title: Effects of surfzone wave transformation on swash dynamics

authors: Guedes, Rafael Marcondes Carvalho

subjects: swash

abstract: Swash oscillations on two natural beaches were measured to show that the shape and magnitude of energy spectra can be largely dependent on processes occurring inside the surfzone. The observations took place on a steep, intermediate beach on the east coast (Tairua Beach), and a low-sloping, dissipative beach located on the west coast of New Zealand (Ngarunui Beach, Raglan), and aimed at improving the understanding of the effects of wave breaking, beach slope, and nonlinear wave interactions on the swash oscillations. These problems were addressed by analysing datasets obtained from field experiments undertaken at these two sites.
A field experiment at Tairua Beach showed that swash oscillations were critically dependent on the stage of the tide which controlled the degree of wave energy dissipation over the sandbar crest. Under mild, near-constant offshore wave conditions, the presence of a sandbar and the tidally-controlled water depth over its crest determined whether most of the incoming waves broke before reaching the shoreline. This forced a change in the pattern of wave energy dissipation across the surfzone between low and high tide, which was reflected by changes to swash elevation (runup) on time-scales of a few hours. Significant runup height Rs, defined as 4 times the standard deviation of the waterline time series, varied by a factor of 2 between low tide, when most of the waves were breaking over the sandbar and high tide, when the waves were barely breaking. The increase in wave energy dissipation during low tide was associated with changes in swash maxima distribution, decrease in mean swash period and increasing energy at infragravity frequencies (0.004–0.05 Hz). Bispectral analysis suggested this infragravity modulation might be connected with the presence of secondary waves at the shoreline.
Swash oscillations at Tairua were not homogeneous along the beach. Alongshore variability in Rs of up to 78% was observed and was mainly driven by changes in the sea-swell (0.05–0.4 Hz) band of the swash. This variability was predominantly controlled by alongshore changes in beach face slope, although alongshore patterning in wave breaking over the sandbar caused alongshore changes in wave dissipation and also resulted in alongshore swash variation in the sea-swell bandwidth. At infragravity frequencies, alongshore swash variability was not well associated either with changes in beach slope or wave breaking and was possibly linked to the presence of low-mode edge waves, observed from frequency-wavenumber spectra of the swash time series.
A final experiment was conducted to understand the surfzone control on incident and infragravity runup on a gently-sloping beach. The observations showed that runup saturation at infragravity frequencies can occur under mild offshore energy conditions if the beach slope is sufficiently gentle. Infragravity saturation was observed for higher-frequency (> 0.025–0.035 Hz) infragravity waves, where typically less than 5% of the (linear) energy flux was reflected from the beach and where, similar to the sea-swell band, the swash energy was independent of offshore wave energy. The infragravity frequency range of saturation was determined by the tide, with saturation extending to lower frequencies at low tide when the local beach face slope over the concave-shaped profile was gentler. Runup was strongly dominated by infragravity frequencies, which accounted on average for 96% of the runup variance, and its energy levels were entirely consistent with strong infragravity wave dissipation observed in the surfzone, particularly when including the nonlinear contributions to the wave energy fluxes. Our observations show evidence of nonlinear interactions involving infragravity and high-frequency, harmonic waves, and suggest that these harmonics could play a role in the wave energy balance near the shoreline on low-sloping, dissipative beaches.

text: Effects of surfzone wave transformation on swash dynamics Swash oscillations on two natural beaches were measured to show that the shape and magnitude of energy spectra can be largely dependent on processes occurring inside the surfzone. The observations took place on a steep, intermediate beach on the east coast (Tairua Beach), and a low-sloping, dissipative beach located on the west coast of New Zealand (Ngarunui Beach, Raglan), and aimed at improving the understanding of the effects of wave breaking, beach slope, and nonlinear wave interactions on the swash oscillations. These problems were addressed by analysing datasets obtained from field experiments undertaken at these two sites.
A field experiment at Tairua Beach showed that swash oscillations were critically dependent on the stage of the tide which controlled the degree of wave energy dissipation over the sandbar crest. Under mild, near-constant offshore wave conditions, the presence of a sandbar and the tidally-controlled water depth over its crest determined whether most of the incoming waves broke before reaching the shoreline. This forced a change in the pattern of wave energy dissipation across the surfzone between low and high tide, which was reflected by changes to swash elevation (runup) on time-scales of a few hours. Significant runup height Rs, defined as 4 times the standard deviation of the waterline time series, varied by a factor of 2 between low tide, when most of the waves were breaking over the sandbar and high tide, when the waves were barely breaking. The increase in wave energy dissipation during low tide was associated with changes in swash maxima distribution, decrease in mean swash period and increasing energy at infragravity frequencies (0.004–0.05 Hz). Bispectral analysis suggested this infragravity modulation might be connected with the presence of secondary waves at the shoreline.
Swash oscillations at Tairua were not homogeneous along the beach. Alongshore variability in Rs of up to 78% was observed and was mainly driven by changes in the sea-swell (0.05–0.4 Hz) band of the swash. This variability was predominantly controlled by alongshore changes in beach face slope, although alongshore patterning in wave breaking over the sandbar caused alongshore changes in wave dissipation and also resulted in alongshore swash variation in the sea-swell bandwidth. At infragravity frequencies, alongshore swash variability was not well associated either with changes in beach slope or wave breaking and was possibly linked to the presence of low-mode edge waves, observed from frequency-wavenumber spectra of the swash time series.
A final experiment was conducted to understand the surfzone control on incident and infragravity runup on a gently-sloping beach. The observations showed that runup saturation at infragravity frequencies can occur under mild offshore energy conditions if the beach slope is sufficiently gentle. Infragravity saturation was observed for higher-frequency (> 0.025–0.035 Hz) infragravity waves, where typically less than 5% of the (linear) energy flux was reflected from the beach and where, similar to the sea-swell band, the swash energy was independent of offshore wave energy. The infragravity frequency range of saturation was determined by the tide, with saturation extending to lower frequencies at low tide when the local beach face slope over the concave-shaped profile was gentler. Runup was strongly dominated by infragravity frequencies, which accounted on average for 96% of the runup variance, and its energy levels were entirely consistent with strong infragravity wave dissipation observed in the surfzone, particularly when including the nonlinear contributions to the wave energy fluxes. Our observations show evidence of nonlinear interactions involving infragravity and high-frequency, harmonic waves, and suggest that these harmonics could play a role in the wave energy balance near the shoreline on low-sloping, dissipative beaches.

year: 2012

title: Reply to “Comment on ‘Evolution of energy-containing turbulent eddies in the solar wind’ by W. H. Matthaeus, S. Oughton, D. H. Pontius Jr., and Y. Zhou”

authors: Matthaeus, William H.

abstract: In their preceding comment on our paper [Matthaeus et al., 1994] (hereinafter reffered to as paper 1), Tu and Marsh [this issue] object vehemently to what they perceive as undeserved criticism of the class of solar wind turbulence models developed by Tu and coworkers[Tu et al., 1984, Tu, 1987, 1988]. Our intent was not to slight the valuable contributions made in those groundbreaking theories for incorporating turbulence into models for spatial transport. Rather, we wished to point out certain shortcomings in existing theories and suggest how they might be improved.

text: Reply to “Comment on ‘Evolution of energy-containing turbulent eddies in the solar wind’ by W. H. Matthaeus, S. Oughton, D. H. Pontius Jr., and Y. Zhou” In their preceding comment on our paper [Matthaeus et al., 1994] (hereinafter reffered to as paper 1), Tu and Marsh [this issue] object vehemently to what they perceive as undeserved criticism of the class of solar wind turbulence models developed by Tu and coworkers[Tu et al., 1984, Tu, 1987, 1988]. Our intent was not to slight the valuable contributions made in those groundbreaking theories for incorporating turbulence into models for spatial transport. Rather, we wished to point out certain shortcomings in existing theories and suggest how they might be improved.

year: 1995

title: A Critical Analysis of a Culturally Responsive Pedagogy Towards Improving Māori Achievement

authors: Richards, Stephanie Moana

subjects: Culturally Responsive Pedagogy

abstract: The research task presented in this thesis examines how one English medium school, provides a culturally responsive practice that ensures the improved educational achievement of Māori students. The thesis begins by looking at some of the discourses that have transpired concerning Māori and the disparity in education that has affected Māori students’ educational outcomes. It investigates kaupapa Māori approaches and interventions that came about to combat Māori education disparity and gave Māori autonomy over their own outlooks. It also focuses on Te Kotahitanga and culturally responsive pedagogy as a response in raising Māori educational achievement.

This study was conducted in a kaupapa Māori and culturally responsive manner with a mixed method approach that included the triangulation of qualitative and quantitative data. Qualitative data included student, their parents and teacher voice as semi-structured interviews and quantitative data comprised of student achievement data and Te Kotahitanga teacher observation data. The discoveries are discussed as to the influence of the culturally responsive discourses that affected Māori student achievement.

This study suggests that when teachers implement culturally responsive practices in their classrooms, students improve educationally. Therefore, to combat the disparity that Māori students in English medium schools experience a change in school and teacher practice needs to occur so that it reflects a culturally responsive pedagogy of relations.

text: A Critical Analysis of a Culturally Responsive Pedagogy Towards Improving Māori Achievement The research task presented in this thesis examines how one English medium school, provides a culturally responsive practice that ensures the improved educational achievement of Māori students. The thesis begins by looking at some of the discourses that have transpired concerning Māori and the disparity in education that has affected Māori students’ educational outcomes. It investigates kaupapa Māori approaches and interventions that came about to combat Māori education disparity and gave Māori autonomy over their own outlooks. It also focuses on Te Kotahitanga and culturally responsive pedagogy as a response in raising Māori educational achievement.

This study was conducted in a kaupapa Māori and culturally responsive manner with a mixed method approach that included the triangulation of qualitative and quantitative data. Qualitative data included student, their parents and teacher voice as semi-structured interviews and quantitative data comprised of student achievement data and Te Kotahitanga teacher observation data. The discoveries are discussed as to the influence of the culturally responsive discourses that affected Māori student achievement.

This study suggests that when teachers implement culturally responsive practices in their classrooms, students improve educationally. Therefore, to combat the disparity that Māori students in English medium schools experience a change in school and teacher practice needs to occur so that it reflects a culturally responsive pedagogy of relations.

year: 2017