London scoping - ukcip

Final Report
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• Inform and gain the support of political and funding partners and stakeholders; and
• Prepare and manage a programme of studies linked with consultation, leading to a
strategy for flood risk management in the Thames Estuary for the next 100 years.
The project will take five years to complete and involve research to build up a detailed
understanding of the physical processes affecting the Thames Estuary. Again, statistical
downscaling techniques could be used to develop scenarios of tidal surges that compliment
existing work with physical models of the estuary.
Development and Flood Risk
As part of its role in the permitting and regulation of flood management and related issues the
EA has been assessing its approach to development and flood risk. PPG25 suggests allowance
should be made for climate change. Recent research has led to the incorporation of an
allowance of 20% extra fluvial flow over a 50 year period, based on Thames and Severn
(Environment Agency). By contrast allowance for sea level rise has been a consideration for the
past few decades. PPG25 currently quotes 6mm per year although during the design in the
1970s of the current tidal defences for the Estuary, a figure of 8mm per year sea level rise was
used. The EA is considering two main issues at present:
• A project to assess whether 20% is an appropriate figure for all watercourses, or
should this be adjusted up or down based on such factors as urbanisation,
catchment size and geology; and
• Can more refined guidance be developed based on the smaller grid size of the
UKCIP 2002 scenarios compared to UKCIP 1998, e.g. a regional London & South
East figure rather than an England figure?
Both of these issues concern accuracy and reliability of current information. Other issues being
considered include:
• Will flood defence standards decline with time (i.e. 100 year standard becomes 50
in the future etc).
• Should defences be upgraded to maintain the current standard or accept a lower
standard in future? The latter option would increase the flood risk at a site, which
may alter the PPG25 risk category, and hence restrict future options for
development.
• Adding 20% to flows enlarges the floodplain, though not necessarily by 20%, the
figure will vary with topography. In areas not at risk now, but at risk in 50 years,
there could be a series of options: (a) do nothing, (b) object now or (c) ensure a
design that allows for changing risk, e.g. raise floor levels to cope with future flood
levels. Should the same option be chosen everywhere, or should it be varied
depending on location/development type or lifespan?
• Planning policies which reflect the changing risk associated with climate change
need to be developed with Local Authorities, GLA etc.
• Flood risk assessments for PPG25 need to include climate change, including work
for strategic sites such as the Thames Gateway.