A decision support model for the rehabilitation of "non-critical" sewers

20% of the UK drainage network is made up of "critical sewers" (those with the highest economic consequences of failure) and in the last 15 years thes e have been systematically rehabilitated. The remaining 80% of non-critical sewers are dealt with by reactive maintenance only. The paper describes ho w a flexible and rational decision support model for rehabilitating non-cri tical sewers has been developed by analysing existing sewer performance dat a and asset information. The method represents information contained in ass et and event databases in a GIS to rank variable sized grid squares into pr iority zones for action. A second stage uses a Bayesian statistical analysi s of each pipe length within those grid squares most at risk from sewer fai lure. The model has been validated on data from several water company regio ns and whilst it does not enable an absolute prediction of sewer condition, the procedures help to distinguish those parts of the system in greatest n eed of attention. (C) 1999 IAWQ Published by Elsevier Science Ltd. All righ ts reserved.