Because much of the new housing expected in the Thames Gateway has yet to be planned, it is not possible to determine accurately the amount that will be built within the floodplain. However, only some 35 per cent. of the entire Thames Gateway area itself is at risk from tidal or fluvial flooding.
Under PPS25—“Development and Flood Risk”—all local planning authorities (LPAs) are required to notify the Environment Agency when they become aware of an application for house building in the functional floodplain. The LPA will then make a judgment as to the acceptability of the risk, and also of the likely effect of the development on floodwater run-off rates. Flood-risk mitigation measures (such as land-raising, improvements to flood defences or porous paving) can then be devised and, if these will render the risk acceptable, make these a condition of planning consent.
The tidal flood defences in the Thames Gateway are of among the highest standards anywhere in the UK (exceeding a 1 in 2000 year event standard in the development areas) and, through its Thames estuary 2100 project, the Environment Agency is devising a detailed programme for maintaining those standards into the future.