New Zealand Journal of Marine and Freshwater Research abstracts
Wind-wave development across a large shallow intertidal estuary: a case
study of Manukau Harbour, New Zealand
MURRAY J. SMITH1
CRAIG L. STEVENS1
RICHARD M. GORMAN2
JOHN A. MCGREGOR1
CAMERON G. NEILSON3
1National Institute of Water & Atmospheric
Research Ltd
P. O. Box 14 901, Kilbirnie
Wellington, New Zealand
email: m.smith@niwa.cri.nz
2National Institute of Water & Atmospheric Research
Ltd
P. O. Box 11 115
Hamilton, New Zealand
3Department of Earth Sciences
University of Waikato
Private Bag 3105
Hamilton, New Zealand
Abstract Locally generated wind-waves in estuaries play an
important role in the sediment dynamics and the transport of biota. Wave growth
in estuaries is complicated by tidally varying depth, fetch, and currents. Wave
development was studied at six sites along a transect across Manukau Harbour,
New Zealand, which is a large intertidal estuary with a tidal range of up to
4 m. Three meteorological masts were also deployed across the measurement
transect to measure wave forcing by the wind. A spatial variation in wind speed
by up to a factor of 2 was observed which has a significant effect on wave
development at short fetches. The wind variation can be explained by the
extreme change in surface roughness at the upwind land-water boundary. The
tidally varying depth results in non-stationary wave development. At the long
fetch sites wave development is dictated by the tidally varying depth with peak
frequencies continuing to decrease after high water, whereas wave height is
attenuated by bottom friction. The non-dimensional energy and peak frequency
parameters commonly used to describe wave growth, clearly exhibit depth
limiting effects, but with wider scatter than in previous studies in simpler
environments. The peak frequency predictions of Young & Verhagen (1996a)
fit our data well. However, the wide variability of energy limits the
usefulness of standard growth prediction curves in such situations, and
highlights the requirement for a validated, shallow-water numerical model.
Keywords wind-waves; wave measurements; shallow water;
estuary
New Zealand Journal of Marine and Freshwater Research, 2001, Vol. 35
M01038
Received 9 May 2001; accepted 18 June 2001
PDF file of entire paper: medium quality (1850K); (scanned from paper original: notes about this process)
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