The Coastal Partnership is currently undertaking a new and innovative study using tagged tracer pebbles deployed around the East Solent coastline. It is hoped that by deploying and tracking these pebbles along our coastline it will provide us with valuable information on the direction of sediment transport movement along our beaches.
Historically various tracer techniques have been utilised, ranging from painting native pebbles to aluminium tracers and copper cored resin pebbles. Each of these techniques has limitations when deployed over longer periods of time, e.g. months to years, as required to study attrition rates, and establish long-term sediment pathways.
A new tracer technique has been developed utilising radio-frequency identification (RFID) technology to track objects in beaches. The system has three main components; PIT (Passive Induced Transponder) tags, an antenna & reader, and PDA or datalogger. PIT tags are small glass encapsulated capsules that broadcast a unique identification number when detected. The tags do not contain an internal power source, and can be embedded within pebbles taken from beaches in the study area. When embedded within suitable pebbles the tags can be used for long-term deployments with no risk of identification markings wearing off the exterior of the pebble. Once detected the position of the pebble can be recorded using GPS technology, and if required the pebble can be recovered from the beach to establish a precise location and burial depth.
Three RFID detection units have been purchased or constructed to enable the efficient location of tagged pebbles once deployed; a short-range wand, a hand-held antenna & a towed antenna array. The detection range varies between antennas, and is also affected by the size and orientation of PIT tag being detected.
The hand-held wand has a limited read range, typically less than 0.2m, and is used during tagging of the pebbles and to home in on individual tags for recovery from the beach. The hand-held antenna has a greater read range, upto one metre, and is used to sweep the beach on foot. The towed array consists of four antennas, covering a 5 metre width of beach. The towed array also has a read range of upto one metre, and is suitable for use on wide open flat areas of the beach where a quad bike can be used to tow the array across the surface.