title: Sediment dynamics of a shallow exposed surfing headland

authors: Phillips, David

subjects: New Zealand

abstract: A study of the wave, current and sediment dynamics was conducted at a shallow and exposed world-class surfing headland at Raglan, on the west coast of New Zealand to determine the mechanism for sustaining the sandy seabed. The location features a large-scale headland with titano-magnetite iron sand dominant on the seabed, adjacent to a rocky reef and boulder shoreline. Field experiments were conducted at the headland involving (i) wave, current and suspended sediment measurements, (ii) side-scan sonar surveys, (iii) hydrographic surveys and (iv) seabed sampling and ground truth observations by divers. Waves and currents were numerically modelled using the 3DD model suite (Black, 2001), with model outputs showing a strong comparison to the measured field data.
The results show that the mechanism responsible for maintaining the sandy seabed at the Raglan headland is a combination of sediment transport around the headland to the east (i.e. west coast littoral drift system), and a local re-circulating sediment pathway transporting sediment in the west direction. Sediment moves continually around the headland supplying the littoral system at the headland, and not in “slugs’ as reported for other large protruding headlands. The net sediment flux was approximately 275000 m³/yr flowing east inshore and 100000 m³/yr to the west offshore. The difference of 175000 m³/yr flows from the headland littoral cell into the northwards flowing longshore transport system of the west coast. This compares well to the previous estimate of 175000 m³/yr of net transport along the coast.
The alignment of the Raglan headland provides an environment where waves of a high oblique angle generate strong wave-driven currents in the surf-zone, flowing inshore along the headland in an easterly direction. Alternatively, a westerly flowing current is generated by the interaction of wave-driven forces and topographic steering where alignment of the headland changes. Numerical model outputs show the presence of recirculating eddy flows in four cells, which compare very closely to the compartmentalisation of the headland characterised by the main surf breaks, with the width and velocity of the current flows depending on both the size of the swell and the level of the tide. Large wave events at low tide generate the strongest currents flowing east along the headland inshore, whilst at high tide the westerly current also reaches its greatest velocity, and the eddy flows are at their most prevalent. The large inshore currents flowing along the headland decrease the surfability of a headland and make the break difficult if not impossible to surf. However, the large scale and variation in topographic alignment of the Raglan headland can allow access for surfers in the zones of lower wave height and decreased current velocity (e.g. Whale Bay reef). It is recommended that the affect of strong currents on surfability be considered in the design of artificial surfing reefs if amenity of the structure is to be maximised.
The wave-orbital interaction with the hydrodynamically ‘rough’ substrate on the rocky boulder reef creates a greater turbulent flow over these beds. Sediment is unable to settle in this zone and is scoured or winnowed away to leave the rocky bed exposed. The regions further shoreward are influenced by the easterly flowing currents more often eroding sand away in the absence of sufficient upstream inputs to maintain the sediment flux. The location of the interface between the sand and rocky seafloor corresponds to the point where the long-term mean currents change from flowing easterly to flowing westerly along the headland. Side scan sonar surveys showed the interface generally followed the shape of the headland and remained fairly stable in position. This is confirmed by the bathymetric surveys where despite significant volume changes in the quantity of sand being transported or deposited at the headland, the seabed level fluctuates about a stable long-term equilibrium position of the bed (quasi permanent position). This is supported by the long-term habitation and zonation of marine organisms on the sub-tidal reef edge, demonstrating an upper level of seabed movement. The characteristics of the seabed in the study area reflect the presence of the surf zone and strong unidirectional currents to the east, and show re-circulating sediment pathways flowing to the west.

text: Sediment dynamics of a shallow exposed surfing headland A study of the wave, current and sediment dynamics was conducted at a shallow and exposed world-class surfing headland at Raglan, on the west coast of New Zealand to determine the mechanism for sustaining the sandy seabed. The location features a large-scale headland with titano-magnetite iron sand dominant on the seabed, adjacent to a rocky reef and boulder shoreline. Field experiments were conducted at the headland involving (i) wave, current and suspended sediment measurements, (ii) side-scan sonar surveys, (iii) hydrographic surveys and (iv) seabed sampling and ground truth observations by divers. Waves and currents were numerically modelled using the 3DD model suite (Black, 2001), with model outputs showing a strong comparison to the measured field data.
The results show that the mechanism responsible for maintaining the sandy seabed at the Raglan headland is a combination of sediment transport around the headland to the east (i.e. west coast littoral drift system), and a local re-circulating sediment pathway transporting sediment in the west direction. Sediment moves continually around the headland supplying the littoral system at the headland, and not in “slugs’ as reported for other large protruding headlands. The net sediment flux was approximately 275000 m³/yr flowing east inshore and 100000 m³/yr to the west offshore. The difference of 175000 m³/yr flows from the headland littoral cell into the northwards flowing longshore transport system of the west coast. This compares well to the previous estimate of 175000 m³/yr of net transport along the coast.
The alignment of the Raglan headland provides an environment where waves of a high oblique angle generate strong wave-driven currents in the surf-zone, flowing inshore along the headland in an easterly direction. Alternatively, a westerly flowing current is generated by the interaction of wave-driven forces and topographic steering where alignment of the headland changes. Numerical model outputs show the presence of recirculating eddy flows in four cells, which compare very closely to the compartmentalisation of the headland characterised by the main surf breaks, with the width and velocity of the current flows depending on both the size of the swell and the level of the tide. Large wave events at low tide generate the strongest currents flowing east along the headland inshore, whilst at high tide the westerly current also reaches its greatest velocity, and the eddy flows are at their most prevalent. The large inshore currents flowing along the headland decrease the surfability of a headland and make the break difficult if not impossible to surf. However, the large scale and variation in topographic alignment of the Raglan headland can allow access for surfers in the zones of lower wave height and decreased current velocity (e.g. Whale Bay reef). It is recommended that the affect of strong currents on surfability be considered in the design of artificial surfing reefs if amenity of the structure is to be maximised.
The wave-orbital interaction with the hydrodynamically ‘rough’ substrate on the rocky boulder reef creates a greater turbulent flow over these beds. Sediment is unable to settle in this zone and is scoured or winnowed away to leave the rocky bed exposed. The regions further shoreward are influenced by the easterly flowing currents more often eroding sand away in the absence of sufficient upstream inputs to maintain the sediment flux. The location of the interface between the sand and rocky seafloor corresponds to the point where the long-term mean currents change from flowing easterly to flowing westerly along the headland. Side scan sonar surveys showed the interface generally followed the shape of the headland and remained fairly stable in position. This is confirmed by the bathymetric surveys where despite significant volume changes in the quantity of sand being transported or deposited at the headland, the seabed level fluctuates about a stable long-term equilibrium position of the bed (quasi permanent position). This is supported by the long-term habitation and zonation of marine organisms on the sub-tidal reef edge, demonstrating an upper level of seabed movement. The characteristics of the seabed in the study area reflect the presence of the surf zone and strong unidirectional currents to the east, and show re-circulating sediment pathways flowing to the west.

year: 2004

title: Environmental context for late Holocene human occupation of the South Wellesley Archipelago, Gulf of Carpentaria, northern Australia

authors: Moss, Patrick

subjects: palynology

abstract: A 2400 year record of environmental change is reported from a wetland on Bentinck Island in the southern Gulf of Carpentaria, northern Australia. Three phases of wetland development are identified, with a protected coastal setting from ca. 2400 to 500 years ago, transitioning into an estuarine mangrove forest from ca. 500 years ago to the 1940s, and finally to a freshwater swamp over the past+60 years. This sequence reflects the influence of falling sea-levels, development of a coastal dune barrier system, prograding shorelines, and an extreme storm (cyclone) event. In addition, there is clear evidence of the impacts that human abandonment and resettlement have on the island's fire regimes and vegetation. A dramatic increase in burning and vegetation thickening was observed after the cessation of traditional Indigenous Kaiadilt fire management practices in the 1940s, and was then reversed when people returned to the island in the 1980s. In terms of the longer context for human occupation of the South Wellesley Archipelago, it is apparent that the mangrove phase provided a stable and productive environment that was conducive for human settlement of this region over the past 1000 years.

text: Environmental context for late Holocene human occupation of the South Wellesley Archipelago, Gulf of Carpentaria, northern Australia A 2400 year record of environmental change is reported from a wetland on Bentinck Island in the southern Gulf of Carpentaria, northern Australia. Three phases of wetland development are identified, with a protected coastal setting from ca. 2400 to 500 years ago, transitioning into an estuarine mangrove forest from ca. 500 years ago to the 1940s, and finally to a freshwater swamp over the past+60 years. This sequence reflects the influence of falling sea-levels, development of a coastal dune barrier system, prograding shorelines, and an extreme storm (cyclone) event. In addition, there is clear evidence of the impacts that human abandonment and resettlement have on the island's fire regimes and vegetation. A dramatic increase in burning and vegetation thickening was observed after the cessation of traditional Indigenous Kaiadilt fire management practices in the 1940s, and was then reversed when people returned to the island in the 1980s. In terms of the longer context for human occupation of the South Wellesley Archipelago, it is apparent that the mangrove phase provided a stable and productive environment that was conducive for human settlement of this region over the past 1000 years.

year: 2015-01-01

title: Talk More: Student Learning Through Reciprocal Conversations

authors: Grant, Sarah

subjects: oral language

abstract: This research explored ways of improving the oral language development of Year 1 children in four low decile mainstream schools who were making limited progress in literacy. Over 82% of these students were Māori.  Due to the continued impact of past educational policies and the subsequent interruption of the intergenerational transmission of the mother tongue, many Māori children are not exposed to proficient and fluent models either of spoken English or of spoken Māori.  Such children struggle to make the English literacy progress expected of them by schools and communities. The central focus of the research was to evaluate a claim that Year 6 students (tuākana)  could make a substantial improvement in the oral language achievement of  Year 1 students (teina), through engaging with them in regular conversational contexts using the TALES (Talk, Ask, Listen, Encourage, and Say) procedures. This pedagogical approach is understood as one which was culturally responsive for these students. 

Quantitative analysis of data from three quantitative outcome measures (Record of Oral Language, Junior Oral Screening Tool, and Auditory-Vocal Association Assessment of Verbal Attainments) demonstrated that there were substantial oral language gains for the 72 teina students involved in the study. The quantitative analysis also demonstrated that these gains occurred most strongly during the phases in which the TALES procedures were being implemented by the 72 tuākana students, in accord with the multiple baseline design. Detailed qualitative analysis of a random sample of six of the 72 pairs illustrated both the effectiveness of the tuākana language interaction with the teina, and the different ways that the tuākana were able to implement the TALES procedure. Analysis of five minute probes of transcripts over six weeks from these six tuākana - teina pairs indicated that a wide range of literacy activities and conversations took place. The unique learning needs and personal learning intentions of each tuakana and teina were successfully monitored using this five minute probe procedure. Powerful reciprocal learning processes were evident in transcripts of conversations between the tuākana and the teina, and also within feedback and feed-forward meetings between the tuākana and key teachers.  

The substantial oral language gains for the teina students in this study  were achieved within learning contexts that were social and  interactive, and that embodied the principles of ako (learning and teaching roles were shared) and whakawhanaungatanga (building caring and  supportive relationships). These principles are among those that underpin pedagogies that are culturally responsive (Bishop  Glynn, 1999; Glynn, Wearmouth,  Berryman, 2006; Ladson-Billings, 1995, 2006) and transformative. The results of this research study give a clear message to mainstream non-Māori teachers, that they can make a positive and substantial difference to the learning outcomes of their Māori students.

text: Talk More: Student Learning Through Reciprocal Conversations This research explored ways of improving the oral language development of Year 1 children in four low decile mainstream schools who were making limited progress in literacy. Over 82% of these students were Māori.  Due to the continued impact of past educational policies and the subsequent interruption of the intergenerational transmission of the mother tongue, many Māori children are not exposed to proficient and fluent models either of spoken English or of spoken Māori.  Such children struggle to make the English literacy progress expected of them by schools and communities. The central focus of the research was to evaluate a claim that Year 6 students (tuākana)  could make a substantial improvement in the oral language achievement of  Year 1 students (teina), through engaging with them in regular conversational contexts using the TALES (Talk, Ask, Listen, Encourage, and Say) procedures. This pedagogical approach is understood as one which was culturally responsive for these students. 

Quantitative analysis of data from three quantitative outcome measures (Record of Oral Language, Junior Oral Screening Tool, and Auditory-Vocal Association Assessment of Verbal Attainments) demonstrated that there were substantial oral language gains for the 72 teina students involved in the study. The quantitative analysis also demonstrated that these gains occurred most strongly during the phases in which the TALES procedures were being implemented by the 72 tuākana students, in accord with the multiple baseline design. Detailed qualitative analysis of a random sample of six of the 72 pairs illustrated both the effectiveness of the tuākana language interaction with the teina, and the different ways that the tuākana were able to implement the TALES procedure. Analysis of five minute probes of transcripts over six weeks from these six tuākana - teina pairs indicated that a wide range of literacy activities and conversations took place. The unique learning needs and personal learning intentions of each tuakana and teina were successfully monitored using this five minute probe procedure. Powerful reciprocal learning processes were evident in transcripts of conversations between the tuākana and the teina, and also within feedback and feed-forward meetings between the tuākana and key teachers.  

The substantial oral language gains for the teina students in this study  were achieved within learning contexts that were social and  interactive, and that embodied the principles of ako (learning and teaching roles were shared) and whakawhanaungatanga (building caring and  supportive relationships). These principles are among those that underpin pedagogies that are culturally responsive (Bishop  Glynn, 1999; Glynn, Wearmouth,  Berryman, 2006; Ladson-Billings, 1995, 2006) and transformative. The results of this research study give a clear message to mainstream non-Māori teachers, that they can make a positive and substantial difference to the learning outcomes of their Māori students.

year: 2009