The decision, whether and how to rehabilitate a damaged sewer is a complex one. Detailed information available from sewer inspection can be used for evaluating its condition and determining the urgency of rehabilitation. There are various rehabilitation techniques, from conventional open trenching to newer trenchless construction. Municipal waste water departments and companies must use their tight budgets in the most efficient and responsible way.

Therefore, a decision support system for choosing the right/best sewer rehab technology is urgently needed. For a computer aided selection of the right technology for sewer rehabilitation a formalised weighing and ranking procedure should be used. That procedure should be based on a detailed description of the rehabilitation task. So the state of the existing sewer has to be identified, future technical requirements have to be formulated and specific local restraints taken into account. First, rehab technologies not capable of solving the problem under given constraints, are eliminated by “knock-out” criteria. Thus the number of potential solutions is reduced to those which are subsequently compared (computer aided) in pairs. There is no scoring hocus-pocus and criteria weighing in this decision system. The result is found just by comparing pairs of options on as many criteria as needed, and these criteria may be measured on different scales and need not be independent from each other.

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