Morphological hysteresis in the evolution of beach profiles under sequences of wave climates - Part 1; observations
Morphological hysteresis in the evolution of beach profiles under sequences of wave climates - Part 1; observations
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DOI：
10.1016/j.coastaleng.2017.08.005
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发表时间：
2017-10
影响因子：
4.4
通讯作者：
T. Baldock;F. Birrien;Alexander L. Atkinson;Tomoko Shimamoto;S. Wu;D. Callaghan;P. Nielsen
中科院分区：
文献类型：
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作者：
T. Baldock;F. Birrien;Alexander L. Atkinson;Tomoko Shimamoto;S. Wu;D. Callaghan;P. Nielsen
一系列新的实验表明，形态滞后的演变平衡的海滩配置文件下的序列不同的波气候。实验在波浪水槽中进行，在中等规模的单色和随机波，代表二维条件。利用激光剖面仪以高空间分辨率获得了海滩剖面图，并从中得出了海岸线位置、沙洲位置和沉积物输运速率。进行了波浪气候序列的实验，其中一个序列包括6-13个连续的测试，每个从前面的测试海滩配置文件开始。进行每个测试，直到获得平衡条件，并且具有恒定的波高，相对于先前的测试增加或减少。循环条件也包括在内，短持续时间的侵蚀和增生波条件交替通过多个周期，使平衡条件在测试期间没有达到。随着一系列的波高增加，海岸线的位置和散装跨岸输沙，在平衡状态下，之间的关系是非单调的，向陆输沙率的最大值。对于测试系列包括一个序列的波高增加，然后由一个序列的波高降低，形态滞后观察到在平衡海岸线的位置和散装跨海岸沉积物运输，这样的海岸线衰退，或近海运输，在某些情况下继续波高降低后。这与经典的平衡型海岸线演化模型是不一致的。然而，当未达到平衡条件时，在循环序列中，没有观察到这种形态滞后，并且达到动态平衡。形态滞后的发生是因为衰减，搁浅，或增加的相对深度，破碎机酒吧波高降低后，往往与一个新的破碎机酒吧产生的进一步海上运输的内碎波区。在文献中的田间数据和较大规模试验中，形态反应的类似序列是明显的。最后，它表明，形态滞后可以解释使用经典的平衡海滩状态模型的赖特等人。（1985）通过引入随后的交替活动海滩状态的概念，这可能在波浪条件变化之后发生。
Novel series of experiments are presented that demonstrate morphological hysteresis in the evolution to equilibrium of beach profiles under sequences of different wave climates. The experiments were conducted in a wave flume at medium scale using both monochromatic and random waves, representing 2D conditions. Beach profiles were obtained with high spatial resolution at frequent intervals with a laser profiler, from which shoreline location, bar position and sediment transport rates were derived. Experiments were conducted for sequences of wave climates, where a sequence comprised of 6–13 sequential tests, each commencing with the beach profile from the preceding test. Each test was run until equilibrium conditions were obtained and had a constant wave height, increased or decreased relative to the preceding test. Cyclical conditions were also included, with erosive and accretive wave conditions of short durations alternating through multiple cycles, so that equilibrium conditions were not reached during a test. With a sequence of increasing wave heights, the relationship between the shoreline position and the bulk cross-shore sediment transport, at equilibrium, was non-monotonic, indicating a maximum in the landward sediment transport rate. For test series comprised of a sequence of increasing wave heights followed by a sequence of decreasing wave heights, morphological hysteresis was observed in the equilibrium shoreline position and bulk cross-shore sediment transport, such that shoreline recession, or offshore transport, continued in some instances after reductions in wave height. This is inconsistent with classical equilibrium type shoreline evolution models. However, when equilibrium conditions were not reached, in the cyclic sequences, no such morphological hysteresis was observed and a dynamic equilibrium is reached. The morphological hysteresis occurs because of the decay, stranding, or increased relative depth, of the breaker bar following a reduction in wave height, often in conjunction with a new breaker bar generated by further offshore transport in the inner surf zone. Similar sequences of morphological response are evident in field data and larger scale tests in the literature. Finally, it is shown that the morphological hysteresis can be explained using the classical equilibrium beach state model of Wright et al. (1985) by introducing the concept of a subsequent alternate active beach state, which may occur following a change in wave conditions.