TECHNIQUES FOR THE IMPROVING STABILITY OF THE SEA WEED ENHANCEMENT STRUCTURE ON THE SEA BOTTOM

Sea weed beds have important functions as water purification, spawning and nursery grounds for valuable marine resources. In recent several decades, sea weed beds have been decreased remarkably by coastal reclamation, pollutant discharge from land area and gathering up of the sand from sea bed in the Seto Inland Sea, Japan. Therefore, the Japanese fisheries research institutes that located coastal areas have been conducted planting experiments of sea weed beds in various coastal areas for about 30 years. However, there are few successful outcomes despite their efforts. In terms of environmental condition, various factors must be considered for developing sea weed bed using the artificial reefs and sea weed enhancement structure. Recently, it is neccesally to consider the stability of structure against sliding resistance, toppling and lifting force on the seabottom. Therefore we developed an artificial reef as the seaweed enhancement structure with the functions of the current control and the high stability on the sea bottom. In this study, we tried realizing the former function by the hydraulic experiment and sliding resistance tests using a real scale model similar to the actual scale spikes. From the results of tests, we developed a theory for calculating the coefficient of static friction of various shapes spikes installed at the bottom of the reef made of concrete. Besides, we proposed a method for calculating the coefficient of static friction of the spike even if the bottom sediment conditions, facility conditions are different. Also, we examined the effect of fouling function of algae around the structure, which was settled at the real sea bottom by measuring the concentration of algae and aggregation of fish juveniles.