A NEW METHOD OF WATER QUALITY CONTROL IN A EUTROPHIC RESERVOIR USING VERTICAL CURTAINS

摘要

In 1994, vertical curtains were installed for the first time in Terauchi Dam Reservoir in Japan to prevent its algal blooming. Since then this method, being cheap compared to other methods, has also been applied to recently completed Hinachi Dam Reservoir and Urayama Dam Reservoir. Inflow has a lower temperature than the epilimnion in the reservoir. Thus, the longitudinal division of epilimnion by curtains curtails the nutrient supply from the underlying inflow into the euphotic epilimnion in the downstream of the curtain, which then prevents the algal blooming there. Although sufficient results were obtained in Terauchi Dam reservoir, experiments were carried out only during the starting period of stratification, from March to June. Therefore, some of important factors such as influences of alteration of thermocline characteristics due to summer-time flooding have not been investigated and quantitative evaluation on the effects has not been sufficient, either. So far, the curtain method has been introduced only to several reservoirs, and too few numerical analyses have been conducted to find the relation between dimensions of method and results. Thus, for the designing of the depth and position of curtains, the case of Terauchi Dam was always adopted although some amount of difference was expected depending on characteristics of reservoirs. Under the circumstances, using numerical analysis, optimal conditions for the withdrawal depth, curtain depth and installation position and the necessary number of curtains are discussed and obtained for a typical middle scale reservoir in Japan and its hydrological and meteorological conditions.