If construction is done badly, marinas and jetties have the potential to impact on the ecology of the estuary through poor working practices during the construction phase (noise and pollution), through loss of habitat or by indirectly causing changes to the way in which the estuary functions.
In order to avoid these impacts, waterfront development should comply with the following measures to reduce the associated impacts.
Sediments can be disturbed from piling. Smothering can be an issue if there are important species in close proximity of the piling. The severity of the impact also depends on the size of the jetty and, therefore, the number of piles needed to construct the jetty.
Stopping sediment disturbance during construction is unavoidable, but you can attempt to reduce impacts by:
• ensuring the structure has minimal interference with coastal processes such as sediment movement to reduce longer term disturbance to sediment.
• using a low maintenance material such as stainless steel or timbers to construct piling to reduce operational impacts of the development.
• sourcing materials from a sustainable facility where possible and reflect as near to a natural structure as possible.
Sediments can be disturbed from piling. If the sediments are contaminated it can be an issue to habitats and species in close proximity of the piling. This can lead to subsequent redistribution of contaminated sediments within the estuary.
• To reduce the risk of pollution incidents during construction phase, the developer is advised to seek and follow Environment Agency guidance.
• Encourage best practice by the provision of waste receptor facilities.
The location of the piling can have impacts on the estuarine hydrodynamics. Erosion of the salt marsh habitat could arise if works are located near significant hydrodynamic areas.
Ensure the structure has minimal interference with coastal processes, such as tidal flows.
Loss of seabed habitat within footprint of jetties, pontoons.
• The size of the structure should be no longer than necessary in terms of protrusion into the estuary.
• If the development involves land-take, create compensatory habitat elsewhere in the estuary, for example by managed realignment.
Increased levels of noise during hammering of piles will disturb birds. If the location of the works is located close to important winter and wildfowl feeding areas then works should be scheduled to avoid sensitive times of year.
During operation, general levels of bird disturbance within the estuary will increase from greater levels of boating activity.
• Locate the development away from important bird feeding areas if possible.
• If the development is situated near bird feeding areas, undertaking construction work outside the bird over-wintering period will minimise this impact.
Water quality issues can arise if sediments are released due to drilling of foundations for the construction of solid structures. The amount of sediment disturbed is dependant on the scale of the development proposed.
Use sustainable urban drainage schemes (SUDS) to minimise run-off and associated impacts.
A pontoon or jetty will cause shading of the habitat beneath and species composition may change as a result. Therefore applicants will need to describe existing habitat, identify the changes likely to occur and make a judgement in terms of the biodiversity gain/loss.
• Adopt more natural coastal protection measures where possible, such as beach nourishment.
• Use materials for construction with complex surfaces with crevices or indentations to encourage colonisation by marine flora and fauna.
• The design of walkways should allow for maximum of amount of light to penetrate to the rock or mud surfaces underneath to minimise loss of biological productivity.
• Design the addition of light column structures into the development to provide an artificial light source.
If the jetty or pontoon extends out into the main migratory route for salmonids then hammering piles can present an acoustic barrier. This can lead to potential changes to morphology of the estuary through interruption of coastal processes. During construction potential disturbance to fish passage during piling or blasting works.
• Design new structures so as to minimise effects on coastal processes, such as open piling rather than solid infill.
• Undertake any works, such as piling which could affect migration of fish outside Salmon and Allis shad migration season (March to October).
