Tauranga Harbour Research Articles

Holocene coastal depositional sequences on a tectonically active setting: southeastern Tauranga Harbour, New Zealand

More than 70 cores, a high-resolution seismic survey, and SCUBA observations provide the basis for the interpretation of depositional environments that accumulated during the Quaternary in the southeastern Tauranga Harbour area of the North Island, New Zealand. Three lithofacies comprise this sequence; in ascending order they are pumiceous sand and gravel, shelly mud and shelly sand. The pumiceous sand is interpreted as fluvial and fan deposits of Pleistocene to early Holocene age with a radiometric date of 9420 ± 100 yr BP near the top of the unit. The shelly mud represents low-energy estuarine deposition of essentially normal marine salinity in a valley-like setting. This unit dates at 8100 ± 80 yr BP. The extensive overlying shelly sand thickens seaward and represents wave-dominated shoreface conditions much like the present nearshore environment. Radiometric dating of samples within the present harbor are all between 6000 and 7000 yr BP and those seaward of the spit to Mt. Maunganui are less than 3370 ± 100 yr BP. The barrier spit that has attached to the volcanic headland began accumulating about 4000–5000 years ago.

Benthos associated with an estuarine outfall, Tauranga Harbour, New Zealand

Abstract Benthos near a sewage outfall discharging 69 000 m3 d−1 of municipal sewage into Tauranga Harbour was studied to determine the nature and extent of the impact caused by a small organic input. Sediment samples were collected about the outfall and analysed for particle size, sorting, mud content, readily oxidisable carbon (ROC), total Kjeldahl nitrogen (TKN), total phosphorus (TP), “oil and grease” (OG), and macroinvertebrates. It is concluded that observed patterns of physical sediment characteristics are mainly natural. Levels of ROC, TKN, TP, and OG were all highest at or nearby the outfall. However, chemical changes in the sediment related to the discharge seemed to be limited to within less than 50 m distance of the outfall. The distributions of ROC, TKN, and TP in the sediments were closely related to natural changes in mud content. The outfall had little effect on the distribution of total numbers of taxa or individuals, or the composition of macro‐invertebrate assemblages. Rather, these wer...

Tauranga Harbour Crossing Stella Passage Bridge

This paper describes the seismic design of the Stella Passage Bridge which was constructed in 1986 to 1988 as part of the Tauranga Harbour Crossing, a road link between Tauranga and Mount Maunganui. The bridge is a 12 span, 478m long incrementally launched continuous prestressed concrete box girder with expansion joints at both abutments. Seismic restraint is provided by means of shear keys to ductile cantilever single stem pier columns supported on large diameter bored pile cylinder foundations.

Two new species of the marine genusLimnodriloidesand a record ofTubificoides fraseriBrinkhurst (Oligochaeta: Tubificidae) from New Zealand

Abstract Limnodriloides thrushi n. sp., from subtidal muddy sands in Otago Harbour, South Island, New Zealand, and L. insolitus n. sp., from a mudflat in Tauranga Harbour, North Island, New Zealand, are described. The first species has both (grooved) spermathecal and (bifid) penial setae, and bears its male pores on apair of bulbous protuberances in segment XI. The latter has a pair of styliforrn penes, of a kind unique for the genus. The estuarine, parthenogenetic (or self‐fertilising?), species Tubificoides fraseri Brinkhurst, 1986, previously known from North America and Australia, is also reported from Manukau Harbour, Auckland, New Zealand.

Basement structure and sediment thickness beneath the continental shelf of the Hauraki Gulf and offshore Coromandel region, New Zealand

Abstract The basement structure and sedimentary history of the continental shelf east of the northern section of North Island, New Zealand, is interpreted from geophysical data collected by petroleum companies. Interpretation of magnetic data shows the basement to be composed of both igneous and nonigneous rocks in the vicinity of the Coromandel Peninsula and Great Barrier Island; further north the basement is almost entirely nonigneous. From seismic reflection data, basement in the region can be seen to have undergone extension, being faulted into a series of fault-angle depressions and grabens. Sea-floor expression indicating continued development of the fault-angle depressions is found locally, especially in the Tauranga Harbour — Cuvier Island region. Outside the Hauraki Gulf, the sedimentary section overlying basement is separated into two units by an unconformity of unknown age. The lower unit is probably late Tertiary — Quaternary sediments and the upper unit is probably late Quaternary sediments. Within the Hauraki Gulf, the poor quality of seismic reflection data precludes analysis of the sedimentary section.

Vertical distribution of New Zealand shipworms (Bivalvia: Teredinidae)

Abstract In Tauranga Harbour, Lyrodus medilobatus was found in greatest numbers on test‐blocks placed near the bottom, while Bankia australis, B. neztalia, and Nototeredo edax had a more uniform vertical distribution. Shipworms occurred in the intertidal zone up to about mean sea level. In Wellington Harbour, B. neztalia was found in test‐blocks up to mean sea level, but was most abundant in blocks near the bottom. In the Bay of Islands, shipworms settled in the intertidal on test‐blocks as high as 30 cm below mean sea level. B. australis was the most abundant species in mangrove wood in northern New Zealand, and L. medilobatus occurred occasionally. No evidence was found for shipworms settling on living mangrove wood, although they frequently tunnelled from dead wood into living wood.

Seasonal settlement of shipworms (Bivalvia: Teredinidae) in Tauranga Harbour and Wellington Harbour

Abstract The seasons of settlement of shipworms in Tauranga and Wellington harbours in 1970–72 were studied using Pinus radiata test‐blocks. At Wellington the seasonal abundance of late‐stage shipworm larvae was monitored in the plankton. In Tauranga Harbour Bankia australis, Lyrodus medilobatus, Lyrodus pedicellatus, and Nototeredo edaxspawned and settled predominantly in summer, when water temperatures were above 17–18°C. Bankia neztalia had peak periods of settlement in winter and early summer and there was no correlation of settlement with water temperature. In Wellington Harbour B. neztalia spawned and settled mainly during winter when water temperatures were 11–15°C. Total larval abundance at the 2 test sites in Wellington Harbour was an approximate indication of the relative intensity of settlement, but seasonal larval abundance did not correlate well with seasonal settlement. B. neztalia larvae settled on air‐dried Pinus radiata wood within 6 days of the immersion of the wood. Annual variations in...

Sediment transport near the Tauranga entrance to Tauranga Harbour

Abstract 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.

Sediment and hydrodynamics of the Tauranga entrance to Tauranga harbour

Abstract 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.

Progradation at the Entrance, Tauranga Harbour, Bay of Plenty

Progradation at the Entrance, Tauranga Harbour, Bay of Plenty

THE USE OF SHORT-ROTATION RYEGRASS ON A BAY OF PLENTY FARM

The farm is situated on an arm of the Tauranga Harbour, on the Omokoroa Peninsula, 12 miles north of Tauranga and is on a narrow strip of rolling country between the Kaimai Hills and the sea. The land on this peninsula consists of a ridge down the centre, with rolling lands going down to sandy swamps and flats on each side. The farm is divided into three by two shallow gullies, which drain a considerable water-shed above the farm, necessitating a lot of draining.

The Volcanic Zone of Tarawera, New Zealand

the map, roughly in the shape of a narrow wedge whose blunted apex includes Lake Taupo and the group of volcanic mountains: Ngauruhoe (7515 feet), still active; Tongariro (6400 feet), with its Ketetahi spring; and Ruapehu (9175 feet), the latter the highest mountain in the North Island, with a hot lake in its snow-bound crater. From here the sides of the wedge run approximately north-east for 100 miles to the Bay of Plenty, where they touch the coast at Tauranga Harbour and the mouth of the Whakatane River respectively. The whole of this area is an elevated pumice plateau, 1000-1500 feet above sealevel, dotted with numerous large lakes, extinct volcanic cones, and hot springs. Activity is further continued in the sea-bed of the Bay of Plenty between the above-mentioned points; in Whale Island, with its hot springs; Mayor Island, with hot springs and a shining, black, obsidian-lined, extinct crater 5 miles in circumference; and White Island, an active volcano in the solfatara stage with warm water-filled crater half a mile in diameter, where, with hot sulphuric acid springs, is found hydrochloric acid of remarkable strength. A little to the north of the centre of this belt of thermal activity, and along side the lake from which it takes its name, is the town of Rotorua (3000 inhabitants) surrounded by and built amongst?one might almost say built on top of?hundreds of geysers, boiling springs, hot mud volcanoes, fumaroles, steaming lakes, and silica terraces. The many therapeutic waters and wellappointed bath houses of Rotorua are known to visitors from many countries. South-east of Rotorua and at a distance of between 10 and 17 miles, in the heart of the thermal belt, lies a group of mountains, lakes, and valleys, which some fifty-four years ago were the scene of volcanic and thermal upheaval of a magnitude never even remotely approached in Australia or New Zealand during the last five or six hundred years. Appreciation of the present topography and general appearance of the district as portrayed by the accompanying photographs is hardly possible without previous description of the country prior to the convulsions which so drastically reshaped it. Running from north-east to south-west was a mountain group whose three summits known to the Maoris as Wahanga, Ruawahia, and Tarawera, formed a rough, rocky, and much-crevassed plateau 3 miles long by half a mile in width, covered with large angular fragments of trachyte, broken and split up as though by frost. Although undoubtedly of volcanic origin, it seems reasonable to conclude from the state of the rocks and from the dense native forests that clothed the lower slopes, that no eruption of any size had taken place for many hundreds of years. The statement of the Maoris that it had never been known to erupt since they came to New Zealand