Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand - Part one: The role of waves

The role of waves in shore platform development has been investigated on Kaikoura Peninsula by direct measurement of waves in deep water and on platforms at high tide. This showed that the deepwater wave environment off the Kaikoura Peninsula is very energetic, but the amount of energy delivered to platforms is very low. In deep water, wave power ranged from 5900 to 106 700 N m s(-1) per m of crest when calculated from mean significant wave height and when calculated from maximum wave height it ranged from 31 400 to 5 370 000 N m s(-1) per m of crest. A comparison of deep water wave energy flux with wave energy flux at the high tide cliff of platforms showed that there was a reduction by as much as five orders of magnitude during storm conditions. An analysis of the role of breaking waves revealed that these are ineffective as an erosional agent because the depth of water offshore causes breaking before waves arrive on platform surfaces. Depth of water controlling wave breaking causes larger storm waves to break further from shore, preventing direct attack at the cliff base. Shear stresses and dynamic forces under waves were calculated from waves measured on shore platforms. This showed that these forces never exceeded the compressive strength of the platform rocks at Kaikoura. It is concluded that wave forces are not directly capable of causing erosion on shore platforms at Kaikoura. (C) 2000 Elsevier Science B.V. All rights reserved.