The current proposal for a revised European Directive concerning the quality of bathing water significantly increases the demands for the control of wet-weather discharges. A densely urbanised combined catchment was modelled for a 19-year long rainfall series in order to assess the current situation and to evaluate the benefits of potential solutions. Storage and advanced physical-chemical treatment of stormwater in the STP may significantly contribute for the reduction of the overflow volumes but reductions of the spill frequency under 2.5 spill days per bathing season are hardly obtained. This study reveals the severe strains that the local rainfall pattern may place on the control of the frequency of wet-weather discharges, pointing to serious technical, social and economical implications, at the local and at the national level, if the current proposal for a revised European Directive on Bathing Water is enforced.

Small urban catchments pose challenges in applying performance metrics when comparing measured and simulated hydrographs. Indeed, results are hampered by the short peak flows, due to rainfall variability and measurement synchronization errors, and it can be both difficult and inconvenient to remove base flows from the analysis, given their influence on combined sewer overflow (CSO) performance. A new approach, based on the application of metrics to peak flows for a selected set of different durations, is proposed and tested to support model quality assessment and calibration. Its advantages are: avoiding inconveniences arising from lags in peak flows and subjectivity of possible adjustments; favouring the assessment of the influence of base flow variability and flow lamination by CSOs; promoting integrated analysis for a wide range of rainfall events; facilitating bias identification and also guiding calibration. However, this new approach tends to provide results (e.g., for NSE, r² and PBIAS) closer to optimal values than when applying metrics to compare the measured and simulated values of hydrographs, so the comparison of results with thresholds widely used in the literature should be done with caution. The various case study examples highlight the importance of using a judicious set of different metrics and graphical analyses.

Green infrastructures can provide multiple benefits and play an important role in cities’ resilience to extreme stormwater events caused by climate change. Additionally, these techniques can contribute to the protection of transport infrastructures, averting major environmental and economical adversities. Stormwater can be treated through several processes, some processes being more effective than others for specific contaminants. A review of some of the most commonly used green infrastructures (GI) for stormwater management in urban environments was carried out, with emphasis on their efficiency in reducing peak flow rates, runoff volumes and the following pollutants: total suspended solids, heavy metals, total phosphorus and total nitrogen. The GI studied were green roofs, bioretention systems, filter strips, vegetated swales and trenches. In addition to the advantages in the urban water cycle, benefits of amenity and ecosystem services of these GI have also been identified. The discussion of the results and the comparative analysis of GI performance were carried out taking advantage of a table that summarizes the range of percentages of GI efficiency obtained in various studies for the different functions.

Gullies are sewer inlets placed in pavements usually covered by bar grates. They are the most common linking-element used to drain a wide range of flows from surface runoff into the buried drainage system. Their hydraulic behavior and their overall hydraulic performance is dependent on the flow conditions, the gully dimension, geometry, and location of the outlet device. Herein a numerical research based on Volume Of Fluid ( V O F ) to detect the interface, and on the Shear Stress Transport S S T k - ω turbulence model was conducted to study the importance of the outlet location and characterize flows through them in drainage conditions. Results provided detailed information about flow features, discharge coefficients, and efficiencies for different outlet locations. The authors identified three different regimes, R 1 , R 2 , and R 3 , and concluded that the outlet location influences the velocity field along the gully, the discharge coefficient, and the drainage efficiency. This allows for the estimation of uncertainty and its variation for different outlet positions.