広域海浜流(沿岸方向流速)の岸沖分布に関する考察

Abstract

本研究は，強風・高波浪を伴う荒天時に発生する広域海浜流(沿岸方向成分)の岸沖方向分布について，限られた外力条件のみを用いての定式化を目的としている。ここで取り扱う広域海浜流は，漂砂を引き起こすに十分な流速を持つことが観測から確認されており，沖側での沿岸漂砂を検討する際に重要となる。ここでは，一様勾配の海浜に沿岸方向に一様の海上風を与えた条件下での岸沖方向の流速分布を，海面，海底面でのせん断応力およびコリオリ力のバランスから定式化し，現地観測結果との比較検討を行った。

Under stormy condition, strong longshore currents were observed in the nearshore zone. Themagnitude of the velocity reachs over 30cm/s at 30m deep when the currents are well-developed by thestrong wind. The currents could be the dominant external force of the change of beach profile andcoastal environment due to the sediment transport.In order to investigate the structure of coastal current fields, especially the cross-shore distribution of thelongshore component, a simplified model is developed. The model presented here needs only windcondition as forcing factors, and it derive the cross-shore distribution of the longshore velocity by usingthe balance among the sea surface and sea bottom stresses and Coriolis force. The normalizedcross-shore distribution has good agreement with the observed results in the Central Japan Sea.