Sand waves are found on shallow, sandy seabeds throughout the world and their dynamics may pose an imminent threat to offshore construction. Therefore, there is a pressing need to understand bed level dynamics in sand wave areas. These bed level dynamics lead to variations in sand wave shape and migration rate over time. However, these variations cannot be explained with the present-day process-based sand wave models, which all include a purely periodic tidal forcing. To explain these fluctuations a more intricate description of the hydrodynamics is necessary. The aim of this study is to explore the importance of time-varying, non-tidal currents for sand wave dynamics in the North Sea. We adopted the three-dimensional Delft3D-Flexible Mesh model, and were able to reconstruct time-varying, non-tidal currents on top of the periodic tidal forcing, while significantly reducing computation times. The simulated currents and water levels showed a good agreement with in-situ measurements. Compared to the situation with only tidal forcing, the simulated sedimentation and erosion rates were amplified up to 15 times due to time-varying, non-tidal currents. Additionally, periods of net erosion were found at locations in the sand wave transect where tidally forced models only showed net-sedimentation. It is therefore important to consider time-varying, non-tidal currents when predicting future sand wave dynamics in the field.

中文翻译：

---

时变非潮流在原位沙波动力学建模中的重要性

沙波存在于世界各地的浅沙海底，其动态可能对海上施工构成迫在眉睫的威胁。因此，迫切需要了解沙波区域的床面动态。这些床位动态导致砂波形状和迁移速率随时间的变化。然而，这些变化无法用当今基于过程的沙波模型来解释，这些模型都包含纯粹的周期性潮汐强迫。为了解释这些波动，需要对流体动力学进行更复杂的描述。本研究的目的是探讨时变非潮汐流对北海沙波动力学的重要性。我们采用三维 Delft3D-Flexible Mesh 模型，能够在周期性潮汐力的基础上重建时变的非潮汐流，同时显着减少计算时间。模拟的水流和水位与现场测量结果非常吻合。与仅有潮汐强迫的情况相比，由于时变的非潮汐流，模拟的沉积和侵蚀速率放大了15倍。此外，在潮汐力模型仅显示净沉积的沙波横断面位置发现了净侵蚀期。因此，在预测现场未来沙波动力学时，考虑时变的非潮汐流非常重要。