In situ estimation of erosion and deposition thresholds by Acoustic Doppler Velocimeter (ADV)
In situ estimation of erosion and deposition thresholds by Acoustic Doppler Velocimeter (ADV)
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DOI：
10.1016/j.ecss.2007.04.039
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发表时间：
2007-11-01
影响因子：
2.8
通讯作者：
Pejrup, M.
中科院分区：
文献类型：
--
作者：
Andersen, T. J.;Fredsoe, J.;Pejrup, M.
在丹麦瓦登海Kongsmark泥滩，使用SonTek/YSI 10 MHz ADVs（声波多普勒测速仪）进行了基于现场的床层剪切应力估计，以测试是否有可能利用单向潮汐和轨道（波）流来原位估计侵蚀和沉积阈值。结果很有希望，侵蚀阈值与在同一地点进行的erome侵蚀实验中观察到的值在同一范围内。同样，可以计算出的短期侵蚀率与EROMES得到的结果非常吻合，并且与另一个细粒度地点公布的大型环形水槽（Sea Carousel）的结果在同一范围内。这表明，用这两种侵蚀仪得到的侵蚀速率是对自然潮流和波浪作用下实际发生侵蚀的合理估计。利用ADVs表征沉积物可蚀性的一个优点是可以进行长时间的测量，这使得可以检查侵蚀阈值、侵蚀速率和沉积的时间变化。在2005年1月的一次强风暴中观测到的最大床层剪切应力仅为0.7 N m(-2)，这比以往研究中erome实验在具有生物膜的沉积物上测量到的最高阈值低三到四倍。这表明，除非被其他机制降解或物理破坏，否则该位点的这种强生物膜不会被侵蚀。确定任何可蚀性和沉积参数的先决条件是详细了解测量地点的实际床面变化。这些信息是由本研究中使用的ADVs自动获得的。在非常浅的水域中，波浪作用下的床层剪切应力很难得到准确的估计，在本研究中，采用了一种基于瞬时速度和对数速度剖面假设的简单方法。为了完善这种计算床层剪应力的简单方法，需要对这些极端条件下的边界层进行进一步的实地研究。(C) 2007 Elsevier Ltd.版权所有。
Field-based estimations of bed shear stress have been made using SonTek/YSI 10 MHz ADVs (Acoustic Doppler Velocimeter) at the Kongsmark mudflat, Danish Wadden Sea, in order to test if it was possible to estimate erosion and deposition thresholds in situ by use of unidirectional tidal and orbital (wave) currents. The results were promising and erosion thresholds were in the same range as those observed in EROMES erosion experiments carried out at the same site. Similarly, the short-term erosion rates which could be calculated matched closely those obtained with EROMES, and were in the same range as those published for a large annular flume (Sea Carousel) from another fine-grained site. This indicates that the erosion rates obtained with those two erosion-instruments are reasonable estimates of the actual erosion taking place under natural tidal current and waves. One advantage of the use of ADVs to characterize sediment erodibility is that measurements can be carried out for long periods, which makes it possible to examine the temporal variation of erosion threshold, erosion rate and sedimentation. The maximum bed shear stresses, which was observed during a strong storm in January 2005, was only 0.7 N m(-2) which is three to four times lower than the highest thresholds measured by EROMES experiments On sediment with biofilms during previous studies. This shows that such strong biofilms at this site will not get eroded unless degraded or physically disrupted by some other mechanism. A prerequisite for the determination of any of the erodibility and sedimentation parameters is that the actual bed level changes at the measuring site are known in detail. This information is obtained automatically by the ADVs used in the present study. Accurate estimates of the bed shear stress under waves in very shallow water are difficult to obtain and, in the present study, a simple method based on instantaneous velocities and assumption of a logarithmic velocity profile was used. Further field-studies are required of the boundary layer under these extreme conditions in order to refine this simple method of calculating bed shear stresses. (C) 2007 Elsevier Ltd. All rights reserved.