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Simplification of Detailed Models of Water Distribution Systems Obtained from GIS Systems

by Fernando Martinez, No affiliation information available.,
Carlos Garcia, No affiliation information available.,



Document Type: Proceeding Paper

Part of: WRPMD'99: Preparing for the 21st Century

Abstract:

For a long time simplified models have been used to simulate the behaviour of large water distribution networks. Often, simplification has been carried out by removing small diameter pipes and substituting branched parts by outlets directly applied to head nodes. Some authors have proposed a more reliable technique based on the aggregation of groups of connected components to obtain an equivalent pipe with a similar transport capacity to those of the real substituted pipes, taking care into accumulate the demands from the removed nodes into the preserved ones. This technique is more cumbersome but it conserves the conductance of the real network. Nevertheless, some difficulties could arise to obtain simplified elements from highly interconnected groups of pipes. Recently, due to the rapid increase in the use of Geographical Information Systems (GIS), the storage and management of all the real components of a water distribution system and its properties on large databases has become available. So the simplest way to build a hydraulic model from the cartographic data stored in database is constructing it as a detailed model where all the components are present. As a consequence, the size of the hydraulic models has increased enormously and more and more capacity is required for simulators. This procedure is practical for programmers in order to connect GIS with hydraulic models but no so interesting for engineers due to: The enormous extra-information to be analysed by the user in order to full understand the global behaviour of the system. The regular hypothesis applied to load the nodes of a hydraulic model, and in particular to associate a demand pattern for them, it fails as the number of properties supplied from these nodes decrease, due to the stocasticity of demands. As a consequence the results obtained from a detailed model on nodes of low relevance would be unreliable. The calibration of a detailed model is more complex due to the great number of parameters to be adjusted and the low reliability of measurements taken on small pipes. Additionally, finding the cause of discrepancies between measured and computed values when all the components are present is much more difficult. The enormous size of the model could result in long computing time, and will increase significantly the time consumption for reading and verify the input data and particularly to process the results. In this paper some computer aid techniques will be introduced to automate the simplification process in order to obtain a reduced model from a detailed one, using the facilities offered by the Geographical Information Systems.

Subject Headings: Geographic information systems | Water supply systems | Hydraulic models | Information systems | Pipes | Computer models | Simulation models

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