An optimised total expenditure approach to sewerage management

Abstract

It is generally accepted by Ofwat, the water industry regulator for England and Wales, that the current investment planning system whereby capital and operational expenditure are accounted for separately is complex and burdensome. In a move towards realising a total expenditure approach, a previously successful sewer rehabilitation optimisation model has been adapted to provide a mechanism for users to evaluate the trade-offs that exist between the capital and operational benefits associated with different sewer rehabilitation schemes. A series of geographic information system tools has been integrated within the model to help prioritise high-benefit sewer rehabilitation schemes by evaluating the potential serviceability improvements that can be realised in addition to the purely structural condition improvements. As a result, the new sewer rehabilitation model can be referred to as a strategic decision support tool that is capable of helping sewerage engineers and planners in the evaluation of different intervention programmes of work. The benefits of adopting this approach are demonstrated in a UK sewerage case study that uses a multi-objective genetic algorithm to consider the three-way trade-off that exists between minimising investment cost against maximising asset life (capital benefit) compared with proactively addressing serviceability problems (operational benefit).