period, water density of the surface layer is much lower than in the bottom layer, and so the density stratification is stable. On the other hand, the gradient of vertical distribution of water density is small and the stratification is unstable in the cooling period.