Sedimentation Dynamics of a Sediment-laden River Intrusions in a Large Alpine Lake

River inflows are often the dominant source of nutrients, sediments and contaminants into an alpine lake system and their fate is critical to understanding lake ecosystem response. The transport of sediments in particular is dependent on the physics of hyperpycnal river inflows in which the density is due to both temperature and suspended sediment. Field observations of sediment-laden inflow intrusions were conducted in 2012 and 2014 in Pallanza Bay, a large western embayment in Lake Maggiore, Italy, in conjunction with three-dimensional numerical modeling using the SUNTANS model (Fringer et al., 2006). We employed a suspended sediment transport module with three distinct sediment size classes to investigate the dependence of deposition dynamics in the bay on inflow characteristics and seasonality during large inflow events (>300m³ s^-1), a handful of which dominate the annual sediment budget (Scheu et al. 2015). The initial stratification and inflow river temperature in the model were based on thermistor measurements and the boundary flow rate and sediment load were specified based on measurements made by Environ Italy in 2014. The model was validated using vertical profile measurements of velocity, temperature, and adjusted acoustic backscatter (a proxy for sediment concentration) for five large inflow events. In addition to the observed events, a number of scenarios were modeled with varying initial and boundary conditions in order to investigate the sensitivity of sediment deposition on flow rate and seasonality. We discuss the deposition dynamics in the context of the relative effects of river inflow, Coriolis effects, and stratification, and show that seasonal variability of the stratification strongly impacts the distribution of sediments in the bay.