‘Robotic’ pebbles with GPS monitoring units deployed on Dorset seashores

High tech marker pebbles with GPS devices attached have been used on Dorset beaches. The project aims to track the pebbles to help scientists understand how sediment is transported across our coastline.

A whopping 1,200 pebbles were first dumped into the sea on May 3 at six different locations along the Bridport coastline between West Bay and Burton Freshwater. The year-long project is expected to provide “valuable information on sediment transport rates and directions along the West Bay Front,” say Coastal Partners – the brains behind the project.

Coastal Partners is a group that monitors coastal flooding and erosion risk on 162km of coastline, representing local authorities in Portsmouth, Fareham, Gosport and Havant. The team has partnered with Dorset Council and Bournemouth, Christchurch and Poole (BCP) Council to collect data on the rocks.

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Impressively, the Coastal Partners team took the pebbles found on beaches around Dorset and carefully inserted a GPS tracking device or Radio Frequency Identification (RFID) kit into each rock to monitor its movements . The devices are set directly into the rock and sealed so that the pebble blends seamlessly with the rest of the beach.

A spokesman for Coastal Partners stated: “The pebbles used for each tracer study are the exact pebbles found at the surveyed site! In May 2021, a total of 1,200 native pebbles were collected from the site and sprayed with water to create a hole into which the small RFID tags could be inserted. The hole is then sealed with resin and is no longer visible to the naked eye.”

They also explained the importance of using the same materials to monitor the movements of the pebbles. The spokesman continued, “The use of native material from the study site is important so that the marker pebbles behave similarly once deployed.

“The tag inserted into each marker pebble transmits a unique ID number when detected with dedicated GPS devices. This ensures that the position of each individual pebble can be tracked over a long period of the year and then further analysis can be performed.”

The pebbles blend seamlessly with the rest of the landscape

While the pebbles can be detected when they are on the beach surface, they become undetectable once they are below the waterline and only become detectable again when the pebbles come back to shore. Although there is a possibility that the stones could be washed away from the coast, scientists believe that the movement of the waves is what keeps the pebbles close to the Dorset coast.

“Since deployment, it appears that some marker pebbles have moved offshore out of bounds, but it is likely that these marker pebbles will move back onshore as the wave climate changes and are ready to be discovered later in the study to become,” said the Coastal spokesman for the partners.

The study is expected to contribute to a better understanding of coastal erosion and sediment movement on the Dorset coast. The data should help to maintain and manage beaches in the future, it is said.

Coastal Partners said: “Monitoring the movement of the marker pebbles will reveal the direction and speed at which material is moving along this front. The results of this study will then feed into and support future beach management activities and programs around West Bay.”

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