Monitoring and record keeping

In the licensing process for the disposal of maintenance dredged material, great emphasis is being placed on verification of the effect of dredging and disposal on marine ecology and sediment regimes, with increasing demands for pre and post dredge monitoring of disposal sites. The licensing authorities identify the potentially sensitive features to be monitored, if considered necessary.

It is suggested that monitoring programmes for dredging and disposal operations should be considered an essential part of the dredging project, particularly when contaminated dredged material is involved (Burt & Paipai 1996). CIRIA’s good practice guidelines for dredging, support the undertaking of post-dredging monitoring of the nature and the rate of change of sediments within the navigation channels, to provide information which can be taken into consideration before the next maintenance dredge is carried out (CIRIA 1997).

In setting up a monitoring plan, it is essential to have site-specific, measurable, attainable and realistic objectives. PIANC stress that post-dredging monitoring plans need to be flexible to allow any unforeseen operational problems to be accommodated (PIANC 1996). There are five main steps for the development of a physical and biological monitoring plan for the dredge and disposal of material (Fredette et al 1990, cited in Burt & Paipai 1996) which are:

  • defining site-specific monitoring objectives,
  • identifying components of the monitoring plan,
  • predicting responses and developing testable hypothesis,
  • designing survey and sampling methods, and
  • identifying management options and design of remedial works.

Further advice and guidance on setting up and undertaking monitoring programmes, before and after, dredging and disposal operations is provided in Volume 3 of the Environmental Aspects of Dredging, Investigation, interpretation and impact (IADC/CEDA 1998) and Management of aquatic disposal of dredged material (PIANC 1997).

It is generally considered good practice in ports and harbours, to keep organised, up-to–date records of dredging operations. These records should incorporate data from hydrographic surveys of ports and harbours which are undertaken on a regular basis for navigation purposes and indicate changes in sedimentation patterns within the dredged channels. Maintaining thorough records has a number of benefits, including:

  • the need to dredge, or otherwise, can be clearly demonstrated,
  • areas within ports and harbours where dredging can be reduced, or not undertaken at all, may be identified, and
  • the collation of this information eases the path to the renewal of dredging licences.

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