Rethinking Wet Weather Modeling: Applying GIM Hydrology to Sanitary Sewer Systems for Long-Term Infiltration

The groundwater infiltration model (GIM) has traditionally been reserved for combined sewer systems—but prolonged wet weather response in separated sanitary systems demands a new approach. This presentation will explore how the Trinity River Authority of Texas (TRA) and its consultants redefined modeling practices by applying GIM to better simulate multi-week infiltration events. Historically considered unsuitable for sanitary systems, GIM proved essential for capturing peak flows and volumes critical to treatment-plant sizing, storage planning, and operational strategy. As the design support needs of engineers and managers evolve, TRA’s hydraulic modeling practices have adapted, expanding run durations and improving calibration methodologies. This case study challenges the status quo and sets a new standard for how InfoWorks ICM software’s hydrology can be used to meet real-world operational demands.