A Monitoring System to Assess the Impact of Anthropogenic Activities on Urban Rivers

Monitoring of rivers is fundamental not only for classifying their status and for identifying the main sources of pollution (Water Framework Directive 2000/60/CE), but, when coupled with numerical modelling, also for defining intervention strategies to improve the water quality status. In the latter case, data must be suitable to evaluate the effects of local actions on a short temporal scale, and to calibrate a numerical model to forecast the effects of actions on a long temporal scale driving the future ones. The water quantity and quality parameters, the choice of sensors, the identification of monitoring locations are just some of the main aspects that must be assessed while planning a monitoring network to obtain useful data with reasonable costs. In this work, a new water quantity and quality monitoring system developed between 2021 and 2023 to assess the impact of the city of Treviso on the quality status of the Sile River, is presented. The Sile River is one of the longest well-spring rivers of Europe and part of one of the nature protection areas of the European Union (Natura 2000). Although originated from springs, it receives the contribution of discharges from a wide agricultural area, and it is affected by the combined sewer system of the city of Treviso. An ongoing project aims at separating the sewer system: the developed monitoring system has thus been designed and used for quantifying the impact of the urban area during normal condition and rainfall events, identifying pollution sources, and for planning actions for water quality restoration. Moreover, the monitoring system has been designed for the calibration of a numerical model which will be used to forecast the effect of present and future actions. To this aim, 6 stations each one of them equipped with radar sensors to retrieve continuously water level and discharge data are installed; 3 stations out of 6 are equipped with multiparametric probes and refrigerated samplers. Two additional portable samplers allow quality data to be collected at other locations. Analysis of data collected up to now is presented to provide insights on the actual status of the river Sile and to check their suitability for building and calibrating a quantity-quality numerical model. Advantages and limitations of developing and maintaining such monitoring system are also discussed.