Does a cleaner thames pass an economic appraisal?: the value of reducing sewage overflows in the River Thames

Due to substantial clean-up efforts, water quality in the River Thames in London has steadily improved over the last three decades. However, London's Victorian sewage system still discharges untreated sewage into the Thames, at times of moderate to heavy rainfall. This happens approximately 60 times every year, creating adverse environmental and amenity impacts on the river. Major and costly engineering works will be required to solve the sewage overflow problem. This paper reports the results of a stated preference study designed to value the multiple non-market benefits—eductions in sewage litter, risk to human health, and risk to fish populations—associated with a range of potential engineering solutions. Our findings indicate that household willingness to pay for these benefits is likely to be significantly greater than the projected costs per household of, at least, some potential technical solutions. Although arguably justifiable on economic grounds, the final decision on whether to proceed with such a large infrastructure project is unlikely to depend wholly on cost-benefit thinking, but involve complex trade-offs with other socially desirable criteria.