| Dispersion of Yasu River Water in Lake Biwa |
| Shuichi ENDOH, Yasuaki OKUMURA, Munetsugu KAWASHIMA, Naonori FUKUYAMA, Yuko ONISHI, Naoko MAKAMURA, Reiko BAMBA and Satoko TANAKA |
| Japanese Journal of Limnology, 68-1, 15-27, 2007 |
| Continuous spatial observations of the water quality of Lake Biwa and
the Yasu River were conducted during 1997 and 1999. The water quality of
the river shows typical seasonal variations, though with sudden increases
in turbidity and decreases in both temperature and electric conductivity
after a heavy rainfall. A comparison of water temperature between the lake
and river indicates a seasonal change of river water dispersion in the
lake. The river water flows into the lake surface layer in spring, intrudes
into the thermocline in summer and fall, and flows into the bottom layer
of the lake in winter. Based on these results, the renewal time of lake water is estimated to be 17.03% a year. This value is the result of a poor renewal ratio in spring and an acceleration of water exchange in summer and fall. The intrusion of a considerable amount of river water into the thermocline caused by a typhoon is especially important for the rapid renewal of lake water. |