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Morphological evolution of a barchan dune migrating past an offshore wind farm foundation
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2020-07-26 , DOI: 10.1002/esp.4937 Amelia J. Couldrey 1 , Thomas Benson 1 , Michiel A.F. Knaapen 1 , Kerry V. Marten 1 , Richard J.S. Whitehouse 1
Earth Surface Processes and Landforms ( IF 2.8 ) Pub Date : 2020-07-26 , DOI: 10.1002/esp.4937 Amelia J. Couldrey 1 , Thomas Benson 1 , Michiel A.F. Knaapen 1 , Kerry V. Marten 1 , Richard J.S. Whitehouse 1
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As the number of manmade structures installed on the seafloor is increasing rapidly, we seek to understand the impact of these immobile obstacles on marine geomorphological processes, such as the evolution of bedforms. A 5.8 m diameter monopile foundation was installed at the case study offshore windfarm approximately 30 m ahead of an approaching barchan (crescent‐shaped) dune. The impact of the monopile on the dune's evolution was analysed using six multibeam bathymetry surveys spanning 20 years. To substantiate this analysis, coupled three‐dimensional numerical modelling of flows and sediment was conducted in which the scour inducing bed shear stresses were calculated from the modelled turbulent kinetic energy. Following the installation of the monopile, the mid‐section of the dune accelerated and stretched in the direction of the wake of the monopile. Four years after the monopile's installation the rest of the dune had caught up, flattening out the slip face within half the dune's length downstream of the monopile. Due to the modified flow field, the dune was scoured deeply at the base of the monopile to a depth of 6.8 m (supported by the model results that predicted a scour depth exceeding 2 m over a period of just a few days). The surveyed volume of material scoured amounted to 8% of the total dune volume. Whilst the process of scouring occurs at a timescale of days to weeks, the dune migrated on average by 25 m/yr. The difference in the timescale of the two processes allowed the scouring to occur through the full thickness of the dune. The scoured dune profile recovered rapidly once the dune migrated downstream of the monopile. This article demonstrates how large geomorphological features can intercept and migrate past a monopile foundation without long‐lasting impacts on the integrity of the feature or the foundation.
中文翻译：
新月形沙丘迁移经过海上风电场基础的形态演变
随着安装在海底的人造结构数量迅速增加，我们试图了解这些不可移动的障碍物对海洋地貌过程的影响，例如海底形态的演变。在案例研究的海上风电场中安装了一个直径为 5.8 m 的单桩基础，距离接近的新月形沙丘大约 30 m。使用跨越 20 年的六次多波束测深调查分析了单桩对沙丘演化的影响。为了证实这一分析，进行了流动和沉积物的耦合三维数值模拟，其中从模拟的湍流动能计算了冲刷引起的床剪应力。安装单桩后，沙丘的中部加速并朝着单桩尾流的方向伸展。安装单桩四年后，沙丘的其余部分已经赶上，在单桩下游沙丘长度的一半内将滑面变平。由于修改了流场，沙丘在单桩底部被深深冲刷到 6.8 m 的深度（得到模型结果的支持，预测在短短几天内冲刷深度超过 2 m）。调查的冲刷材料量占沙丘总体积的 8%。虽然冲刷过程发生在数天到数周的时间尺度上，但沙丘的平均迁移速度为 25 米/年。两个过程的时间跨度不同，使得冲刷过程贯穿沙丘的整个厚度。一旦沙丘迁移到单桩下游，冲刷过的沙丘剖面就会迅速恢复。本文展示了大型地貌特征如何拦截和迁移经过单桩基础，而不会对特征或基础的完整性产生长期影响。
更新日期：2020-07-26
中文翻译：
新月形沙丘迁移经过海上风电场基础的形态演变
随着安装在海底的人造结构数量迅速增加，我们试图了解这些不可移动的障碍物对海洋地貌过程的影响，例如海底形态的演变。在案例研究的海上风电场中安装了一个直径为 5.8 m 的单桩基础，距离接近的新月形沙丘大约 30 m。使用跨越 20 年的六次多波束测深调查分析了单桩对沙丘演化的影响。为了证实这一分析，进行了流动和沉积物的耦合三维数值模拟，其中从模拟的湍流动能计算了冲刷引起的床剪应力。安装单桩后，沙丘的中部加速并朝着单桩尾流的方向伸展。安装单桩四年后，沙丘的其余部分已经赶上，在单桩下游沙丘长度的一半内将滑面变平。由于修改了流场，沙丘在单桩底部被深深冲刷到 6.8 m 的深度（得到模型结果的支持，预测在短短几天内冲刷深度超过 2 m）。调查的冲刷材料量占沙丘总体积的 8%。虽然冲刷过程发生在数天到数周的时间尺度上，但沙丘的平均迁移速度为 25 米/年。两个过程的时间跨度不同，使得冲刷过程贯穿沙丘的整个厚度。一旦沙丘迁移到单桩下游，冲刷过的沙丘剖面就会迅速恢复。本文展示了大型地貌特征如何拦截和迁移经过单桩基础，而不会对特征或基础的完整性产生长期影响。
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