Suspended sediment connectivity analysis: Snowmelt-driven dynamics in an alpine basin

Abstract

Understanding snowmelt and its related suspended sediment transport in mountain streams is a crucial issue in the world of hydraulic and sediment research. Field-based approaches are still poorly used to investigate the response of mountain basins to different stages of snowmelt. To explain the suspended sediment dynamics of the Rio Cordon basin (Italy, Dolomites), the snowmelt in the year 2021 was analysed. First, a descriptive analysis of temporal trends of meteorological, hydrological, and sedimentological variables was carried out. Second, suspended sediment budgets of the main channel were quantified, considering the contribution of the tributaries at week- and event- scale, and supported by hysteresis analyses. Third, the role of sediment sources and snow cover was examined and integrated to comprehend variations in sediment supply from tributaries. Data were collected using a (i) multiparametric sonde installed at the outlet, (ii) water and sediment samples at significant points along the channel network, (iii) satellite images and sediment sources inventory. The whole snowmelt period 2021 featured 210.8 mm of precipitation and a mean temperature of 4.6°C. The total load of suspended sediment was 100 t. The main period of ablation was May, which showed contrasting suspended sediment dynamics in the four weeks. Sediment availability exceeded transport capacity in the initial two weeks, whereas transport capacity exceeded sediment availability in the subsequent two weeks. The main snowmelt event analysis mirrored the same trend: limited transport during the rising limb and the opposite during the falling limb. Such results were confirmed by the hysteresis analysis, proving to be an effective tool for detecting changes in suspended sediment connectivity. The variations of snow cover and the extent of sediment sources across the sub-basins influence the sediment supply. This study enhances our comprehension of snowmelt-driven hydrological and sedimentological dynamics, providing insights into the resilience of mountains to changing climate conditions.