No abstract

We evaluated the safety of two moored ships in the port of Shimizu against the Tokai earthquake tsunami based on the numerical simulations. We first carried out the tsunami simulation and obtained the tsunami wave profiles at two berths in the target port. And then we performed the ship motion simulations by using the tsunami waves as the external forces. The main results are: 1) The surging is the significant motion of the moored ship against the tsunami, 2) The tensions of the spring and breast lines are larger than those of the head and stern lines, 3) The larger moored ship moves widely and influences the mooring system, and 4) The moored ships and mooring systems are safe against the tsunami.

Field observations of water quality in the summer of 2010 reveal that the wind wave is one of key factors for temporary recovery of near bed dissolved oxygen DO concentration from hypoxic state in the inner Tokyo bay. The observation was a part of monitoring campaign to elucidate the behavior of the hypoxic water in the area. Basic parameters of water quality such as dissolved oxygen, salinity, temperature and turbidity were measured by a mooring system for 3 month from July through September in 2010. Physical parameters were also obtained for current profile by a bottom mounted ADCPs and for wind waves by an ultrasonic wave gauge respectively. DO concentration measured at 50 cm above the bottom intermittently increased especially after relatively higher wave events. The data also shows that the DO concentration near the bed is highly correlated with suspended sediment concentrations.

In order to clarify the effect of wind and fresh water discharge on the hypoxia inside Tokyo Bay, we investigated the sea surface residual current measured by the HF radar data. Numerical simulation which solves non-hydrostatic 3-D flow and multiple ecosystem was also conducted. At the sea surface of the head of Tokyo Bay, a clockwise circulation appears due to south wind from spring to autumn. The clockwise circulation piles up the fresh water from river which causes the growth of stratification and hypoxia at sea bottom. South wind stirs the sea surface and bottom water and causes the low density bottom water which promotes the intrusion of high density water and strengthens the hypoxia.