Closing the Gap Between Field Reality and Your SWMM Model

Accurate system representation is essential for reliable hydraulic and hydrologic (H&H) modeling, asset management, and informed capital planning. This case study presents an integrated workflow that connects RTK-grade GPS data, GIS, a computerized maintenance management system (CMMS), and the PCSWMM modeling platform to improve the accuracy, usability, and long-term value of a large regional sewer system model. Implemented by the Allegheny County Sanitary Authority (ALCOSAN) in Pittsburgh, Pennsylvania, the effort demonstrates how modern survey methods and data synchronization can significantly enhance model fidelity.

ALCOSAN’s service area spans approximately 310 square miles and includes a complex network of about 90 miles of interceptor sewers and regulators. As part of a regionalization effort, ALCOSAN is assuming ownership of roughly 180 miles of large municipal sewers, creating a need for continuous updates as new field data become available. RTK GPS surveys were used to verify pipe alignments, node locations, and invert elevations, achieving centimeter-level vertical accuracy. These measurements were integrated into ESRI ArcGIS and synchronized with Autodesk’s InfoAsset Manager (IAM), ALCOSAN’s asset management database. The model was aligned spatially and by asset IDs to maintain consistency with the authoritative asset data.

This one-to-one alignment allows modelers to efficiently compare modeled configurations with current field conditions and make informed decisions regarding hydraulic parameterization. Comparisons of pre- and post-synchronization model geometries show substantial improvements in pipe alignments and node locations, reducing uncertainty and resolving discrepancies caused by legacy datasets. The workflow streamlines access to verified asset data, reduces manual data entry, and supports future updates, while still relying on modeler judgment to validate and apply changes.

This methodology is highly relevant for communities where older models no longer align with present-day asset data. It provides a practical path for modernizing workflows, improving confidence in model-based decisions, and supporting long-term H&H model sustainability and adaptability.

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