Swirad, Z.M. and Rosser, N.J. and Brain, M.J. (2019) 'Identifying mechanisms of shore platform erosion using Structure-from-Motion (SfM) photogrammetry.', Earth surface processes and landforms., 44 (8). pp. 1542-1558.
Shore platforms control wave energy transformation which, in turn, controls energy delivery to the cliff toe and nearshore sediment transport. Insight into shore platform erosion rates has conventionally been constrained at mm-scales using micro-erosion metres, and at m-scales using cartographic data. On apparently slowly eroding coasts, such approaches are fundamentally reliant upon long-term observation to capture emergent erosion patterns. Where in practise timescales are short, and where change is either below the resolution or saturates the mode of measurement, the collection of data that enables the identification of the actual mechanisms of erosion is hindered. We developed a method to monitor shore platform erosion at millimetre resolution within metre-scale monitoring plots using Structure-from-Motion photogrammetry. We conducted monthly surveys at 15 0.25 m2 sites distributed across the Hartle Loup platform in North Yorkshire, UK, over one year. We derived topographic data at 0.001 m resolution, retaining a vertical precision of change detection of 0.001 m. We captured a mean erosion rate of 0.528 mm yr-1, but this varied considerably both across the platform and through the year. We characterised the volume and shape of eroded material. The detachment volume-frequency and shape distributions suggest that erosion happens primarily via removal of shale platelets. We identify that the at-a-point erosion rate can be predicted by the distance from the cliff and the tidal level, whereby erosion rates are higher closer to the cliff and at locations of higher tidal duration. The size of individual detachments is controlled by local micro-topography and rock structure, whereby larger detachments are observed on more rough sections of the platform. Faster erosion rates and larger detachments occur in summer months, rather than in more energetic winter conditions. These results have the potential to form the basis of improved models of how platforms erode over both short- and long-timescales.
|Keywords:||Bedrock erosion, Micro-erosion, Down-wearing, Shore platforms, Rocky coasts, Structure-from-Motion|
|Full text:||(AM) Accepted Manuscript|
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|Publisher Web site:||https://doi.org/10.1002/esp.4591|
|Publisher statement:||This is the accepted version of the following article: Swirad, Z.M., Rosser, N.J. & Brain, M.J. (2019). Identifying mechanisms of shore platform erosion using Structure-from-Motion (SfM) photogrammetry. Earth Surface Processes and Landforms 44(8): 1542-1558, which has been published in final form at https://doi.org/10.1002/esp.4591. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.|
|Date accepted:||24 January 2019|
|Date deposited:||31 January 2019|
|Date of first online publication:||01 April 2019|
|Date first made open access:||01 April 2020|
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