Natural lakes in Hokkaido

本研究旨在弄清日本北海道东北部的网走湖的水文水力特性，并提出净化网走湖的方法。从1993年的实地观察。结果表明，该湖的生态系统和环境已受到淡水和咸水双层结构及富营养化的影响。基于这些结果和数值分析，我们预测了盐跃层的长期行为，并在1994年调查了河流入湖诱导射流的行为。结果表明，网走盆地近60年来的盐跃层逐渐上升，与年降水量的减少有密切关系。在网走湖这样的小型湖泊中，考虑科里奥利力是必要的。1995年明确了湖泊双层结构与水流的关系，并提出了湖泊淡水化的方法。结果表明，在密层结构、风、地层、科氏力和河流的共同作用下，绕湖中心的水流在垂向上形成四层结构。青潮是在刮了很长时间的大风中发生的。为了控制青潮，降低淡水和盐水的分界面是有效的。我们证实了引入淡水人工方法的必要性。

This study was carried out for the purpose of making clear the hydrogical and hydraulic properties of Lake abashiri which located in northeast of Hokkaido Island in Japan, and suggesting purification method of the lake. From the field observations in 1993. We concluded that ecological system and environment of the lake have been influenced by two-layr structure of fresh and salt water and eutrophication in the lake. Based on these results and numerical analysis, we predicted the long-term behavior of the salinecline, and investigated behaviors of jet induced by river flow into the lake in 1994. We found that the salinecline gradually has been rising, closely linked with decreasing of annual precipitation in the Abashiri Basin in these 60 years. It is necessary to consider coriolis force in small sized lake like Lake Abashiri. In 1995, we made clear the relationships between two-layr structures and flow of the lake, and suggested methods for freshwater in the lake. We found that the flow around center of the lake formed four-layr structure in vertical direction, influenced by dense layr structure, wind, formation, coriolis force and river. Aoshio occured with the strong wind which blows for a long time. In order to control Aoshio, it is effective descending the boundary surface between fresh and salt water. We confirmed that it is necessary to induce artificial method for fresh water.