This study investigates the effect of driftwood on submerged culverts through scale experiments, focusing on their accumulation and the hydrodynamic processes occurring underneath. Examining temporal evolution and velocity measurements, this research delves into the implications of driftwood accumulation, including its geometry, hydraulic conditions and associated backwater rise. Findings reveal that accumulation shape is strongly influenced by hydraulic conditions, with higher Froude numbers pulling logs toward the bottom and thus yielding more compact accumulations. This effect holds implications for submerged culverts, where the opening near the bottom diminishes the importance of surface flow resistance. Accurate prediction of accumulation lengths is achieved using wood volume and initial flow velocity. The study also provides valuable data for developing quantitative design equations for backwater rise from driftwood accumulation at culverts. Additionally, detailed measurements of velocity profiles and Reynolds stresses under the accumulations highlight a slightly lower flow velocity, prompting the need for future research to discern its generality and implications for driftwood-induced scour at submerged culverts.@en

This paper presents a dataset documenting 71 floating debris accumulations at bridges following an extreme hydrological event that hit Belgium and Germany in July 2021. Data were collected from various sources including public authorities’ documents, public online databases, post event pictures and field visits. The dataset covers bridges geometry, flood conditions and debris accumulation. In particular, it systematically details accumulations dimensions and quantifies accumulations components, which contain a significant portion of anthropogenic objects, in addition to driftwood. This dataset constitutes a unique set of invaluable data to better understand debris accumulation at bridges but also to analyze their impact on both the affected structures and flood conditions.@en

During the European flood of 2021, large debris accumulations were observed at numerous bridges, causing backwater rise, increased upstream flooding, and extended damage. To date, debris accumulation studies mainly focused on debris consisting of logs, at bridge piers or debris racks. However, during the 2021 flood, debris contained a large share of man-made materials in various shapes, often reaching the bridge deck and railing. Therefore, flume experiments on debris accumulation at bridges were conducted at three laboratories in Belgium, Germany and the Netherlands. Hereby, we investigated how backwater rise depends on flow conditions and on debris composition – using debris mixtures of 75% logs with either 25% cubes or 25% plates. Results showed that mixtures with plates caused 1.8 – 2.9 times more backwater rise than those with cubes. This means that previous studies on natural log accumulations may substantially underestimate backwater rise at debris accumulations with e.g. building rubble during flood events. Almost no backwater rise occurred below approximately Fr = 0.2, after which backwater rise increased with the Froude number. Comparison of results between labs agreed relatively well, with backwater rise under the same conditions varying often by 10% to 35%. However, the results of a single series of experiments were higher by up to a factor 2.5. This implies that any multi-flume or multi-lab study should ensure sufficient overlap between test conditions, rather than a pure workload split. Moreover, the observed inter-lab variability implies that multi-lab setups can increase confidence for the generalization of test results to real-world conclusions.@en

Follett et al. (2020a, https://doi.org/10.1029/2020gl089346) developed an analytical model to predict backwater rise by log jams, using the size and packing density of logs and the jam length, as well as river slope and bed roughness. We show that the model formulas can be rewritten using the Froude number instead of river slope and roughness, thus improving their applicability in engineering practice. The equation terms and results of Follett et al. (2020a, https://doi.org/10.1029/2020gl089346) are found to be similar to those of the empirically derived formula by Schalko et al. (2018, https://doi.org/10.1061/(asce)hy.1943-7900.0001501). However, some differences are identified, calling for further study. Most notably, these distinctions pertain to the effect of accumulation porosity, with additional minor differences in the exponent of the Froude number. Lastly, model implications for some broader applications are explored, showing a methodology to calculate the representative log size for log mixtures, and the expected effect of log orientation on backwater rise.

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This report investigates how embankments in Bangladesh could be upgraded with no or limited footprint increase. Many Bangladesh embankments need to be upgraded to improve flood protection. Traditionally, embankments are upgraded by adding more soil, heightening the crests while simultaneously widening the embankment maintain slope stability. However, in many cases there is insufficient space for embankment widening. Case studies show that in Bangladesh, private assets often directly border embankments at both the landward and seaward side. Also land is scarce in general and the land directly adjacent to embankments is often in use by the communities. For traditional embankment heightening and widening, these buildings need to be (re)moved. So owners of private assets and land need to be identified and compensated and the land must be acquired leading additional project costs and delays. This problem could be mitigated by using embankment upgrade techniques with a limited footprint increase. This requires knowledge of the available techniques and their suitability in the Bangladesh situation. Therefore, this study aims to provide an inventory of low-footprint embankment up-grade techniques used around the world, their (dis)advantages in terms of land use, risks, costs and O&M aspects, and their suit-ability for the situation in Bangladesh. @en

In July 2021, extreme flooding occurred in Belgium, The Netherlands and Germany, causing over 30 billion euro of damage. Numerous river structures were blocked by floating debris, increasing upstream water levels and thereby the extent of flooding. Moreover, debris accumulation frequently caused structural damage at bridges. This event forms both the motivation for the EMfloodResilience project and an opportunity to study floating debris accumulation better. In this report, we present the results of the floating debris work package of the project. First, a database of floating debris accumulation during the 2021 floods is presented, documenting the geometry and characteristics of both the affected structures and the debris deposits. The data collection, performed by ULiege, RWTH Aachen and TUDelft teams, focuses on three rivers particularly affected by the flood: the Vesdre in Belgium, the Ahr in Germany and the Geul in The Netherlands. The resulting database includes 33 bridges in Belgium, 38 bridges in Germany and one culvert in the Netherlands, and encompasses around 60 parameters for each identified structure. Results highlighted the severity of the flood, with peak water levels reaching more than 1 m above the bridge deck for 40% of the bridges, 32 of the 71 bridges too damaged to be kept in service. The largest debris accumulations occurred at bridges with simultaneously a pier spacing of less than 10 meters and peak water levels at or above the deck. About 50% of the debris in both countries consisted of trees, the remainder predominantly of building rubble, construction wood, tanks and, in Germany, cars and caravans. Based on these data, physical experiments were conducted at all three universities in order to determine how backwater rise (the increase of the upstream water level due to debris blockage) depends on the debris composition, hydraulic conditions and bridge and handrail design. The results of the experimental modelling were reported in a second database, which documents more than 280 tests. The presence of plates (i.e. flat objects) in the debris mixture resulted in higher backwater rise. At last, tests with modified bridge designs show that a reduction of the number of piers reduces the clogging probability. Without handrail, debris passed over the bridge sooner, resulting in lower backwater rise. Based on the observed debris accumulations and experiments, the recommendation for bridge design is to use thinner bridge decks, large freeboard between bridge deck and water level, implement collapsible or foldable handrails and reduce the number of piers. Moreover, the effect of clogging should be implemented in flood hazard and flood risk maps as well as emergency plans, and measures to reduce the accumulation of debris at bridges should be integrated in river basin management. @en

Buildings affect aeolian sediment transport and bedform development in sandy environments. Cellular automaton (CA) models have, however, only been used to simulate natural bedform dynamics. This study extends a well-known aeolian CA model to include sediment dynamics around buildings, and uses this model to explore the interaction of building-induced deposition and erosion with natural bedform dynamics. New CA rules are introduced to represent acceleration, deceleration and sideward transport of sediment around obstacles. The simulated deposition and erosion patterns show good agreement with field experiments. The model reproduces the shape and location of the morphological pattern around a single building, and effects of building spacing on this pattern for building groups. Model results further demonstrate that building-induced effects interact with local bedform dynamics and can alter the shape, growth and migration of sand dunes.

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