Session D6 - Tools for monitoring flow and quality of stormwater runoff

The reduction of overflow volumes from Combined Sewer Overflows (CSOs) progressively leads to hydraulic conditions where water level and velocity sensors operate near their detection limits, making overflow volume measurements particularly uncertain. This study proposes a method to characterize the Limit of Quantification (LOQ) for overflow volumes (LOQV), defined as a geometric zone in the overflow volume–duration space, derived from historical data. This zone, referred to as “< LOQV,” includes volumes that are detected but not quantified due to excessive relative uncertainty. Three imputation strategies are then compared to handle these unquantified volumes: a zero-replacement approach, a geometric imputation based on the centroid of the “< LOQV” polygon, and a statistical imputation using a bivariate log-normal distribution. Application to six instrumented CSOs shows that the statistical approach provides the most consistent estimates for low volumes. These results highlight the importance of a reasoned treatment of “< LOQV” volumes to improve the reliability of overflow balances and ensure inter-site comparability.

Monitoring of urban drainage systems plays a key role in operation, compliance assessment, design, modelling, decision-making, and planning activities. Nevertheless, experience indicates that metrology applied to urban drainage systems is frequently of insufficient quality. That is why the Urban Drainage Metrology Toolbox (UDMT) has been developed in the H2020 European Project Co-UDlabs, aiming to facilitate the adoption and application of best practices and advanced methods in metrology. The UDMT is a unique, free, online, and open-source software tool, available in French, English and Spanish, providing a set of coordinated functionalities including various methods for sensor calibration, data correction, uncertainty assessment, data validation, and tracing experiments. Based on comprehensive documentary resources available on internet, the UDMT is also a tool for both i) education of master and doctoral students, and ii) professional training courses dedicated to practitioners.

Urban water systems are transitioning towards circular, sustainable models. This transition requires comprehensive water quality data to identify pollution hotspots, plan mitigation strategies, and evaluate their effectiveness. However, current monitoring methods are costly, generate fragmented data, and are insufficient for city-wide applications. The URBAN M2O project addresses these challenges by developing integrated monitoring and modeling solutions tailored to end-user needs, including water utilities and environmental authorities. This paper presents preliminary results from mapping current and future monitoring requirements across Europe through legislative reviews, stakeholder questionnaires, and co-creation workshops. Findings reveal significant discrepancies between EU and national regulations, gaps in data sharing, and emerging needs for high-resolution indicators covering chemical, microbial, and microplastic contaminants. These insights will guide the design of next-generation tools for cost-effective, system-wide monitoring, enabling robust pollution control strategies.

Human-made small urban waterbodies (SUWs), such as stormwater management ponds, wastewater lagoons, and reclaimed quarries, are common infrastructure assets throughout many communities. As global efforts to quantify greenhouse gas (GHG) emissions intensify, SUWs have been identified as potential sources of carbon dioxide (CO2) and methane (CH4), although there is large variation in the way emissions are measured. A low-cost floating flux chamber with real-time CO2 and CH4 sensors was designed and constructed with 3D-printed parts and hardware store materials for $1,150 CAD to address problems associated with typical monitoring methods, such as sample contamination during syringe sampling, failing to capture the true flux due to low sampling frequency, and neglecting spatial variability due to the high cost of GHG analyzers. The sensors were calibrated and validated in the laboratory by injecting known volumes of gas and comparing with syringe samples analyzed using gas chromatography (GC). Validation experiments showed that the real-time sensors reported 99.62% (R^2 = 0.9950) and 99.22% (R^2 = 0.9987) of the values the GC measured for CO2 and CH4, respectively. The chamber was deployed in an attenuation pond in Almonte, Ontario, on August 20th, 2025, to provide proof of concept and calculate CO2 flux in a real SUW. Exponential and linear fits were applied to the recorded concentrations, giving fluxes of 28.12 mg m^2 min^-1 and 22.19 mg m^2 min^-1, respectively. Additional field tests will be performed with the flux chamber in Spring 2026 to determine how emissions vary spatially across SUWs.