Obstructions at bridge can exacerbate flood hazard: when woody debris occlude a bridge, backwater increases, and sometimes a temporary reservoir can form. If the condition for the collapse of the jam exists, the phenomenon can evolve into a dam break flow resulting in an increase in downstream discharge or a steepening in the flow hydrograph. A rigorous description of backwater formed by debris at the bridge, and more generally of the interaction between flood and structure, is still a challenge and only few studies focus on the breakage phase and its consequence on flood dynamic. Unfortunately, analyzing the hydraulics of so many localized situations within a large area in detail would involve considerable modeling and calculation costs. Therefore, treatment methods are desirable that provide correct results in terms of the reference hydraulic variables for assessing the hazard without the need to model extremely local phenomena. The purpose of this study is to evaluate the possibility to reproduce an observed or estimated backwater by the use of an equivalent roughness at the place of the bridge and simulate the breakage phase by a sudden variation of its value. The method, applied to the numerical reconstruction of the experimental tests of dam break performed by the Waterways Experiment Station in 1961, has provided results that overlap well with the experimental values. Furthermore, it was applied to the reconstruction of the historical flood occurred in the Soverato river (Calabria, Italy). It did not require local grid refinement and provided results faithful to flood marks.

中文翻译：

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在流域尺度洪水建模中模拟桥梁木屑堵塞和破裂的水力后果的基于粗糙度的方法

桥梁的障碍物会加剧洪水灾害：当木屑堵塞桥梁时，回水增加，有时会形成临时水库。如果存在堵塞坍塌的条件，则该现象会演变为溃坝流，导致下游流量增加或流量过程线变陡。对桥梁碎片形成的回水的严格描述，以及更普遍的洪水与结构之间的相互作用，仍然是一个挑战，只有少数研究关注破裂阶段及其对洪水动态的影响。不幸的是，在大范围内详细分析如此多局部情况的水力学将涉及相当大的建模和计算成本。所以，理想的处理方法是根据参考水力变量​​提供正确的结果，以评估危险，而无需对极端局部现象进行建模。本研究的目的是评估通过在桥梁位置使用等效粗糙度并通过其值的突然变化模拟破裂阶段来再现观察或估计的回水的可能性。该方法应用于1961年水道试验站溃坝试验的数值重建，得到的结果与试验值吻合较好。此外，它被应用于重建发生在索韦拉托河（意大利卡拉布里亚）的历史洪水。它不需要局部网格细化，并提供忠实于洪水标记的结果。