Recording inter-annual changes on a boulder beach in Galicia, NW Spain using an unmanned aerial vehicle

An unmanned aerial vehicle (UAV) was flown over a boulder beach (area 20 000m(2)) on the southern coast of Galicia (northwestern Spain) in May 2016, continuing earlier work based on flights over the same beach in July 2012, May 2013, and late March 2014. Digital surface models (DSMs) with 1.8cm resolution were constructed from the 2014 and 2016 data to identify changes in beach morphology over the intervening period. Analyses were conducted using a Limit of Detection (LoD) of 0cm and 3.71cm. In both cases, the analyses showed that erosion dominated over 19% of the beach area. Accretion occurred over the rest of the beach, which acquired an additional 1500m(3) of material over the study period. Re-analysis of the data from earlier flights suggested that erosion dominated on the beach in 2012-2013 and deposition in 2013-2014. Without any clear relationship between beach behaviour and storm severity during each winter period, it is proposed that gravitationally induced erosion and storm-wave induced deposition are the result of perturbations about an equilibrium beach gradient. The UAV data also suggested that an essentially random component modulates regional patterns of movement. (c) 2018 John Wiley & Sons, Ltd.