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首页> 外文期刊>Estuarine Coastal and Shelf Science >Anthropogenic influences on shoreline and nearshore evolution in the San Francisco Bay coastal system
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Anthropogenic influences on shoreline and nearshore evolution in the San Francisco Bay coastal system

机译：人为因素对旧金山湾沿岸系统海岸线和近岸演变的影响

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摘要

Analysis of four historical bathymetric surveys over a 132-year period has revealed significant changes to the morphology of the San Francisco Bar, an ebb-tidal delta at the mouth of San Francisco Bay estuary. From 1873 to 2005 the San Francisco Bar vertically-eroded an average of 80 cm over a 125 km~2 area, which equates to a total volume loss of 100 ± 52 million m3 of fine- to coarse-grained sand. Comparison of the surveys indicates the entire ebb-tidal delta contracted radially, with the crest moving landward an average of 1 km. Long-term erosion of the ebb-tidal delta is hypothesized to be due to a reduction in the tidal prism of San Francisco Bay and a decrease in coastal sediment supply, both as a result of anthropogenic activities. Prior research indicates that the tidal prism of the estuary was reduced by 9% from filling, diking, and sedimentation. Compilation of historical records dating back to 1900 reveals that a minimum of 200 million m~3 of sediment has been permanently removed from the San Francisco Bay coastal system through dredging, aggregate mining, and borrow pit mining. Of this total, ~54 million m~3 of sand-sized or coarser sediment was removed from central San Francisco Bay. With grain sizes comparable to the ebb-tidal delta, and its direct connection to the bay mouth, removal of sediments from central San Francisco Bay may limit the sand supply to the delta and open coast beaches. SWAN wave modeling illustrates that changes to the morphology of the San Francisco Bar have altered the alongshore wave energy distribution at adjacent Ocean Beach, and thus may be a significant factor in a persistent beach erosion 'hot spot' occurring in the area. Shoreline change analyses show that the sandy shoreline in the shadow of the ebb-tidal delta experienced long-term (1850s/1890s to 2002) and short-term (1960s/1980s to 2002) accretion while the adjacent sandy shoreline exposed to open-ocean waves experienced long-term and short-term erosion. Therefore, the recently observed accelerating rates of bay sediment removal, ebb-tidal delta erosion, and open coast beach erosion are all correlated temporally.
机译：对过去132年的四次历史测深调查的分析表明，旧金山酒吧（San Francisco Bar）的形态发生了显着变化，旧金山酒吧是旧金山湾河口口处的潮汐三角洲。从1873年到2005年，旧金山酒吧在125 km〜2的区域内平均垂直侵蚀80厘米，这意味着细颗粒至粗颗粒沙子的总体积损失为100±5200万立方米。测量结果的比较表明，整个潮汐三角洲呈放射状收缩，波峰平均向内移动1公里。据推测，潮汐三角洲的长期侵蚀是由于人为活动引起的旧金山湾潮汐棱镜的减少和沿海沉积物供应的减少。先前的研究表明，河口的潮汐棱镜由于填充，筑堤和沉积而减少了9％。追溯到1900年的历史记录表明，至少有2亿立方米3的沉积物已通过疏,、集料开采和借坑开采永久性地从旧金山湾沿岸系统清除。其中，从旧金山湾中部清除了约5400万立方米的沙粒或更粗的沉积物。由于颗粒大小可与潮汐三角洲相提并论，且与海湾口直接相连，因此从旧金山湾中部清除沉积物可能会限制向三角洲和开放海岸海滩的沙子供应。 SWAN波浪建模表明，旧金山酒吧形态的变化已改变了邻近海洋海滩的近岸波浪能量分布，因此可能是该地区持续发生海滩侵蚀“热点”的重要因素。海岸线变化分析表明，在潮汐三角洲附近的沙质海岸线经历了长期（1850s / 1890s至2002年）和短期（1960s / 1980s至2002年）的增生，而相邻的沙质海岸线暴露于开阔海洋波浪经历了长期和短期的侵蚀。因此，最近观察到的海湾沉积物清除率，潮汐三角洲侵蚀和沿海海岸滩侵蚀的加速速率在时间上都是相关的。

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