A Model Maintenance Tool - Moving Forward with an Investment in a System-Wide Model
In 2000, the Metropolitan Sewer District of Greater Cincinnati (MSDGC) initiated the development of a system-wide computer model (SWM) of their wastewater collection system to assist the agency in the assessment of the hydraulic performance of its system and in the prioritization of short- and long-term system improvements. The 42,000-node SWM was developed and calibrated, using EPA SWMM 4 (Huber, 1988), over a three-year period and represents over 1,500 miles of pipe (CDM, 2003).
In response to Consent Decree requirements (United States of America, 2002 & 2003), the SWM was used to perform a comprehensive hydraulic capacity assessment of the wastewater collection system under both dry- and wet-weather flow conditions and is currently being applied to find solutions to assure system capacity. The SWM has been integrated into the agency operations and is being applied to meet a variety of objectives, some of which will extend well into the future.
The SWM was built primarily with data from the Cincinnati Area Geographic Information System (CAGIS), a consortium of public and private entities with the goal of developing and maintaining infrastructure inventories in a common framework, in which MSDGC has participated since 1989. The inventory of sewer data in CAGIS has been diligently maintained by MSDGC over the years. Weekly updates, including additions of new information and modifications to existing data, have ensured accurate, up-to-date representation of the existing sewer network. It is important that the SWM reflect the updated sewer data in order to assure that the proposed rehabilitative solutions identified by using the model properly reflect field conditions. This will help reduce the risk of over- or under-designing system improvements and lead to more cost-effective planning.
A comparison between recent CAGIS sewer data and SWM data showed that approximately six thousand sewers have at least one attribute that is different. The large number of differences to review led to the development of a tool that will assist with the maintenance of the SWM. The tool compares the most up-to-date CAGIS data with current SWM data, documents the differences, allows for visualization of where the differences are located, provides a mechanism to methodically evaluate the differences and decide whether to incorporate the changes in the updated model, documents the decision making process so that it is available for subsequent maintenance iterations, and creates updated model data formatted for the model input files. This chapter presents the Cincinnati SWM Maintenance Tool in its first development phase, including the results from the comparison task highlighting the need for a tool, the logic behind the tool, and its functionality.
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