Long term recovery rates obtained using RFID technology at a mixed beach

Abstract

Recovery rates were obtained by radio frequency identification (RFID) technology in pebbles and cobbles at San Felipe beach, Gran Canaria. The aim of this work was to define which factors affected the recovery of tagged gravels. Several tests were performed to determine the detection depth threshold, and 16 field experiments were carried out over seventeen months after tracer deployment on the beach. Recovery rates are highly variable with time, ranging from 72.2% in the first recovery session to 25.8% in the last one. Nevertheless, a nearly stable situation was found for the final eight months. Apart from the effect of time, there were several factors that affected the recovery rate. Some of these were related to the particle, such as the position of the tag within the particle, as well as its weight, size and shape. Two environmental factors were considered. First, the elevation of the tracer on the beach showed that the recovery rate was higher with particles located above the storm berm. Second, wave height, which showed no relation with recovery rates even though during the experiment significant storms and periods of calm took place.