The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform

Alan S. Trenhaile - One of the best experts on this subject based on the ideXlab platform.

  • Shore Platform downwearing in eastern canada a 9 14 year micro erosion meter record
    Geomorphology, 2018
    Co-Authors: Alan S. Trenhaile, Neil J. Porter
    Abstract:

    Abstract Downwearing rates (erosion in the vertical plane) were measured with a micro-erosion meter (MEM) in eastern Canada, on an argillacious, sub-horizontal Shore Platform at Mont Louis in eastern Quebec, and on two sloping, basaltic and sandstone Platforms at, respectively, Scots Bay and Burntcoat Head in the Bay of Fundy, Nova Scotia. The original data covered a period from 2002 to 2009. This dataset was extended by measurements repeated at surviving MEM stations in 2017, producing records ranging over 9–14 years, depending on when each station was installed. Because of rapid surface downwearing, many of the original MEM stations were inoperable in 2017, especially at Burntcoat Head. Nevertheless, data were obtained from 19 stations at Burntcoat (35% of the 2009 original), 25 at Mont Louis (83% of the original), and 38 at Scots Bay (75% of the original). For the stations at Mont Louis and Scots Bay that were still functioning in 2017, there were no significant differences in rates of downwearing over the shorter (from station installation up to 2009) and extended periods (from installation to 2017). Mean rates of downwearing calculated from all the stations in each area declined through time, however, due to the loss of the more rapidly eroding stations. A simple procedure, which was proposed to compensate for this decrease, produced mean downwearing rates that were broadly similar to those reported over the original measurement period. There were significant relationships between downwearing rates and elevation (R2 = 0.32) and downwearing rates and rock hardness (R2 = 0.41) in the extended record at Scots Bay, and a small but significant relationship between downwearing rates and rock hardness at Mont Louis (R2 = 0.17). Differences in downwearing rates across the Platforms suggest that salt weathering and wetting and drying are dominant weathering mechanisms at Scots Bay and Mont Louis. Chemical weathering of the sandstone cementing agent and the premature removal of weathered grains by wave-generated bottom currents may, however, be more important at Burntcoat Head.

  • Shore Platform erosion and evolution: Implications for cosmogenic nuclide analysis
    Marine Geology, 2018
    Co-Authors: Alan S. Trenhaile
    Abstract:

    Abstract Determining rates and modes of Shore Platform development and the age of associated elements are among the greatest challenges facing rock coast researchers today. These coasts generally lack dateable deposits but cosmogenic nuclide analysis (CNA) can be applied directly to bare rock surfaces to estimate erosion rates or the time that a surface has been exposed over millennial timescales. Therefore this technique has the potential to revolutionize current theories on rock coast evolution and modes of development. Because environmental and geomorphological factors affect rates of nuclide accumulation and retention, however, the results of CNA analysis are dependent on the validity of the theoretical models that have to be employed according to the particular application. Among the important assumptions that may be made are those concerned with shading, tidal immersion, beach sediment covers, and other factors that influence rates of nuclide accumulation, and with possible spatial and temporal patterns in Shore Platform erosion, primarily by wave-generated backwearing and weathering-induced downwearing, that reduce nuclide concentrations. Our lack of understanding of the factors that control these variables, and in particular Shore Platform erosion, which is the subject of this review, has important implications for modelling rock coast evolution, assessing the possible contribution of inheritance, and dating, especially by CNA, the occurrence of important, formative events.

  • Shore Platform and cliff notch transitions along the la paz peninsula southern baja mexico
    Geologica Acta, 2015
    Co-Authors: Alan S. Trenhaile, N I Porter, Kyle J Prestanski
    Abstract:

    Increasing exposure to wave action produces a northerly transition from high tidal notches to Shore Platforms inthe andesitic lahar deposits of the La Paz Peninsula, southern Baja, Mexico. Twenty-four notches were surveyedand wear pins were cemented into the apex of each notch. Thirty-six transverse micro-erosion meter (TMEM)stations were installed on three surveyed Platforms. Field measurements were made over a 2.5 year period.The wear pins suggested notch backwearing (horizontal erosion) is <2mm yr -1 . The Shore Platforms were fairlynarrow (a few tens of metres) and steeper (1o) than most Platforms in similar microtidal environments, reflectinga weak wave environment and resistant rocks. Mean TMEM downwearing (vertical erosion) rates for each of thethree Platforms ranged from 0.14mm yr -1 to 0.42mm yr -1 . There was a good relationship between notch height(difference in elevation between the floor and the roof at the front of the notch) and exposure to wave action, butnotch depth is time-dependent and the relationship with exposure was not statistically significant. Notch heightwas also related to the orientation and wave fetch of the site. Field evidence suggested that the notches were notproduced by bioerosion or chemical weathering but by alternate wetting and drying or salt weathering from hightidal immersion and wave-generated splash and spray. Coastal morphology is fairly well adjusted to present sealevel although notch occurrence in the upper portion of the high tidal zone suggests that there is slow tectonic uplift in this region.

  • The effect of boulders on Shore Platform development and morphology in Galicia, north west Spain
    Continental Shelf Research, 2012
    Co-Authors: Augusto Pérez-alberti, Alan S. Trenhaile, Ana Pires, J. López-bedoya, Helder I. Chaminé, Alberto Gomes
    Abstract:

    This paper is concerned with the effect of sediment accumulation on Shore Platform development. Boulder accumulations are common on the granitic Shore Platforms of Galicia, northwestern Spain. Boulders are produced by erosion of Shore Platforms and of cliffs consisting of cold-climate deposits from the last glacial period. Measurements were made of the long axis length of more than 800 boulders, and additionally of the short and intermediate axes of 340 of these boulders, as well as of their orientation and gradient. There were two study areas. The boulders on the Barbanza Peninsula are generally a little smaller than those in southern Galicia with, respectively; mean long axis lengths of 0.98 and 1.14, and masses of 1.06 and 1.59 t. There are also some isolated, very coarse boulders and megaclasts in southern Galicia. The distribution and extent of the deposits and boulder imbrication and orientation testify to the high levels of wave energy produced by northwesterly and westerly storms in this region. Although the boulders, as well as the underlying Shore Platforms, were inherited, in part, from previous interglacial stages, some boulder detachment and movement is occurring today during storms, when significant deep water wave heights exceed 8 to 10 m. Despite some abrasion of the Shore Platforms, the primary effect of large boulder accumulations is protective. The role of sediment on Shore Platforms has been neglected, but this study suggests that because of arrested development under thick accumulations, Platform gradient in areas with abundant sediment increases with the grain size of the material. The occurrence and type of sediment on Shore Platforms may therefore help to explain the distribution of sloping and subhorizontal Platforms under different morphogenic and geological conditions.

  • freeze thaw and Shore Platform development in gaspe quebec
    Geographie Physique Et Quaternaire, 2011
    Co-Authors: Alan S. Trenhaile, P A Rudakas
    Abstract:

    The role of freeze-thaw action in coastal environments, with particular reference to the formation of sub-horizontal Shore Platforms in Gaspe, Quebec, was investigated experimentally. Rock cores and crushed rock samples were subjected to: two freeze-thaw cycles of twelve and twenty-four hour durations; fresh water and three artificial sea water solutions of about half, one and a half, and 'normal' salinity; and two drainage conditions representing rock pools and vertical well drained surfaces. These variables were selected to simulate some of the local environments which exist between the cliff top and low tide level in coastal Gaspe. Shales were the most susceptible to frost breakdown, followed in turn by argillites, calcisiltites and dolomitic silty argillites, and graywackes. Greatest disintegration tended to be associated with sea water solutions of about half-normal salinity. The data suggest that breakdown is greatest in the lower portions of the cliff. Freeze-thaw may produce the moat-like pools commonly found at the back of Shore Platforms. Although the process undoubtedly facilitates wave erosion of the Platform and cliff, however, there is no evidence to suggest that it causes Shore Platforms to assume subhorizontal gradients.

Mark E. Dickson - One of the best experts on this subject based on the ideXlab platform.

  • Wind Waves and Cliff Shaking on Macrotidal Shore Platforms: A Case-study from North Yorkshire, U.K.
    Journal of Coastal Research, 2018
    Co-Authors: David M. Kennedy, Mark E. Dickson, Emma C. Vann Jones, Nick Rosser
    Abstract:

    ABSTRACT Kennedy, D.M.; Vann Jones, E.C.; Dickson, M.E., and Rosser, N.J., 2018. Wind waves and cliff shaking on macrotidal Shore Platforms: A case-study from North Yorkshire, U.K. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 436–440. Coconut Creek (Florida), ISSN 0749-0208. Wind waves are a major erosive agent on the rocky coast. The physical impact of waves is also important in driving erosion above the splash zone. This occurs through the transferral of energy into the bedrock by the action of wave breaking causing microseismic shaking. In this study we concurrently measure wave energy and resultant microseismic shaking on a macrotidal Shore Platform at Staithes, North Yorkshire, U.K. It is found that infragravity wave generation is limited when compared to microtidal coasts and where it does occur it is confined to the wave breaking zone. Cliff shaking ...

  • New insights on the relative contributions of coastal processes and tectonics to Shore Platform development following the Kaikōura earthquake
    Earth Surface Processes and Landforms, 2017
    Co-Authors: Wayne J. Stephenson, Mark E. Dickson, Paul Denys
    Abstract:

    We describe the immediate impact of the 14 November 2016 Kaikoura magnitude 7.8 (Mw) earthquake on Shore Platforms and cliffs around Kaikoura Peninsula. The earthquake caused an instantaneous uplift of ~1.01 m of the peninsula. We resurveyed 7 profiles previously used for erosion monitoring and observed changes in the configuration of the Shoreline. The coseismic uplift has fundamentally changed the process regime operating on the Platforms and altered the future trajectory of Shore Platform and cliff development. Our observations highlight the interplay of waves, weathering, biology and tectonics. At this location tectonism strongly modulates the process regime, driving instantaneous changes in morphology and altering rates and patterns of erosion. Finally, the uplift of the Kaikoura coast has implications for changing resilience to climate change and sea level rise.

  • Systematic analysis of rocky Shore Platform morphology at large spatial scale using LiDAR-derived digital elevation models
    Geomorphology, 2017
    Co-Authors: Hironori Matsumoto, Mark E. Dickson, Gerd Masselink
    Abstract:

    Abstract Much of the existing research on rocky Shore Platforms describes results from carefully selected field sites, or comparisons between a relatively small number of selected sites. Here we describe a method to systematically analyse rocky Shore morphology over a large area using LiDAR-derived digital elevation models. The method was applied to 700 km of coastline in southwest England; a region where there is considerable variation in wave climate and lithological settings, and a large alongShore variation in tidal range. Across-Shore profiles were automatically extracted at 50 m intervals around the coast where information was available from the Coastal Channel Observatory coastal classification. Routines were developed to automatically remove non-Platform profiles. The remaining 612 Shore Platform profiles were then subject to automated morphometric analyses, and correlation analysis in respect to three possible environmental controls: wave height, mean spring tidal range and rock strength. As expected, considerable scatter exists in the correlation analysis because only very coarse estimates of rock strength and wave height were applied, whereas variability in factors such as these can locally be the most important control on Shoreline morphology. In view of this, it is somewhat surprising that overall consistency was found between previous published findings and the results from the systematic, automated analysis of LiDAR data: Platform gradient increases as rock strength and tidal range increase, but decreases as wave height increases; Platform width increases as wave height and tidal range increase, but decreases as rock strength increases. Previous studies have predicted Shore Platform gradient using tidal range alone. A multi-regression analysis of LiDAR data confirms that tidal range is the strongest predictor, but a new multi-factor empirical model considering tidal range, wave height, and rock strength yields better predictions of Shore Platform gradient (root mean square error of predictions reduced by 5%). The key finding of this study is that large-scale semi-automated morphometric analyses have the potential to reveal dominant process controls in the face of small-scale local variability.

  • an exploratory numerical model of rocky Shore profile evolution
    Geomorphology, 2016
    Co-Authors: Hironori Matsumoto, Mark E. Dickson, Paul S Kench
    Abstract:

    Abstract Rocky Shores occur along much of the world's coastline and include a wide range of coastal morphologies, such as intertidal Shore Platforms. Considerable research effort has been placed on trying to understand developmental processes on rocky Shores, but progress has been forestalled because these landscapes develop slowly and preserve little evidence of evolution through time. This paper presents a new exploratory numerical model developed to study long-term Shore profile evolution on rock coasts. The model purposely considers only a limited number of processes, each represented in a highly abstracted way. Despite these simplifications, the model exhibits a large range of emergent Shore profile shapes. This behavior is enabled both by broader spatial representation of the driving erosion forces and the flexibility provided by a grid discretization scheme. Initial model testing shows the development of varied rocky profile geometries, ranging from steep plunging cliffs, cliffs with narrow benches, and cliffs with a variety of Shore Platform shapes. Most of the model geometries are similar to those observed in the field, and model behavior is robust and internally consistent across a relatively large parameter space. This paper provides a detailed description of the new model and its subsequent testing. Emphasis is placed on comparison of model results with published field observations in which morphometric relationships are described between Shore Platform gradient and tidal range, and Platform elevation and Platform width. The model adequately simulates these morphometric relationships, while retaining its ability to simulate a wide range of profile shapes. The simplicity of process representations, and the limited number of processes implemented, means that model outputs can be interpreted reasonably easily. Hence, an opportunity is now provided, following the testing described in this paper, to use the model to systematically investigate the broader controlling conditions on rock Shore profile development.

  • Generalised observations of wave characteristics on near‐horizontal Shore Platforms: Synthesis of six case studies from the North Island, New Zealand
    New Zealand Geographer, 2016
    Co-Authors: Hiroki Ogawa, Mark E. Dickson, Paul S Kench
    Abstract:

    Most field studies of wave processes on Shore Platforms in front of eroding cliffs focus on a single site, revealing aspects of wave dynamics at that location. Here, we analyse data from six Platforms around northeastern New Zealand and describe the fundamental control of Shore Platform width, gradient and elevation on wave processes, including greater attenuation of short-period waves at lower tidal stages and increases in longer period wave energy towards the cliff toe. These data suggest that empirical formulae developed from coral-reef environments provide better predictions of wave height on Platforms than formulae currently used in Shore Platform models.

David M. Kennedy - One of the best experts on this subject based on the ideXlab platform.

  • treating risk as relational on Shore Platforms and implications for public safety on microtidal rocky coasts
    Natural Hazards, 2018
    Co-Authors: Peter Kamstra, David M. Kennedy, Brian R Cook, Barbara Brighton
    Abstract:

    Drowning on rocky coasts is a problem with global significance, but it is a particularly acute issue in Australia where rocky coasts account for 19% of coastal drownings. The risk of drowning is often framed as a consequence of waves washing over Shore Platforms, which sweep unsuspecting victims into the sea. Although the physical processes of ‘wave overtopping’ are understood, few studies have investigated which elements of Shore Platform environments are perceived as being hazardous. Using coastal regions of Victoria, Australia, as the case, this study explores how Victoria’s lifesaving community perceives risk on Shore Platforms. These perceptions are then compared to quantitative risk ratings to analyse whether physical risk assessments designed by coastal risk experts align with lifesavers’ perceptions. Lifesavers are non-certified risk ‘experts’, whose safety training and exposure to hazardous situations inform their ‘experiential-expertise’, which is contrasted with the more common quantitative and science-based ‘expert’ risk assessments. The aim is to explore lifesavers perceptions of risk and to contrast two different ‘expert’ constructions of risk; one of which is experience based and the other a more traditional quantitative output of modelling. Exploration of this type of ‘expert’–expert hazard contrast is lacking with a management focus on lay perceptions. To understand how lifesavers perceive risk on Shore Platforms, the authors explore risk as relational. This conceptual approach takes an important first step towards thinking about risk as more than the simple combination of physical wave overtopping process and social perceptions. Instead, it seeks to understand the socio-environmental interactions that are perceived as hazardous. Data for this analysis were collected via an online questionnaire of Surf Life Saving Australia membership whose patrols are within 1 km of a Shore Platform in Victoria, Australia (n = 4683). By thinking about risk as relational, ‘slipping’ emerges as an under-explored hazard on Shore Platforms, despite being the main contributor to how lifesavers, themselves, unintentionally entered the sea. This study shows that the prevailing way of framing risk—perpetuated by the media and expert risk models—is often divorced from how risk is perceived by ‘experiential-experts’. This suggests coastal risk policy needs to integrate perceptions of the socio-environmental interactions that produce risk with the aim of accommodating the relational ways people perceive risk on Shore Platforms.

  • Wind Waves and Cliff Shaking on Macrotidal Shore Platforms: A Case-study from North Yorkshire, U.K.
    Journal of Coastal Research, 2018
    Co-Authors: David M. Kennedy, Mark E. Dickson, Emma C. Vann Jones, Nick Rosser
    Abstract:

    ABSTRACT Kennedy, D.M.; Vann Jones, E.C.; Dickson, M.E., and Rosser, N.J., 2018. Wind waves and cliff shaking on macrotidal Shore Platforms: A case-study from North Yorkshire, U.K. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 436–440. Coconut Creek (Florida), ISSN 0749-0208. Wind waves are a major erosive agent on the rocky coast. The physical impact of waves is also important in driving erosion above the splash zone. This occurs through the transferral of energy into the bedrock by the action of wave breaking causing microseismic shaking. In this study we concurrently measure wave energy and resultant microseismic shaking on a macrotidal Shore Platform at Staithes, North Yorkshire, U.K. It is found that infragravity wave generation is limited when compared to microtidal coasts and where it does occur it is confined to the wave breaking zone. Cliff shaking ...

  • Where is the seaward edge? A review and definition of Shore Platform morphology
    Earth-Science Reviews, 2015
    Co-Authors: David M. Kennedy
    Abstract:

    Abstract Shore Platforms are erosional coastal landforms that have attracted scientific attention since the mid 19th century. The defining element of a Platform is width that is used in many calculations such as determining a Platform's evolutionary state or inferring how wave energy is distributed along the Shore. Although a critical variable, there are no uniform criteria for defining the seaward edge. Quantification of Platform width has been driven by site-specific variables, with the seaward edge defined on the basis of tides, morphology, biology, processes and sediment coverage. The lack of a uniform definition has meant that comparative studies are difficult and results are possibly spurious, as widths derived from very different criteria can vary by an order of magnitude just on the basis of which criteria is used to determine its edge. In this review a combination of morphologic and process elements is used to define the seaward edge of a Shore Platform. The development of strict criteria is especially needed in an environment of rising sea levels if measurements of landscape change are to be made. In addition, the advent of seamless datasets that cross the land–sea boundary means that the delineation of Platform morphology is no longer limited by physical access. This review concludes that the seaward edge of a Shore Platform will occur at or landward of wave base and should be defined as: the point where active erosion of the bedrock ceases, characterised by erosional features such as notches and block-plucking scars or the deposition of sediment of such a thickness that the underlying bedrock is not exposed during storm events.

  • the application of ground penetrating radar in delineating Shore Platform morphology a case study from wellington new zealand
    Journal of Coastal Research, 2013
    Co-Authors: Miles Calder, David M. Kennedy
    Abstract:

    ABSTRACT Calder, M. and Kennedy, D.M., 2013. The application of ground penetrating radar in delineating Shore Platform morphology: a case study from Wellington, New Zealand. Ground penetrating radar (GPR) is a new technique in field sciences and is now commonly applied to studies of coastal dunes and beaches. The technique has yet to be applied on hard rocky coasts, and its ability to discern subsurface stratigraphy has great potential for investigating landform evolution on tectonically active Shorelines where erosional surfaces are often buried by sediments derived from marine and nonmarine sources. In this study, we test the resolution of a 100- and 250-MHz GPR system on a series of Holocene uplifted Shore Platforms and gravel beaches in Wellington, New Zealand. The sediment thickness at the sites investigated ranged from a thin veneer to many meters and is composed of a mix of sand and gravel-sized material. It was found that the 100-MHz antenna did not have the resolution of the 250-MHz antenna and c...

  • Shore Platform development on an uplifting limestone island over multiple sea level cycles niue south pacific
    Geomorphology, 2012
    Co-Authors: David M. Kennedy, Helene T Marsters, Josephine L D Woods, Colin D Woodroffe
    Abstract:

    Abstract Niue is an uplifted limestone island, which preserves an atoll morphology with a sequence of terraces around its outer margin. A modern terrace fringes much of the island and this paper examines the extent to which this terrace can be considered accretionary and constructed by coral and coralline algae, or erosional and truncated by those processes that form Shore Platforms. The occurrence of Pleistocene limestone outcropping across this terrace and the continuation of caves and other karst features, dissecting the sub-aerial limestones, onto the forereef indicate the overall significance of erosion. At present live coral cover is restricted to isolated colonies growing in grooves, potholes and karstic channels eroded into the modern terrace surface. Coralline algae coat the outer margin of this terrace, and also veneer prominent surf benches that occur on the windward Shore, 1–2 m above the terrace surface. Terrace evolution on Niue therefore appears to be primarily erosional in origin. There is little accommodation space for reef growth and, as a result, accretional fringing reefs are absent around most of the island. Erosional processes have also dominated landscape evolution for at least the past few eustatic cycles. Fringing reef growth is absent or severely restricted during the last interglacial and occurs as sporadic small reefs on the seaward margin of an erosional terrace during the penultimate interglacial. The development of terrace features in uplifting reef settings does not necessarily originate through accretional reef processes and may in fact be entirely erosional. Although reef terraces are frequently depositional in other settings, those present on Niue indicate a predominance of erosion, indicating the need to discriminate emergent terraces in terms of the extent to which they are erosional or accretionary when using such features to reconstruct island palaeoenvironments.

Wayne J. Stephenson - One of the best experts on this subject based on the ideXlab platform.

  • Wave transformation across a macrotidal Shore Platform under low to moderate energy conditions
    Earth Surface Processes and Landforms, 2017
    Co-Authors: Wayne J. Stephenson, Larissa A. Naylor, Helen C.m. Smith, Bin Chen, Ralph P. Brayne
    Abstract:

    We investigate how waves are transformed across a Shore Platform as this is a central question in rock coast geomorphology. We present results from deployment of three pressure transducers over four days, across a sloping, wide (~200 m) cliff-backed Shore Platform in a macrotidal setting, in South Wales, United Kingdom. Cross Shore variations in wave heights were evident under the predominantly low to moderate (significant wave height < 1.4 m) energy conditions measured. At the outer transducer 50 m from the seaward edge of the Platform (163 m from the cliff) high tide water depths were 8+ m meaning that waves crossed the Shore Platform without breaking. At the mid Platform position water depth was 5 m. Water depth at the inner transducer (6 m from the cliff Platform junction) at high tide was 1.4 m. This shallow water depth forced wave breaking, thereby limiting wave heights on the inner Platform. Maximum wave height at the middle and inner transducers were 2.41 and 2.39 m respectively and significant wave height 1.35 m and 1.34 m respectively. Inner Platform high tide wave heights were generally larger where energy was up to 335% greater than near the seaward edge where waves were smaller. Infragravity energy was less than 13% of the total energy spectra with energy in the swell, wind and capillary frequencies accounting for 87% of the total energy. Wave transformation is thus spatially variable and is strongly modulated by Platform elevation and the tidal range. While Shore Platforms in microtidal environments have been shown to be highly dissipative, in this macro-tidal setting up to 90% of the offShore wave energy reached the landward cliff at high tide, so that the Shore Platform cliff is much more reflective.

  • New insights on the relative contributions of coastal processes and tectonics to Shore Platform development following the Kaikōura earthquake
    Earth Surface Processes and Landforms, 2017
    Co-Authors: Wayne J. Stephenson, Mark E. Dickson, Paul Denys
    Abstract:

    We describe the immediate impact of the 14 November 2016 Kaikoura magnitude 7.8 (Mw) earthquake on Shore Platforms and cliffs around Kaikoura Peninsula. The earthquake caused an instantaneous uplift of ~1.01 m of the peninsula. We resurveyed 7 profiles previously used for erosion monitoring and observed changes in the configuration of the Shoreline. The coseismic uplift has fundamentally changed the process regime operating on the Platforms and altered the future trajectory of Shore Platform and cliff development. Our observations highlight the interplay of waves, weathering, biology and tectonics. At this location tectonism strongly modulates the process regime, driving instantaneous changes in morphology and altering rates and patterns of erosion. Finally, the uplift of the Kaikoura coast has implications for changing resilience to climate change and sea level rise.

  • Long term Shore Platform surface lowering rates: Revisiting Gill and Lang after 32 years
    Marine Geology, 2012
    Co-Authors: Wayne J. Stephenson, David M. Kennedy, R.m. Kirk, Brian Finlayson, Zhongyuan Chen
    Abstract:

    Abstract In 1978 E.D. Gill and J.G. Lang installed 53 micro-erosion meter (MEM) sites on Shore Platforms along the Otway coast in south eastern Australia. Surface lowering rates were originally determined from 2 yr of measurements (1979 and 1980) and showed that the mean annual rate of lowering from all sites was 0.37 mm/yr − 1 . We re-measured these MEM sites 32 yr after the first set of readings were taken in February 1979. We relocated 49 of the original 53 bolt sites and were able to measure 45 of them. From the sites we measured, the mean annual rate of Shore Platform lowering was 0.31 mm/yr − 1 . Rates of surface lowering on Shore Platforms are commonly reported from studies of only two or three years and only one other record exceeds 30 yr (Kaikoura Peninsula, NZ; 1.09 mm/yr − 1 ), in that case fewer than half of the original bolt sites were functioning because erosion had removed bolts. Along the Otway coast rates of erosion are much slower hence the greater number of still readable sites after 32 yr. Compared to other micro-erosion meter studies the rates reported here are at the lower end of the range of values from around the world but nevertheless consistent with rates from the Otway Coast and others in similar lithology. We found no statistical difference between erosion rates calculated over 2 yr (1979 to 1980) and 32 (1979 to 2011) years supporting the view that Shore Platform lowering rates measured over 2 yr are representative of decadal scales.

  • Analysis of relationships between micro-topography and short- and long-term erosion rates on Shore Platforms at Kaikoura Peninsula, South Island, New Zealand
    Geomorphology, 2010
    Co-Authors: Robert Inkpen, Wayne J. Stephenson, R.m. Kirk, Maree A Hemmingsen, S.a. Hemmingsen
    Abstract:

    Using long-term data sets of erosion rates for the Shore Platform at Kaikoura it is possible to assess the relationships between erosion rates over two and ten years. Erosion rates do not tend to vary significantly between the two measurement periods. Using linear regression analysis a difference in the nature of topographic change is identified between mudstone and limestone Shore Platforms. The mudstone Platforms show a consistent mode of topographic change, parallel retreat or smoothing, between the short and long terms. Limestone Shore Platforms show no consistent mode of topographic change. It is suggested that the consistent behaviour of the mudstone Platforms occurs because the mudstone surface is responding as a single unit at this scale of measurement. Erosion rates tend to increase with distance from the seaward edge of the Platforms and this may reflect the increasing significance of wetting and drying cycles, as well as the increasing mix of erosional processes as sub-aerial processes increase in importance. This changing mix of erosional processes may also explain the variations in gradient coefficients between short- and long-term erosion rates with distance from the seaward edge of the Platforms.

  • Rock Strength: A Control of Shore Platform Elevation
    Journal of Coastal Research, 2006
    Co-Authors: Lukar E. Thornton, Wayne J. Stephenson
    Abstract:

    This study determined whether a previous laboratory finding relating Platform elevation to rock strength could be verified when tested in the field. Testing took place along the Otway coast in southeastern Australia. Fourteen Platforms were profiled using a total station while rock strength tests were performed with a type L Schmidt hammer. Results established that higher mean Platform elevation correlated with increased rock strength (r = 0.661, p < 0.05). This confirmed that a relation exists between elevation and rock strength when tested in the field. This finding has implications for the interpretation of Shore Platforms and marine terrace elevations in relation to sea level.

Paul S Kench - One of the best experts on this subject based on the ideXlab platform.

  • an exploratory numerical model of rocky Shore profile evolution
    Geomorphology, 2016
    Co-Authors: Hironori Matsumoto, Mark E. Dickson, Paul S Kench
    Abstract:

    Abstract Rocky Shores occur along much of the world's coastline and include a wide range of coastal morphologies, such as intertidal Shore Platforms. Considerable research effort has been placed on trying to understand developmental processes on rocky Shores, but progress has been forestalled because these landscapes develop slowly and preserve little evidence of evolution through time. This paper presents a new exploratory numerical model developed to study long-term Shore profile evolution on rock coasts. The model purposely considers only a limited number of processes, each represented in a highly abstracted way. Despite these simplifications, the model exhibits a large range of emergent Shore profile shapes. This behavior is enabled both by broader spatial representation of the driving erosion forces and the flexibility provided by a grid discretization scheme. Initial model testing shows the development of varied rocky profile geometries, ranging from steep plunging cliffs, cliffs with narrow benches, and cliffs with a variety of Shore Platform shapes. Most of the model geometries are similar to those observed in the field, and model behavior is robust and internally consistent across a relatively large parameter space. This paper provides a detailed description of the new model and its subsequent testing. Emphasis is placed on comparison of model results with published field observations in which morphometric relationships are described between Shore Platform gradient and tidal range, and Platform elevation and Platform width. The model adequately simulates these morphometric relationships, while retaining its ability to simulate a wide range of profile shapes. The simplicity of process representations, and the limited number of processes implemented, means that model outputs can be interpreted reasonably easily. Hence, an opportunity is now provided, following the testing described in this paper, to use the model to systematically investigate the broader controlling conditions on rock Shore profile development.

  • Generalised observations of wave characteristics on near‐horizontal Shore Platforms: Synthesis of six case studies from the North Island, New Zealand
    New Zealand Geographer, 2016
    Co-Authors: Hiroki Ogawa, Mark E. Dickson, Paul S Kench
    Abstract:

    Most field studies of wave processes on Shore Platforms in front of eroding cliffs focus on a single site, revealing aspects of wave dynamics at that location. Here, we analyse data from six Platforms around northeastern New Zealand and describe the fundamental control of Shore Platform width, gradient and elevation on wave processes, including greater attenuation of short-period waves at lower tidal stages and increases in longer period wave energy towards the cliff toe. These data suggest that empirical formulae developed from coral-reef environments provide better predictions of wave height on Platforms than formulae currently used in Shore Platform models.

  • hydrodynamic constraints and storm wave characteristics on a sub horizontal Shore Platform
    Earth Surface Processes and Landforms, 2015
    Co-Authors: Hiroki Ogawa, Mark E. Dickson, Paul S Kench
    Abstract:

    Few studies of wave processes on Shore Platforms have addressed the hydrodynamic thresholds that control wave transformation and energy dissipation, especially under storm conditions. We present results of a field experiment conducted during a storm on a sub-horizontal Shore Platform on the east coast of Auckland, New Zealand. Small (  2.5 times the gravity wave height (0.05–0.33 Hz) is necessary for waves to propagate onto the Platform without breaking. On the Platform surface the wave height is a direct function of water depth, with limiting maximum wave height to water depth ratios of 0.55 and 0.78 at the centre of the Platform and cliff toe, respectively. A relative ‘Platform edge submergence’ (water depth/water height ratio) threshold of 1.1 is identified, below which infragravity (<0.05 Hz) wave energy dominates the Platform energy spectra, and above which gravity waves are dominant. Infragravity wave height transformation across the Platform is governed by the relative Platform edge submergence. Finally, the paper describes the first observations of wave setup on a Shore Platform. During the peak of the storm, wave setup on the Platform at low tide (0.21 m) is consistent with measurements from planar sandy beaches, but at higher tidal stages the ratio between incident wave height and maximum setup was lower than expected. Copyright © 2014 John Wiley & Sons, Ltd.

  • Hydrodynamic constraints and storm wave characteristics on a sub‐horizontal Shore Platform
    Earth Surface Processes and Landforms, 2014
    Co-Authors: Hiroki Ogawa, Mark E. Dickson, Paul S Kench
    Abstract:

    Few studies of wave processes on Shore Platforms have addressed the hydrodynamic thresholds that control wave transformation and energy dissipation, especially under storm conditions. We present results of a field experiment conducted during a storm on a sub-horizontal Shore Platform on the east coast of Auckland, New Zealand. Small (  2.5 times the gravity wave height (0.05–0.33 Hz) is necessary for waves to propagate onto the Platform without breaking. On the Platform surface the wave height is a direct function of water depth, with limiting maximum wave height to water depth ratios of 0.55 and 0.78 at the centre of the Platform and cliff toe, respectively. A relative ‘Platform edge submergence’ (water depth/water height ratio) threshold of 1.1 is identified, below which infragravity (

  • sea cliff retreat and Shore Platform widening steady state equilibrium
    Earth Surface Processes and Landforms, 2013
    Co-Authors: Mark E. Dickson, Hiroki Ogawa, Paul S Kench, Andrew Hutchinson
    Abstract:

    We challenge the notion of steady-state equilibrium in the context of progressive cliff retreat on micro-tidal coasts. Ocean waves break at or close to the abrupt seaward edge of near-horizontal Shore Platforms and then rapidly lose height due to turbulence and friction. Conceptual models assume that wave height decays exponentially with distance from the Platform edge, and that the Platform edge does not erode under stable sea-level. These assumptions combine to a steady-state view of Holocene cliff retreat. We argue that this model is not generally applicable. Recent data show that: (1) exponential decay in wave height is not the most appropriate conceptual model of wave decay; (2) by solely considering wave energy at gravity wave frequencies the steady-state model neglects a possible formative role for infragravity waves. Here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances (and longer timescales) than imaginable under the established conceptual model. Copyright © 2013 John Wiley & Sons, Ltd.