The precision and accuracy of measuring micro-scale erosion on shore platforms

Shore platforms evolve over millennial scales but understanding precisely how instantaneous processes scale over these longer periods is a major scientific quandary. A reason for this, is that erosion often occurs on the granular scale and measurement of magnitude and frequency of this decay is difficult. Over the past 50 years, a number of techniques have been used to quantify the micro-scale (0.01–10 mm) erosion of coastal bedrock, from direct surface contact techniques to those which involve remote sensing. The micro-erosion meter (MEM) and traversing micro-erosion meter (TMEM) are the most common techniques, recording erosion rates from <0.1 to 5 mm/yr on rock surfaces of c. 50 cm2. The traversing erosion beam (TEB) is specifically designed to measure rapid erosion (>10 mm/yr) while the Swantesson laser scanner (SLS) and close-range Structure-from-motion (SfM) photogrammetry have been used for observation of larger rock surfaces of 0.2 m2. The rock tablet method is used to investigate the individual processes operating on downwearing. By comparing their advantages and disadvantages, the T/MEM is suggested to continue to play an important role in monitoring surface lowering in conditions where the total erosion is 20 mm over the monitoring period, with close-range SfM recommended as ideal for quantifying erosion of 2–50 mm. However, all the instruments are biased in the field conditions under which they can be operated, and it is important for researchers to contextualise their measured surfaces in regards to a whole platform. Future studies will benefit from the combination of the ground-based methods with new techniques that provide finer morphological features at the regional scale or interpret the evolution of shore platforms over long timescales.