Coupled penetrometer, MBES and ADCP assessments of tidal variations in surface sediment layer characteristics along active subaqueous dunes, Danish Wadden Sea
Coupled penetrometer, MBES and ADCP assessments of tidal variations in surface sediment layer characteristics along active subaqueous dunes, Danish Wadden Sea
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耦合贯入计、MBES 和 ADCP 评估丹麦瓦登海沿活动水下沙丘表面沉积层特征的潮汐变化
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发表时间：
2011
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通讯作者：
A. Kopf
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作者：
N. Stark;H. Hanff;C. Svenson;V. Ernstsen;A. Lefebvre;C. Winter;A. Kopf
利用小型自由落体渗透仪，在丹麦瓦登海Knudedyb潮汐入海口航道的大型水下沙丘上对表层沉积物进行了现场岩土测量。垂直剖面表现出典型的层化模式，分辨率为∼1×10-4 cm，反映了低沉积强度的薄表层和较硬的底层(准静态承载能力当量：上层为1-3 kpa，下层为20-140kpa；顶层厚度约为5-8 kpa)。将观测到的潮汐周期中表层厚度和强度的变化与平均流速(使用声学多普勒海流剖面仪测量)、高分辨率水深测量(基于多波束回波测深)和对水柱中悬浮泥沙分布的定性估计(根据ADCP后向散射强度估计)进行了比较。结果表明，泥沙再动员以退潮为主，向枯水方向发展。整个潮汐周期都存在一个松散的表层，可能受到推移质输运和悬浮泥沙重新安置的小事件(厚度：6 ± 2 cm)的影响。此外，这一层显示出与总体沉积时期相关的显著厚度增加(例如从8厘米增加到16厘米)。这些发现表明，动态渗透仪可以方便地用于(1)通过确定疏松沉积物表层的厚度来量化潜在的可移动沉积物，(2)揭示潜在可移动沉积物中的沉积物强度发展，以及(3)识别沉积物的堆积。在调查高度动态的沿海环境中的沉积物再动员过程中，这些数据是一个重要的补充，并增加了一个新的岩土工程观点。
In-situ geotechnical measurements of surface sediments were carried out along large subaqueous dunes in the Knudedyb tidal inlet channel in the Danish Wadden Sea using a small free-falling penetrometer. Vertical profiles showed a typical stratification pattern with a resolution of ∼1 cm depicting a thin surface layer of low sediment strength and a stiffer substratum below (quasi-static bearing capacity equivalent: 1–3 kPa in the top layer, 20–140 kPa in the underlying sediment; thickness of the top layer ca. 5–8 cm). Observed variations in the thickness and strength of the surface layer during a tidal cycle were compared to mean current velocities (measured using an acoustic Doppler current profiler, ADCP), high-resolution bathymetry (based on multibeam echo sounding, MBES) and qualitative estimates of suspended sediment distributions in the water column (estimated from ADCP backscatter intensity). The results revealed an ebb dominance in sediment remobilization, and a general accretion of the bed towards low water. A loose top layer occurred throughout the tidal cycle, likely influenced by bedload transport and small events of suspended sediment resettlement (thickness: 6 ± 2 cm). Furthermore, this layer showed a significant increase in thickness (e.g. from 8 cm to 16 cm) related to periods of overall deposition. These findings imply that dynamic penetrometers can conveniently serve to (1) quantify potentially mobile sediments by determining the thickness of a loose sediment surface layer, (2) unravel sediment strength development in potentially mobile sediments and (3) identify sediment accumulation. Such data are an important complement and add a new geotechnical perspective during investigations of sediment remobilization processes in highly dynamic coastal environments.