title: Sedimentology and tephrochronology of last-glacial and holocene lake sediments and peat from south Westland, New Zealand

authors: Cole-Baker, Jeremy R.

subjects: geology

abstract: A high resolution study of lake sediments and peat from three ice marginal sites in South Westland was carried out with the aim of determining the nature and timing of abrupt climate change during the last glaciation and the glacial-interglacial transition. The flux and composition of aeolian dust were used as proxies for the extent of exposed outwash surfaces and hence the extent of ice advance in the vicinity of the core sites. Cores were collected from Skiffington Swamp, Galway Tarn, and Okarito Pakihi in South Westland and the sediments characterised by measuring magnetic susceptibility (MS), combustible organic carbon (COC), grain size and mineralogy. Previously analysed pollen assemblages (Vandergoes, 2000; Vandergoes and Fitzsimons, 2003; Vandergoes et al., 2005; M. J. Vandergoes, unpublished data) were correlated with the data from this study to interpret the relationship between climate and glacial extent. Cores from Skiffington Swamp and Galway Tarn contained a visible tephra layer identified as the Kawakawa Tephra (c. 26,500 cal. years B.P.) based on stratigraphic position and glass shard composition. This layer provided an excellent chronostratigraphic reference point. 
The results from this study show that between 58,000 and 38,000 cal. years B.P., the climate was cool and variable in South Westland. Minor glacier advances occurred within a few kilometres of the Southern Alps. More significant glacier advance was recorded by MS and COC data at Skiffington Swamp after 38,000 cal. years B.P., which implies that glacial advance occurred earlier than the climate cooling recorded by pollen studies. Data from the most distal site (Galway Tarn, located approximately 10 km to the west of Skiffington Swamp) show that ice advanced near to that site at 32,000 cal. years B.P. This marks the start of maximum post-MIS 4 glacier extent. MS values were lowered at Skiffington Swamp during the interval from 30,000 to 22,000 cal. years B.P., indicating that the glacier margins and outwash plains were located well to the west. A decline in MS values at Galway Tarn and a peak in MS values at Skiffington Swamp occurred at 20,000 cal. years B.P., as glaciers retreated and outwash areas moved closer to the Southern Alps. There is no clear evidence at these three sites for a late glacial ice advance. Any such advance had limited impact 10-20 km from the present ice position.

text: Sedimentology and tephrochronology of last-glacial and holocene lake sediments and peat from south Westland, New Zealand A high resolution study of lake sediments and peat from three ice marginal sites in South Westland was carried out with the aim of determining the nature and timing of abrupt climate change during the last glaciation and the glacial-interglacial transition. The flux and composition of aeolian dust were used as proxies for the extent of exposed outwash surfaces and hence the extent of ice advance in the vicinity of the core sites. Cores were collected from Skiffington Swamp, Galway Tarn, and Okarito Pakihi in South Westland and the sediments characterised by measuring magnetic susceptibility (MS), combustible organic carbon (COC), grain size and mineralogy. Previously analysed pollen assemblages (Vandergoes, 2000; Vandergoes and Fitzsimons, 2003; Vandergoes et al., 2005; M. J. Vandergoes, unpublished data) were correlated with the data from this study to interpret the relationship between climate and glacial extent. Cores from Skiffington Swamp and Galway Tarn contained a visible tephra layer identified as the Kawakawa Tephra (c. 26,500 cal. years B.P.) based on stratigraphic position and glass shard composition. This layer provided an excellent chronostratigraphic reference point. 
The results from this study show that between 58,000 and 38,000 cal. years B.P., the climate was cool and variable in South Westland. Minor glacier advances occurred within a few kilometres of the Southern Alps. More significant glacier advance was recorded by MS and COC data at Skiffington Swamp after 38,000 cal. years B.P., which implies that glacial advance occurred earlier than the climate cooling recorded by pollen studies. Data from the most distal site (Galway Tarn, located approximately 10 km to the west of Skiffington Swamp) show that ice advanced near to that site at 32,000 cal. years B.P. This marks the start of maximum post-MIS 4 glacier extent. MS values were lowered at Skiffington Swamp during the interval from 30,000 to 22,000 cal. years B.P., indicating that the glacier margins and outwash plains were located well to the west. A decline in MS values at Galway Tarn and a peak in MS values at Skiffington Swamp occurred at 20,000 cal. years B.P., as glaciers retreated and outwash areas moved closer to the Southern Alps. There is no clear evidence at these three sites for a late glacial ice advance. Any such advance had limited impact 10-20 km from the present ice position.

year: 2006

title: Nearshore sediment dynamics in a mixed sand/mud environment

authors: Beamsley, Brett James

abstract: Poverty Bay, on the New Zealand's northeast coastline, is a high-energy coastal embayment that receives significant quantities of fine, fluvial sediment from two river systems. Examining seabed geomechanical characteristics, sediment fluxes and morphological features in northern Poverty Bay provided the opportunity to study interactive processes, including sediment entrainment rates over the cohesively bound mixed sand/mud seabeds, and the dispersion of a turbid river plume. Three field experiments and an extensive seabed-sampling programme were undertaken, and a 2-cell numerical model was developed and validated against infilling rates of the port of Gisborne navigation channel. The implications for existing and future operations at the port of Gisborne, including the suitability of capital and maintenance dredged material for use in reclamation, have been evaluated. 

Within the study site, near-bed wave orbital velocities and fluvial inputs control the spatial variability in the seabed sediment textural characteristics, with the seabed grain size decreasing with depth and distance from the mouth of the Turanganui River. A hand-held shear vane was used to quantify the in-situ shear strength of the cohesively bonded mud/sand surficial sediment, and the in-situ shear strength has been correlated (R² = 0.83) with the cumulative effect of several of the sediment textural and environmental parameters. 

Near-bed sediment diffusion and entrainment was examined using an array of micro-scale inline pumps. The effect that cohesive bonding of the mixed sand/mud seabed has on retarding the entrainment rate was examined by considering both the textural and geomechanical characteristics of the seabed. No correlation was found between the ratios of estimated to predicted near bed reference concentration (ζ) and either the median grain size (d₅₀) or the ratio of percent sand to mud of the seabed. However, a good correlation was found between ζ and the normalised in-situ shear strength (𝑥) of the seabed (adjusted R² = 0.99), with the relationship of the form, 

𝑙n(ζ) = -0.51-1.30 𝑥³ 

The conversion of the downward flux from sediment traps to a time-averaged suspended sediment concentration (SSC), and near bed reference concentration (C₀) was found to be critically dependant on the fall velocity statistic (w∫) of the grain size distribution. Due to flocculation of the near-bed suspended sediment, the dispersed equivalent w∫ distribution and median w∫ of the distribution resulted in poor predictions of C₀. Instead, an in-situ ‘effective’ w∫ distribution of the suspended sediment was developed using the measured 𝑙ₛ from individual dispersed grain size bins within the SSC profile and the predicted sediment diffusivity (εₛ). C₀ predicted using the effective w∫ distribution agreed with pumped samples and theory predicted C₀, and provided a robust method of determining the time-averaged SSC of mixed sand/mud sediment using sediment traps. 

The diffusion of sediment within the near-bed SSC profile varied as a function of w∫, with relatively finer sediment exhibiting less diffusion. The mixing length (𝑙ₛ) profile was well approximated by a linear profile, with 𝑙ₛ varying as a function of elevation (z) and the von Karman constant (κ), i.e. 𝑙ₛ = κ𝚣. Within 4-8 cm of the bed 𝑙ₛ is constant and equal to 0.06 m.

β is defined as the ratio of sediment diffusivity (εₛ) to eddy viscosity (ε∫), and is commonly used as a correction factor for predictive SSC profile equations. By examining the diffusion of sediment within the near-bed SSC profile a new equation for β was obtained,

 	𝑙n( β ) = -0. 95 - 0.4ψ / 𝑙n(ψ) 

The horizontal diffusion of sediment within the Turanganui River plume was found to be a function of the distance (x) from the mouth of the Turanganui River and a decay rate factor (Dₓ), where

 	Cₓ = Cₒbe ⁽⁻ ͯ/ᴰͯ ⁾

The form of the equation is similar to the Nielsen time-averaged gradient diffusion equation. Dₓ was correlated (R² = 0.92) with river discharge (φᵣᵢᵥₑᵣ), and found to exponentially decrease with increasing φᵣᵢᵥₑᵣ, where 

	Dₓ = 591+2850 exp(⁻ᵠʳⁱᵛᵉʳ/2.1)

The relationship suggests that the effective w∫ of the suspended sediment within the plume increases with increasing SSC, presumably due to increased flocculated particle size. Based on the developed empirical formulae the Turanganui River is predicted to discharge 7.6x10⁷ kg of fluvial derived sediment into Poverty Bay on an annual basis. 

The developed relationships and formulae that describe the hydrodynamical processes within northern Poverty Bay have been implemented in a 2-cell numerical model that considers both downward and horizontal sediment fluxes. The port of Gisborne shipping channel infilling rate, as determined from hydrographic surveys and dredging records, was used to validate the model. The 2-cell numerical model accurately predicts channel infilling rates, and provides an insight into the governing hydrodynamical processes in northern Poverty Bay. The developed model represents an alternative to the implementation of a full 3-dimensional hydrodynamic model. 

Hydrographic surveys and dredging records show the channel area passes through the beach nearshore zone, and during the monitoring period maintenance dredging only maintained the channel design depth along the channel leads, while significant infilling occurred near the channel edges (Δh = -1 m). Extrapolation of the results suggests an annual channel infilling rate of 171,400 m³ per year, corresponding to a maintenance dredging cost of approximately $857,000 to $1,200,000 per annum. Wave and river discharge conditions during the monitoring period were smaller than average, and more infilling is expected during stormy years. 

Relocating the channel and port entrance to a site in deeper water, further from the mouth of the Turanganui River, with relatively strong seabed in-situ shear strength is identified as a means of reducing dredging costs. The material dredged from the shipping channel is suitable for use in land-based reclamation, particularly if the soil structure is improved by addition of a coarser material such as of the underlying mudstone unit. The bearing capacity of the reclamation can be improved by mixing the mud/sand with concrete to create mudcrete.

text: Nearshore sediment dynamics in a mixed sand/mud environment Poverty Bay, on the New Zealand's northeast coastline, is a high-energy coastal embayment that receives significant quantities of fine, fluvial sediment from two river systems. Examining seabed geomechanical characteristics, sediment fluxes and morphological features in northern Poverty Bay provided the opportunity to study interactive processes, including sediment entrainment rates over the cohesively bound mixed sand/mud seabeds, and the dispersion of a turbid river plume. Three field experiments and an extensive seabed-sampling programme were undertaken, and a 2-cell numerical model was developed and validated against infilling rates of the port of Gisborne navigation channel. The implications for existing and future operations at the port of Gisborne, including the suitability of capital and maintenance dredged material for use in reclamation, have been evaluated. 

Within the study site, near-bed wave orbital velocities and fluvial inputs control the spatial variability in the seabed sediment textural characteristics, with the seabed grain size decreasing with depth and distance from the mouth of the Turanganui River. A hand-held shear vane was used to quantify the in-situ shear strength of the cohesively bonded mud/sand surficial sediment, and the in-situ shear strength has been correlated (R² = 0.83) with the cumulative effect of several of the sediment textural and environmental parameters. 

Near-bed sediment diffusion and entrainment was examined using an array of micro-scale inline pumps. The effect that cohesive bonding of the mixed sand/mud seabed has on retarding the entrainment rate was examined by considering both the textural and geomechanical characteristics of the seabed. No correlation was found between the ratios of estimated to predicted near bed reference concentration (ζ) and either the median grain size (d₅₀) or the ratio of percent sand to mud of the seabed. However, a good correlation was found between ζ and the normalised in-situ shear strength (𝑥) of the seabed (adjusted R² = 0.99), with the relationship of the form, 

𝑙n(ζ) = -0.51-1.30 𝑥³ 

The conversion of the downward flux from sediment traps to a time-averaged suspended sediment concentration (SSC), and near bed reference concentration (C₀) was found to be critically dependant on the fall velocity statistic (w∫) of the grain size distribution. Due to flocculation of the near-bed suspended sediment, the dispersed equivalent w∫ distribution and median w∫ of the distribution resulted in poor predictions of C₀. Instead, an in-situ ‘effective’ w∫ distribution of the suspended sediment was developed using the measured 𝑙ₛ from individual dispersed grain size bins within the SSC profile and the predicted sediment diffusivity (εₛ). C₀ predicted using the effective w∫ distribution agreed with pumped samples and theory predicted C₀, and provided a robust method of determining the time-averaged SSC of mixed sand/mud sediment using sediment traps. 

The diffusion of sediment within the near-bed SSC profile varied as a function of w∫, with relatively finer sediment exhibiting less diffusion. The mixing length (𝑙ₛ) profile was well approximated by a linear profile, with 𝑙ₛ varying as a function of elevation (z) and the von Karman constant (κ), i.e. 𝑙ₛ = κ𝚣. Within 4-8 cm of the bed 𝑙ₛ is constant and equal to 0.06 m.

β is defined as the ratio of sediment diffusivity (εₛ) to eddy viscosity (ε∫), and is commonly used as a correction factor for predictive SSC profile equations. By examining the diffusion of sediment within the near-bed SSC profile a new equation for β was obtained,

 	𝑙n( β ) = -0. 95 - 0.4ψ / 𝑙n(ψ) 

The horizontal diffusion of sediment within the Turanganui River plume was found to be a function of the distance (x) from the mouth of the Turanganui River and a decay rate factor (Dₓ), where

 	Cₓ = Cₒbe ⁽⁻ ͯ/ᴰͯ ⁾

The form of the equation is similar to the Nielsen time-averaged gradient diffusion equation. Dₓ was correlated (R² = 0.92) with river discharge (φᵣᵢᵥₑᵣ), and found to exponentially decrease with increasing φᵣᵢᵥₑᵣ, where 

	Dₓ = 591+2850 exp(⁻ᵠʳⁱᵛᵉʳ/2.1)

The relationship suggests that the effective w∫ of the suspended sediment within the plume increases with increasing SSC, presumably due to increased flocculated particle size. Based on the developed empirical formulae the Turanganui River is predicted to discharge 7.6x10⁷ kg of fluvial derived sediment into Poverty Bay on an annual basis. 

The developed relationships and formulae that describe the hydrodynamical processes within northern Poverty Bay have been implemented in a 2-cell numerical model that considers both downward and horizontal sediment fluxes. The port of Gisborne shipping channel infilling rate, as determined from hydrographic surveys and dredging records, was used to validate the model. The 2-cell numerical model accurately predicts channel infilling rates, and provides an insight into the governing hydrodynamical processes in northern Poverty Bay. The developed model represents an alternative to the implementation of a full 3-dimensional hydrodynamic model. 

Hydrographic surveys and dredging records show the channel area passes through the beach nearshore zone, and during the monitoring period maintenance dredging only maintained the channel design depth along the channel leads, while significant infilling occurred near the channel edges (Δh = -1 m). Extrapolation of the results suggests an annual channel infilling rate of 171,400 m³ per year, corresponding to a maintenance dredging cost of approximately $857,000 to $1,200,000 per annum. Wave and river discharge conditions during the monitoring period were smaller than average, and more infilling is expected during stormy years. 

Relocating the channel and port entrance to a site in deeper water, further from the mouth of the Turanganui River, with relatively strong seabed in-situ shear strength is identified as a means of reducing dredging costs. The material dredged from the shipping channel is suitable for use in land-based reclamation, particularly if the soil structure is improved by addition of a coarser material such as of the underlying mudstone unit. The bearing capacity of the reclamation can be improved by mixing the mud/sand with concrete to create mudcrete.

year: 2003

title: 1999 Professorial Address: Nau te rourou, naku te rourou… Māori education: setting an agenda.

authors: Bishop, Russell

subjects: educational outcomes

abstract: Current educational policies and practices in Aotearoa/New Zealand were developed and continue to be developed within a framework of power imbalances, which effects Maori the greatest. An alternative model that seeks to address indigenous Māori aspirations and Treaty of Waitangi guarantees for self determination is presented here. This model suggests how a tertiary teacher education institution might create learning contexts wherein power-sharing images, principles and practices will facilitate successful participation by Māori students in mainstream classrooms. This model constitutes the classroom as a place where young people's sense-making processes (cultures) are incorporated and enhanced, where the existing knowledges of young people are seen as "acceptable" and "official" and where the teacher interacts with students in such a way that new knowledge is co-created. Such a classroom will generate totally different interaction and participation patterns and educational outcomes from a classroom where knowledge is seen as something that the teacher makes sense of and then passes on to students.

text: 1999 Professorial Address: Nau te rourou, naku te rourou… Māori education: setting an agenda. Current educational policies and practices in Aotearoa/New Zealand were developed and continue to be developed within a framework of power imbalances, which effects Maori the greatest. An alternative model that seeks to address indigenous Māori aspirations and Treaty of Waitangi guarantees for self determination is presented here. This model suggests how a tertiary teacher education institution might create learning contexts wherein power-sharing images, principles and practices will facilitate successful participation by Māori students in mainstream classrooms. This model constitutes the classroom as a place where young people's sense-making processes (cultures) are incorporated and enhanced, where the existing knowledges of young people are seen as "acceptable" and "official" and where the teacher interacts with students in such a way that new knowledge is co-created. Such a classroom will generate totally different interaction and participation patterns and educational outcomes from a classroom where knowledge is seen as something that the teacher makes sense of and then passes on to students.

year: 2000