In 1770, while sailing down the northeast coast of Australia, Captain Cook began experiencing erratic behavior from his compass. He attributed this phenomenon to the likelihood of iron ore deposits on a nearby island, which he subsequently named Magnetic Island. While these alleged magnetic forces have long since been disproved, the physical attraction of the area continues to draw people. Townsville, a thriving mainland city adjacent to Magnetic Island, is now the fastest growing city in the state of Queensland. With growth, of course, comes increasing strain on a city’s infrastructure. Townsville’s water and sewer business unit, Citiwater, is responsible for monitoring the capabilities of the existing system and managing infrastructure improvements to ensure it can support the expansion.
“With the increasing demands being placed on the sewer network by constant development, Citiwater must be able to accurately predict how the sewerage system is performing and what augmentations are going to be required to accommodate the increasing future loads,” explained Peter Turl, manager of the Technical Services Division at Citiwater. “A crucial part of this process was the development of a computer model of the system using SewerCAD.”
“SewerCAD is providing Citiwater with a fast, accurate assessment of the sewerage system,” added Turl. “With this tool in hand, we can now make informed, rational, and cost-effective decisions regarding future infrastructure expenditures. We intend to use SewerCAD to assess the current and future system capacity over a fifteen-year horizon.”
In a plan to model the four main regions of Townsville, Citiwater began the first stage by commissioning GHD Pty. Ltd. to develop a calibrated SewerCAD model and to provide a fifteen-year planning report for the southern suburbs of Townsville. The collection network that serves the region is comprised of 134 km of gravity mains, 17.5 km of rising mains (force mains), and 20 pumping stations.
SewerCAD’s shapefile/database connection feature proved to be a valuable asset in developing the model, as geospatial and topological data was available directly from Citiwater’s GIS. However, as with many GIS systems presently used by water and sewer utilities, Citiwater’s was developed primarily for asset management. Thus the quality of data, the data models, and the corresponding business rules did not have a strong correlation to what was needed for building the sewer model. GHD was able to work around these data limitations by developing an automated process by which the data was “cleansed” prior to using the SewerCAD shapefile connection to import the data.
"SewerCAD’s drawing review and profile tools were invaluable and saved an enormous amount of time in validating the data,” explained Jim Greatorex, the project manager at GHD. “These tools allowed us to quickly review the raw data imports and then make the necessary adjustment to the cleansing algorithms as problems were discovered.”
In the end, the model for the system incorporated all pipes with diameters of 150 mm and greater, for a total of over 2,500 pipes. The sanitary loading data for the model was developed for the 250 subcatchments using MapInfo GIS and then imported into SewerCAD using the shapefile connections. An important aspect of this modeling project was calibration and validation of the model with existing flow data. The model was calibrated using four separate scenarios: average daily and peak daily for both steady-state and extended-period simulations. The two steady-state scenarios were used to calibrate and validate the observed flows in the gravity sewer while the extended-period simulation scenarios were used to calibrate the flows in the pumping stations and rising mains (force mains).
As with all models, the one for Citiwater is a living system that will require ongoing calibration and adjustment in the future, as the various characteristics of the system are more completely understood. Information such as measured pump curves, pump station control settings, additional real-time flow data, and inflow/infiltration (I/I) data will be used in the future to increase the accuracy of the model even further.
“Achieving a high level of validation has allowed Citiwater to use the model to confidently make important financial decisions regarding future augmentation work,” added Greatorex. “They are also using it to undertake capital works planning and design, make overall operations and maintenance adjustments, increase the accuracy of emergency planning, and conduct financial analysis.”
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