¹Ujigawa Hydraulics Laboratory, DPRI, Kyoto University Kyoto, JAPAN

baba@uh31.dpri.kyoto-u.ac.jp

　

²Disaster Prevention Research Institute, Kyoto University Kyoto, JAPAN

　

The principal object of this paper is to show some empirical equations of coastal currents and sediment transport under the storm condition. The cross-shore and longshore sediment transport systems are significant components for the prediction of beach profile change. Especially, for the long-term prediction, simple equations of offshore sediment transport in the surf zone and longshore sediment transport out of the surf zone are needed extremely.

　

The distribution of coastal currents under the storm condition was investigated by the field observation. It is obvious from the results that strong offshore-going currents in the surf zone, such as undertow, induced by waves and longshore currents in the wide area of nearshore region by wind. The velocity of the offshore-going currents is dominated by wave condition, and the normalized velocity has the relationship with the ratio of wave height to depth within the field observations. The longshore currents are generated by the wind, however, the velocity of the observed longshore currents is beyond the one simulated by the bulk formula using the drag coefficient CD and wind speed. In this paper, the velocity of the longshore currents is calculated from sea-surface stress generated by wind and whitecap dissipation.

　

Using the distribution of coastal currents and the wave condition, the distribution of the sediment transport in the nearshore region is simulated. Bailard model is adopted in the simulation, and cross-shore sediment transport by the asymmetry of wave motion and the high wave condition is considered in addition to longshore sediment transport by wind-driven and wave-induced currents. The simulation results show the offshore sediment transport in the surf zone and the longshore sediment transport outside of the surf zone, corresponding to the distribution of coastal currents. Furthermore the sediment transport model is applied to N-line model, and the beach profile change is simulated in several cases.

　

　

Disaster Prevention Research Institute, Kyoto University Uji, JAPAN

katou@rcde.dpri.kyoto-u.ac.jp

　

The severe beach erosion under the strong wind and wave conditions is caused by offshore-going sediment. In the surf zone, cross-shore currents going offshore are caused by the set-up induced by wind and waves. These currents are strong enough to transport sediment through the surf zone. It is very important to measure offshore-going sediment, particularly suspended load, due to these currents from the surf zone.

　

The field observation of vertical mean current profile by ADCP, concentration of suspended load and mean diameter of its material by LISST-25 and wave condition by ultrasonic wave gauges in the nearshore zone has been conducted using the observation pier at Ogata Wave Observatory. Using these data, the vertical profile of suspended load and flux of offshore-going suspended load were estimated under the storm condition. In addition, it will be possible to estimate the vertical distribution of the bubble concentration trapped by wave breaking, which may be measured by LISST. Moreover bed load transport by an array of sea-bottom level meter will be evaluated in this study.

　

　

School of Civil, Urban, and Geosystem Engineering Seoul National University Seoul, KOREA

kdsuh@snu.ac.kr

dragon5@snu.ac.kr

　

The Naari Beach located at the southern part of the east coast of Korean Peninsula has experienced severe shoreline change during the first three years after the construction of the intake breakwaters of the Wolsung Nuclear Power Plant. The beach was largely accreted at the northern part, while severe erosion occurred at the southern part, eventually causing the damage of the seawall behind the beach.

　

In the present study, we analyze the shoreline change using the aerial photographs taken before and after the construction of the nuclear power plant. Also a curvilinear-coordinate shoreline evolution model combined with the RCPWAVE model is used to calculate the shoreline change, which is compared with the observed shoreline change through the analysis of the aerial photographs.

　

　

¹Department of Civil Engineering, Tomakomai National College of Technology Hokkaido, JAPAN

Urashima@civil.tomakomai-ct.ac.jp

　

²Coastsphere Systems Institute Company Limited Hokkaido, JAPAN

　

³Alpha Hydraulic Engineering Consultants Incorporated Hokkaido, JAPAN

　

Problems of the coastal change by the sediment transport phenomenon are various by the temporal scale of change, and the spatial scale. The macro scale shore prediction is important to countermeasures for long-term shore protection. A macro model typically cover prototype areas of several km or more, and durations of ten years or longer. Most of previous numerical analysis models are effective in the shore prediction of durations of one year or less. Those models simulated a micro sediment transport, hence those models are not useful for the long-term sediment transport. The greatest factor which governs long-term coastal change is the macro sediment budget. A model named Macro Scale Shore Prediction Model has been developed, which aims to cover prototype durations of 10 to 100 years and areas of several km or more of shoreline length. The littoral cell is divided at the headland, river and bay. In one cell, the exerting force condition is almost constant, and the accretion or erosion is simulated by this model. In the few coastal areas of Iburi coast in Hokkaido, Japan, we have carried out shoreline prediction by the model. The results show predictions are good for shoreline changes of several km lengths and the period of more than 10 years.

　

　

¹Disaster Prevention Research Institute, Kyoto University Uji, JAPAN

yamashit@rcde.dpri.kyoto-u.ac.jp

　

²Department of Civil Engineering, Graduate School of Science Kyoto University Uji, JAPAN

　

³Department of Civil Engineering, Graduate School of Engineering Kyoto University Uji, JAPAN

　

Simulation or estimation of sea surface wind field is important matter in the field of Ocean and Coastal Engineering. Predictions of wind waves and wind-induced currents, even sediment transport in the nearshore region, need the high quality data of wind field on the sea surface, which is affected by land topography.

　

This paper investigated the applicability of meso-scale weather prediction model, PSU/NCAR MM5 to prediction of surface wind vector field in the nearshore region under the condition of two types of storms in winter monsoon. A model test was conducted in the costal area of Joetsu City, Niigata Prefecture, Japan, facing the Japan Sea. One storm is a stable atmospheric pressure field case and the other is a case of traveling and forming low pressure with across the Japan Sea. It can be confirmed that MM5 simulation is applicable to both cases.