潮汐의 影響이 있는 沿岸海域에서의 海岸過程의 變化

Abstract

Today, coastal development to maximize the utilization of ocean space, both economically and environmentally, brought interests to many peoples. However, neglecting the negative effect of development and difficulties on forecasting for the change of environments have made the situation worse than the time untouched. Especially, the development nearshore zone causes change of coastline or topography. Sometimes we face to more serious sedimentation and erosion problems oriented either by nature or artifical action and thereafter we find damages to the ecosystem. Therefore, it is necessary to cope with the changes in order to raise up the usage reasonably.

Change of beach and topography appears differently according to the regional environmental condition, but the most important factor we might point would be wave and littoral drift. Furthermore, in an area of a wide tide tidal range, displacement of breaking zone appears and we need to trace variation of the surf zone. In the past, the predictions of beach processes and harbor sedimentation were mainly relied on the hydraulic model tests and empirical methods. In recent years, however, as computers have come into wide use, more accurate models have gradually been developed and thus replaced those conventional methods. For prediction of topography change near the coastal area, we need information of wave and current conditions in the numerical model which should be calculated in advance.

Numerical model introduced in this study combines wave refraction-diffraction, breaking, bottom friction, lateral mixing, and critical shear stress and three sub-models for simulating waves, currents, and bottom change were briefly discussed. Simulations of beach processes and harbor sedimentation were also described at the coast neighboring Bangpo Harbor, Anmyundo, Chungnam, where the area has suffered from accumulation of drifting sand in a small fishing harbor with a wide tidal range. We also made model test for the case of a narrow tidal range at Nakdong river's estuary area to understand the effect of water level variation on the littoral drift. Simulations are conducted in terms of incident wave direction and tidal level. Characteristics of wave transformation, nearshore current, sediment transport, and bottom change are shown and analyzed. We found from the simulation that the tidal level impact to the sediment transport is very important and we should apply the numerical model with different water level to analyze sediment transport mechanism correctly.

Although the model study gave reasonable description of beach processes and harbor sedimentation mechanism, it is necessary to collect lots of field observation data, including waves, tides and bottom materials, etc. for better prediction.