抄録
In an intermountain lake, Lake Okotanpe, Hokkaido, the effects of a river on the seasonal circulation of the lake were investigated through the observations at low-water stage of lake and river.
From the observations of lake currents and water temperature, the following results were obtained.
1) The influent rivers have an almost constant diurnal variation in water temperature during the period of rainfall, ranging from 6 to 13, and, as a result, the inflow water may be transferred into density currents with the three flowing conditions according to the seasonal variation of thermal conditions in the lake. They could be described by interflow in spring, interflow-underflow in summer, and persistent underflow in autumn.
2) Density underflow was discovered in October 1983, more conspicuously in the lake basin north of the 'threshold', but in the southern basin, followed by its bifurcation and subsequent decay possibly due to extensive and turbulent entrainment from the open basin.
3) During the ice-covered period of no river inflow, a little outflow can induce a baroclinic field and consequent circulation in the whole lake with stronger currents near the bottom at 5-6 cm Es-1.
The above results of October 1983 can be simulated consistently by a numerical experiment with a vertically integrated model, except that inflow water does not reach the maximum-depth area of lake, because the intrusion of cold river water is not taken into account.
