Dredging of marinas
Marinas and yacht harbour managers are facing similar problems to those of larger commercial ports regarding dredging and dredged material management: ever increasing stringent environmental regulation, lack of available disposal facilities and complex contamination control.Sediment sampling and testing procedures are equal for all ports but may differ significantly from one country to another. Standards and reference values for the classification of the sediment quality also vary within broad ranges from country to country. Hence it is difficult to assess whether marinas are differently contaminated compared to commercial ports. Even for one country no evidence can be found about a differential contamination. Nevertheless, special attention is given to organotin and organic compounds in marina waters and sediments. Despite strict bans on e.g. TBT-use it is disappointing to see that high concentrations persist. Apparently historic contaminations and/or remote sources will influence the sediment quality for many years to come. In marinas no specific dredging plant requirements are to be formulated but special care""-measures are to be given to:
- solid anchoring of floating lines
- careful berthing/mooring of tugs
- protection of fragile pontoons, catways, ...
- high-accuracy dredging tools.
Actual dredging equipments are generally well-fitted to the small scale of the work, the high positioning accuracy and the selective dredging ability. However, the most critical issue of these dredging works is linked to:
- the disposal facility: permit, cost and capacity
- the distance between marina and disposal facility.
There is a clear tendency to implement stringent environmental regulations and to restrict open-water discharge and even beneficial re-use of dredged material. This tendency limits the possibilities for correct maintenance of marinas. This critical situation may favour the use of bottom-levelling.Source control of sediment and contaminant inflow into the marina basin offer sustainable and cost-efficient solutions. Practical solutions are presented in chapter 8. In chapter 9 'Practical Recommendations' are formulated toward the Regulatory Bodies, towards the Marina Managers and towards the Dredging Contractors.