Methodology for Controlling Beach Erosion by Large Coastal Structures and Its Application

点击翻译按钮获取中文摘要

Based on the mechanism of beach erosion by a large coastal structure, a methodology for beach erosion control has been developed, and its applicability has also been investigated. The main results can be summarized as :1. Beach erosion by a large coastal structure is due to 1) impediment of longshore sediment transport by the structure, 2) formation of nearshore, circulation by changing wave field by the structure, and 3) reflected waves by sea walls and dikes. The mechanism of beach erosion was clearly shown by numerical simulations of shoreline change and nearshore circulation. Based on the mechanism a methodology for beach erosion control by headlands was proposed in relation to the formation of stable sandy beaches.2. Proposed are 1) a 3D model for sea bottom topography change prediction based on the coupled system of the governing equations of wair transformation, nearshore currents and bottom topography change, and 2) a long-term shoreline change prediction model by introducing the sorting phenomena of bottom sediment and horizontal mixing coefficients in surf zones. By the 3D model, sea bottom topography changes were shown in the formation process of stable sandy beach. By the long-term model, changes of shoreline and sediment properties in beach erosion were numerically predicted. By use of the numerical simulations, the applicability of the proposed methodology was discussed.3. An application of the methodology was made to Ogata coast. Construction of a headland has been being made. Sea bottom topography change by constructing a headland was observed, and predicted by the proposed models. Additionally, beach erosion in the reduction process of river deltas was investigated to find the applicability of the methodology for beach erosion control.It was concluded from these results that the proposed methodology for beach erosion control by headlands is applicable to stabilize the sandy beaches being eroded by large coastal structures.