Measuring beach pebbles and cobbles abrasion with RFID technology on a mixed sand and gravel beach, South Island, New Zealand

The measurement of in situ abrasion has been investigated since the early 20th Century and it is thought to represent a significant loss from coastal sediment budgets of some mixed sediment beaches. Traditional methods of tracking pebbles or cobbles to assess abrasion have numerous shortcomings, however, Radio Frequency Identification (RFID) now makes it feasible to track and relocate tagged particles on a beach. In this study, RFID was used to quantify pebble and cobble abrasion on a mixed sand and gravel beach, South Island, New Zealand. A total of 228 greywacke pebbles and cobbles were tagged and released on two occasions on the study beach. Some of these pebbles and cobbles were relocated on the first two days after release and then again at intervals of months with a maximum recovery period of 15 months. Particles were weighed each time they were relocated to assess abrasion and their positions recorded to calculate the distance travelled from the initial release point. The mean daily abrasion rate of pebbles and cobbles was 0.02 %/day in weight, equivalent to 7.30 %/year in weight. A significant correlation was found between abrasion and transport distance and wave energy. These results contribute to the small database of abrasion rates for mixed sediment beaches. The study also provides detailed data on cross-shore and alongshore displacement, as well as burial depth. Comparison with previous studies from around the world suggests that a universally applicable abrasion rate for all mixed beaches is unattainable.