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Water utility companies, responsible for providing water supply and sewerage services to the urban population, are constantly seeking to improve their service.In the case of sewer systems, effective scheduling of preventive maintenance of urban water infrastructure has been identified as an important activity in order to reduce costs and protect the integrity of citizens and the surrounding, both built and natural, environments. Consequently, with particular focus on Bogotá (Colombia), we developed an optimization model that generates a preventive maintenance plan on a set of zones withinthe city. These zones have in common a high failure probability over a defined time period due to sediment-related blockages. Failure probabilities are obtained from the statistical model proposed by Rodríguez et al. (2012) which uses an exceptionally long and spatially detailed failure data set obtained from a customer complaints database. The mixed integer optimization model implemented here, which is an adaptation from the one presented by Medaglia et al.(2008), considers a multi-objective function which maximizes the protection of the city. For the maximization process we take into account the entities that would be affected in case of flooding (health centers, education centers, market places, etc.) caused by a sediment-related sewer system blockage. The information about the entities is obtained and modified through Geographic Information Systems (GIS) and Analytic Hierarchy Process (AHP). Furthermore, the model satisfies budget and operational capacity restrictions, due to their finite nature. Based on a model sensitivity analysis, we can conclude that the ratio between preventive and corrective maintenance costs is critical to define a proactive maintenance schedule, while other parameters such as the available budget are not. Making a comparison of the methodology currently used by the local water utility and our model, the later obtained better results in terms of city protection and budget and resources allocation.


Session R52, Sanitary Sewer Networks



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