Minimising Ecological Impacts on Marine Estuarine Complex

General coastal developments - Stilted

These types of development include waterfront, coastal defence schemes and other schemes which involve construction of structures adjacent to the shoreline or below mean high water springs. Also included are slipways and boathouses.

If construction is done badly, waterfront development and coastal defence schemes have the potential to impact on the ecology of the estuary through poor working practices during 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.

Topics covered on this page

• Disturbance to sediments smothering
• Releasing contaminated sediments
• Impact to hydrodynamics
• Direct loss of habitat
• Noise disturbance (birds)
• Water quality issues
• Shading impacts to habitat
• Impacts to migratory fish
• Impact on otters
• Impact on bats
• Impact on lichen communities

Affect of impact

Sediments can be disturbed from creation of stilted structures such as a slipway, steps, boathouses from drilling into the seabed resulting in localised impacts. Smothering can be an issue if there are important species in close proximity of the drilling work. Stilted structures are likely to cause a lower level of sediment disturbance due to the nature of how they are constructed in comparison to solid structures.

Suggested measures to reduce impact(s)

• Stopping sediment disturbance during construction is unavoidable, however ensuring the design of the built structure has minimal interference with coastal processes such as sediment movement will improve longer term disturbance to sediment.
• The use of a low maintenance material such as stainless steel or timbers to construct piling to reduce operational impacts of the development. These materials should be sourced from a sustainable facility where possible and reflect a near as natural structure as possible.

Affect of impact

Sediments can be disturbed from creation of stilted structures such as; a slipway, steps, boathouses from drilling into the seabed resulting in localised impacts. Smothering can be an issue if there are important species in close proximity of the drilling work. Stilted structures are likely to cause a lower level of sediment disturbance due to the nature of how they are constructed in comparison to solid structures.

Suggested measures to reduce impact(s)

• To reduce the risk of pollution incidents during construction phase, the developer is advised to follow the relevant guidelines, Environment Agency Pollution Prevention Guidelines. Further information can be obtained from the Environment Agency.

Affect of impact

The location of where the drilling occurs can have impacts on the estuarine hydrodynamics.

Suggested measures to reduce impact(s)

• Ensuring the structure has minimal interference with coastal processes, such as tidal flows.

Affect of impact

Dependent on the size of the structure, construction of a slipway and steps will cause a lower level of loss in comparison to the construction of a boathouse; however some direct loss will occur within the footprint of the structure. Stilted structures are likely to impact less than solid structures due to a minimal amount of the structure interfering in the environment.

Suggested measures to reduce impact(s)

• The size of the structure should be no longer than is 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.

Affect of impact

Increase levels of noise during construction of the foundations for a given structure, which disturbs birds. If the location of the works is located close to important winter and wildfowl feeding areas then works should be timed to avoid sensitive times of year.

Suggested measures to reduce impact(s)

• If the development is situated near bird feeding areas, undertaking construction work outside the bird over-wintering period will minimise this impact.

Affect of 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 and is likely to be less significant compared to solid structures due to less of the sediment needing to be disturbed during construction.

Suggested measures to reduce impact(s)

• Use sustainable urban drainage schemes (SUDS) to minimise run-off and associated impacts.

Affect of impact

A slipway, steps and boathouses will cause shading of the habitat beneath to varying levels depending on the scale of the development. This will in turn change the species composition due to the change in conditions previously. 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. Construction of stilted developments has the potential to create less shading than solid structures and it can allow for a greater amount of light to penetrate through.

Suggested measures to reduce impact(s)

• 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 the rock or mud surfaces underneath to minimise loss of biological productivity to reduce the impacts of shading.

Affect of impact

Loss of fish nursery areas if the development involves land claim or disturbance to the foreshore.

Suggested measures to reduce impact(s)

• Minimise working area during construction and only allow construction plant onto the shore if strictly necessary.

Affect of impact

Potential impact on otters using the estuarine waters, within the water and the land surrounding the estuary.

Suggested measures to reduce impact(s)

• Ensure that bridges and culverts are designed to accommodate the safe passage of otters and migratory fish.

Affect of impact

Potential impact on bat roosts due to modification of waterfront properties and/or loss of tree roots.

Suggested measures to reduce impact(s)

• Ensure planning application is screened for potential impact to bat roost. Developments should be informed by a Bat Roost Survey if necessary. Outlining a strategy of minimising unnecessary artificial lighting for proposed development.

Affect of impact

Potential impact on lichen communities on river side trees, exposed substrate and mining heritage buildings in the Upper Tamar.

Suggested measures to reduce impact(s)

• Developments with the potential to impact on river side trees, exposed substrate and mining heritage buildings on the Upper Tamar should be informed by a Lichen Survey.

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