Coupling Hydrus-1d and Epa Swmm to Assess the Multiscale Hydrological Benefits of a Green Infrastructure

Abstract Urbanization and climate change have intensified the challenges of managing stormwater due to increased impervious surfaces and more frequent extreme weather events. Effective water management strategies are essential to mitigate flood risks, enhance water quality, and improve urban resilience. Green infrastructure (GI) represents a key nature-based solution to address these challenges by integrating natural processes into the built environment. Numerical modelling plays a crucial role in the widespread adoption of GIs at the urban scale. In this study, the hydrological models, HYDRUS-1D and SWMM, are coupled to assess the hydrological performance of GIs in managing urban runoff. The methodology involves characterizing GI components, defining representative hydrological scenarios, and applying stratified models. This integrated approach enables accurate simulation of water flow dynamics within GI systems and their interaction with the urban drainage network. The results of the coupled models highlight the effectiveness of GI in reducing runoff volumes and delaying peak flows, thereby alleviating hydraulic pressure on conventional drainage systems and enhancing urban resilience to extreme weather events. To define the soil hydraulic properties in the HYDRUS model, the evaporation method was used, and the van Genuchten-Mualem model was selected to characterize the Soil Water Retention Curve of the substrate. This model showed a saturated volumetric water content of 0.543 cm³ cm⁻³ and high permeability, ensuring efficient drainage and avoiding ponding. Building-scale modeling demonstrated a 36% reduction in runoff volume, while urban-scale simulations showed decreased surcharge of nodes and conduits, confirming improved stormwater management and flood risk mitigation. By combining the analytical strengths of both models, this study provides a robust tool for evaluating performance under varying environmental conditions. The findings support the broader adoption of nature-based solutions in sustainable urban planning, aligning with global initiatives such as the SDG 11 and SDG 13, which focus on fostering resilient and sustainable cities. This research underscores the importance of integrating advanced modeling tools into the design and management of green infrastructure to effectively address contemporary urban water management challenges.