Naoko Kohashi

A three-dimensional numerical model of hydrodynamics and water quality in Hakata Bay

The hydrodynamics and water quality in Hakata Bay, Japan, are strongly affected by the seasonal variations in both the gravitational circulation and the stratification in the bay. The three-dimensional hydrodynamics and water quality model has been developed to simulate the long-term transport and fate of pollutants in the system. The model is unique in that it completely integrates the refined modelling of the hydrodynamics, biochemical reactions and the ecosystem in the coastal areas. It is a 3-dimensional segmented model which is capable of resolving mean daily variations in all the parameters relevant to pollution control. It predicts daily fluctuations in the oxygen content at different depths in water throughout the year. It takes into account transport and settling of pollutant particles. It predicts light penetration from computed turbidity variations. It includes interactions between the ecosystem and water quality, through nutrient cycling and photosynthesis. The model has been calibrated well against the data set of historical water quality observations in Hakata Bay.

AWARENESS SURVEY ON EVACUATION BEHAVIOR IN HOKUSATSU HEAVY RAIN DISASTER

In order to make clear the awareness in evacuation behavior in Hokusatsu heavy rain disaster, we conducted a questionnaire survey. The questionnaires were distributed to local sections where many rescuees reside, and the answers were analyzed by regarding the rescuees as the persons who could not determine an adequate behavior in a risky situation. As a result, it was clarified that many rescuees did not evacuate because of the action of normalcy bias and cognitive dissonance. In addition a possibility was suggested that the evacuation information for disaster might not be understood sufficiently by some residents and that it might delay the timing of evacuation.

CONTROL OF SEDIMENT TRASPORT BY BaNK BLOCKS WITH DIRECTIONAL RESISTANCE PROPERTIES

The problem of beach erosion in our country grows more and more serious, so we must countermeasure against this problem without delay. Then we develop a effective method (we call the blocks used in this method BaNK block) to control sediment transport to cope with this serious problem. In this paper, we examine the fundamental properties of this method by laboratory experiments and field works in Nogita Coast. Firstly, we investigated the condition of flow occurrd when BaNK blocks were set in a wave progressing field by laboratory experiments. We confirmed that this method could make a flow at bottom layer and made a proper layout of BaNKblocks dear. Secondly, we set two kinds of blocks in Nogita Coast and observed a sediment transport around these blocks. By this field works we confirmed that sediment was transported by BaNKblocks to the direction we expected. From these results, we confirmed the possibility of beach nourishment by using BaNK blocks.

AN APPROACH TO THE APPLICATION OF THE METHOD TO IMPROVE WAFER QUALITY BY USING BOTTOM ROUGHNESS

Nowadays water pollution caused by eutrophication in a semi-enclosed bay has been a serious problem. In order to solve this problem, a method has been proposed to activate the water exchange between an inner bay and its outer sea area by using Bottom Roughness with directional resistance properties. In this paper, a possibility for practical use of this method was examined from many angles. First, the basic effect of Bottom Roughness on substance transport was examined by a laboratory experiment Next, 2-dimensional numerical simulations were carried out to estimate the validity of this method in the Nagoya Port that has a complicated topography. Lastly, it was it-ported that four kinds of Bottom Roughness were sunk to investigate their influence on the scour of seabed and the water environment. From these results, it becomes clear that this method is efficient to improve the water quality in real sea areas.