Urban flood protection post-project appraisal in England and Wales

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Abstract
Post-project appraisals were carried out for flood protection projects completed during 1960–1987 in six locations in England and Wales. The methodology focused on assessing the implications of new hydrological-hydraulic analyses of flood risks, and of urban land use changes. With hindsight, four of the projects showed higher economic returns than expected, but not all of these were subject to a pre-scheme benefit-cost analysis. Urbanisation tends to increase the value of flood damages prevented, and remaining damage potential, but induced development may represent a partial economic gain to society. However, revised hydrological analysis may reduce or raise benefit estimates and can mean that the standard of flood protection enjoyed by floodplain residents is less than previously believed. Periodic reassessment of flood frequencies in protected urban areas will help to avoid complacency concerning flood risks.