Sediment transport and connectivity in Mediterranean ephemeral streams at the network scale: The case of Rambla de la Viuda catchment (E Spain)

Sediment transport models at the network scale, encompassing rates, sources and sinks, play a crucial role in understanding the dynamics of sediment movement within river basins. Most of these models have focused on perennial rivers, whereas their application in ephemeral streams remains relatively scarce. Here, we present a methodology applied to a Mediterranean ephemeral stream, the Rambla de la Viuda (⁓ 1500 km 2 ), to estimate sediment fluxes during two discrete flow events. The approach combines a catchment-scale sediment transport model (CASCADE), a fully distributed hydrological model (TETIS), and field data including UAV photogrammetric surveys and grain size analysis to provide independent reach-scale sediment budget estimates for model evaluation. CASCADE results reveal a spatially coherent pattern of sediment entrainment, transport, and deposition consistent with the geomorphological character of each channel type across the network. Headwater step-pool segments, intermountain pool-riffle, and plane-bed segments show limited to moderate entrainment and transport, reflecting supply-limited conditions. Semi-confined alluvial-bedrock channels yield moderate to high transport rates (600–4000 m 3 per event), consistent with their active gravel-bar morphology and their role as efficient sediment transfer corridors. Wide, low-gradient alluvial segments exhibit the highest deposition rates, reflecting transport-limited conditions driven by low stream power per unit width, functioning as sediment sinks whose connectivity is enhanced only during extreme events. In terms of prediction accuracy, CASCADE-derived sediment fluxes (2000–4000 m 3 ) agree in order of magnitude with both independent DoD based budgets and previously published field estimates for the same reaches (780–3100 m 3 ) under comparable flow conditions. Net sediment balances show close agreement with DoD estimates in hydraulically simple reaches, whereas divergences in complex meandering sections reflect the limitations of the one-dimensional hydraulic approximation. Overall, the combined modelling and field-data framework provide a first-order characterisation of sediment budgets, sources, pathways and storage areas, supporting catchment-scale sediment management in ephemeral streams.