EFFECTS OF BUBBLE CIRCULATION ON STRATIFICATION IN A SMALL RESERVOIR IN SUBTROPICAL ISLAND

Abstract

 The effects of a bubble circulation system on water temperature stratification in the Gima Dam reservoir in Kume Island, Okinawa were evaluated based on the field surveys and numerical analysis. Approximately 240 NL/min. of compressed air produced by a 2.2 kw compressor is distributed to four diffusers. Approximately 60 NL/min. of compressed air per unit is released from the bottom of the lake at a depth of about 10 meters. As an evaluation of the effects, the bubble plume structure, which is the local flow around a rising bubble, and the stratification in the entire reservoir were studied respectively. In spite of the extremely small air volume, less than one-tenth of the air volume of the existing cases of this countermeasure, the local bubble plume structure was formed even in mid-summer, which is necessary for water quality preservation. Furthermore, the whole reservoir was found to be mixed.