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In recent years, Lake Abashiri has been confronted with serious problems due to water accidents induced by aoshio and eutrophication. By using a fish detector and ADCP, we could make clear the spatial and temporal structure of density stratified flow, the short-term behaviors of salinocline(halocline) just after the occurrence of aoshio, and the overall characteristics of the flow in this lake. Based on the results of the observation, we carried out the numerical analysis regarding to the time-varying behaviors of the density interface and the wind-driven flow. Comparing the calculation results with field data, we could evaluate the influence of wind, the horizontal and vertical structure of the lake on the flow and the behaviors of salinocline.

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This paper deals with the characteristics of the salinity intiusion in Abashiri River, which located in thenortheast of Hokkaido Island we found that the chief factors influencing mechanical properties of salinity irittusion istidal current and the river profile in Abashiri River. The present authors had alirady proposed the changing condition of mixing pattern of salt wedge under the influence of tidal cunrnt. By using these concept, it is possible to evaluate the change of the mixing pattern with salinity inbusion under the influences of the disturbance due to wind on the surface of the water and the river profile couldbe negligible in Abashiri River. However, we found that the salt wedge was completely broken down without the influence of tidal current at the 4km poirit (Kagamibasi-bridge) away from mouth of river, where a large projection exists on the bed. Hence it is necessary to apply the modified changing condition