Effects of Density Current Generator In Semi-Enclosed Bay

A research on "density current generator (DCG)" which is a new concept machine to agitate the stratified water area widely and calmly by using a density current has been carried out. The machine draws the water from both surface and bottom layer in a stratified water area, and mixes and discharges it on the middle layer. The discharged water is spreading and staying on a same density layer horizontally as a density current driven by the gravity. By making use of the machine, the hypoxic water that appears quite often in the bottom of semi-enclosed bay is pumped up and may be eliminated. The prototype machine, which discharges the density current of 120,000 m³/day driven by 5kw electric motor impeller was developed and set up in Gokasho Bay, Mie Prefecture Japan, in June 1997. Since then, the machine is running for ten years continuously except winter season when the stratification disappears. After 3 years continuous running of the machine, an effectiveness of the machine such as the prevention of red tide at the bay end, outstanding increase of clams inside of the bay, etc. have been observed. Furthermore, after 9 years, the outstanding increase of seaweeds on the seafloor of the whole area of the experimental region is confirmed by the on-site investigations. These results lead us to believe that the DCG has excellent potential in terms of agitating and purifying stratified water of very large area, and also in terms of increasing seaweeds and benthos on the seafloor by eliminating the hypoxic water.