Spatial-Temporal Fluctuation Of Salinity In Lake Jusan

Mikio Sasaki, Hitoshi Tanaka, Makoto Umeda

Wednesday 1 july 2015

11:45 - 12:00h at Asia (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 9G. Environment - Impact

1. Background Iwaki River in Aomori Prefecture, Japan, flows through Tsugaru plains to Japan Sea after going out through Lake Jusan. Iwaki River is a 1st class river managed by Ministry of Land, Infrastructure and Transport. The river mouth has been defeated at rough seas by higher waves caused by the strong wind from the west in winter. In the past the river mouth had repeated blockage. However, after the construction of the jetties on the both shores of the lake mouth, the blockage of the lake mouth has not occurred since 1930. After constructing the embankments, seawater comes to enter the lake regularly, due to it, the corbicula as black shellfish grows in the lake, and, consequentially, the corbicula fishing becomes active. The lake is the best productive water area of the shellfish in Japan in 2013. Now, Lake Jusan is very important lake in Aomori Prefecture as corbicula’s home. Because the corbicula grows up in the brackish lake, the motion of salt water to the lake causes the important effect for the growth of the corbicula. Then, it is important to make clear the characteristics of the motion of salt water in Lake Jusan. 2 Study Aims and Study Method The present study aims to investigate the characteristics of the motion of salt water in the lake and to show spatial-temporal fluctuation of salinity in Lake Jusan. Field observations for the motion of the salt water going up to the Lake Jusan and going down from the Lake Jusan to the sea are carried out from June to October. In the observations, water temperature, the flow direction, the flow velocity, and the salinity are measured. By using the velocity in the lake mouth obtained by the continuity of the water in the lake from the observed data of the lake-water-level, the salinity fluctuation in the lake are shown spatially and temporally. 3. Main conclusions The motion of salt water in the river mouth of Iwaki River in 2014 is shown in the present study. The time change of the salinity distribution in a perpendicular direction is investigated by using the field observation in the present study. The vertical distributions of the salinity are shown clearly by theory and observations. And the present study shows that the theory given by Sasaki, Tanaka and Umeda can generate well the movement of the saltwater in the lake. Key words: river mouth, saltwater, stratified flow, salt wedge