Rip Current Dynamics in a Complex Beach Environment

该项目将补充与海军研究生院和特拉华大学的合作努力，作为欧洲实地试验的一部分，通过观测和数值模拟，研究在具有很大水深变异性的海滩上湍流、入射波、亚重力波、甚低频和平均时间尺度上的三维近岸流动动力学。现场实验计划于2008年春天进行，将在法国波尔多附近大西洋海岸的Truc Vert海滩进行。这个海滩的特点是充满活力的波浪气候，强烈的潮汐调制，典型的复杂平面形态，有新月形的沙洲、裂口水道和带有海脊和水道的潮间带。在现场实验之前，将使用最先进的数值模拟来设计和优化由相干共置压力和速度传感器、压力传感器、ADCP？S和底部边界层仪器组成的现场场阵列。现场仪器在初始部署后很难移动，因此实验前的计算是必不可少的。在现场试验中，还将使用数值模拟来优化冲浪带漂移器的部署，以绘制激流系统的表面速度场。为此，数值模式将使用拉格朗日/欧拉混合描述近地表速度场。这些计算将使我们深入了解最初漂流部署的最佳位置，以捕获我们研究感兴趣的近岸环流。这些最佳位置受到(变化的)波浪和潮汐条件的影响，这些条件可以很容易地通过数值模拟来评估。更广泛的影响：拟议研究的影响包括为游泳者安全预测激流的位置、持续时间和强度，模拟泥沙和污染物的扩散(既来自点源，如暴雨排水沟排放，也来自分布式源，如农业径流)，以及预测岸线和沙丘侵蚀。Truc Vert的海滩平面比迄今已被全面研究的任何海滩平面都要复杂得多。因此，它对高能波条件下的三维水动力响应的建模提出了巨大的挑战，而且将获得的数据集在世界任何地方的现有数据集中都是独一无二的。最后，现场实验的参与将使数值建模者获得第一手经验，使用所获得的测量数据来进行未来的模型数据比较。

This project will supplement a collaborative effort with the Naval Postgraduate School and the University of Delaware as part of a European field experiment to examine through observations and numerical modeling the three dimensional nearshore flow dynamics at the turbulent, incident wave, infragravity wave, very low frequency and mean times scales on a beach with large bathymetric variability. The field experiment is planned for the spring of 2008 and will be conducted at Truc Vert Beach on the Atlantic coast near Bordeaux, France. This beach features an energetic wave climate, strong tidal modulation, and a typically complex planform with crescentic bars, rip channels and an inter-tidal zone with ridges and runnels. State of the art numerical modeling will be used to design and optimize the in-situ field arrays composed of coherent co-located pressure and velocity sensors, pressure sensors, ADCP?s, and a bottom boundary layer instruments prior to the field experiment. The in-situ instruments are very difficult to move after the initial deployment and therefore pre-experiment computations are essential. Numerical modeling will also be used during the field experiment to optimize the deployment of surf zone drifters to map the surface velocity field of the rip current systems. To that end the numerical model will use a mixed Lagrangian/Eulerian description of the near surface velocity field. These computations will give insight in the optimal location of the initial drifter deployments to capture nearshore circulations that are of interest to our research. These optimal locations are subject to the (changing) wave and tidal conditions which can be easily assessed with the numerical modeling. Broader Impacts: The impacts of the proposed research include predicting location, persistence, and strength of rip currents for swimmer safety, modeling dispersion of sediment and pollutants (both from point sources such as storm drain discharge and from distributed sources such as agricultural runoff) and anticipating shore line and dune erosion. The beach planform at Truc Vert is more complex than any that has been studied up to date in a comprehensive fashion. As such it poses a formidable challenge in the modeling of the three dimensional hydrodynamic response during energetic wave conditions and the data set to be obtained would be unique among available data sets anywhere in the world. Finally, participation in the field experiment will give first hand experience to a numerical modeler with the acquired measurement data allowing for future model-data comparisons.