directives have we solved the problems? Roger Morris Bright Angel - - PowerPoint PPT Presentation

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Dredging and environmental directives – have we solved the problems?

Roger Morris Bright Angel Coastal Consultants

http://bacoastal.co.uk

What does dredging do?

• Deepening changes the energy regime.
• Can change tidal propagation.
• Removes sub-tidal animal and plant

communities.

• Creates a sink for suspended sediment.
• Creates sediment plumes - potentially

affecting BOD.

• Creates underwater noise.

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Impacts on wildlife

• Reduces sediment availability.
• Changes levels of inter-tidal exposure.
• Removes certain habitats.
• Smothers some habitats such as biogenic reefs
• Impacts upon water quality:
• Mobilises sediments, affecting BOD.
• Re-mobilises contaminants.
• Affects fish movement.

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Reduced sediment availability

• Dredging leads to a requirement for

maintenance dredging.

• Maintenance dredging removes sediment that

might otherwise be deposited on foreshores.

• Reduced sediment load changes the

relationship between deposition and erosion - erosion is countered to a lesser extent than previously.

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• Harwich Haven Capital dredge
• Immediate loss of 4.5 ha of inter-tidal through

reduced exposure.

• Proposed Southampton Capital Dredge
• Mixture of reduced exposure and increased exposure
• less mud and more sand
• 1996 Southampton Capital Dredge
• Illustrated how cut sediment could be used to

provide a one-off foreshore replenishment.

We can predict changes to tidal propagation

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Sediment loss = condition change

• Sea level rise is affecting sedimentation -

need more sediment to feed mudflats and saltmarshes.

• Reduced sediment load = potential for

winnowing - system becomes sandier. This potentially changes in-fauna and bird carrying capacity.

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Sub-tidal habitat loss

• Rarely an issue for Natura 2000.
• But, Falmouth is an exception.
• But, potentially an issue under the WFD:
• Loss of extent of habitat.
• Increase in extent of modification (shift from

Unmodified to heavily modified = shift away from GEC).

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Is dredging a Habitats Regulations issue?

• YES
• Loss of extent.
• Changes to foreshore evolution - erosion.
• Possible impacts on some sub-tidal habitats (e.g.

maerl).

• Possible impacts on protected species, especially

Atlantic Salmon.

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WFD Impacts

• Changes to hydromorphology
• Changes extent of modification
• Impacts on water quality
• Impacts on fish
• Loss of biological assemblages

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Do we have solutions?

• YES & NO
• We understand sediment management

issues.

• We have no solution to loss of sub-tidal

habitats or to some water quality problems.

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• Changes to tidal propagation can be

measured and compensated for.

• Reduced sediment loads can be offset ….
• … or can they?
• Timing can be varied …..
• … or can it?
• Sub-tidal impacts will be re-colonised …..
• … or will they?

Dredging solutions in the UK

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Are known solutions compatible with all the issues?

• NO
• Sediment feeding is compatible with

geomorphological objectives (which in the UK have taken priority).

• Sediment feeding is ok in muddy estuaries but not

in clear-water estuaries.

• Sediment feeding can have an impact on BOD and

water quality, especially in clear water estuaries

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What does this mean in real terms 1?

• Techniques for

sediment feeding may not be acceptable:

• Rainbowing
• Overspilling
• Timing for sediment

feeding may be confined to the wrong time of year.

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What does this mean in real terms 2?

• Some dredges are not

compatible with EU Environmental Directives.

• The impacts are most

likely to be severe in clear-water estuaries.

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What does this mean in real terms 3?

• Port expansion may not be

possible in some Atlantic coast locations.

• Guidance on port

development needs to be better differentiated between North Sea, Atlantic, Mediterranian, Baltic and Black Sea environments.

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Some concluding thoughts

• The arrival of the

WFD re-introduces a new tension.

• Some water quality
• bjectives may not

accord with N2k geomorphological

• bjectives.
• There is much more to

do!