WATER QUALITY RESTORATION BY INJECTING INTERMITIENTLY SURFACE WATER INTO HYPOLIMNION

The problem that oxygen depletion observed in eutrophic natural lakes and reservoirs damages natural benthonic organisms and induces nutrient release from the sediment is becoming serious. For this problem, we proposed a method which transports surface water including a large amount of dissolved oxygen (DO) to a bottom layer in which DO is not usually enough. The effect of injection of surface water into hypolimnion on water quality restoration by this system has already been proved. In this study, we investigate the degree of water quality restoration in case of intermittent injection of surface water into hypolimnion by field experiments and numerical experiments.From numerical experiments, we find that it is expected that the water quality can be restored, even if the period of supplying surface water is shorter than the period of supplying no surface water.