The Mayor's draft water strategy - london.gov.uk - Greater London ...

4.16 With regard to tidal flood risk the
Environment Agency’s Thames Estuary
2100 Project is developing a tidal flood
risk management plan for London and the
Thames Estuary. The plan was released for
consultation in March 2009 66 and sets out the
range of options that can manage increasing
tidal flood risk over the next century.
4.17 Our options to reduce the probability
of fluvial flood risk are constrained.
Regeneration and redevelopment within the
floodplain offers the biggest opportunity
for reducing flood risk in London. Planning
Policy Statement 25: Development and Flood
Risk 67 and the Environment Agency’s Thames
Catchment Flood Management Plan (CFMP)
expand on this message:
• Flood defences cannot be built to protect
everything
• Climate change will be the major cause of
increased flood risk in the future.
• The floodplain is our most important asset
in managing flood risk.
• Development and urban regeneration
provide a crucial opportunity to manage
the risk
• Alongside this we need to re-create river
corridors so that rivers can flow and
flood more naturally. All of these issues
are addressed in more detail in the draft
London climate change and adaptation
strategy 68 .
Flooding from the surface water drains
4.18 Surface water flooding happens when
rainfall can neither soak into the ground nor
drain away through the drainage system.
Therefore, surface water flooding can result
from prolonged periods of rainfall, when rain
falls on ground that is already waterlogged,
or during very heavy rainfall, when the
intensity of the rainfall overcomes the
capacity of the drainage system.
4.19 Because so much of London’s surface
is concrete and tarmac, and therefore
impermeable to rainfall, we are very reliant
upon our drainage system to keep us dry.
However, the responsibility for drainage
currently rests with many agencies, including
Thames Water, the London boroughs (for
land drainage and the local road network),
Transport for London and the Highways
Agency (for their road networks) and private
landowners. In addition, no single agency
has responsibility for reporting or recording
surface water flooding when it occurs.
4.20 This confusion over responsibilities led the
Mayor to create a partnership involving all
the organisations with responsibility for and
information on surface water management
in London. The partnership, called the Drain
London Forum, undertook a scoping study
to assess how much was known about the
location and ownership of London’s drainage
network and to propose a process by which
information can be shared and maintained
in order to develop a regional Surface Water
Management Plan for London.
4.21 The scoping study recommends undertaking a
hierarchical assessment of surface water flood
risk in order to focus efforts on the areas most
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