An Approach to Update a Large Hydraulic Sewer Collection Model

Mi Chen, Joe Koran, Derek Wride, Rod Moeller and Ben Gamble


Using a fully dynamic hydraulic model as a tool to study a large-scale, system wide sewer collection system has become widely acceptable with the advancement of computer and information technology. However, an existing developed model only represents the sewer collection system status as of a particular time. As time passes, the real sewer collection system is changed by the implementation of the Operations and Maintenance (O&M) program and Capital Improvement Program (CIP) under the Wet Weather Improvement Plan (WWIP), sometimes as a result of various studies that used the existing developed model. Therefore, it is inevitable and essential to update the existing model periodically in order to maintain an accurate representation of the real collection system so that the hydraulics can be correctly simulated. Updating the physical attributes of a collection system in a computer model may at first sound simple, especially with current computer and GIS technology. Adding new manholes, pipes, facilities, or updating the old data with new information into the existing developed model may sound like a straightforward data processing effort. In reality, for a large scale sewer collection system, the model updating process often deals with hundreds or thousands of nodes or pipes to be reviewed and updated, which is very time consuming and tedious. An efficient approach to update a large-scale system wide model by replacing or adding new data necessary to represent the current status of the sewer collection system is required.

This presentation addresses a general guideline for updating a large scale system wide model. It discusses the model update approach, auto-process tools, QAQC procedures, and recommendations from a recent case study. The Metropolitan Sewer District of Great Cincinnati (MSDGC)’s hydraulic system-wide model (SWM) that was developed originally between 2000 and 2003 was recently updated to 2007 data. Approximately 15,400 out of the 42,000 modeled pipes had at least one attribute that differed between the SWM and the updated recent Cincinnati Area Geographic Information System (CAGIS) data. Of these, 9,132 pipes were determined to be included in the model update based on the recent CAGIS indication and engineering judgment. This project demonstrates that a model update process involves more than a simple data processing effort (i.e. replacing or adding new pipes and manholes); experienced engineering judgment with detailed documentation is essential in order to assure that the updated information can be accurately incorporated into the model, and an auto-process tool is necessary to ensure an efficient execution of the model updating process.

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