Urban wet-weather discharges to the Vernavola river (Pavia, Italy): impacts and control strategies

This paper shows the results of experimental studies and numerical modelling for the evaluation of urban wet-weather discharges to the Vernavola river (Pavia, Italy). First of all, the research focuses on the sewer system that discharges wet-weather flows to the Vernavola river: first of all it carries out an accurate census of CSOs of this water-course and its secondary branches and secondly it develops an in-depth investigation on the functioning of CSOs and the related pumping stations. Subsequently, the study presents the main results of experimental campaigns carried out during rainfall events on the Vernavola river when CSOs activate. Annual pollutant load of TSS moved during wet-weather runoff is obtained simulating the systems basin-sewer network upstream CSOs by mean of a conceptual model based on the instantaneous unit hydrograph of a single linear reservoir system (Ciaponi et al., 2002). Water volume and pollutant loads of discharges to the Vernavola river are estimated from the geometric characteristics of the CSOs and the functioning conditions of the related pumping stations. The memory also furnishes an estimation of CSOs efficacy and a list of critical situations in terms of impact on the receiving water body. This study represents the starting point needed do define the most appropriate control strategies to reduce pollutant load discharged into the Vernavola river.