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Disposal options for muddy dredged material, especially if lightly contaminated, is an issue facing many countries, particularly if environmental protection and adherence to the Protocols of the London Dumping Convention is a regulatory requirement. For the case of the oceanic islands of New Zealand, disposal of muddy dredged material has become an issue for the prime city of Auckland. Accordingly, it has been necessary to investigate a suitable marine disposal site outside of the territorial seas in the exclusive economic zone (EEZ). Ideal properties for such a disposal site include a near flat surface on the continental shelf, with sediments of similar textural characteristics to the material being disposed, a site of non-critical benthic ecology, water depths sufficient to enable the disposal site to be monitored (as required under the London Dumping Convention), a site experiencing low shelf currents, not affected by significant wave agitation, and a site not of cultural significance. The approach for...

Cross‐correlations between along‐shelf wind stress and both along‐ and cross‐shelf currents within the central Bay of Plenty, New Zealand show the circulation during spring‐summer to be highly responsive to wind events. Current meter records indicate that upwelling‐favourable wind stresses generate upwelling dynamics in both mean and fluctuating senses. Both thermistor moorings and satellite inferred temperature data record the outcropping of this cool water following upwelling‐favourable wind stresses. The upwelling circulation provides an efficient mechanism for the periodic delivery of cool (c. 80 μg litre‐1) water to the coastal zone during spring. Historical wind forcing data suggest that the wind‐forced dynamics described were responsible for a major toxic algal bloom within the Bay of Plenty during 1992–93.

Infaunal bivalve molluscs on the flood tidal delta of Tauranga Harbour, north‐eastern New Zealand, were surveyed twice over a 6‐month period, with the aim of assessing shellfish resources, assessing the magnitudes of temporal and spatial variability in abundances, and identifying potentially important processes. The surveys identified a total of 31 bivalve taxa from 27 sites. Species richness per site ranged between 0 and 9, and varied greatly in space and time, as did two other measures of diversity. Extremely high densities of bivalves (>20 000 m‐2) were encountered at several sites. Densities of several abundant species varied greatly in time, as a result of recruitment pulses. The abundances of the three species that dominated the fauna (Paphies australis, Tawera spissa, and Ruditapes largillierti) had characteristic spatial scales on the order of 200 m. Comparisons of size frequency distributions for individual sites suggested that mortality or emigration in the first year of benthic life wa...

Laboratory and field experiments examining the burrowing behaviour of the estuarine infaunal bivalve Paphies australis (Bivalvia: Mesodesmatidae) were conducted in two areas of northeastern New Zealand. Field experiments examining reburial showed that when exposed on the sediment surface most P. australis were able to bury within 40 min. Slightly fewer pipi buried during high‐tide trials than during mid‐tide trials. Laboratory experiments established the ability of P. australis of various sizes to burrow up to the sediment surface after being inundated with sediment to a depth of up to 40 cm. P. australis buried under 10 cm of sediment burrowed to the surface at a slower mean rate than those buried under lesser depths of sediment, and variability in ascension rates increased with increasing burial depth. P. australis with an initial upright orientation burrowed and ascended at a greater rate than P. australis placed laterally or inverted. Though capable of ascending through as much as 50 cm of sand in lab...

This paper reviews research that has taken place on physical oceanography and sedimentology on New Zealand's estuaries and the inner shelf since c. 1967. It includes estuarine sedimentation, tidal inlets, beach morphodynamics, nearshore and inner shelf sedimentation, tides and coastal currents, numerical modelling, short‐period waves, tsunamis, and storm surges. An extensive reference list covering both published and unpublished material is included. Formal teaching and research programmes dealing with coastal landforms and the processes that shape them were only introduced to New Zealand universities in 1964; the history of the New Zealand Journal of Marine and Freshwater Research parallels and chronicles the development of physical coastal science in New Zealand, most of which has been accomplished in last 25 years.

To relate the textural characteristics of the bottom sediments of a tidal inlet to hydrodynamics, 45 sediment samples from the Tauranga Entrance to Tauranga Harbour were analysed for textural parameters, and tidal currents and waves were monitored. Tidal currents dominate sediment transport processes near the Tauranga Entrance although swell waves are significant on the ebb tidal delta, and wind waves may influence intertidal sediments within the harbour. The bulk of the sediment is probably derived from marine sand from the Bay of Plenty continental shelf, but tidal currents and waves have changed its textural character. In areas of swift tidal currents, particularly in the inlet channel itself, sediment is coarser, more poorly sorted, and more coarsely skewed than that in areas of slower currents.

Onyx River has three characteristic reaches, bedrock incision, moraine breaches, and alluvial. Antecedent geomorphological events control the slope of these reaches and to some extent the bed material. Coarse bed materials occur in the steep reaches of the bedrock and moraine breach channels. Discharge hydrographs and flow-duration curves reveal a division into two flow regimes with a hiatus at about 1 m3/s. The modern channel form and pattern and distribution of bed materials may be related to these flow regimes. Channel-in-channel features, berms, overspill channels, and longitudinal bars are related to flow characteristics. The evolution of the river and its terraces is discussed in terms of changes in discharge and sediment supply. Prominent terraces are explained in terms of relative contributions of water and sediment from Wright Lower Glacier and from other glaciers. The terraces reflect climatic changes and their chronology is related to recent glacier activity and changes in level of Lak...

Since the 1940s, severe dune erosion has threatened property at Waihi Beach. This paper investigates beach erosion and dune recession in relation to wave climate, sedimentoldgy and mineralogy of the beach sediments, cyclical beach changes and sediment budget, and the littoral drift. Average dune recession along the entire beach between 1948 and 1977 was 27 m, although maximum recession recorded to 1977 was 83 m. Sand loss rates 1948–1977 average 3.4 m3 per metre of beach per year. The sediment budget of the entire beach is about 850 × 103 m3 and up to 74% of this was recorded as being ‘cut’ from the beach in one erosive episode. The cut and fill cycles are dominantly controlled by wave steepness, which has a critical value of 2.1 × 10−3 for breaking waves on Waihi Beach. Net littoral drift is towards the south‐east, and the basic reason for beach erosion at Waihi Beach is the lack of sediment to supply the littoral drift.

Astract Previous hypotheses to explain the origin of the Labyrinth have invoked floods, glacial erosion, and uniformitarian arguments of salt weathering and deflation. The landscape is one of reticulate troughs, deeper to the east than west, with irregular long profiles and enclosed depressions. The troughs are shown to belong to a hierarchy and display curvilinear form. Their origin is related to glacial plucking along joints and subsequent deepening by ice-marginal and proglacial meltwater systems. Periglacial alteration of the primary form, particularly asymmetric infill by solifluction and scree, is largely a result of debris supplied by freeze-thaw processes. Intertrough blocks initially formed upstanding masses between reticulate, joint-controlled depressions, and were subject to subglacial abrasion by a glacier sliding over its bed. The required wet-based ice conditions imply either extremely thick ice or a warmer climate than present. Landform is used to deduce a complex origin for the Labyrinth w...

Sediment transport at the Tauranga Entrance was studied in relation to tidal currents and waves. Bedforms resulting from tidal flow were investigated with scuba divers and echo‐soundings. The alignment and scale of bedforms indicated the direction and approximate rate of sediment transport. Sediment transport was measured directly using sediment traps, and results were compared with rates calculated by another method. Maximum sediment transport rates of 20 000–30 000 g.m−1 per half tidal cycle occur near the inlet gorge, but rates vary considerably in time and space, depending mainly upon power of tidal currents. A model of sediment transport for this inlet has been evolved based on tidal flow streamlines, bedform features, and the measured and calculated rates of sediment transport.

Side-scan sonographs of the shallow (2–22 m) sea floor off Gisborne Harbour, northern Poverty Bay, New Zealand, include areas of scattered to locally prominent, subcircular, flat-floored depressions, resembling pockmarks, typically 5–20 m across and 0.3–0.5 m deep, in muddy very fine sands. Because of their geologic setting, it is speculated that the structures are exhalative pits for ascending streamers of mud, water, and/or natural gas from underlying diapiric intrusions of predominantly Paleogene shale, and that they may be submarine equivalents of the subaerial quiescent mud volcanoes occurring in the Gisborne district. Because of their possible significance in hydrocarbon prospecting, tsunami generation, and siting of subsea cables, pipelines, and offshore structures, they require further research.

Rectilinear slopes in the Olympus Range, Southern Victoria Land, Antarctica were termed Richter slopes and attributed to formation by salt weathering and deflation. Existing theoretical models for Richter slope development are invalid when the processes of salt weathering and deflation act without scree movement. Removal of all slope debris by salt weathering and deflation corresponds to the solution y = 0 in Lehmann's differential equation of slope retreat form. An alternative process of slope retreat is based on undercutting of the free face under the influence of wind drifted snow. Bedrock slope forms measured in the field correspond to observed snow configuration. The stepped microrelief profile is as expected under the nivation hypothesis. Compound slopes with a range of declivities are related to variations in form of debris accumulation and snow conditions under changing climate.

An extensive search of newspaper reports, archival material, and the literature has revealed that many more tsunamis have affected the New Zealand coast than hitherto realised. 32 tsunami events are listed, including their probability of occurrence, the maximum runup height, as well as the epicentre and Richter magnitude for those events associated with earthquakes. Most coastal regions of New Zealand are reported as experiencing tsunamis. Generally these events have been associated with earthquakes, although the tsunami source mechanisms have also been attributed to large rotational slumps, submarine slumping along the Chatham Rise, and submarine mud volcanism associated with diapiric intrusions on the continental shelf off Poverty Bay. Tsunami waves and seiching accompanying the Krakatoa eruption of 1883 appear to have been induced by pressure coupling between the atmosphere and oceans. Most tsunamis have affected the east coast. This largely reflects both exposure to pan-Pacific origins and th...

Ohiwa Harbour is a 24 km2 estuarine lagoon impounded by the 6 km long Ohope spit in the west and the 0.7 km long Ohiwa spit in the east. These barrier sand spits are presently separated by a c. 340 m‐wide inlet channel where the maximum harbour depth of 14 m occurs. Seventy percent of the harbour consists of tidal flats supporting a rich shelly benthos and diversified by stands of mangrove and backed locally by salt marsh. Lower harbour sediments in barrier beach, dune, and entrance shoal and channel environments are well sorted, negatively‐skewed, medium to fine sands. In contrast, upper harbour sediments are poorly to very poorly sorted, positively‐skewed, medium to very fine (silty) sands, the coarser of these deposits occurring in channel and restricted harbour beach environments, and the finer in inter‐tidal flat, creek, and channel bank areas. The terrigenous mineralogy is consistent with a dominantly acid volcanic provenance, directly from the tephra mantle of the catchment and, most impor...