CALIBRATION TECHNIQUES FOR MODELING COMPLEX SYSTEMS – A MADISON, WISCONSIN CASE STUDY

Wastewater collection system models have become important planning and management tools, commonly used for Capital Improvement Project (CIP) development. With the advent of sophisticated modeling software, improved flow monitoring technology, and Geographic Information Systems (GIS), dynamic modeling is being taken one step further towards design. With modeling software, agencies are recognizing significant cost-savings by quantifying specific facility needs to maintain desired performance levels, as opposed to more traditional methods of applying design criteria equally throughout an entire collection system. Models used for design, however, are only as good as the calibration. For an agency like the Madison Metropolitan Sewerage District (MMSD), whose aging collection system includes over 100 miles of interceptor sewer and 17 large pumping stations, calibration can be challenging.In MMSD's system, pump stations have a profound effect on the overall model results. The Danish Hydraulic Institute's (DHI) MOUSE model, developed for the MMSD system, includes 22 pump stations containing 62 pumps. Each pump station has different operational settings and sequencing, which include variable speed pumps and complex parallel pumping scenarios. Because downstream flow rates are dependent on upstream pump station operation, accurately simulating pump station operation was critical to the overall model calibration. Therefore this paper will provide a discussion on the techniques used to accurately simulate the pump station operation using MOUSE's real time control (RTC) module, by comparing model results against detailed pump station flow data, pump run-time data, and wet-well levels. Spending the time to accurately calibrate the pump station operation will allow the District to evaluate, with certainty, different pumping scenarios and operational settings, allowing them to optimize flows in their system and reduce potential capital improvement costs.Additionally, this paper will discuss the use of advanced tools like MOUSE's Rainfall Dependent Infiltration (RDII) module to accurately simulate all forms of Inflow and Infiltration (I/I) including overland flow, interflow, and groundwater flow. This allows the District to better understand the type of I/I flow response in each calibration basin. Understanding the type and quantity of I/I will help determine what types of I/I control measures should be implemented for each particular basin, allowing the District to select the most cost-effective set of I/I control measures. Additionally, accounting for lake level influence on wastewater flows (indirectly through increased groundwater levels) in the Madison system was only possible through the use of advanced tools in the RDII module.Finally, the paper will describe the various data sources used for dry-weather calibration and the calibration challenges and limitations associated with each data type including pump station flow data; temporary flow meter data; water utility records; billing records, and pump station wet-well level data.