Catherine Swartenbroekx

Dam-break flows over mobile beds: Experiments and benchmark tests for numerical models

In this paper, the results of a benchmark test launched within the framework of the NSF–PIRE project “Modelling of Flood Hazards and Geomorphic Impacts of Levee Breach and Dam Failure” are presented. Experiments of two-dimensional dam-break flows over a sand bed were conducted at Université catholique de Louvain, Belgium. The water level evolution at eight gauging points was measured as well as the final bed topography. Intense scour occurred close to the failed dam, while significant deposition was observed further downstream. From these experiments, a benchmark was proposed to the scientific community, consisting of blind test simulations, that is, without any prior knowledge of the measurements. Twelve different teams of modellers from eight countries participated in the study. Here, the numerical models used in this test are briefly presented. The results are commented upon, in view of evaluating the modelling capabilities and identifying the challenges that may open pathways for further research.

Two-dimensional operator for bank failures induced by water-level rise in dam-break flows

Bank failure in a stream generally originates from bed erosion at the bank toe. This research proposes a novel two-dimensional (2D) bank-failure operator, based on a simple local failure criterion and on the conservation of sediment mass. This operator is inserted into a 2D Saint-Venant–Exner model to simulate both bed and bank geomorphic processes and their interaction with the flow, especially during dam-break events. This shallow-water model is solved by a first-order finite-volume scheme on an unstructured triangular mesh. After an erosion or deposition update, the bed inclination is compared locally with the sediment stability angles, considering the impact of water-level rise. Assuming material homogeneity, the unstable bed elements are tilted around an appropriate axis of rotation, ensuring mass conservation. The numerical model is tested for a collapsing circular hole and against laboratory tests of a dam-break flow: first in a prismatic channel made of coarse sand and then over an initial bed step.