Scale dependency of dune erosion models
Scale dependency of dune erosion models
复制标题
沙丘侵蚀模型的尺度依赖性
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
J. Ribberink
中科院分区：
文献类型：
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作者：
P. Brandenburg;J. T. D. Vries;K. Wijnberg;J. Ribberink
这份报告代表了一个研究的沙丘侵蚀模型的可扩展性。沙丘侵蚀模型用于荷兰海岸桑迪的安全评估。目前，安全评估是基于相对简单的跨海岸沙丘侵蚀模型DUROS。经验DUROS模型是为沿岸均匀海岸线设计的。由于DUROS模型不适合评估复杂情况下的风暴影响，因此包括沿岸尺度的更通用的模型可能是一个有用的工具。在这项研究中，DUROS模型与通用模型XBeach进行了比较。XBeach模型包含了对跨岸和沿岸方向沙丘侵蚀最重要过程的物理描述。由于沙丘被评估为从未发生过的规范条件，大多数模型都是基于实验室实验。由于DUROS和XBeach基于相同的实验室实验，但在真实的尺度上预测了不同的风暴影响（DUROS估计沙丘侵蚀多40%），因此两个模型中的实验室原型转换是不同的。上述问题导致了下一个目标：更好地理解DUROS和XBeach对风暴影响预测差异的根本原因。从目标，制定了两个研究问题：是什么原因导致的差异，风暴影响预测的DUROS和XBeach的参考条件？风暴影响的这些差异对原型尺度的预测有什么影响？为了回答这些问题，研究了一系列室内实验（M1263）和现场案例的实验结果。研究项目M1263包含26个不同规模的实验室实验，范围超过590。选择这些实验是因为当前的DUROS模型是根据这些实验的结果构建的。其次，对一个典型的风暴潮--76年风暴潮进行了调查。DUROS模型和XBeach模型适用于这两种情况。在分析M1263试验时，发现模型变形和所用粒度对沙丘侵蚀强度有重要影响。实验室实验是由Vellinga和货车de Graaff在80年代后期进行的。在研究过程中，发展了一个比例尺规则，其中畸变率（nd/nl）是实验室比例尺（nd）和沉积物下落速度（nws）的函数。创建缩放规则的目的是在各种尺度之间匡威侵蚀量。根据该关系和实验结果建立了DUROS模型。DUROS模型能够很好地再现大规模的实验。然而，当将该模型应用于小规模实验时，发现该模型缺乏性能，这是由于对助跑区的不正确模拟造成的。在模型（DUROS研究版）中实施助跑区后，新模型在所有尺度上表现出一致（良好）的性能。XBeach模型在大规模实验中也表现出良好的性能，但在小规模实验中表现不佳。由于该模型是基于过程的，因此选择它来调整数值参数，以便能够再现小规模实验。六个参数，需要改变不同的尺度：雪崩模型的三个参数（dzmax，wetslp和hswitch），截止水深的斯托克斯漂移包括回流（hmin），截止水深的泥沙输运（eps）和近床湍流（turb）。这些变化共同导致了小规模实验的BSS 10.0到BSS 10.5的模型改进。通过对模型中的输运公式进行调整，得到了较好的性能（BSS≥0.8）。2010年11月25日，沙丘侵蚀模型的最终尺度依赖性iii在76年风暴的实地案例中，选择了荷兰海岸的三个断面：Julianadorp、卑尔根aan Zee和卡斯特里克姆。两种模型对三种情况下的预测侵蚀量相似。模型对参考情况和相对“平静”条件的预测不同，这意味着两种模型的敏感性不同。的水动力和morphdynamic边界条件的敏感性分析表明，XBeach模型是不太敏感的涌浪水平，泥沙的大小和陡度的初始配置文件，相比DUROS。DUROS对波浪周期不太敏感，对波高的敏感性相当相似。这两个修正模型在各种实验室规模的实验中表现出更好的性能。对于原型应用程序，这些变化导致DUROS和XBeach之间的差异较小。
This report represents a study to the scalability of the dune erosion models. Dune erosion models are used for the safety assessment of the sandy dunes of the Dutch coast. Presently, the safety assessment is based on the relatively simple cross-shore dune erosion model DUROS. The empirical DUROS-model is designed for alongshore uniform coastlines. Since the DUROS-model is not qualified to assess storm impact in complex cases, a more generic model that includes the long-shore dimension can be a helpful instrument. In this study the DUROS-model is compared with the generic model XBeach. The XBeach-model contains a physical description of the most important processes that are of relevance to dune erosion in both cross-shore and long-shore direction. As the dunes are assessed to normative conditions that have never occurred, most models are based on laboratory experiments. Since DUROS and XBeach are based on the same lab experiments but predict different storm impact on real scale (DUROS estimates 40% more dune erosion), the lab-prototype conversion in the two models is different. The above problem led to the next objective: getting a better understanding of the underlying causes for differences in storm impact predictions by DUROS and XBeach. From the objective, two research questions were formulated: What causes the difference in storm impact predicted by DUROS and XBeach for reference conditions? And what consequences do these differences in storm impact have on the prediction for prototype scale? In order to answer these questions, the laboratory results of a series of lab experiments (M1263) and a field case are studied. The research project M1263 contains 26 laboratory experiments on various scales over a range of 590. These experiments are chosen because the current DUROS-model was constructed with the results of these experiments. Secondly, a field case storm is investigated, the ’76 storm surge. The DUROS-model and the XBeach-model are applied to both cases. When analyzing the M1263 experiments, the model distortion and the applied grain size were found to be very important for the intensity of dune erosion. The laboratory experiments were carried out by Vellinga and Van de Graaff in the late ’80. During the research program, a scaling rule was developed, in which the distortion rate (nd/nl) is a function of the lab scale (nd) and the sediment fall velocity (nws). The scaling rule was created with the goal to converse erosion amounts between various scales. The DUROS-model was created with this relation and the experimental results. The DUROS-model is very well capable of reproducing the large-scale experiments. However when applying the model to small-scale experiments, it was found that the model lacks performance, caused by incorrect simulation of the run-up zone. After implementing the run-up zone in the model (DUROS research version), the new model shows consistent (good) performance for all scales. The XBeach-model shows also good performance for large-scale experiments, but performs insufficient for small-scale. Since the model is process-based, it was chosen to adjust numerical parameters in order to be able to reproduce small-scale experiments. Six parameters were introduced that need to be changed for different scales: Three parameters of the avalanche model (dzmax, wetslp and hswitch), a cut-off water depth for the Stokes drift included return flow (hmin), a cut-off water depth for sediment transport (eps) and the near-bed turbulence (turb). The changes altogether lead to a model improvement of BSS≈0 to BSS≈0.5 for small-scale experiments. A better performance (BSS≥0.8) is obtained when the transport formulations in the model are adjusted. 25 November 2010, final Scale dependency of dune erosion models iii In the field case of the ’76 storm three transects of the Dutch coast are chosen: Julianadorp, Bergen aan Zee and Castricum. The two models perform similar for the three cases in terms of predicted erosion amount. That the models predict differently for the reference case and for relatively ‘calm’ conditions, implies that the sensitivity of both models is different. A sensitivity analysis to the hydrodynamic and morphdynamic boundary conditions showed that the XBeachmodel is less sensitive to the surge level, the sediment size and the steepness of the initial profile, compared to DUROS. DUROS is less sensitive to the wave period and for the wave height the sensitivities are fairly similar. The two revised models showed a better performance for the experiments on various lab scales. For the prototype application the changes led to less difference between DUROS and XBeach.