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Urban water balances are strongly shaped by the complex interplay between infiltrated stormwater, subsurface soil, and buried infrastructures. Sewer-mediated subsurface fluxes such as inflow and infiltration (I&I) and exfiltration can significantly alter the path and fate of stormwater. However, these processes are often overlooked in hydrologic analysis; the relative contribution of rainfall and groundwater on sewer-mediated fluxes and the combined and relative influence of interacting environmental and structural factors on these fluxes remain largely underexplored. In this study, we developed an integrated hydrologic model using HYDRUS-2D to represent the detailed geometry of a defective sewer pipe with a colmation layer within a trench-scale domain. We validated it with prior data and applied it on various hypothetical scenarios to evaluate how does sewer- mediated subsurface fluxes respond to variations in environmental and structural factors such as soil type, water table depth, pipe defect size, and trench backfill materials. We also performed a feature importance statistical analysis among different factors to further quantify the relative importance of these factors. Findings reveal that the rainwater partitioning and the resulting water balances exhibited notable variations across different native soil types and water table depths. Comparatively, sewer-mediated fluxes are more sensitive to water table depth and pipe defect sizes; while natural fluxes of surface runoff and evapotranspiration are more sensitive to surrounding native soil and trench backfill soil types. Backfilling trenches with native soils (particularly clayey soils) instead of granular imported soils reduced sewer fluxes and enhanced natural outflows. This study can inform catchment-scale hydrologic models to identify hotspots for operation and maintenance in urban sewers and evaluate the impact of sewer-mediated fluxes on watershed hydrology and streamflow regimes. 

This data is the outcome of a research study titled as "Variations of Urban Water Balances Considering Subsurface Sewer Fluxes: A Hydrologic Modeling Study" which is currently in preparation. The study investigates the overlooked yet critical interactions between urban stormwater infiltration, subsurface soils, and buried sewer infrastructure. Using HYDRUS-2D, a series of simulations were conducted to evaluate how sewer-related water fluxes — specifically inflow and infiltration (I&I) and exfiltration—respond to variations in soil texture, groundwater table depth, pipe defect size, and trench backfill material. The analysis demonstrated that soil texture and groundwater depth significantly influence water partitioning. Fine-textured soils led to increased surface runoff and evapotranspiration, while limiting groundwater interactions and I&I. In contrast, shallow groundwater conditions significantly elevated I&I, with minimal impact on surface processes. Larger pipe defects further intensified both I&I and exfiltration. A statistical feature importance analysis reinforced the influence of groundwater depth and pipe integrity. The findings highlight the necessity of incorporating detailed subsurface interactions into urban hydrologic modeling to better inform infrastructure design and management.