Rainfall, run-off, and sediment transport dynamics in a humid mountain badland area: Long-term results from a small catchment

In this study, we investigated rainfall, run-off, and sediment transport dynamics (414 run-off events and 231 events with sediment information) of a humid mountain badland areathe Araguas catchment (Central Pyrenees, Spain)from October 2005 to September 2016. Use of this long-term database allows characterization of the hydrological response, which consist of low-magnitude/high-frequency events and high-magnitude/low-frequency events, and identification of seasonal dynamics and rainfall-run-off thresholds. Our results indicate that the Araguas catchment, similarly to other humid badlands, had high hydrological responsiveness (mean annual run-off coefficient: 0.52), a non-linear relationship of rainfall with run-off (common in Mediterranean environments), and seasonal hydrological and sedimentological dynamics. We created and validated a multivariate regression model to characterize the hydrological variables (stormflow and peak discharge) and sedimentological variables (mean and maximum suspended sediment concentrations and total suspended sediment load). In summer and at the beginning of autumn, the response was mainly related to rainfall intensity, suggesting a predomination of Hortonian flows. In contrast, in spring and winter, the responses were mainly related to the antecedent conditions (previous rainfall and baseflow), suggesting the occurrence of saturated excess flow processes, and the contribution of neighbouring vegetated areas. The multivariate analysis also showed that total sediment load is better predicted by a multivariate regression model that integrates pre-event, rainfall, and run-off variables. In general, our models provided more accurate predictions of small-magnitude/high-frequency events than high-magnitude/low-frequency events. This study highlights the high inter- and intra-annual variability response in humid badland areas and that long-term records are needed to reduce the uncertainty of hydrological and sedimentological responses in Mediterranean badland areas.