Erosion of a cyclic saltmarsh in Morecambe Bay, North‐West England
Erosion of a cyclic saltmarsh in Morecambe Bay, North‐West England
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DOI：
10.1002/esp.3290200502
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发表时间：
1995-08
影响因子：
3.3
通讯作者：
A. Pringle
中科院分区：
文献类型：
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作者：
A. Pringle
本文介绍了1983-1992年对莫雷坎贝湾循环盐沼在当前侵蚀阶段的变化率、形态和过程的调查结果。1000米（1975年）到C。150米（1992年）。每月监测沼泽边缘侵蚀和小溪缺口退缩揭示了时间和空间的变化。低量级的最高频率变化与非风暴条件和超过5·80 m OD的沼泽潮汐相一致，这些潮汐淹没了整个沼泽。频率较低但幅度较大的变化与沼泽潮和超过15 ms−1的强烈陆上风有关，这些风产生了高能量波。最大幅度的最低频率变化发生在极端陆上风暴事件和激增期间。在形态上，在侵蚀阶段，一个低角度的向陆斜坡产生的侵蚀的c。0.5 m高的活动向海悬崖与沼泽表面上0.07 ma−1的相对粗的沉积物垂直加积相吻合。潮汐水动力对盐沼影响很大，仅限于大潮差的上部2·5 m（最大c. 10·5m）。在过度沼泽的大潮期间（最大的小溪洪水流量为0·13 ms−1，达到满岸水位），洪水开始淹没较低的向陆小溪河岸，然后淹没较高的沼泽边缘。在落潮时，被这一较高边缘截留的水只能通过小溪（最大落潮速度低于平岸水位2.07 ms−1）向大海逃逸。波浪侵蚀也仅限于大潮。每月绘制的肯特河口通道模式向海的盐沼显示，中期较高的侵蚀率与存在一个大的通道，降低了相邻的小溪基准面，并允许更大的波浪攻击沼泽边缘比当沙洲两侧的沼泽。主要的肯特河通道的变化似乎开始加积或侵蚀阶段的循环盐沼发展。
This paper presents results of investigations (1983–1992) into rates of change, morphology and processes occurring during the current erosional phase in a Morecambe Bay cyclic saltmarsh, in which it has narrowed from c. 1000 m (1975) to c. 150 m (1992). Monthly monitoring of marsh edge erosion and creek knickpoint retreat has revealed temporal and spatial variations. Highest frequency changes of low magnitude coincided with non-storm conditions and overmarsh tides above 5·80 m OD, which submerged the whole marsh. Less frequent changes of greater magnitude were associated with both overmarsh tides and strong onshore winds over 15 ms−1, which generated high energy waves. The lowest frequency change of greatest magnitude occurred during an extreme onshore storm event and surge. Morphologically, during the erosional phase, a low angled landward slope was generated as erosion of the c. 0·5 m high active seaward cliff coincided with vertical accretion of 0·07 ma−1 of relatively coarse sediment on the marsh surface immediately landward. Tidal hydrodynamics strongly influence the saltmarsh, which is confined to the upper 2·5 m of the macrotidal range (maximum c. 10·5 m). During overmarsh spring tides (maximum creek flood flow rate 0·13 ms−1, up to bankfull level), flooding begins over lower landward creek banks before submerging the higher marsh edge. During ebb tides, water trapped by this higher edge can escape seaward only via the creeks (maximum ebb velocities 2·07 ms−1 below bankfull level). Wave erosion also is limited to spring tides. Monthly mapping of the Kent Estuary channel pattern seaward of the saltmarsh showed that medium term higher erosion rates were related to the presence of a large channel, which lowered the adjacent creek base level and allowed larger waves to attack the marsh edge than when a sandbank flanked the marsh. Major River Kent channel shifts appear to initiate accretional or erosional phases of cyclic saltmarsh development.