Topographical changes caused by moderate and small floods in a gravelly ephemeral river – 2D morphodynamic simulation approach

Abstract

Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes performed by a flood. In most cases, the channel shape and bedform evolution during different phases of a flood hydrograph 15 are not recognized from field evidence. This paper analyzes the capabilities of morphodynamic modelling (Delft 2D) for resolving the evolution of a gravelly ephemeral river channel during consecutive, moderate-and low-magnitude discharge events. We pursue for schematic concepts for simulations in ephemeral gravely rivers that provide an outcome with the closest similarity to the post-flood reality. Based on the simulations, we analyze the morphodynamic evolution of Rambla de la Viuda The spatially varying grain size data and transport equations were the most important factors, in addition to the quality of recorded discharge, for the simulation results of the channel evolution. The total load equation worked better, compared to the 25 deterministic equation. The erosion and deposition can be in total greater during the long-lasting receding phase than during the rising phase. The deposition and erosion peaks are predicted to occur at the beginning of the moderate-magnitude discharge event, whereas deposition dominates throughout the event. On the contrary, the low-magnitude discharge event only experiences the peak of channel changes after the discharge peak. These different predicted erosion/deposition patterns suggest a hysteresis effect on the morphodynamic changes, and stress the importance of previous flood history (timing, succession and 30 magnitude) in understanding the geomorphic response of gravelly ephemeral rivers.Earth Surf. Dynam. Discuss., https://doi