Harbour Design: Waves, IG & FIG

Actions to mitigate harbour motions range from site selection or harbour design (large scale), through asset positioning or water / vessel motions (medium scale) down to mooring or jetty designs (small scale). In general, getting larger scale mitigation right is the most cost-effective outcome, with other forms of mitigation useful to deal with assessment uncertainty, local issues, or post-construction refinement of harbour use.

Identification of internal motions can be challenging - excessive movement is often developed through resonance, with conditions being rare but potentially having severe impact.

Significant modelling effort is usually undertaken as part of harbour design. However, there will almost always be adverse motions that have not been predicted, or a desire to develop new facilities in 'unused' parts of the harbour. Development of an approach to mitigate harbour motions typically requires an understanding of when and where problems are occurring, with wide ranging consideration of drivers, mechanisms and receptors.

Strategies to manage harbour motions are also further affected by perceptions of responsibility and ownership - with the costs of management using mooring systems rarely borne by harbour managers... Over the last 30 years, I have rarely seen this issue managed efficiently - often taking 10-15 years to suitably characterise an issue, and then another 5-10 years to develop and implement a solution.

For those of you interested in reading more on this topic:

• Alberto Montanari (University of Bologna) has an easy to read website on some of these topics.

• Alexander Rabinovich (Institute of Oceanology, Russia) provides some more high level technical research.

I'll lay the credit for the scrimmikins of knowledge that I hold to Dr Bill Andrew, Prof Chari Pattiaratchi and Grant Ryan of Tremarfon, and apologise for any misrepresentations I may have made! Hopefully the harbours of Western Australia are better for the transfer of knowledge...