D.W. Poppema
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12 records found
1
A Full-Size Hybrid Dune Field Experiment
Design and First Results
A Matter of Debris Composition
Analyzing Debris Accumulations at Bridges After the 2021 Flood
This study presents an analysis of debris accumulations at bridges and flume experiments, based on field data collected after the extreme flood event which hit Belgium and Germany in 2021. Post-flood photos were analyzed regarding bridge designs, debris accumulation volumes and debris compositions as well as flooding conditions. This showed that the voluminous debris accumulations contained a large share of anthropogenic materials characterized by various shapes. Based on averaged bridge data, prototype bridges were chosen for the experimental modelling, which was conducted in three laboratories in Belgium, Germany and the Netherlands. Thanks to this multi-lab approach, over 250 experiments were conducted, determining the effect of upstream hydraulic conditions, debris shape and bridge design on backwater rise. Compared to debris accumulations with only logs, backwater rise increased with larger shares of plates in the debris compositions, while decreasing with the same shares of cuboid elements. The number of piers and the geometry of the bridge deck showed a strong effect on the clogging behavior, and a closed handrail led to higher backwater rise compared to a porous or no handrail. As a result of various test set-ups and continuous comparisons, inter-lab differences could be determined and reduced, and therefore resulting in a more reliable dataset. On this basis, recommendations for future bridge design and operational flood protection measures were derived.
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.
Deliverable D.T. 4.1.1
Data collection, modelling and prediction
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.
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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.
Floating debris during the 2021 European floods
An experimental study and observations
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.
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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.
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.