Ports | NIRAS Fraenkel T
he outer harbour at Peterhead was originally constructed as a harbour of refuge providing a safe
haven for mariners seeking shelter in North Sea gales. The bay in which the harbour is located has natural shelter from the Scottish mainland to the west but had to be protected against waves from easterly directions by massive concrete blockwork breakwaters rising more than 25m above the seabed and extending into water over 20m deep. Work on the breakwaters started in the last decade of the nineteenth century and it was not until 1956 that the breakwaters were completed. In their basic function of protecting the bay as a harbour of refuge they were designed to have a relatively wide entrance of 208m so that sailing vessels could pass through safely in severe storm conditions. This has consequences for berths within the harbour, however, as considerable wave energy also passes through the entrance and downtime at berths can be considerable in stormy weather, despite the general protection provided. The port authority decided, therefore, to construct new all weather berths and commissioned consulting engineers Peter Fraenkel & Partners Ltd, now NIRAS FRAENKEL LTD to develop a scheme for the berths with wave protection as necessary. The primary objective of the development was to provide berths for pelagic fishing vessels, but the berths were also to accommodate general cargo and other vessels up to 160m in length. The area designated for the
new development in the harbour was on the west side of the bay partially protected by a secondary breakwater. The consultant’s brief was to investigate the length by which this breakwater would need to be extended to protect the new berths such that there would be no downtime at the berths up to once in ten year storm events. The berths themselves would have a quay deck
‘It became clear that traditional forms of quay deck structure would all be too expensive for the available budget for the project which could not proceed unless significant cost savings could be made.’
suitable for general cargo and heavy lift use. Additionally, the layout and form of the facility would require to be designed so that it would not cause adverse wave reflections which could downgrade berths elsewhere in the harbour. Hydraulic modelling of the harbour as existing and with various options for the breakwater extension and the new quay was undertaken in conjunction with HR Wallingford using Wallingford’s numerical wave model program Artemis. Significant wave heights in the main harbour entrance in once in 10 year storms from SE are of the order of 8m and even within the harbour waves can reach over 3m significant height.
After a number of iterations a layout for the new quay and breakwater extension was established which does not cause any undesirable effects anywhere else in the harbour. While the client had a preference for having a solid faced quay structure as opposed to an open quay with a suspended deck, this was shown by modelling not to be possible as solid faced quays would cause wave resonance in adjacent parts of the harbour. A comprehensive value engineering exercise was carried out comparing various forms of breakwater and quay deck arrangements which might be adopted. It became clear that traditional forms of quay deck structure would all be too expensive for the available budget for the project which could not proceed unless significant cost savings could be made.
A problem with suspended quay decks built over revetments is
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