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The System Wide Model
The Metropolitan Sewer District of Greater Cincinnati (MSDGC) has recently completed a three-year project to develop a hydraulic model of the sewer system. One of the largest models of its kind ever constructed, the System Wide Model provides the District with an extraordinary tool to evaluate existing and projected conditions within the sewer collection system.
Armed with a better understanding of the system dynamics, the location and cause of capacity constraints can be identified. A solid foundation then exists for the development of capital projects that will address overflows, basement backups, and yield a more efficient operation of the wastewater collection and treatment system through real-time control.
What is a Model?
In sewer system lingo, a hydraulic model is a computer-generated replication
of the sewer system that can simulate the movement of flow 
through a piped network. The image to the left is an example
of flow simulation taken from MikeSWMM, the modeling software utilized by MSDGC
for this project. Within the District's service area, all sanitary sewers 12" and
larger, and combined sewers, 18" and larger are included in the System Wide
Model.
What are the benefits?
Overloaded pipes can create a myriad of problems. Sewer backups and overflows present some of the more severe problems attributed to overloaded pipes. The causes are oftentimes extremely complex in nature and therefore difficult to both understand and resolve. A system model provides the means to view flow levels and velocities, and surcharge conditions in many areas of the sewer network all at the same time. By making changes to the computerized model, “what if” scenarios are developed to simulate proposed system modifications prior to construction . In addition to determing the impact to the immediate area, these simulations allow for the evaluation of downstream impacts to determine the best holistic design solution.
The benefits of the Model do not stop there. As development continues at a rapid pace throughout many parts of Hamilton County, the need increases to extend the sewer system. Well-informed decisions can be made when determining the impact of the added flow to the downstream system and to the receiving treatment plants.
MSDGC owns and operates over 3000 miles of sewers. Of this,
approximately 42,000 sections of pipe comprise the SWM. To better manage the
project study area, Hamilton County was divided into three major basins.
- Great Miami
- Mill Creek
- Little Miami
Much of the information used to “build” the model foundation is taken from existing CAGIS data and meticulously checked for accuracy. Field surveys supplement and/or verify the CAGIS data.
Approximately 145 sites were selected for the installation of flow monitors, used to calibrate the model to actual flow conditions. Rainfall data is obtained through radar-rainfall technology, supplemented by a network of over 30 rain gauges.
April of 2003 marked an exciting event with the completion of the System Wide Model, comprised of over 42,000 segments. Although the calibrated Model is complete and presently in use at MSDGC, updates and maintenance to the model will continue indefinitely.
