Iwao Hasegawa

EXPERIMENTAL STUDY ON THE EFFECT OF GRAVITY DRAINAGE SYSTEM ON BEACH STABILIZATION

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

EXPERIMENTAL STUDY ON THE DESIGN OF SUBMERGED BREAKWATER AND END SECTION OF LARGE-SCALE SHORE PROTECTION FACILITIES

Large-scale submerged breakwater, jetties and nourishment has been constructed as shore protection facilities. The facilities of 1,630m long within the 2,540m overall length have been constructed. A belt-shaped scour is formed behind the submerged breakwater, and fill sand is flow out through the end section of the facilities. The remainder section 910m long will be constructed in the near future. The present study is, therefore, considering the adoption of the submerged breakwater of two rows and the plane configuration of end section of facilities to prevent or reduce the belt-shaped scour and outflow of fill sand at the remainder section. Three-dimensional hydraulic model test and twodimensional numerical model test were carried out to decide the standard section and the configuration of the end section. As a result, it is confirmed that submerged breakwater of two rows is more effective than conventional submerged breakwater. And the plane configuration of the end section of the facilities is decided.

Risk Analysis of Drifting Timber for Jacket-type Structures Located in River Mouth

Large jacket-type structures are employed in the construction of the forth runway, Tokyo International Airport (Haneda). The runway is located at the mouth of Tama River flowing into the Tokyo Bay and the jackets are employed in the one -third part of runway so that the flood from the river may not be disturbed by the runway. Meanwhile many timbers may be floated from the upstream in the flood and they may cause the collision on a pier composing the jacket structures. This paper describes at the first an experiment for the probability of collision by the drifting timber in a basin with the scale of 1/25. The horizontal motion of five model timbers is analyzed using the 3-D video camera tracker. Secondary an experiment for the collision force measurement is carried out in a channel with the scale of 1/10. The model test result shows that the high risk of collision by the drifting timber exists. A calculation formula of collision force is proposed.

Estimation of Transmitted Waves by Overtopping Based on Field Observation and Model Experiment and Simple Approach in Numerical Simulation

Katsuya HIRAYAMA, Junzo HASEGAWA, Iwao HASEGAWA, Tetsuya HIRAISHI Transmitted waves by overtopping over a breakwater sometimes affect safe navigation and mooring of aship. In this paper, they are evaluated by wave data analysis in a field observation provided at both inside and outside of the breakwater where the wave overtopping is frequently observed. And their significant heights can be estimated by the approximate formula obtained in the model experiment conducted with a thin vertical breakwater in section. On the other hand, the results of the model experiment are reproduced by numerical simulation using the Boussinesq-type wave transformation model equipped the wave overtopping model proposed by Hirayama et al (2006). Therefore, their spreading on Sakata port is calculated by the Boussinesq model with an assumption the offshore breakwater is thin.

FIELD EXPERIMENTS IN RELATION TO A GRAVITY -DRAINED SYSTEM AS A SOFT SHORE PROTECTION MEASURE

Many years of observing the fluctuation in the beach width at Hasaki Beach, which overlooks the Pacific Ocean, have shown that rapid beach retreat occurs under storm conditions. Spectral analyses of incoming waves and beach profile surveys have revealled that infragravity waves in high wave trains play an important role in rapid beach retreat. Infiltration of swashing water due to infragravity waves raises the water table below the beach, and this gives rise to fluidisation of the beach surface.