Hydrodynamic Modelling of FlowBehaviour and Microplastic Transportin an Urban Stormwater Pond:A Scenario-Based Study ofKungsängsdammen, Uppsala

Sammanfattning

This study evaluates the hydrodynamic performance and pollutant retention behaviour of the Kungsängsdammen stormwater pond in Uppsala, Sweden, using scenario-based three-dimensional modelling with MIKE 3 FM. The modelling approach investigated how pond geometry, inflow rates, wind conditions, and microplastic settling properties affect residence time and pollutant transport within the pond. Scenarios included geometric modification, increased hydraulic loading, variable wind forcing, and simulations with settling and non-settling microplastic particles.Results showed that modifying the pond geometry by extending the central island significantly increased residence time and redirected flow paths, reducing short-circuiting. Conversely, increased inflow rates mimicking storm events and high wind speeds in both directions led to shorter residence times and more mixed flow conditions. Microplastic simulations revealed that non-settling particles passed through the pond largely unretained, while settleable particles accumulated near the inlet, confirming the role of particle-specific behaviour in pollutant retention.This research highlights the importance of hydraulic flow conditions in determining pollutant fate and emphasizes the value of hydrodynamic modelling for optimizing stormwater pond design. The findings contribute to the development of improved urban water quality management strategies and support the creation of treatment solutions tailored to emerging pollutants, such as microplastics.