A threatened world city: the benefits of protecting London from the sea

This paper describes the options appraisal undertaken in the UK within the major TE2100 project to investigate the future of protecting London from flooding from the sea. An economic analysis, within a Benefit-Cost framework complemented by Multi-Criteria Analysis, shows that improving the existing flood defences and, in 2070, constructing a new Thames Barrier downstream from the existing one are the “front runner” options for tackling the increase in flood risk that is anticipated in the future. Both sensitivity and scenario analysis have little effect on option choice. Uncertainties inevitably remain, however, when looking so far ahead, but it is clear that continuing to protect this area from the sea is highly cost-beneficial. Also the very high standard of protection now, and the robustness of the existing flood defence assets, mean that major new interventions will not be needed for some time (i.e. until c. 2070). We therefore have time to monitor the situation, carefully plan measures to maintain and enhance the existing defences, and to seek to restrain the growth of risk in the Estuary and in London through carefully designed and implemented resilience-building flood plain management measures. Rather than having to rush to new engineering works, because we have not anticipated what is needed but are forced to respond hastily to a “crisis” situation, the adaptive approach that is now possible is a key legacy of the TE2100 project.