Methods for measuring shore platform micro erosion: A comparison of the micro-erosion meter and laser scanner

Between 1999 and 2001, accurate measurements of downwearing rates were made with micro-erosion meters (MEMs) and with laser scanners at twenty coastal sections on rock shore platforms in France, Portugal, Spain, Sweden and the UK. The two methods are compared and their possibilities and limitations are discussed. The MEM is versatile and easy to use on all parts of shore platforms. The laser scanner gives far more detail and accurate micro maps can be made of scanned sites measuring up to 40 × 40 cm. Because a complete scan takes more than an hour, measurements cannot be made near the low-tide mark and the size of the machinery prevents use in confined spaces. Results from the two methods are somewhat divergent. The reason is the great spatial variability in rock breakdown even within very small areas and MEM measurements are only spot values. Average downwearing rates are several millimetres per annum in soft chalks on both sides of the English Channel while they are almost negligible in crystalline rocks in micro-tidal environments on Swedish coasts. Breakdown rates on exposed coasts in other rock types and on coasts in hard limestone lie between the two extremes.