以3个典型个例探讨养护海滩侵蚀热点的特征及其成因类型

Taking three typical nourished beaches for example to explore the character and mechanism of erosional hot spot at nourished beach

基于厦门香山—长尾礁海滩、北戴河西海滩和平潭龙凤头海滩3个典型海滩养护后多期地形地貌测量数据、观测记录和遥感影像等,分析了养护海滩侵蚀热点的分布和形态特征,探讨了各处侵蚀热点的形成原因和控制因素.从野外调查来看,侵蚀热点在各养护海滩皆有分布,热点宽度为20～260 m不等.研究表明沿岸水下地形、排污管道的布设、岬角和岸线走向突变是诱发侵蚀热点的主要因素,具体表现为:(1)沿岸水下地形分布有离岸潜堤、沙坝、带有缺口的连续暗礁等结构时,会因波浪绕射引起波能辐聚而造成沙滩局部的强侵蚀,形成侵蚀热点;(2)排污管道的埋设会阻断沉积物的沿岸运移,会在其下游形成侵蚀热点;(3)岬湾海岸两端岬角或者人工拦沙堤对波浪的折射和反射作用会造成岬角周边局部强侵蚀;(4)养护海滩岸线方向突变,特别是向海凸出的岸线,波浪会使这一位置岸线趋于平滑,造成突变点的强侵蚀.

Based on the data of multi-period topography survey, observation records and remote sensing images from 3 typical beach nourishment projects,i, e. Xiangshan--Changwei Reef beach in Xiamen, West Beach in Beidaihe and Longfengtou beach in Pingtan, the distribution and morphological characteristics of beach erosional hot spots were investigated, and their causes and control factors were further analyzed. The results show that the dift^rent scales of erosional hot spots are found at nourished beaches, ranging from 20 to 260m. This study shows that the main factors causing beach erosional hot spots are coastal underwater topography, sewage pipes or groins, head- lands and the abrupt change of shoreline direction. They can be specially expressed as ： （ 1 ） When there existed offshore submerged breakwaters, bars or continuous reefs with gaps under water, erosional hot spots would emerge as wave energy accumulation induced by wave diffraction. （2） Sewage pipes buried across the beach will block the sediment transport along the coast, causing erosional hot spots at its downstream. （3） The headlands at both ends of a bay coast could cause partially serious erosion surrounding the headland by wave refraction and reflection. （4） In the ease of the shoreline direction of a nourished beach has an abrupt change, especially protruding seaward, it will be smoothed by wave action, resulting serious erosion at the abrupt point.