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.

Debris flows represent some of the most relevant phenomena in geomorphological events. Because of the potential destructiveness of such flows, they are the subject of a vast amount of research. This paper addresses the need for a numerical model applicable to granular-fluid mixtures featuring high spatial and temporal resolution, and thus capable of resolving the motion of individual particles, including all interparticle contacts. The DualSPHysics meshless numerical implementation based on smoothed particle hydrodynamics (SPH) is expanded with a distributed-contact discrete-element method (DCDEM) in order to explicitly solve the fluid and solid phases. The specific objective is to test the SPH-DCDEM approach by comparing its results with experimental data. An experimental setup for stony debris flows in a slit check dam is reproduced numerically, where solid material is introduced through a hopper, assuring a constant solid discharge for the considered time interval. With each sediment particle possibly undergoing several simultaneous contacts, thousands of time-evolving interactions are efficiently treated because of the model’s algorithmic structure and the HPC implementation of DualSPHysics. The results, composed of mainly retention curves, are in good agreement with the measurements, correctly reproducing the changes in efficiency with slit spacing and density.