Entec
Bulletin
Thames Gateway
…helping to create sustainable communities
Entec Case Study
Greater London is probably unique in Britain in that no other urban area in the country has as great potential for flood damage. However many of the inhabitants are unaware that any risk exists - this is mainly due to the existing tidal defence system which protects the city to a high standard. Nevertheless the consequence of any failure of these defences, however improbable, is very great.
The London Plan provides for a substantial number of additional homes and the creation of new jobs and these targets have been extended in the Thames Gateway Development and Investment Framework with East London planning for a minimum of 104,000 additional homes and 249,000 jobs by 2016.
In October 2004 The Thames Gateway London Partnership (TGLP) commissioned Entec and JBA to undertake a Strategic Flood Risk Assessment (SFRA) of East London. The primary goal of the study was to enable the 11 participating partner boroughs to undertake the PPG25 Sequential Flood Risk Test (SFRT) and thereby directly inform strategic planning of East London by analysing the consequence of existing and proposed development in high flood risk areas.
The study, funded by the Office of the Deputy Prime Minister through its sustainable communities programme will ultimately be used to inform the future strategic planning of East London and inform the preparation of the investment programme for Thames Gateway London.
Entec was required to fully explore the sequential test recommended in PPG25 to test proposed development and the existing development policies with respect to flood risk, using a multi-tiered approach combined with flood risk data, maps and modelling output at varying levels of detail. More than half of the sites identified in the Thames Gateway Development and Investment Framework (TGDIF) database were found to be in high flood risk areas.
Historically this risk has been managed by the provision of primary defences, but for a sustainable community the residual risk of flooding behind the defences must also be managed, consequently providing a clear challenge for spatial planning. To mitigate this residual flood risk, specific options were developed and costed, including land raising, non-habitable ground floor and secondary defences such as flood storage and drainage improvements. In addition site specific mitigation methods were also developed and costed for each of the housing sites depending on their associated flood risk. A cost-based prioritisation criterion was then proposed, splitting development into four different cost categories. This data, in addition to the graduation of risk within high risk areas, will allow robust spatial planning decisions to be made and give strong direction on where to prioritise development.
A significant number
of proposed development sites fall within the higher risk zone, and in order
to fully develop
the sequential test to examine the sustainability of these proposals,
the scale and robustness of mitigation measures has been considered.
However,
it is clear
that even after the costing and identification of flood risk mitigation,
careful consideration should still be given as to whether to proceed
with development
on some of the higher risk sites.
The SFRA results will be used to inform the Core Strategy within Local Development Frameworks (LDFs) which are required to be in place by 2007. Entec has also advised that the SFRA outputs are updated on a regular basis using the latest information available.
Entec believes that a real opportunity exists for the integration of the spatial planning process and the delivery of a sustainable flood risk management strategy for the Thames and its tributaries. Key to the future success is the co-ordination and communication between the Environment Agency, the London Boroughs, developers and water companies to improve the understanding of flood risk and the development of suitable mitigation measures.
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