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The Thames
Estuary is one of the United Kingdom’s major east-coast estuaries. It
extends from the tidal limit of the River Thames at Teddington Lock in
the west, through the heart of London, out to the North Sea. The
character of the flooding changes from a fluvial dominance in the
upstream reaches to the hazards posed by storm surges and waves in the
downstream reaches. The estuary has a dynamic sediment regime with
sequences of erosion and deposition on each tide.
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There are
approximately 500,000 properties, housing 1.25 million people, and a
significant proportion of London’s essential infrastructure at risk
from flooding. The area also has tidal salt marsh and extensive
mudflats exposed at low water, which provide important habitat to a
wide variety of species.
London’s existing defences (including the Thames Barrier) provide a
very high level of protection against flooding, but this will gradually
decline over time. Flood risk is increasing in the Thames Estuary
because of:
- Climate change – as the oceans warm the
level of the seas around the
British coast is rising and intense rainfall and extreme stormy
conditions are likely to increase in the future
- Land levels lowering – the south-east of
England is slowly sinking in
relation to the sea; a legacy from the last ice age
- Ageing flood defences – the current flood
defences that protect
London and the other communities along the estuary are getting older
and more costly to maintain
- Increasing development – the pressure for
more houses and jobs within
the tidal floodplain is increasing.
Thames Estuary 2100 project is
being undertaken by the Environment
Agency in order to develop a strategy for flood risk management in the
estuary for the next 100 years. This site was chosen as one of
FLOODsite’s pilots to take advantage of the large amount of work
already undertaken to collect data, such as the condition of defences,
and to understand how weather conditions, sea levels, river flows, the
operation of flood defences and the changing shape of the estuary
itself, affect the likelihood of flooding.
The 1953 flood was caused by a storm surge, that has been described as
‘the worst peacetime disaster that the UK has known’. The tidal surge
reached Canvey Island at around 1.00 am in the morning on Sunday 1
February 1953 and around this time the first breach of the flood
defences happened. In 1953 there was no accurate tidal surge
forecasting system in place and there was no single body responsible
for flood warnings.
Canvey Island archive web site states site that “whilst
communities did
have emergency plans, many telephone lines had been brought down by the
gales and affected by the flooding, so large scale evacuations were not
possible. As a consequence virtually no warning of the impending
disaster was received at Canvey Island until it was too late. Under a
plan termed Operation King Canute the fire brigade were sent out to
alert the people of Canvey. At the same time the siren and fore maroons
were sounded in such a way that it was hoped islanders would become
curious enough to get out of bed to look outside. Fortunately some did
and were evacuated; others were soundly sleep and did not hear anything
above the howling winds. They either woke up much later when the icy
water lapped over them, or sadly never woke up at all. Many of the
victims were in the holiday bungalows in the eastern Newlands part of
the island and perished as the water reached ceiling level”.
The
photograph shows a view of Canvey Island looking out to sea from the
mainland taken a week after the flood occurred.
Archive film
footage from 1953 of the Canvey Island flood:
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The FLOODsite
project team is working closely with the Environment Agency for this
study.
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| Westminster Bridge and the
Houses of Parliament
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QEII Bridge |
Thames Barrier in Operation |
A number of methods
were used to provide estimates of wither evacuation times or the
percentage of people that were evacuated from the following to areas in
the Thames Estuary:
The majority of
both these areas
are at or below sea level, and they are protected against inundation by
a series of flood embankments and walls. The location of the two sites
within the Thames Estuary is shown in Figure 1. The background to
these sites is discussed below.
Figure 1: The locations of
Thamesmead and Canvey Island within the Thames Estuary
The following data
was available for the two pilot areas for use in the evacuation
modelling research:
- Population data – This
is from the 2001 census data and is available at an Output Area level.
Output Areas contain an average of around 125 houses. The 2001 survey
data provides details of the age distribution of the population and
other socio-economic details Office for National Statistics, 2002);
- Number of vehicles –
The total number of cars at an Output Area level is available from the
2001 census (Office for National Statistics, 2002);
- Topographic data –
LIDAR survey data was available for both Thamesmead and Canvey Island
with a vertical accuracy of approximately ±25 mm;
- Flood depths and velocities
- Two dimensional hydrodynamic modelling results, undertaken using the
TUFLOW software, were available for both pilot areas for a number of
flood defence breach scenarios;
- National property data set
– A national property data set that provides geo-referenced details of
each of the properties in England and Wales was available. This data is
in the form of a geo-referenced point (Environment Agency/Defra, 2005).
- Road network – Details
of the major roads were digitised from existing maps;
- Historical data –
Historical data for the 1953 flood was available from a number of
sources for Canvey Island.
Three methods have
been tested that are applicable at three different spatial scales:
Although time
consuming to set up the BC Hydro LSM micro scale model provides the
most useful results. Not only can evacuation times be assessed for a
number of emergency management interventions (e.g. road closures, safe
havens) but the model also computes the injuries and loss of life for
each method. Once the initial “virtual” world has been set up in the
LSM is relatively quick to make changes to the model to assess the
impact of different interventions and management strategies. However,
at this stage the LSM is not user friendly. Other meso and macro scale
models only provided first order of magnitude in terms of the
evacuation times. These could be useful at high level planning stage
but are unlikely to be useful for detailed emergency planning
A one day end user
workshop was held at HR
Wallingford in January 2008 to discuss the research that had been
undertaken and its relevance to end users. Twenty end users from the
following organisations attended the workshop:
- The Environment Agency;
- Coast Guard;
- Local authority emergency planners based
in the Thames Estuary;
- Government Resilience Forum members;
- Department of Communities and Local
Government.
The end user
response was encouraging. All the end
users felt that the tools presented were useful in improving the
formulation of emergency plans for flood event management. The key
points made by the end users were summarised as follows:
- The tools allow the risks involved in
evacuation to be assessed;
- The software presented could be used to
analyses not only flood defence breaches but also dam breaks;
- Emergency planners could use the results
to identify safe havens
and alert people in the at-risk area where to move before a flood event
occurred.
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