Roughness‐Based Method for Simulating Hydraulic Consequences of Both Woody Debris Clogging and Breakage at Bridges in Basin‐Scale Flood Modeling

Abstract

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.

Large wood debris that clogged bridges followed by a sudden release. The 2019 flash flood in Catalonia.

“…12, is not contradictory to the lack of damping in flood routing over steep slopes (Jain, 2001), because the volume of water involved here, i.e. the small reservoir at the rear of bridge C, is very small (as in Macchione and Lombardo, 2021).…”

“…Lassettre and Kondolf (2012) advocated for enlarging bridges instead of removing debris on financial grounds. Using the field data from a flash flood in a small basin (84.4 km 2 ), Macchione and Lombardo (2021) studied the effect that the breakage of a wood debris jam at a bridge had on flood levels. Similar to this last study mentioned, but on a much larger basin, our work is a case-study of the breaking of large wood debris at bridges in a flash flood.…”

Bridge obstruction caused by debris flow: A practical procedure for its management in debris-flow simulations

“…In Aosta Valley, a region located in north-west side of the Italian Alps, the problem of bridge occlusion due to debris flow is quite common and causes large damages to infrastructures and, if the bridge occlusion occurs in the villages, also to buildings and cultivated areas (Figure 1). While the clogging caused by wood debris is a topic recently tackled in the scientific literature [1][2][3], the clogging caused by stony debris flows is far less studied and the mechanism and the conditions of occurrence are * Corresponding author: daniel.zugliani@unitn.it still largely unknown. Due to this lack of knowledge, this scenario is rarely considered for the design and verification of the hydraulic section of a bridge, leading to a potential underestimation of the hazard induced by such structures when a debris flow occurs.…”

Analysis of two sources of variability of basin outflow hydrographs computed with the 2D shallow water model Iber: Digital Terrain Model and unstructured mesh size

“…One of the most valued features of such complex models is the fact that they allow hydrodynamic calculations to be carried out on a basin scale, but taking into account local flow phenomena. In order to capture the potential effects that hydraulic structures, such as bridges or weirs, have on the propagation of the flood, it is required a high resolution numerical model (e.g., Macchione and Lombardo, 2021). Although at the local scale the hydrostatic pressure approximation (essential assumption in 2D-SWE models) is not valid in the surroundings of these structures, these models still provide reliable results at the catchment scale (García-Alén et al, 2021;Luis et al, 2022).…”