Modification of habitats
Estuaries have always been affected by human
exploitation. The major direct impacts on the areas have come
from land claim for industrial and agricultural purposes, coastal
protection work, port expansion and water-based recreational
developments, including recreational infrastructure. Damage
has also been caused by mineral extraction, bait digging, industrial
and agricultural pollutants and barrages, which alter the tidal
In a comprehensive study of the UK's estuaries
in 1989, the then Nature Conservancy Council looked at the reasons
for the continuing pressures on the resource. It found that
of all land claim activities at that time in the zone, marinas
and provision for water based recreation accounted for 11.5%
of the land claim cases by number and 18.5% of all land claim
proposals by number.
Whilst the recession of the early 1990s slowed
down the growth in the demand for leisure boating facilities,
the economic recovery has once again placed pressure on facilities
provision and there are a growing number of planning applications
being placed, mainly for extension to existing facilities. It
is unlikely, however, that demand will reach the levels once
predicted by the RYA, at the height of the economic boom, of
3000-4000 new boats per annum requiring deep-water berths.
It is important to note that the provision
of berthing facilities for recreational craft does not necessarily
have to result in habitat loss. Saltmarshes in their
natural state already provide half-tide berths for many boats.
However, the potential impact of such berthing provision on
soft habitats and related species needs to be examined at the
The following section looks at specific aspects
of boating facilities development.
The creation of a fixed artificial breakwater,
by the deposition of large quantities of stones or the building
of a concrete structure, is often the first stage in a large-scale
coastal development. Behind this structure, the marina basin
itself is constructed. The environmental impact of a fixed breakwater
is related largely to the effect that such a structure may have
on the flow of the water in its vicinity. Where it reduces tidal
amplitude significantly the breakwater may affect coastal processes
and therefore erosion and accretion along the coastline.
The base of fixed breakwaters can cover a large
area of the bed of the water body and this is likely to have
an effect on the organisms which inhabit the bottom sediment.
Breakwaters also have a visual impact, but
this issue lies outside the scope of this report
Dredging undertaken in relation to commercial
port and harbour activities is considered in more detail in
ABP Research (1999).
Dredging is often required during the construction
and modification of marinas (‘capital dredging’) and it is usually
essential for the continuing maintenance of channels and basins
(‘maintenance dredging’). Without dredging, channels can quickly
silt up and prevent navigation by all but the smallest craft.
Dredging can cause long term effects including
increased turbidity and, depending on the scale of the dredging
operation, possible changes in flow characteristics of the water
body. Large scale dredging can remove entire benthic communities
which inhabit the water bed. There is some evidence, however,
that the impact of the turbidity caused by such dredging operations
is short term in nature and limited in extent (Bendel, 1986).
It is also the case that dredging can improve water quality
in some areas by enhancing water depth and flow characteristics.
The disposal of the resultant dredge spoil
in coastal areas can result in the release of contaminants such
as heavy metals, resuspension and dispersion of sediments and
smothering of benthic communities. Disposal of spoil from dredging
activities is tightly controlled by legislation mainly designed
to prevent the deposition of contaminated sediment in sensitive
All dredging activities require disposal licensing
by the Ministry of Agriculture, Food and Fisheries (MAFF). Before
such a licence is granted there is a requirement that all beneficial
uses of dredge material should have been considered, including
intertidal/subtidal habitat creation/restoration. Licences are
often refused if there is evidence that the dredge spoil contains
large concentrations of heavy metals or contaminates such as
TBT. It should be noted that contamination from metals is largely
the result of industrial activities unrelated to leisure boating.
It is also important to bear in mind, that where contaminated
spoil is able to be removed, this can reduce concentrations
of contaminants in the areas from which it is removed, although
the resultant impact on the chosen disposal site is an important
Although the impact of the required dredging
activities depends on the size of the development, it is those
new developments which modify the intertidal habitat that will
have potentially the greatest physical impact. For example,
a large-scale development with permanent breakwater provision
and landside development is likely to require either a substantial
area of land claim and/or flooding of existing land.
Pontoons are put in place either by piling
into the waterbed or by anchorage. This may result in short
term disturbance, possible loss of habitat and cause localised
turbidity but is unlikely to have significant long term effects.
Indeed the piling often provides ideal habitat for a range of
molluscs and other organisms. The pontoon structure may have
an impact on current flow and other coastal processes but this
is likely to be fairly minimal in all but the largest projects.
The cumulative effect of a large number of pontoons in a localised
area may also have an effect on coastal processes but little
work has been carried out to quantify such effects.
Locked marina basins are generally required
in those locations which normally experience wide tidal ranges.
The cost of lock provision is high and installation is usually
undertaken for reasons of engineering necessity. Locked basins
have, however, occasionally been required for aesthetic reasons
where the marina developer or planning authority has sought
to provide a facility at permanent high tide.
The effect of marinas with locked basins on
water flow characteristics and consequent impacts on fauna and
flora are likely to be of a larger magnitude than that of similar
non-locked marinas. Intertidal habitat is also permanently lost
from locked basins.