Flood events in a Mediterranean badlands area - recording in suspended sediment concentration in an instrumented catchment

Kurzfassung/Abstract

Among the numerous erosion landscapes worldwide, badlands are characterised by particularly high erosion rates and surface dynamics. In many cases, they constitute the primary source of sediments within the catchment area. The methods used to assess sediment yield and surface changes in these landscapes can be categorised as dynamic or volumetric. The dynamic approach quantifies the amount of sediment transported from a hillslope or a catchment, while the volumetric method estimates material loss by analyzing surface changes over time. This study introduces an integrated approach to quantify the off-site effects of erosion at the catchment scale using a dynamic method while also analyzing geomorphodynamic processes at the hillslope scale through volumetric assessments. Suspended sediment yield (SSY) and water discharge were monitored in the Scalonca stream catchment, located in the Upper Orcia Valley (Southern Tuscany, Italy). The catchment covers an area of 2.3 km2. The catchment is predominantly agricultural - 1.02 km2, with a forested area of 0.62 km2 and areas without vegetation or bare soil are 0.66 km2. The upper part of the catchment features badlands landform known as Calanchi, characterized by highly dissected, rapidly developing landscape, with rill, gully and gravitational landforms, and a dense dendritic drainage network. The presence of such formations increases the availability of fresh, unconsolidated material, which is transported by the stream out of the catchment. SSY measurements began in December 2024, capturing the main hydrometeorological events of the 2024-2025 winter season. These events led to significant increases in suspended sediment concentration (SSC), water levels in the channel. In the Scalonca stream, the average water level was at 6.4 cm, with nephelometric turbidity of 140 NTU and a suspended sediment concentration of 6.3 g/l. The data collected during several flood events of different intensity were statistically analysed to investigate the geomorphodynamics in the catchment and to determine the event-related hysteresis at the event level. The results show an exceptionally high variability in hydrological and SSY parameters and provide valuable insights to improve the process understanding of discharge and sediment dynamics of badlands streams. In addition, the high-resolution SfM-DTMs provided a better understanding of the morphodynamics in the catchment, supporting an integrated hillslope-channel coupling approach.