Maintenance dredging of navigation channels in French estuaries Evaluation of the incidences with re

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Maintenance dredging of navigation channels in
French estuariesEvaluation of the incidences
with regards to conservation of Natura
2000sites
Groupe dEtude et dObservation sur le Dragage et
lEnvironnement
September 2006
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Evaluation of the incidences of maintenance
dredging in ship canals

• The development programs or construction
  projects subject to authorisations or
  administrative approbation and whose realisation
  is of nature to affect notably a Natura 2000
  site, must evaluate the project incidences with
  regards to the conservation objectives of the
  site
• The port authorities have evaluated the
  incidences on habitats and species of community
  interest with regard to the French legislation
  (incidence document on water systems / permit
  application for immersion), being assisted by
  preliminary works from the management plan
  (DOCOB) of each Natura 2000 site, when available.
  

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Habitats and species in estuaries
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Presentation of the incidences of maintenance
dredging (1)

• On the physical environment
• On the chemical and bacteriologi-cal quality of
  the environment

• Bathymetry,
• Hydrodynamism,
• Increase of turbidity
• Decrease in oxygen content,
• Contamination by bacterias,
• And organic compounds

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Presentation of the incidences of maintenance
dredging (2)

• On habitats of community interest
• On estuarine organisms and species of community
  interest

•  Estuaries  (1130) and  Mudflats and sandflats
  not covered by seawater all time)
• ?
•  Salicornia and other annual colonizing mud and
  sand  (1310)
• ?
•  Spartina swards  (1320)
• ?
•  Atlantic salt meadows  (1330)
• ?
•  Mediterranean and thermo-Atlantic halophilous
  scrubs  (1420)
• Angelica heterocarpa,
• Plankton organisms,
• Benthic organisms,
• Fishes,
• Birds,
• Otter

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Measures taken to remove or reduce the incidences
of maintenance dredging

• Some dredging methods have been given up
• Some reducing measures are now systematic

•  American  dredging,
• Suppression of direct immersion / disposal on the
  banks
• Optimisation of the sediment volume to be
  dredged,
• Disposal management by rotation,
• Machines checking and  clean operations 

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Environmental monitoring

• Monitoring during the dredging operation
• Monitoring / assessment in order to evaluate the
  mid term and long term incidences

• Controling the environmental quality of the
  project
• Learning from experience of previous dredging
  operations so that these can be improved in the
  future

Bathymetry, turbidity, hydraulics, sedimentology,
chemical and bacterological quality of water and
sediments, phytoplankton, benthic communities,
fishes, birds, marine mammals, habitats
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Some conclusions at this stage

• Improve the maintenance dredging activities in
  French estuaries.
• Ports authorities in the French estuaries carry
  an approach of progress in the environmental
  incidences of maintenance dredging.
• The progress margins of the environmental
  evaluation of the incidences of maintenance
  dredging are still important. This is because the
  evolution of techniques in the future and of the
  new knowledge that will be learned.
• Maintenance dredging operations are to be
  integrated in the general management plan of each
  estuary.

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Ongoing work

• gt Reporting the experience and knowledge
• gathered on integrated management
• practices in coastal zones especially in
  estuaries
• (management objectives, partnerships, juridical
  tools, )
• gt Methodological guide for the evaluation of the
• incidences of dredging and immersion / disposal
• operations on Natura 2000 sites
• (appreciation of level of incidence evaluation
  methods what is a significative effect ? )