Scale model experiment on density current in Sagami Bay

The project to create a fishing ground in the open ocean by raising deep ocean water (DOW) and discharging it in the euphotic layer as a density current where photosynthesis can be done by DOW rich nutrient salt has been carried out since April 2000, sponsored by Japanese Government Fisheries Agency and Marino-Forum 21. The name of this machine is the caged Ocean Nutrient Enhancer (ONE for short). The outline concept of ONE is: raising DOW of 500 m depth and 500,000 m³/day with a special impeller, which also sucks the surface water in order to make a mixed water of proper density. Discharging the nutrient-rich mixed water continuously and making a density current in the euphotic region. Increasing the phytoplankton (primary production) in the layer of the density current increasing fishes in the above sea area. Power for driving the impeller is supplied by OTEC (ocean thermal energy conversion) using the cold characteristics of DOW. To confirm the characteristics of the density current in Sagami Bay where the real sea experiment is scheduled, a scale model experiment of 1/200 in a continuously stratified salty water tank was carried out. The suitable discharge velocity to maintain the rich nutrient in the density current layer was researched in the way of 2 and 3 dimensional flow experiments. In conclusion, the thickness of the layer of density current in Sagami Bay in the summer season was estimated to be about 12 m, and the thinning ratio of DOW in the case of using a 3 dimensional ring nozzle is from 3 to 4 times. These results are very valuable for designing the ONE that is scheduled to be set up in Sagami Bay in the year 2003