New Zealand Journal of Marine and Freshwater Research abstracts
Synthesis of extreme wave climate for the Canterbury Bight, New Zealand
G. H. MACKY*
A. I. MCKERCHAR
A. K. LAING
G. S. CARTER
A. M. CHATER**
National Institute of Water & Atmospheric
Research Ltd
P. O. Box
8602
Christchurch, New Zealand
email: a.laing@niwa.cri.nz
* Present address: Harrison Grierson Consultants Ltd,
Auckland, New Zealand.
** Present address: Canterbury Regional
Council, Timaru, New Zealand.
Abstract Numerical models of the marine wind field and wave
generation offer a technique for estimating the severity of extreme wave
events. Measured and modelled waves in the Canterbury Bight, New Zealand, were
used to examine the hypothesis that extreme conditions can be more confidently
estimated by modelling the wave climate over a decade than by analysing shorter
measured records. The meteorological conditions causing high waves in the
Canterbury Bight were examined by inspecting wind measurements at Christchurch
Airport and wave buoy measurements made in 1983-85 near the Rakaia River mouth.
Although the arrival of high waves was sometimes associated with wind changes
at the airport, peak wave heights generally occurred at least several hours
after such wind changes and were associated with south-westerly or southerly
winds in the Bight and a depression south-east of the South Island. Wave
conditions at the buoy site for 1980-89 were modelled using marine winds
obtained from a global circulation model, running a wave generation model for
the seas around New Zealand, and then applying a refraction model. The decade
modelled included two El Niño events and one La Niña event, and
the ocean wind climate should therefore have been reasonably representative of
the long-term range of conditions. The model results were verified against the
buoy measurements. Estimates of extreme wave heights were then made from 10
years of modelled record and also the measured buoy record. Application of the
Gumbel distribution to the monthly maxima gave a significant wave height of
9.5 m for the wave event with an annual exceedance probability of 1 in 50.
Model predictions indicate that the most severe waves arrive in the Bight from
due south. Estimates of extremes from the measurements and model hindcast were
close, indicating that the hindcast represents a population of events similar
to those measured.
Keywords extreme waves; buoy measurements; wave climate; wave
modelling
M98060
Received 25 August 1998; accepted 21 July 1999
PDF file of entire paper: medium quality (1795K); (scanned from paper original: notes about this process)
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