Morphodynamics of prograding beaches: A synthesis of seasonal- to century-scale observations of the Columbia River littoral cell
Morphodynamics of prograding beaches: A synthesis of seasonal- to century-scale observations of the Columbia River littoral cell
复制标题
前进海滩的形态动力学：哥伦比亚河沿岸细胞季节性至世纪尺度观测的综合
DOI：
10.1016/j.margeo.2016.03.012
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发表时间：
2016
期刊：
影响因子：
2.9
通讯作者：
N. Cohn
中科院分区：
文献类型：
--
作者：
P. Ruggiero;G. Kaminsky;G. Gelfenbaum;N. Cohn
本文综合了近20年来对哥伦比亚河滨海单元(CRLC)的研究结果，以研究与海岸演变相关的地貌动力学。CRLC是美国太平洋西北部一组快速演变的海岸屏障和滨海平原。由于哥伦比亚河的大量沉积物供应，CRLC是美国西海岸唯一一条在全新世晚期显著向大海推进的广阔海岸线。自1700年卡斯卡迪亚俯冲带(CSZ)最后一次地震以来，伴随着同震下沉和海啸，CRLC的大部分已经向前推进了数百米。然而，泥沙堆积的速率和最主要的堆积过程，取决于时间尺度和所讨论的形态单位。值得注意的是，20世纪和21世纪初的海岸线变化率是史前晚期的两倍多，包括从上一次CSZ重大事件中恢复过来，最有可能的原因是进水口码头建设导致沉积物供应增加。在一些地区，详细的海滩形态监测显示，年际到年代际尺度上，上滨面加厚约2 cm/年，潮下沙洲向近岸迁移并衰退，潮间带砂坝向岸上迁移并焊接到岸线上，岸线向前推进约4m/年，形成1~2个新的前山沙脊。在沿海单元内的一个地点进行的详细的中尺度沉积物收支分析表明，在−-12米(数据向海的界限)和+9.9米(向陆地最前面的沙丘的顶部)之间积累了大约100亿立方米/米/年。在观测期间，近岸泥沙输送的梯度、海浪带内净的岸上定向跨岸泥沙输送以及与强迫条件不平衡的岸面的跨岸输送，都是向CRLC海滩和沙丘提供大量泥沙的部分原因。在季节到十年尺度的海滩进积的直接观测放在几十到几百年的时间尺度上测量或推断的变化的背景下进行。
Findings from nearly two decades of research focused on the Columbia River littoral cell (CRLC), a set of rapidly prograding coastal barriers and strand-plains in the U.S. Pacific Northwest, are synthesized to investigate the morphodynamics associated with prograding beaches. Due to a large sediment supply from the Columbia River, the CRLC is the only extensive stretch of shoreline on the U.S. west coast to have advanced significantly seaward during the late Holocene. Since the last Cascadia Subduction Zone (CSZ) earthquake in 1700, with associated co-seismic subsidence and tsunami, much of the CRLC has prograded hundreds of meters. However, the rates of progradation, and the processes most responsible for sediment accumulation, vary depending on time scale and the morphological unit in question. Remarkably, the 20th and early 21st century shoreline change rates were more than double the late prehistoric rates that include recovery from the last major CSZ event, most likely due to an increase in sediment supply resulting from inlet jetty construction. In some locations detailed beach morphology monitoring reveals that at interannual- to decadal-scale the upper shoreface aggraded about 2 cm/yr, subtidal sandbars migrated offshore and decayed while intertidal bars migrated onshore and welded to the shoreline, the shoreline prograded about 4 m/yr, and 1 to 2 new foredune ridges were generated. A detailed meso-scale sediment budget analysis in one location within the littoral cell shows that approximately 100 m3/m/yr accumulated between − 12 m (seaward limit of data) and + 9 m (crest of landward-most foredune). Gradients in alongshore sediment transport, net onshore-directed cross-shore sediment transport within the surf zone, and cross-shore feeding from a shoreface out of equilibrium with forcing conditions are each partially responsible for the significant rates of sediment supplied to the beaches and dunes of the CRLC during the observational period. Direct observations of beach progradation at seasonal- to decadal-scale are put in context of measured or inferred changes over time scales of decades to centuries.