Estimation of service life of pipes: alternative measures to prevent blockages and flooding events in the wastewater network in Oslo VAV

Oslo VAV (Vann og Avlopsetaten) – the water and wastewater department of the Municipality of the Norwegian capital of Oslo is working on reining in its expenses and optimising the levels of service it provides to the inhabitants of Oslo. Blockages of pipelines leading to basement flooding are by far the dominant challenges which Oslo VAV faces and counters every year. Pipelines which get blocked and lead to basement flooding and excessive phosphorus discharges into the receiving fjord, may either be maintained without rehabilitation at lower cost, or rehabilitated at a higher cost. In the former case, the chance of recurrence of flooding would be higher. When flooding occurs, in addition to the additional post-damage maintenance expenses, compensation would have to be paid. In the latter case, one could eliminate the risk of recurrence, by expending a little more. However, Oslo VAV has to operate within some limits and would do well to rein in the costs and strike the perfect balance between service levels and expenditures. This paper, using the blockage and basement flooding records of the last 16 years (1991-2006) and the financials associated therewith, and using suitable assumptions, attempts to chart a picture for the future (till 2027) to enable intelligent decision-making. With the assumptions made, rehabilitation emerges as an economically-wiser option. One however, has to look beyond just the numbers born out of the calculations based on the assumptions made. It is difficult to absorb numerous factors belying the simple mathematical inequalities obtained in this paper, into the model adopted for the study. The economic analysis conducted in this paper is a logical sequel to the analysis of blockages carried out in Ugarelli et al. 2010.