Hirokazu Sumi

Survey of Disaster Preparedness in Municipalities in Chiba Prefecture and Study on Ability to Respond to Disasters

In this study, a survey by questionnaire was conducted on the realities of disaster preparedness in 54 municipalities in Chiba Prefecture and six municipalities on the coast of Ibaraki Prefecture. In the study, the knowledge and ability to respond smoothly to a disaster were also examined based on the survey results. There was a significant difference between municipalities in Chiba Prefecture in 2013 in terms of whether they had the standards and process for issuing evacuation orders or not. The ability to respond to a disaster is an important ability for implementing appropriate disaster preparedness for challenges relating to disasters. The ability to respond to a disaster is defined as consisting of specialized knowledge and skills in civil engineering.

A Study on the Dependence of the Migration Rate of Bottom Sediment on Different Equilibrium Beach Profiles

The relation between the migration rate of sand and water particle velocities in the two phase flow of a solid-liquid involving suspended sediments in the surf zone has not been satisfactorily understood yet. This study presents the effects of the different equilibrium beach profiles on the temporal and spatial distribution of migration rate of suspended sediments in the two phase flow of a solid-liquid, where sediments at the flow bottom are suspended under breaking waves. As a result, we have found that the migration rate of sediments averaged over a wave period between Type I and Type II of the beach profiles change. Type I has showed larger flow velocities than Type II in the entire region, particularly under wave crests. The migration direction of sand particles in Type I is the same as that in Type II. Specially, the migration direction is shoreward near the wave crests and seaward near the wave troughs in both types.

EXPERIMENTAL STUDY ON TIME AND SPACE DISTRIBUTION VORTICES GENERATED AROUND SUBMERGED BREAKWATER

This study investigates the characteristics of the vortex and the velocity field around a submerged breakwater utilizing flow visualization by PIV technique. From experimental observation, it is found that the Triple type breaking causes energy higher rate dissipation than the Plunging breaking. In addition, the steady vortex is generated at seaward edge of the submerged breakwater in case of the Triple type breaking. That is, the structural vortex on the crown strongly depends on the breaker type.

EXAMINATION OF NEARSHORE CURRENTS AND LITTORAL DRIFT AROUND ARTIFICIAL REEF

When installing an artificial reef on the shore, the general practice is to provide an opening width between breakwater bodies. The condition of the nearshore current and littoral drift varies depending on the setting of breakwater length and opening width. In this research, the nearshore current, littoral driftand wave height distribution at the time when the breakwater length and opening width were changed is discussed on the basis of experimental results. The wave height distribution was analyzed numerically. The results of calculations by the time-dependent mild slope equation agree with experimental results. The nearshore current is dependent upon the, breakwater length and opening width, and the larger theopening width is reference to the breakwater length the more easily the circulating current is general. The topographic change is affected by flow patterns and deposition occurs on the front shore when circulating current is generated. It was also confirmed that the artificial reef is effective in controlling the littoral drift.