To solve the water quality problems in the Lake Nakaumi and the Lake Shinji, it is necessary to make clear the characteristics of flow and water level variation in these two lakes. Flows in these two lakes are dependent on each other, because these two lakes are connected by the Ohashi River. We have to investigate flows in the Lake Nakaumi, the Lake Shinji and the Ohashi River together.
We compared meteorological external forces, the water level variation and the flow of the Lake Shinji with those of the Lake Nakaumi. We made clear the propagation mechanism of water level variation in the Lake Nakaumi, the Lake Shinji and the Ohashi River, respectively, by calculating time lags of water level variations in many observation points. Furthermore, the propagation mechanism of water level changes by wind set up was also investigated.