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首页> 外文期刊>Natural hazards and earth system sciences >Coastal flooding of urban areas by overtopping: dynamic modelling application to the Johanna storm (2008) in Gavres (France)
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Coastal flooding of urban areas by overtopping: dynamic modelling application to the Johanna storm (2008) in Gavres (France)

机译：过度覆盖市区沿海洪水：动态模型在法国加夫尔（Javres）的约翰娜风暴（2008）中的应用

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Recent dramatic events have allowed significant progress to be achieved incoastal flood modelling over recent years. Classical approaches generallyestimate wave overtopping by means of empirical formulas or 1-Dsimulations, and the flood is simulated on a DTM (digital terrain model),using soil roughness to characterize land use. The limits of these methodsare typically linked to the accuracy of overtopping estimation (spatial andtemporal distribution) and to the reliability of the results in urban areas,which are places where the assets are the most crucial.This paper intends to propose and apply a methodology to simulatesimultaneously wave overtopping and the resulting flood in an urban area ata very high resolution. This type of 2-D simulation presents theadvantage of allowing both the chronology of the storm and the particulareffect of urban areas on the flows to be integrated. This methodology isbased on a downscaling approach, from regional to local scales, usinghydrodynamic simulations to characterize the sea level and the wave spectra.A time series is then generated including the evolutions of these twoparameters, and imposed upon a time-dependent phase-resolving model tosimulate the overtopping over the dike. The flood is dynamically simulateddirectly by this model: if the model uses adapted schemes (well balanced,shock capturing), the calculation can be led on a DEM (digital elevationmodel) that includes buildings and walls, thereby achieving a realisticrepresentation of the urban areas.This methodology has been applied to an actual event, the Johanna storm (10March 2008) in Gavres (South Brittany, in western France). The use of theSURF-WB model, a very stable time-dependent phase-resolving model usingnon-linear shallow water equations and well-balancedshock-capturing schemes, allowed simulating both the dynamics of theovertopping and the flooding in the urban area, taking into account buildingsand streets thanks to a very high resolution (1 m). The results obtainedproved to be very coherent with the available reports in terms of overtoppingsectors, flooded area, water depths and chronology. This method makes itpossible to estimate very precisely not only the overtopping flows, but alsothe main characteristics of flooding in a complex topography like an urbanarea, and indeed the hazard at a very high resolution (water depths andvertically integrated current speeds).The comparison with a similar flooding simulation using a more classicalapproach (a digital terrain model with no buildings, and a representation ofthe urban area by an increased soil roughness) has allowed the advantages ofan explicit representation of the buildings and the streets to beidentified: if, in the studied case, the impact of the urbanizationrepresentation on water levels does indeed remain negligible, the flooddynamics and the current speeds can be considerably underestimated when noexplicit representation of the buildings is provided, especially along themain streets. Moreover, on the seaside, recourse to a time-dependentphase-resolving model using non-stationary conditions allows a betterrepresentation of the flows caused by overtopping.Finally, this type of simulation is shown to be of value for hazard studies,thanks to the high level of accuracy of the results in urban areas whereassets are concentrated. This methodology, although it is currently stillquite difficult to implement and costly in terms of calculation time, canexpect to be increasingly resorted to in years to come, thanks to the recentdevelopments in wave models and to the increasing availability of LiDARdata.
机译：最近的戏剧性事件使得近几年内陆洪水建模取得了重大进展。经典方法通常通过经验公式或1-Dimulations来估算波浪的过顶现象，然后在DTM（数字地形模型）上模拟洪水，并利用土壤粗糙度来表征土地利用。这些方法的局限性通常与覆盖估计（空间和时间分布）的准确性以及城市地区（资产最重要的地方）结果的可靠性有关。 本文旨在提出并应用了一种方法来同时模拟波浪超顶和由此引起的城市地区洪水的高分辨率。这种类型的二维模拟显示了既可以将风暴的时间顺序又可以将城市地区对流量的特殊影响整合在一起的优势。该方法基于从区域尺度到局部尺度的缩减方法，使用流体动力学模拟来表征海平面和波谱，然后生成一个包括这两个参数的演化的时间序列，并施加于一个与时间有关的相位解析模型上模拟堤坝上的超车该模型直接对洪水进行动态模拟：如果该模型使用自适应方案（均衡，震荡捕获），则可以在包含建筑物和墙壁的DEM（数字高程模型）上进行计算，从而实现对市区的真实表示。 此方法已应用于实际事件，即加弗尔（法国西部南布列塔尼）的约翰娜风暴（2008年3月10日）。 SURF-WB模型的使用是一个非常稳定的时间相关的相位解析模型，它使用非线性浅水方程式和均衡的减震方案，可以模拟城市上空和洪水的动态。建筑物和街道的分辨率很高（1 m）。事实证明，所获得的结果与现有的报告在超界，洪水泛滥，水深和年代顺序方面非常一致。这种方法不仅可以非常精确地估算出过顶水流，而且还可以非常精确地估算出像城市地区这样的复杂地形中的洪水的主要特征，以及非常高分辨率下的危害（水深和垂直积分流速）。 <与使用更经典的方法（没有建筑物的数字地形模型，并且通过增加的土壤粗糙度来表示城市区域）的类似洪水模拟的比较，可以识别建筑物和街道的明确表示的优点：如果在所研究的情况下，城市化表示对水位的影响确实仍然可以忽略不计，则当没有提供建筑物的明确表示时，尤其是沿主要街道时，洪水动力学和当前速度可能会大大低估。此外，在海边，使用非平稳条件求助于时间相关的相变模型，可以更好地表示由过顶引起的流量。 最后，这种类型的模拟被证明对危险性具有价值研究表明，由于城市地区的结果高度集中，因此结果的准确性很高。尽管目前该方法仍然难以实施且计算时间昂贵，但由于波浪模型的最新发展以及LiDARdata可用性的提高，可以期望在未来几年内越来越多地采用这种方法。

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