Tidal Thames Habitat Audit
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the complete Audit
Summary
The Thames and
its tidal creeks encompass the entire length of the river
in London and the tidal limit of its tributaries. In many
cases this tidal limit is artificially restricted by the
operation of various barriers and weirs. The
River Thames runs 42 miles through Greater London from Hampton
in the west to Dartford Creek in the east. For much of its
length it is tidal, the tidal influence reaching as far
upriver as Teddington Lock. There are several tributaries
of the Thames which enter the river within Greater London,
a number of which (notably the Wandle, Ravensbourne, Lea,
Roding, Darent and Ingrebourne) have tidal creeks.
The
Thames in London covers an area of approximately 2400 ha,
about 1.5% of London's surface area. At low tide the river
comprises c2050 ha of open water (85% of the river's surface
area), 310 ha of intertidal mud, sand or shingle (13% of
the surface area) and 17 ha of saltmarsh (0.5%). The remaining
area comprises patches of neutral grassland, woodland and
scrub associated with the islands in the Thames, and remains
of former river walls that are within the existing flood
defence. Several areas of tidal reedbed have developed in
recent years, particularly in areas such as Barking Creek
and Bow Creek (see Reedbed Audit).
The
flood defences (river walls) on the Thames vary in nature
and characterise the different reaches of the river. Upstream
of Putney Bridge much of the flood defence is sloping revetment,
often vegetated, which softens the river's edge and riverbank.
Between Wandsworth Bridge and the Greenwich Peninsula the
river is largely constrained between vertical concrete and
sheet metal piled walls (although areas of mud, sands and
gravel are exposed at low tide). Downstream of the Greenwich
Peninsula, despite much of the flood defence still consisting
of vertical concrete walls and sheet-metal piling, it is
set further back from the main river channel thus exposing
extensive areas of intertidal mud at low tide.
Management of the Thames rests primarily with two organisations;
the Port of London Authority (PLA) and the Environment Agency
(EA). The PLA is concerned primarily with navigation, pollution
control and land-use planning issues related to the river;
the EA has responsibilities covering flood defence, pollution
control, fisheries, water quality, environmental protection
and nature conservation.
The
Thames represents the largest continuous natural habitat
in Greater London. The whole of the Thames and its tidal
tributaries has been identified by the London Ecology Unit
as a Site of Metropolitan Importance for nature conservation.
More than 100 fish species
have been recorded in the Thames estuary over the past 30
years, many of these in the river within London.
Although
there is very little natural riverbank along the Thames
and its tidal tributaries (the only significant stretch
being the riverbank at Syon Park), several quite large stretches
of riverbank consist of earth embankment set back from the
river. These sites have allowed saltmarsh, tidal reedbeds
and other intertidal habitats to develop. Furthermore, the
sloping revetment that forms the flood defences in certain
stretches of the river provides an opportunity for aquatic
vegetation to become established along the river’s
edge. Downstream of Tower Bridge, sloping revetment provides
an opportunity for the establishment of saltmarsh.
The two most
significant threats to the biodiversity of the Thames in
London are pollution and the loss of intertidal habitat
by the encroachment of built development. Although
the severe pollution of the river in the 19th
and early 20th centuries is now a thing of the
past, because it flows through the largest conurbation in
Europe the potential for pollution of the Thames is ever
present.
Encroachment of built development
on the river corridor is a major threat to biodiversity
in the Thames. The river, particularly in the central London
reaches, has already been severely constricted so that at
low tide only a very narrow fringe of foreshore is exposed.
Further encroachment is likely to prevent or hinder fish
movements and restrict opportunities for diversifying riverside
habitats.
Opportunities
exist for retreat from the river as riverside sites are
redeveloped, enabling the establishment of sloping embankments.
With appropriate design riverside walks can enable people
to enjoy the river without undue disturbance of birdlife.
There is
a significant potential for restoring and recreating some
of the habitats along the Thames which were lost when flood
defences were installed without due regard to biodiversity.
Innovative
approaches to enhancing the value of the river corridor
for wildlife include installing timber cladding on concrete
and sheet-steel flood defences to provide niches for plants
and invertebrates and stepping back (or otherwise adapting)
flood defences to enable habitat enhancement.
The Thames,
as a familiar feature of London, provides great potential
for raising awareness of the biodiversity of the river and
beyond. Illustrating the value of the Thames and its tributaries
as a nationally important corridor for migrant birds, for
example, will be an important element of an Action Plan.
Hundreds of thousands of people a day cross the river or
travel along its banks. Some of London’s major areas
of open space (Kew Gardens, Battersea Park and Greenwich
Park) and some of its major attractions (The Millennium
Dome and the Wetland Centre - both opening in 2000 - and
the Tower of London) adjoin, or lie adjacent to the river.
Furthermore, the seats of both central government and the
new local government for London are, or will be located
alongside the Thames in central London.
Download
the full Audit - this is only a summary
Tidal Thames Habitat Action Plan - coming soon
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