Measuring pebble abrasion on a mixed sand and gravel beach using abrasion baskets

Abstract

The abrasion of sediments on mixed sand and gravel beaches has important consequences for local sediment budgets as abrasion often accounts for the major loss of beach volume. Here we report an innovative method using abrasion baskets to measure abrasion in the swash zone of mixed sand and gravel beaches. This method offers significant advantages over laboratory-based tumbler experiments traditionally used to determine abrasion rates. The very high recovery rate from our method is also a significant advantage over previous field methods using radio frequency identification technology to measure abrasion where tagged particles are often lost. Either three or five abrasion baskets were placed across the swash zone on a mixed sand and gravel beach at Timaru, South Island, New Zealand, to measure the abrasion occurring on labeled sediments placed in the baskets. Over two experiments, results showed measurable abrasion across the swash zone with higher abrasion rates occurring in the middle of the swash zone and lower rates towards the swash limit and at the breaker zone. Results also illustrate the role of changing wave energy on abrasion loss. A relationship between particle size and abrasion rate was also found, similar to previous laboratory results reported in the literature. Our preliminary experiments lead us to define an abrasion zone and this idea may help shape future research on abrasion processes on mixed sand and gravel beaches.