The impact of anthropic activities on the urban rivers' water quality: insights from the monitoring activities and modeling of the Sile River (Treviso, IT)

Urbanization is a significant factor in altering the hydrologic cycle and compromising receiving water bodies quality status. Indeed, changes in the built environment (e.g. imperviousness), together with climatic forces (e.g. intense rainfall events after long dry periods), contribute to the increase of combined sewer system overflows and of stormwater directly conveyed to water bodies (e.g. Carle et al., 2005; Riechle et al., 2016), responsible for water quality deterioration, as a result of high concentrations of pathogens, BOD, suspended solids, heavy metals, hy-drocarbons and nutrients (e.g. Ji et al., 2022). In this note, the first results of an ongoing project focusing on monitoring and modeling the Sile River, one of the longest European spring rivers, and some of its main tributaries, to assess the different discharge contributions (springs, sewer and drainage system) and the impact of the urban activities of the city of Treviso, are presented. A monitoring system consisting of six monitoring stations (3 upstream and 3 downstream the historical center of Treviso) has been developed. Each monitoring station is equipped with two radar sensors, to measure surface ve-locity and water level. Three out of six monitoring stations will be equipped with multiparametric water probes and automatic samplers, to continuously monitor and quantify rural and urban area’s drainage system outflows, and pollutants trend, during both dry conditions and rainfall events. Data collected from the monitoring stations will be used to calibrate and validate a model of the urban drain-age/sewer system coupled with the 1D hydrodynamic model of the river network crossing the city of Treviso. Starting from the hypothesis that the quality aspect depends on the quantity aspect (e.g. Depetris, 2021), data col-lected from the radar sensors is here analyzed, assessing possible issues that may occur, to test the hydrodynamic 1D model. A first water balance, during dry conditions, is presented and differences between input and output discharges enables a first estimate of the contribution given by springs and the sewer system. Results and considerations here presented are fundamental to assess the accuracy of data collected and results obtained from the model, and define the possible contributions given by springs and the sewer system. The ob-tained results set the basis for future analysis to gain an overview of the current status of the Sile River conditions, identifying and quantifying the main sources of pollution, to identify the more suitable mitigation strategies.