Breakwaters

Dredging operations

Pontoons

Lock provision

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 regime.

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 site level.

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 environments.

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 consideration.

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.

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