Sydney's Kogarah Council has become the first local government in Australia to introduce "fuzzy logic" modelling into its Stormwater Drainage Assets Condition Model.
The model is the first of its type being used to determine the condition of underground infrastructure assets.
Council's manager Catchment and Waterways, Isabelle Ghetti, says the beauty of the model is its ability to predict the condition of Council's 96 kilometres of underground pipes without the need to use expensive closed circuit television cameras (CCTV).
The fuzzy logic modelling uses everyday language descriptors to mathematically predict the condition of pipes before the output is compared to limited CCTV surveys of a small pipe network for validation and calibration.
A collaborative effort between Council and the University of Technology Sydney, the model uses a range of criteria in determining the condition of the pipes, including traffic loads and volumes on the road, maintenance regimes of pipes, composition of pipe material, the age and size of the pipe, and the land use that predominates where the pipe is located.
"The new Stormwater Drainage Assets Condition Model incorporates the use of advanced technical software and fuzzy logic," Ghetti said. "The premise behind fuzzy logic is that everyday language descriptors are defined in a mathematical manner. The model is then able to mathematically define the basis for poor, average, good or excellent maintenance, as part of calculating the condition index of a pipe. As a result, certain specified criteria are combined mathematically to predict the condition of pipes."
The model has been validated and calibrated by the use of comparisons of output, which have been generated by limited CCTV surveys using a small pipe network. Results show that there is a high correlation between the results predicted by Council's Stormwater Drainage Asset Condition Model and the results obtained by CCTV.
The work has been completed with the help of a PhD-qualified Modeller using the resources of UTS, including advanced technical software and journals to undertake the task.
The Beverley Park Catchment has been completed using this model. A CCTV survey of some pipes shows a close correlation between the predicted condition given by the model and actual footage.
Stormwater drainage is one of the important infrastructures of any modern urban city, but high population growth, changing land use, pollution and deteriorating infrastructure can all threaten its effectiveness.
With many of Kogarah Council's assets having been constructed in the 1930s, the problem is particularly acute.
While the council possesses a large database of information pertaining to its infrastructure much of the data is available in a subjective form which doesn't lend itself to a typical engineering analysis. The rule-based fuzzy logic system is seen as a major solution.
Given that the average expected life of Kogarah's stormwater infrastructure assets is in the range of 20 to 30 years, the use of this model will certainly generate advantage in forecasting higher 'at cost' valuations and hence provide Council with a better understanding of depreciation expenditure for its infrastructure assets. This model will also yield better estimates for 'true asset values' with regards to infrastructure assets like Council's underground stormwater assets, with less replacement.
As a result of the new model, Kogarah expects more advanced understanding of research in this area, sustainability, reduction in costs and increased efficiency in terms of Council's operations with its infrastructure assets. Council also envisages it will deliver at least a 20 to 30 percent increase in serviceability levels as opposed to the standard model.
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