Author(s): Yasunori Totsuka; Hitoshi Tanaka; Yutaka Fujita; Hiroto Yamaji; Manabu Takuwa; Masaki Sawamoto
Linked Author(s): Hitoshi Tanaka
Keywords: Stratification; Thermocline; Internal seiche; Two layer model; Colioris force; Internal Kelvin wave
Abstract: Lake Inawashiro is a typical deep acid lake in Japan. The water from Nagase river is the cause of acid water in this lake. Deep lakes have a possibility of occurring internal seiche, which is very important in terms of not only hydraulics but also water quality, because it contributes to the water purification and mixture. Field observation was carried out in autumn season when the thermocline breaks down gradually. From the result of water temperature observation, the existence of internal seiche was confirmed. The wave height and difference of water temperature attain to about 15m and 8 degree, respectively and internal seiche continued about6 days. After this event the thermocline was disappeared. It thus suggests that the internal seiche mixed the lake water all over the depth. To examine three dimensional interface response to wind stress, two layer model using a constant depth was applied. The nonlinear term and the interface stress are neglected to calculate this model. The input external force is only wind stress, which is obtained at AMeDAS (Automated Meteorological Data Acquisition System, Japan Meteorological Agency) station located about 3km north from Lake Inawashiro. From the result of calculation, computation and observation shows fairly good agreement, and the existence of internal Kelvin wave was confirmed in Lake Inawashiro. However there are some differences between observed and calculated. One of the reasons about it, the difference of actual wind and AMeDAS data is regarded.