|
The Thames flood system is complex – not only is it subject to flooding from different sources, but it has a wide range of fixed and active structures (including the Thames Barrier), varied floodplain topography, and properties and assets, some of which are very valuable. The primary source of flooding to the London region is from high sea levels propagating up the Thames Estuary (due to high tides combining with meteorological surges). However, extreme river flows can overtop defences in West London.
Flood risk analysis underpins the decision-making that goes into flood risk management. However, current methods are often limited in how they assess the potential of flood defences to fail. To avoid underestimating true risk, and to clarify which mitigation measures such as maintenance and replacement of defences are really needed, a new methodology has been developed. The method assesses flood risk from fluvial and coastal sources and uses fragility curves to analyse potential flood defence failures. This enables flooding scenarios that involve failure of many flood defence sections to be analysed against a range of flood severities. In support of the Environment Agency, HR Wallingford have applied the method to the Thames Estuary. The outputs, including spatial maps of flood risk and defences with residual risk, are being used to assist in the development of the flood risk management strategy for London and the Thames Estuary over the coming century.
The risk analysis method provides a step change over traditional flood risk methodologies. The method includes defence failures and incorporates an efficient but robust Rapid Flood Spreading Method. The successful application of RFSM to the complexities of the tidal Thames demonstrates its robustness. The model is particularly relevant for areas where defences need to be raised.
This work was funded by the Thames Estuary 2100 Project of the Environment Agency, the EU’s FP6 FLOODsite Project, the joint Defra/EA research programme (Performance-based Asset Management),and the Flood Risk Management Research Consortium( funded by EPSRC & EA).
For further information about the RFSM method please contact Ben Gouldby, Principal Scientist, Floods Group, HR Wallingford Ltd (01491 822273; E-mail b.gouldby@hrwallingford.co.uk).
Captions (above):
Top: Thames Barrier, London
Bottom: The RFSM model's predictions of flooding extent in Thamesmead as a result of a simulated breach of flood defences. This technique has been used to assess flood inundation areas throughout the whole of the Thames region. This map is based upon OS 1:50k Raster Map by HR Wallingford with the permission of the Controller of Her Majesty's Stationery Office, Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings: Licence Number 100019904
|
