A comparison of the cost effectiveness of property-level adaptation and community-scale flood defences in reducing flood risk

Adaptations to flood-proof individual properties (referred to here as property-level adaptation, PLA) provide a potential means of reducing flood risk at isolated properties, whilst conventional community-scale flood protection (CSFP) is usually more economical in protecting high-density urban spaces. This paper develops a risk-based framework to identify the tipping point when PLA measures become more cost-beneficial when compared to CSFP in different urban densities. The framework was demonstrated using a hypothetical case study based on a residential area in Teddington, London. Sensitivity analysis was performed by varying the building densities in the urban space. Results show that PLA can have a role to supplement CSFP even in dense urban areas if the CSFP standard of protection is low. However, adding some element of CSFP to PLA can be more cost-effective than implementing a single higher protection standard of PLA. Given the unique flood risk condition of most urban spaces, and the sensitivity of cost-effectiveness of flood adaptation measures such as those demonstrated in this work, this approach can provide additional information to assist decisions in finding a sensible portfolio of measures that match that risk condition.