Mark Dickson

Dynamic simulation and visualisation of coastal erosion

A key requirement for effective coastal zone management is good knowledge and prediction of land erosion rates due to encroachment of the sea. However, in addition to demarcation of the hazard through modelling and mapping, a policy of risk mitigation necessitates significant attention should also be addressed to communicating the transient behaviour of the predictions and associated uncertainty. With climate change and sea level rise implying that historical rates of change may not be a reliable guide for the future, enhanced visualisation of the evolving coastline has the potential to improve awareness of this changing risk. This visual content is developed by linking scientific modelling with the transformation of digital elevation models, and then using GIS to integrate other spatiotemporal content. The resulting high-resolution visualisations may meet demands from decision-makers for tools to communicate scientific results more effectively, due to their realism and apparent authenticity. Nevertheless they can also produces a tension with the underlying scientific content because of the necessary extrapolation of extra detail, and the lack of established procedures to communicate the resulting uncertainty in the visualisation. Coastal managers also have concerns about releasing the visualisations to the general public. These issues are explored through analysis of future cliff erosion in Norfolk on the eastern coast of Great Britain.

Carbonate sedimentation on subtropical shelves around Lord Howe Island and Balls Pyramid, Southwest Pacific

Abstract Lord Howe Island and Balls Pyramid are mid-oceanic basaltic islands, 20 km apart, in the Tasman Sea. Subaerial carbonates dating back at least 350 ka and a Holocene fringing reef occur on Lord Howe Island. No reefs or subaerial carbonate deposits occur on Balls Pyramid. Both islands sit near the centre of wide shelves that are on average 40–50 m deep with a distinct break of slope, between 70 and 100 m depth. The Lord Howe shelf is characterised by a discontinuous drowned ridge, which rises to 30 m depth and is located between the mid-shelf and shelf edge. It is composed of limestone and is interpreted as a fossil reef being veneered by Holocene coralline algae. Early to Middle Holocene branching-coral gravel is found in the lee of the fossil reef, indicating limited give-up reef growth during the Postglacial transgression. The surface sediments across the shelf are calcareous, except in close proximity to the island where volcanic content is significant. Coralline algae represent the dominant grain type, with minor amounts of coral. Bryozoans, Halimeda and foraminifera are common; however, they are not volumetrically important. Rhodoliths and molluscs occur near the shelf edge, and appear to have accumulated at times of lower sea level. These subtropical shelves are mid-oceanic examples of the transition between tropical and temperate carbonate sedimentation. They indicate the potential for carbonate production on broad planated shelves outside reef-forming seas.

Cliffed coasts of New Zealand: Perspectives and future directions

Abstract About one‐quarter of New Zealands shoreline is composed of cliffs. In some areas erosion rates are sufficiently rapid to be of concern to planners, whereas other cliffs have eroded imperceptibly slowly over human timescales. This paper reviews work conducted on New Zealands cliffed coasts, from the pioneering studies of Sir Charles Cotton, who used Davisian theoretical methods to elucidate the evolution of hard‐rock coasts, to Jeremy Gibbs nationwide benchmark measurements of historical erosion rates. This review is augmented with a description of state‐of‐the art methods in use globally for investigating processes of cliff evolution. Key methods identified include detailed measurements using the micro‐erosion meter as well as novel geophysical methods of studying cliff movement under wave loading. Such process‐based studies build on previous research that has been largely confined to explanatory description and observation. It is recognised that the combined impact of such studies has been relatively muted, owing particularly to the difficulty of unravelling ambiguous process‐form interactions. However, the increasingly widespread availability of terrestrial and aerial remote laser scanning systems now provides an opportunity to re‐invigorate such studies by extending the scale from local to regional. The paper concludes by outlining prospects within New Zealand for further research. In particular, the development and use of numerical models is seen as an important avenue both for clarifying some basic behaviours observed on cliffed coasts, and for studying the likely response of eroding cliffs to future climate change.

A GIS TOOL FOR ANALYSIS AND INTERPRETATION OF COASTAL EROSION MODEL OUTPUTS (SCAPEGIS)

The SCAPE (Soft Cliff and Platform Erosion) model of cliffntoe retreat, and a cliff-top recession model, have been linked with a new flexible GIS tool (SCAPEGIS) to provide visualisation and analytical capability for the model results. 45 model runs exploring different sealevel rise and wave climate scenarios and protection choices are available. Outputs are available in the form of maps, dynamic visualisation, and descriptive statistics of key parameters such as cliff toe and cliff top position. It also allows analysis with other datasets such as land use and building location for impact evaluation, and hence supports shoreline management and cliff-top land use planning. Some preliminary results and ideas for further development are presented.