Modelling transportation of pollutants in urban drainage systems

Water bodies in Europe face pressure from multiple sources. This condition is especially critical in areas affected by combined sewer overflows, urban runoff from impervious surfaces and highways, agricultural land uses, forests, and leakages. Modelling and quantification of pollutant sources and transport in sewers are crucial to support municipal planning and design efficient mitigation measures. This study applied the SWMM model to simulate pollutant transportation, focusing on Total Nitrogen (TN) and Ammonia (NH4-N) in urban sewer systems. A lumped SWMM model demonstrated good performance in simulating stormwater runoff and NH4-N transport, showing reliable accuracy for estimating pollutant loads at the catchment outlet. However, the lumped model is limited in identifying specific pollution sources or problematic areas within the drainage network. To address this, a methodology was developed and demonstrated by analysing TN loads. The results revealed differences between observed and expected values based on land use, suggesting additional pollution sources in certain locations. The methodology also identified parts of the network requiring more attention due to large differences between measured and expected loads. Future work will focus on refining this methodology and applying it to multiple pollutants to improve urban water quality management.