New Zealand Journal of Marine and Freshwater Research abstracts
M99005Received 27 January 1999; accepted 27 April 2000
Sediment facies and pathways of sand transport about a large deep water
headland, Cape Rodney, New Zealand
TERRY M. HUME
JOHN W. OLDMAN
KERRY P. BLACK
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 11 115
Hamilton, New Zealand
email: t.hume@niwa.cri.nz
Abstract Cape Rodney is a large headland that protrudes
3-4 km into deep water in the Hauraki Gulf and separates the
Mangawhai-Pakiri and Omaha littoral cells. Detailed swath mapping of seabed
sediments around Cape Rodney was carried out using by side-scan sonar and
ground-truthed by SCUBA, grab sampling, and video. Despite the barrier imposed
by the headland two pathways of sand transport around the headland, separated
by the topographic high of Leigh Reef, have been identified. One lies close to
the headland, where sand from the beach and nearshore of the Mangawhai-Pakiri
embayment is driven by waves and currents along a 500-m-wide pathway in
c. 20-25 m depth around the headland to the vicinity of Leigh
Harbour. The other lies in 50 m water-depth seawards of Leigh Reef. Here
fine sand, sourced from the nearshore of the Mangawhai-Pakiri embayment and
driven offshore from the tip of the headland, is transported back and forth by
tidal currents in 50 m water depth on the floor of the Jellicoe Channel.
The sand bodies along both these pathways are thin and so sand leakage from the
Mangawhai-Pakiri embayment is thought to be small. Transport at these depths is
dependent on both tide and wave generated currents and episodic occurring
during storm events. The sediment facies associated with little sand transport
about a headland in deep water is one of thin and discontinuous and patchy sand
cover between rocky areas and over coarser megarippled substrate. Ocean swell,
tidally driven phase eddies that spin up on both sides of the headland, and
bathymetry all play a role in shaping those facies.
Keywords surficial sediments; sediment transport; sand
by-passing; tidal currents; waves; littoral cell; headland; coastal processes;
New Zealand
New Zealand Journal of Marine and Freshwater Research, 2000, Vol. 34:
719-726
0028-8330/00/3404-0719 $7.00 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (5723K); (scanned from paper original: notes about this process)
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