Abstract
During the years 2004-2008, investigate of the oxygen concentration distribution and seasonal changes of thermocline form in hypolimnetic water were conducted in the Sanbe reservoir. In 2006, high - oxygen - concentration water was supplied into hypolimnetic water using a new type of oxygenator (WEP system). As a result, the thermocline formed at 12 m depth, and water temperature was 7°C throughout the year in the hypolimnion. The amount of dissolved oxygen in the hypolimnetic water (528,000 m3) after the turn over was observed at about 5,000 kgO2 (Feb. 2007) - 6,000 kgO2 (Feb. 2008) and the oxygen consumption was 58.6-32.0 kgO2·d-1. For this reason, it was predicted that the dissolved oxygen depletion would occur every summer. Several weeks after the WEP system was used, the high - oxygen - concentration water widely spread to 800 m (dam's bottom area: 8.7 ha) from the WEP system without destratification. The oxygen transfer efficiency of the WEP system was observed to be between 82 and 87%.
