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Spatial Scaling in Geomorphology

Yuan et al., 2022

Downwearing rates of shore platform have been quantified with a number of ground-based techniques (such as the micro-erosion meter (MEM)), providing knowledge of the evolution of coastal landforms. However, it remains problematic to extrapolate the micro erosion results to the landform scale. This is because only a very small proportion of the platform is monitored and usually biased to flat rock surfaces. In this study, we used the shore platforms in south-eastern Australia, which has the world's longest continual erosion records, as an example to address the fundamental question of how to extrapolate across spatial scales. Surveying using an unoccupied aerial vehicle (UAV) – post-processing kinematic (PPK) – structure-from-motion (SfM) workflow, indicates the shore platforms at Marengo and Jump Rock have similar morphology. The generated mm-scale dataset was used to contextualize 4 and 12 MEM sites into the orthomosaics and digital surface models (DSMs) at each location. By using two different methods, we assessed how these monitored surfaces were representative of the morphology of the entire platform.

On average, the 4 MEM sites represented 52.2% of platform surfaces at Marengo and 73.2% with the 12 MEM sites at Jump Rock. To improve the representativeness of sampled surfaces, it was found that 20 randomly sampled MEM-size (4.33 × 10−3 m2) surfaces were able to represent (~90%) the landform morphology at the scale of 104 m2. The representativeness was only slightly improved by upscaling the surface size from original cm2, to dm2 (0.16 m2) and m2 (1 m2) scales, implying the importance of sample number over sample size. Using the cm-scale dataset covering a larger geographic region, a bias of MEM installation was found with all 43 MEM sites concentrated at the fast-eroding upper intertidal zone. An elevation-weighted erosion rate of 0.21 mm/yr was calculated, lower than the original mean of 0.25 mm/yr provided by the MEM network. Moreover, a spatial pattern of rock surface morphology was observed across the platform with higher slope and roughness at the seaward end, suggesting more intensive wave processes and varying erosion agents compared to those surfaces further inland.

This publication was led by Runjie Yuan (The University of Melbourne, Victoria, Australia) and Daniel Ierodiaconou from our group contributed to the publication.

Congrats to all the authors and the DU Marine Mapping Group!

To read the full article, click here.

Last edited on the July 30th, 2022.


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