Strategic water network rehabilitation planning

This paper presents the approach taken and the tools developed and advanced within the European research project CARE-W (Computer Aided REhabilitation of Water networks) for strategic rehabilitation investment planning as a complement to short-term performance monitoring and annual rehabilitation (rehab) budget allocation planning. In a first step, future rehab needs are quantified with a cohort-survival model from the present stock of assets taking into account the specific service lives of its components. Utility managers may choose in the short and medium range from many rehab options: doing more or less, sooner or later, on particular network components and with specific rehab technologies at lower or higher cost. So, in a second step, alternative medium-term rehab programs are specified and tested for their effects. The annual costs and benefits of these alternative rehab programs are forecast with the cohort-survival model beyond the rehab program period to capture the long-term effects of rehabilitating these long-lived assets. Advantages and disadvantages of alternative rehab programs are systematically compared to find out which one is most appropriate under local constraints. However, whereas the survival of network components can be forecast over very long periods with sufficient accuracy, many other characteristics of the water supply system that must be considered for finding the best network rehab strategy may take unforeseeable paths into the far future. Therefore, a scenario writing tool was developed allowing consistent scenarios for particular water utilities to be created and to test whether the alternative rehab programs are robust enough to meet all eventualities of the future. This approach is illustrated by a case study from East Germany.