title: Evolution of the Tauranga Harbour Entrance: Influences of tsunami, geology and dredging

authors: de Lange, Willem P.

abstract: The eastern entrance to Tauranga Harbour has been modified by capital and maintenance dredging since 1968, raising concerns that there have been, or will be, adverse impacts. This paper reviews the effects that extreme events, such as tsunami, and the influence that the underlying geological structures have had on the evolution of the present day entrance; and assesses the possible effects of historic dredging. A regional tsunami around the start of the 15th Century removed ~3 km from the eastern end of Matakana Island. Seismic data indicate the harbour entrance was probably located ~2 km west of the present position. Panepane Pt accreted eastward between the 15th and 19th Centuries displacing the harbour entrance until further migration was prevented by the rhyolite dome of Mauao. 
Seismic and core data indicate that the present-day ebb tidal delta consists of a thin veneer of Holocene sediments over a relict topography of Pleistocene volcaniclastic sediments. These form subsurface ridges parallel to the coast and one is connected at the eastern end to Mauao. The Entrance Channel was excavated through this ridge in 1968. Previously, the Pleistocene ridge restricted the depth to which the ebb jet could excavate a channel through the delta to ~10 m.
 The first complete bathymetric survey of the harbour entrance was in 1852. At this time the entrance was wide and shallow. By 1954, Panepane Pt had accreted 300 m eastward, and the harbour entrance had deepened in response. Over this period the ebb jet orientation became increasingly oblique to the shoreline, and the width of the jet decreased with an increase in velocity and offshore extent.
 Dredging since 1968 has had two main direct effects on the morphology of the entrance: a shallow shelf of boulders has been largely removed, deepening the channel along the flanks of Mauao; and creating a deep channel through the Pleistocene ridge. Indirect effects have included further accretion of Panepane Pt, an increase in the offshore extent of the ebb tidal delta, and the development of multiple lines of swash bars on the swash platform.

text: Evolution of the Tauranga Harbour Entrance: Influences of tsunami, geology and dredging The eastern entrance to Tauranga Harbour has been modified by capital and maintenance dredging since 1968, raising concerns that there have been, or will be, adverse impacts. This paper reviews the effects that extreme events, such as tsunami, and the influence that the underlying geological structures have had on the evolution of the present day entrance; and assesses the possible effects of historic dredging. A regional tsunami around the start of the 15th Century removed ~3 km from the eastern end of Matakana Island. Seismic data indicate the harbour entrance was probably located ~2 km west of the present position. Panepane Pt accreted eastward between the 15th and 19th Centuries displacing the harbour entrance until further migration was prevented by the rhyolite dome of Mauao. 
Seismic and core data indicate that the present-day ebb tidal delta consists of a thin veneer of Holocene sediments over a relict topography of Pleistocene volcaniclastic sediments. These form subsurface ridges parallel to the coast and one is connected at the eastern end to Mauao. The Entrance Channel was excavated through this ridge in 1968. Previously, the Pleistocene ridge restricted the depth to which the ebb jet could excavate a channel through the delta to ~10 m.
 The first complete bathymetric survey of the harbour entrance was in 1852. At this time the entrance was wide and shallow. By 1954, Panepane Pt had accreted 300 m eastward, and the harbour entrance had deepened in response. Over this period the ebb jet orientation became increasingly oblique to the shoreline, and the width of the jet decreased with an increase in velocity and offshore extent.
 Dredging since 1968 has had two main direct effects on the morphology of the entrance: a shallow shelf of boulders has been largely removed, deepening the channel along the flanks of Mauao; and creating a deep channel through the Pleistocene ridge. Indirect effects have included further accretion of Panepane Pt, an increase in the offshore extent of the ebb tidal delta, and the development of multiple lines of swash bars on the swash platform.

year: 2015-09-16

title: Microstructure and magnetic properties of nanostructured Al₂O₃-20vol%Fe₇₀Co₃₀ composite prepared by high energy mechanical milling

authors: Yusop, Masleeyati

subjects: ceramic-alloy composite

abstract: Al₂o₃-20vol%Fe₇₀Co₃₀ composite powders have been prepared by high energy ball milling a mixture of Al₂O₃ powder and Fe₇₀Co₃₀ alloy powder. The Fe₇₀Co₃₀ alloy powder was also prepared by mechanical alloying of Fe and Co powders using the same process. The effects of milling duration from 8 to 48 hours on microstructure and magnetic properties of the nanostructured composite powders have been studied by means of X-ray Diffractometry (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). It was found that the nanostructured composite powder particles with irregular shapes and Fe₇₀Co₃₀  alloy particles being embedded in them formed after 8 hours of milling. The average grain size of the Al₂O₃  matrix reduced drastically to less than 18nm after 16 hours of milling. On the other hand, the embedded alloy particles demonstrated almost unchanged average grain size in the range of 14-15nm. Magnetic properties of the powder compacts at room temperature were measured from hysteresis curves, and show strong dependence of the milling time, with the coercivity increasing from 67.1 up to 127.9kOe with increasing the milling time from 8 to 48 hours. The possible microstructural reasons for this dependence are discussed.

text: Microstructure and magnetic properties of nanostructured Al₂O₃-20vol%Fe₇₀Co₃₀ composite prepared by high energy mechanical milling Al₂o₃-20vol%Fe₇₀Co₃₀ composite powders have been prepared by high energy ball milling a mixture of Al₂O₃ powder and Fe₇₀Co₃₀ alloy powder. The Fe₇₀Co₃₀ alloy powder was also prepared by mechanical alloying of Fe and Co powders using the same process. The effects of milling duration from 8 to 48 hours on microstructure and magnetic properties of the nanostructured composite powders have been studied by means of X-ray Diffractometry (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). It was found that the nanostructured composite powder particles with irregular shapes and Fe₇₀Co₃₀  alloy particles being embedded in them formed after 8 hours of milling. The average grain size of the Al₂O₃  matrix reduced drastically to less than 18nm after 16 hours of milling. On the other hand, the embedded alloy particles demonstrated almost unchanged average grain size in the range of 14-15nm. Magnetic properties of the powder compacts at room temperature were measured from hysteresis curves, and show strong dependence of the milling time, with the coercivity increasing from 67.1 up to 127.9kOe with increasing the milling time from 8 to 48 hours. The possible microstructural reasons for this dependence are discussed.

year: 2009

title: Unpacking media narratives: Racism and problematic reasonings

authors: Tan, Kyle K. H.

abstract: In this research brief, we present summaries of four case studies of racism in mainstream and social media in Aotearoa. Through a series of carefully selected datasets sourced from TV episodes (Police TEN 7), print media such as news articles (including Northland checkpoints), and tweets (Three Waters reform), we outline how Māori are represented across these mediums. With an expert in language modelling on our team, we analysed large datasets that give us sufficient statistical power to infer specific Māori discourses on respective platforms. Further, we examined key themes that characterise how Māori are represented in the media and signal the scale of anti-Māori attacks. For instance, we found that the predominant discussion on Three Waters reform on Twitter focused on ‘conflict’ (distrust towards government; 33%) and ‘capability’ (questioning the credibility of the reform; 23%) rather than its core intention of promoting water ‘safety’ (7%). The modelling analysis was supplemented by in-depth qualitative analysis that integrates anti-Māori themes (Moewaka-Barnes et al., 2012) and problematic reasoning tactics (Sturgill, 2021) to elucidate how false, deficit-based rhetoric about Māori is deployed to fuel racism and disinformation. In summary, our findings reinforce Kupu Taea’s call for new media sectors to integrate Te Tiriti o Waitangi into their practices to safeguard Māori and other minoritised groups who are likely to be at the fore of racist attacks.

text: Unpacking media narratives: Racism and problematic reasonings In this research brief, we present summaries of four case studies of racism in mainstream and social media in Aotearoa. Through a series of carefully selected datasets sourced from TV episodes (Police TEN 7), print media such as news articles (including Northland checkpoints), and tweets (Three Waters reform), we outline how Māori are represented across these mediums. With an expert in language modelling on our team, we analysed large datasets that give us sufficient statistical power to infer specific Māori discourses on respective platforms. Further, we examined key themes that characterise how Māori are represented in the media and signal the scale of anti-Māori attacks. For instance, we found that the predominant discussion on Three Waters reform on Twitter focused on ‘conflict’ (distrust towards government; 33%) and ‘capability’ (questioning the credibility of the reform; 23%) rather than its core intention of promoting water ‘safety’ (7%). The modelling analysis was supplemented by in-depth qualitative analysis that integrates anti-Māori themes (Moewaka-Barnes et al., 2012) and problematic reasoning tactics (Sturgill, 2021) to elucidate how false, deficit-based rhetoric about Māori is deployed to fuel racism and disinformation. In summary, our findings reinforce Kupu Taea’s call for new media sectors to integrate Te Tiriti o Waitangi into their practices to safeguard Māori and other minoritised groups who are likely to be at the fore of racist attacks.

year: 2025