| Storm surges often lead to enormous disasters in coastal areas, and accurate predictions are crucial for disaster prevention. Recently storm surge predictions using numerical models have advanced and been operationally used in several countries. JMA operates a 2-dimensional linear storm surge model with horizontal grid resolution of 1 minute in each direction, which is much finer than those of weather models. Accuracy of this model is reasonable for inland bay areas, since the topographies of coasts and water depth mainly determine storm surges in inland bay.On the other hand, it is difficult to estimate storm surges accurately along coasts and islands shores where high waves tend to hit, even using a 3-dimensional storm surge model. This reason could be due to effects of ocean waves like wave set-up, which is not included in conventional storm surge models. A development of a storm surge model, which includes effects of ocean waves, is necessary. We have developed such a storm surge model for operational predictions. It consists of a storm surge model based on Princeton Ocean Model (POM) and the third generation wave model MRI-3 originally developed at MRI. Radiation stresses are calculated in the wave model and used in storm surge calculation. The expression of stress to storm surge is parameterized, since grid resolution is coarser than the scale of wave set-up phenomena. In August 2000, TY KIROGI (0003) passed by Hachijo Island located in the Pacific Ocean and a large storm surge of almost 250cm is observed at the Yaene tidal station located on the western coast of Hachijo Island. We simulated this case by this new model. The maximum storm surge at Yaene tidal station simulated by a conventional storm surge model was much lower (about 50cm) than the observation. This calculated value is explained just by static pressure balance. The effect of wind set-up is not crucial since Yaene Port is quite small bay with rather deep water depth. From our wave calculation, quite high waves (wave height of 7 m) hit Yaene Port when the storm surge occurred. As a result, wave set-up must play a significant role in the storm surge. Our new model estimated maximum storm surge of about 170cm, and the value of about 120cm is improved by considering wave set-up. This value still indicates underestimation and it seems to result from some factors like grid resolution or wind estimation.We simulated other cases and the results of the simulations indicate that improvements are quite well. We have a plan to put this model into operation in near future. |
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