Morphodynamics of intermittent density inflow on fan‐deltas: Physical experiments and sedimentological implications

ABSTRACT Fan‐deltas experience a range of flow conditions, from clear‐water baseflow to suspended sediment‐laden flows. The characteristics of these flows influence delta morphology, sediment transport patterns and the development of depositional features across both topset and foreset regions. However, the morphodynamic response of fan‐deltas to different intermittent flood patterns is poorly understood. This study uses physical experiments to explore how varying inflow densities and inflow‐to‐sediment discharge ratios affect fan‐delta morphodynamics. Baseflow was simulated using clear‐water inflow and flood events were simulated using saltwater inflow of varying densities to represent suspended sediment‐laden flows with different concentrations. Intermittent density inflows that mimic natural baseflow and flood events were generated by systematically alternating inflow conditions. High‐resolution Digital Elevation Models (DEMs) were used to analyse fan‐delta morphological evolution. Results show that flow occupation frequency and DEM of Differences (DoDs) captured the flow patterns and trends of sediment distribution, respectively. This study found that dimensionless stream power () negatively correlates with topset erosion‐deposition intensity (), as higher inflow discharge reduces deposition efficiency and increased inflow density promotes erosion. Conversely, on the foreset, dimensionless stream power positively correlates with foreset deposition index () – higher inflow densities enhance sediment transport efficiency, resulting in the development of thick and localised fan‐lobes. These patterns and scaling relationships shed light on the interpretation and prediction of fan‐delta morphodynamics with intermittent flood events.