Mobilization of large wood in river channels during floods represents a hazardous factor, augmenting flood risk and endangering infrastructures such as bridges, weirs, and reservoir dams. A hybrid modeling approach combining numerical models with field-based surveys has been recently used to elucidate the processes of LW entrainment and deposition in rivers. We used two-dimensional hydraulic modeling performed in HEC-RAS to simulate LW entrainment in two valley bottom segments of the Dyje River, Czechia, where LW deposition is a significant hazard to the dam of the downstream Znojmo reservoir. We surveyed all LW pieces in the inundation area of the 2002 extreme (>Q₁₀₀) flood and simulated their entrainment for eight flood scenarios (1–100-year recurrence interval). We used the equations of Braudrick and Grant (2000, https://doi.org/10.1029/1999WR900290) to calculate the LW entrainment threshold; we introduced coefficient k accounting for the incomplete submersion of LW pieces resting on an inclined surface into the original equations. Four entrainment categories — stable, wetted stable, wetted buoyant, and wetted entrained — were defined, and the proportion of LW pieces in each category was calculated for the flood scenarios. We found marked differences in entrainment categories for respective flood scenarios between the two valley segments. These were attributed to the differences in pieces' dimensions, their spatial distribution within the inundation area, and valley-bottom topography, which affects the hydraulic conditions for a given discharge. The presented approach enables the calculation of the LW quantity potentially mobilized by the flood of a certain magnitude indicating the degree of potential risk for the infrastructures located downstream.

中文翻译：

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河流中潜在的大量木材夹带的数值模拟：混合模拟在捷克 Dyje 河坝间河段的应用

洪水期间河道中大量木材的流动是一种危险因素，会增加洪水风险并危及桥梁、堰和水库大坝等基础设施。最近采用了一种将数值模型与实地调查相结合的混合建模方法来阐明河流中轻水的夹带和沉积过程。我们使用 HEC-RAS 中的二维水力模型来模拟捷克 Dyje 河两个谷底段的轻水夹带，其中轻水沉积对下游兹诺伊莫水库的大坝造成重大危害。我们调查了 2002 年极端洪水（>Q ₁₀₀ ）淹没区的所有 LW 件，并模拟了八种洪水场景（1-100 年复发间隔）的夹带情况。我们使用 Braudrick 和 Grant (2000, https://doi.org/10.1029/1999WR900290) 的方程来计算 LW 夹带阈值；我们将系数k引入到原始方程中，以解释位于倾斜表面上的 LW 件不完全浸没的情况。定义了四种夹带类别：稳定、湿稳定、湿浮力和湿夹带，并针对洪水情景计算了每个类别中 LW 件的比例。我们发现两个山谷段之间各自洪水情景的夹带类别存在显着差异。这些归因于碎片的尺寸、淹没区域内的空间分布以及谷底地形的差异，这些差异影响给定流量的水力条件。所提出的方法能够计算一定程度的洪水可能动员的 LW 量，表明下游基础设施的潜在风险程度。