Application of a flood risk model to the Thames Estuary for economic benefit assessment

Abstract

The UK Environment Agency is developing a strategic plan for managing flood risk on the Thames Estuary. The flood system is complex, involving flood risk arising from tidal and fluvial sources and the operation and reliability of “active” defence structures such as the Thames Barrier. This is set against the floodplain backdrop that comprises variable topography and high value assets worth over £60 billion. The plan needs to consider the temporal and spatial changes in flood risk that could occur over the next century. Climate change, in particular rising sea levels, ageing of defence infrastructure and new development in the floodplain can all increase flood risk. A flood risk assessment model of the Thames Flood System has been constructed to quantify the magnitude of this problem. The model includes the potential failure of flood defence structures, a purpose built probabilistic flood spreading method that enables consideration of multiple failures and multiple loading events. These modules are linked into the National Property Database that contains information on the location and type of property in the floodplain, thereby enabling quantification of the economic damages associated with flood events and hence flood risk. The model readily facilitates risk assessment related to asset deterioration, climate change and land use change in the floodplain. This paper details the methods underpinning the flood risk model, and describes how it has been used to assess the performance of a range of flood risk management intervention scenarios, including flood storage as well as new barrier construction, under different climate change scenarios.