Tm. Hume et al., Sediment facies and pathways of sand transport about a large deep water headland, Cape Rodney, New Zealand, NZ J MAR FR, 34(4), 2000, pp. 695-717
Citations number
43
Categorie Soggetti
Aquatic Sciences
Journal title
NEW ZEALAND JOURNAL OF MARINE AND FRESHWATER RESEARCH
Cape Rodney is a large headland that protrudes 3-4 km into deep water in th
e 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, an
d video. Despite the barrier imposed by the headland two pathways of sand t
ransport around the headland, separated by the topographic high of Leigh Re
ef, have been identified. One lies close to the headland, where sand from t
he 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 hea
dland 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 M
angawhai-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 a
re 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 g
enerated 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.