Nov. 6, 2008 In France, drinking water is transported to the tap via an 850,000 km network of underground pipes: the condition of this network directly influences the quality of the water and the health of millions of consumers. Such a large network – accounting for more than 80% of the value of this national legacy, i.e., the installations of a service providing the population with drinking water – is of major importance to the public bodies managing this resource.
How should the frequency of equipment renewal be assessed and these works be prioritized while containing costs? To aid the managers of this network, Cemagref scientists in Bordeaux have developed software that can forecast the network’s aging, thus identifying the pipes that are at the highest risk.
With time, the hydraulic performance and the quality of the water transported by the pipes in place decrease and water losses and damage to the infrastructure increase. The latter phenomena, which can cause spectacular damage (floods, water cuts, disturbances in road traffic), are generally recorded by the agencies responsible for their maintenance within the local government bodies. Corrosion, an increase in water pressure in the network, destabilization of the underlying land by roadworks, the conditions at installation, and age can all cause damage. While the duration and lifespan of the pipes can be long: some, put in place more than 150 years ago, continue to function properly; certain sections, however, deteriorate more quickly and should be replaced earlier.
Modeling the risk of damage
To assist the managers of this network in evaluating how often various sections of the network need to be replaced, as well as in organizing and planning the works in sync with roadworks, for example, Cemagref’s Netwater team scientists are developing tools that can supervise network aging, from data collection to the decision to renew pipes. Software called Casses, on the market since October 2007, was developed after research lasting more than 10 years.
The approach chosen estimates, for a future period, the number of breakages that each section of piping will undergo. It is based on data available in the archives that describes the pipes, their environment, and the past history of damage. Initiated in 1994, this work was pursued within a CARE-W 1 European research program, from 1999 to 2002, during which comparison with field data made it possible to assess the relevance of this approach and refine it. Since then, the Casses software has been successfully applied in France and abroad, notably in the cities of Oslo and Las Vegas. Designed to adapt to the diversity of management practices, it has been shown to perform well in predicting the number of future breakages and in identifying the pipes that are at the greatest risk.
Evaluating the extent of damage
A second software program, baptized Criticité, also developed and marketed by Cemagref, was designed to quantify the distruptions in water distribution when a section is damaged. Distribution is not disrupted in the same proportions if the damage occurs at the end of the network that serves a few users or in a water main coming out of a reservoir. For a given event, the interaction between its probability, calculated by Casses, and its impact, provided by Criticité, provides information on the extent of the risk related to this event. Studies are ongoing so the users that are particularly deprived of water as well as those who have no water can be taken into account, as the current version of the software forecasts.
Mutualizing the data of small towns so that they can take advantage of statistical modeling: such is the objective of the SIROCO program. This software was developed by Cemagref and G2C Environnement R&D. Individually, these small towns do not have sufficient data for an optimal use of the Casses forecasting models. In addition to Casses and Criticité, SIROCO uses a geographical information system, the Cart@jour GIS to mutualize data. This is an integrated system that allows the user to prioritize the sections of the network that are candidates for renewal.
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