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The Long-term sedimentary regime of the outer Medway Estuary

机译：梅德韦河口外长期沉积体系

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Estuary evolution over the last 300 years is evaluated, based on pronouncements by some that the recent erosional phase was a temporary response to human intervention and is now shifting back in favour of accretion. In contrast, a painting from 1698, 1700's surveys and accurate surveys from 1800 and 1865 confirm that the erosional phase commenced naturally around 1700. From the early 1840s the salt-marshes were heavily exploited for their clay by the brick and cement industries. One or more storm surges in 1875, 1877, 1881 and 1897 breached embankments of many "inned" (reclaimed) marsh pastures. In deference to this exploitative industry these were never reclaimed. Natural loss due to sea level rise-induced erosion was thus exacerbated by saltmarsh digging. Fine sediment budget measurements show saltmarsh cliff, creek and tidal flat surface losses greatly exceed gains on vegetated salt-marsh surfaces. Stoke Marshes is losing about 160,000 tonnes/yr and loss for the entire intertidal zone is thought to lie close to 1 M tonnes/yr. The exceptionally low-lying tidal flats are highly vulnerable to sea level rise. Relative sea level will rise due to 3 overlapping factors and is suggested to be accelerating. 50 cm increments of relative rise would induce losses to 28,44, 72 and 83% respectively. In respect of the major tributary and estuary channels, in a short period coupled embankment breaching together with mud digging greatly increased the tidal volume passing Sheerness. Tidal velocities rose significantly. North Sea Pilot extracts, plus tidal cycle measurements at major creek entrances, reveal a strong ebb-dominance, which is further confirmed by a fluorescent tracer test on labelled muddy dredge material. Over a 132 year period the estuary bed has self-deepened and a further increase in tidal volume has arisen. With accelerating sea level rise in a starved ebb-dominated system there is no known mechanism which could shift the Medway back in the direction of accretion.
机译：根据一些人的声明，评估了最近300年的河口演变，认为最近的侵蚀期是对人为干预的暂时反应，现在正朝着增生的方向转移。相比之下，从1698年，1700年的调查以及1800年和1865年的准确调查得出的一幅画确认了侵蚀阶段自然地始于1700年左右。从1840年代初开始，盐沼被砖和水泥工业大量开采为其粘土。 1875年，1877年，1881年和1897年的一次或多次风暴潮破坏了许多“固定”（开垦）的沼泽牧场的堤防。为了顺应这一剥削性行业，这些产品从未被回收。盐沼的挖掘加剧了因海平面上升引起的侵蚀而造成的自然损失。精细的沉积物预算测量表明，盐沼悬崖，小河和潮汐平面损失大大超过了植被盐沼表面的损失。斯托克沼泽（Stoke Marshes）每年损失约160,000吨，而整个潮间带的损失被认为接近每年100万吨。地势低洼的滩涂极易受到海平面上升的影响。相对海平面将由于3个重叠因素而上升，并被认为正在加速。 50 cm的相对上升增量会分别导致损耗分别为28.44％，72％和83％。在主要的支流和河口通道上，在短时间内，路堤的破裂和泥浆的挖掘相结合，大大增加了通过赤潮的潮汐量。潮汐速度明显上升。北海领航员提取物，加上主要小溪入口处的潮汐周期测量，显示出强烈的退潮优势，这一点已通过对标记的泥泞疏edge材料进行的荧光示踪测试进一步证实。在132年的时间里，河床逐渐变深，潮汐量进一步增加。由于饥饿导致的退潮占主导的系统中海平面上升的加快，没有已知的机制可以使Medway向着吸积的方向移动。

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  • 来源
    《Ocean & coastal management》 |2013年第7期|20-33|共14页
  • 作者

    R. Kirby;

  • 作者单位

    Ravensrodd Consultants Ltd,, 6 Qtieen's Drive, Taunton, Somerset TA1 4XW, UK;

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