Integrating Sewer Inspection Data into SWMM Model Calibration
Developing and calibrating a large scale SWMM model in coordination with sewer cleaning and CCTV inspection can be a challenging, labor-intensive and time-consuming task. The common model calibration approach on closed conduit hydraulics involves estimating roughness coefficients and sediment depths throughout the sewer system, when detailed sewer condition parameters are available from CCTV inspections. If those conditions are changing throughout the calibration period due to sewer cleaning, this task becomes more complicated.
For the City of Columbus’s Livingston/James Sewer System I/I Remediation Project, the project team developed a comprehensive database application tool to integrate the condition parameters from 130 miles of sewer inspection into the model calibration process. The project’s SWMM EXTRAN model contains 2,900-conduits ranging from 8 in. (203 mm) to 102 in. (2590 mm) in diameter. This tool takes defects recorded for each of the sewer segments being inspected, and relates them to appropriate Manning’s roughness coefficients and/or sediment depths used in the calibration process. For sewers with multiple defects, the defects are rated and the calibration is based on the most severe defects. The time that pipe cleaning was performed is also taken into account because three calibration storms were selected at different times during the cleaning process. This new tool helps to shorten the calibration time and still maintains accuracy, while accounting for approximately 43,000 sewer defects, including roots, in the SWMM model calibration.
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