title: Site characterisation of the Hamilton Basin using surface wave methods

authors: Cave, Ashley

abstract: Observed amplification and reverberation of ground motions in the Heathcote Valley during the 2010-2011 Canterbury Earthquake Sequence highlighted the lack of data on the subsurface velocity structure of sedimentary basins across New Zealand. A similar lack of data applies to the Hamilton Basin, a deep, predominantly alluvial, basin in the Waikato Region. In response, 13 deep shear wave velocity profiles have been measured in this study. Dispersion data obtained through active and passive methods were inverted with fundamental frequencies deduced from the horizontal-to-vertical spectral ratio method and a suite of layering ratios in the absence of detailed geological information. Potential for amplification is inferred from the large impedance contrasts at the soil-basement interface in the developed Vₛ profiles. The fundamental site period is over 5s in the Te Rapa and Gordonton depressions in the northern basin, where basement rock is up to 1400m deep. As basement shallows towards the south, fundamental periods shorten. Complex wave propagation occurs towards the southeastern basin influenced by ignimbrite deposition interspersed within the alluvial sediments of the Tauranga Group. Despite the variation in basement structure, velocities associated with lithology changes tend to be relatively consistent, allowing for the use of a four-unit velocity structure to represent basin deposits. The peat bogs which dominate the surficial landscape have significantly low shear wave velocities (28-38m/s), which presented unique difficulties in near surface velocity resolution. The soft near surface soil deposits across the basin have Vₛ₃₀ values ranging from 166-234m/s and four class E sites have been identified. Based on the new Vₛ profiles, a refined fundamental frequency-depth correlation was developed for the region. The results in this thesis are intended to inform site response analysis and seismic risk assessment.

text: Site characterisation of the Hamilton Basin using surface wave methods Observed amplification and reverberation of ground motions in the Heathcote Valley during the 2010-2011 Canterbury Earthquake Sequence highlighted the lack of data on the subsurface velocity structure of sedimentary basins across New Zealand. A similar lack of data applies to the Hamilton Basin, a deep, predominantly alluvial, basin in the Waikato Region. In response, 13 deep shear wave velocity profiles have been measured in this study. Dispersion data obtained through active and passive methods were inverted with fundamental frequencies deduced from the horizontal-to-vertical spectral ratio method and a suite of layering ratios in the absence of detailed geological information. Potential for amplification is inferred from the large impedance contrasts at the soil-basement interface in the developed Vₛ profiles. The fundamental site period is over 5s in the Te Rapa and Gordonton depressions in the northern basin, where basement rock is up to 1400m deep. As basement shallows towards the south, fundamental periods shorten. Complex wave propagation occurs towards the southeastern basin influenced by ignimbrite deposition interspersed within the alluvial sediments of the Tauranga Group. Despite the variation in basement structure, velocities associated with lithology changes tend to be relatively consistent, allowing for the use of a four-unit velocity structure to represent basin deposits. The peat bogs which dominate the surficial landscape have significantly low shear wave velocities (28-38m/s), which presented unique difficulties in near surface velocity resolution. The soft near surface soil deposits across the basin have Vₛ₃₀ values ranging from 166-234m/s and four class E sites have been identified. Based on the new Vₛ profiles, a refined fundamental frequency-depth correlation was developed for the region. The results in this thesis are intended to inform site response analysis and seismic risk assessment.

year: 2020

title: Landslides research at Omokoroa

authors: Moon, Vicki G.

abstract: Summary of research progress into causes of landsliding at Omokora to the Operations and Monitoring Committee (Komiti Whakahaere) of the Western Bays District Council

text: Landslides research at Omokoroa Summary of research progress into causes of landsliding at Omokora to the Operations and Monitoring Committee (Komiti Whakahaere) of the Western Bays District Council

year: 2017-10-26

title: Harakeke (Phormium tenax) ecology and historical management by Maori: The changing landscape in New Zealand

authors: Wehi, Priscilla M.

subjects: ethnobotany

abstract: Harakeke (Phormium tenax: Phormiaceae) is an important weaving resource for the indigenous Maori people of New Zealand. This research project investigates Maori knowledge of harakeke ecology and management practices prior to the early 20th century within the context of a study of relevant environmental parameters that limit its natural distribution. Ecological information referring to harakeke was analysed from interviews with elders and ancestral sayings (whakatauki). As well, documents from the late 181h to the early 20th century were examined, and environmental parameters for both harakeke and wharariki (Phormium cookianum) were quantified and analysed using correlative models. 
Interviews with 11 elders (from Waikato and Northland) identified key issues in harakeke management, including 'correct' harvesting procedures, use of natural harakeke stands, and specific use of different varieties. Planting practices varied regionally. Three different methods of excess harakeke disposal were reported, including burning. The 15 whakatauki analysed emphasise the interconnectedness of ecosystems, including pollinator-plant relationships for kaka and bellbirds. Four whakataukirefer to environmental tolerances for harakeke and two to the use of fire to stimulate harakeke growth. Others refer to competition between shoots, nutrient requirements, and the growth and multiplication of harakeke offsets. 
Numerous early reports indicate that harakeke has been cultivated throughout much of New Zealand, with cultivations ranging in size from a few bushes to at least several acres. Thirty six varieties were linked to specific weaving uses. Twenty varieties were cultivated, but ten prized fibre varieties were also harvested from natural stands. Numbers of recorded varieties varied between districts, with 31 recorded in Taranaki but only two recorded by name for Northland. Valued varieties, including raumoa and oue, were dispersed throughout the North Island. Mapping different varieties revealed a wide spatial spread for varieties such as rataroa and oue. Specific management techniques included seed germination as well as vegetative propagation. Early records of harakeke pests were not found. Records of harakeke irrigation and the use of fire indicate that Maori created suitable conditions for new cultivations or pii harakeke, which may also have prevented insect infestation. Cumulatively, there is evidence of extensive active management of harakeke. Wharariki and harakeke were found to have distinct environmental niches, with wharariki better able to withstand cooler temperatures, higher rainfall and greater frequency of ground frost than harakeke.
Predictive mapping of harakeke for the northern region of New Zealand shows a low probability of naturally occurring harakeke in much of the Northland and Waikato interior, and a high probability in coastal areas with warm temperatures. It seems likely that Maori transported harakeke into areas where it was unlikely to have occurred naturally and that some apparently 'natural' stands ofharakeke were created and maintained by Maori.
Maori cultivation, dispersal and active management of harakeke, as well as possible creation of wetland areas, emphasises the importance of harakeke as an economic resource prior to European colonisation, and indicates how the New Zealand landscape may have been transformed. Maori ecological knowledge can contribute new perspectives to restoration ecology and ecosystem research.

text: Harakeke (Phormium tenax) ecology and historical management by Maori: The changing landscape in New Zealand Harakeke (Phormium tenax: Phormiaceae) is an important weaving resource for the indigenous Maori people of New Zealand. This research project investigates Maori knowledge of harakeke ecology and management practices prior to the early 20th century within the context of a study of relevant environmental parameters that limit its natural distribution. Ecological information referring to harakeke was analysed from interviews with elders and ancestral sayings (whakatauki). As well, documents from the late 181h to the early 20th century were examined, and environmental parameters for both harakeke and wharariki (Phormium cookianum) were quantified and analysed using correlative models. 
Interviews with 11 elders (from Waikato and Northland) identified key issues in harakeke management, including 'correct' harvesting procedures, use of natural harakeke stands, and specific use of different varieties. Planting practices varied regionally. Three different methods of excess harakeke disposal were reported, including burning. The 15 whakatauki analysed emphasise the interconnectedness of ecosystems, including pollinator-plant relationships for kaka and bellbirds. Four whakataukirefer to environmental tolerances for harakeke and two to the use of fire to stimulate harakeke growth. Others refer to competition between shoots, nutrient requirements, and the growth and multiplication of harakeke offsets. 
Numerous early reports indicate that harakeke has been cultivated throughout much of New Zealand, with cultivations ranging in size from a few bushes to at least several acres. Thirty six varieties were linked to specific weaving uses. Twenty varieties were cultivated, but ten prized fibre varieties were also harvested from natural stands. Numbers of recorded varieties varied between districts, with 31 recorded in Taranaki but only two recorded by name for Northland. Valued varieties, including raumoa and oue, were dispersed throughout the North Island. Mapping different varieties revealed a wide spatial spread for varieties such as rataroa and oue. Specific management techniques included seed germination as well as vegetative propagation. Early records of harakeke pests were not found. Records of harakeke irrigation and the use of fire indicate that Maori created suitable conditions for new cultivations or pii harakeke, which may also have prevented insect infestation. Cumulatively, there is evidence of extensive active management of harakeke. Wharariki and harakeke were found to have distinct environmental niches, with wharariki better able to withstand cooler temperatures, higher rainfall and greater frequency of ground frost than harakeke.
Predictive mapping of harakeke for the northern region of New Zealand shows a low probability of naturally occurring harakeke in much of the Northland and Waikato interior, and a high probability in coastal areas with warm temperatures. It seems likely that Maori transported harakeke into areas where it was unlikely to have occurred naturally and that some apparently 'natural' stands ofharakeke were created and maintained by Maori.
Maori cultivation, dispersal and active management of harakeke, as well as possible creation of wetland areas, emphasises the importance of harakeke as an economic resource prior to European colonisation, and indicates how the New Zealand landscape may have been transformed. Maori ecological knowledge can contribute new perspectives to restoration ecology and ecosystem research.

year: 2005