Tracer Pebble Study, Preston Beach

Dave Picksley, Environment Agency and Sacha Neill, Coastal Partners: £5,000 (2018-2020)

In order to better understand the complex coastal processes around Preston Beach in Weymouth (Figure 1), SCOPAC is contributing £5,000 towards a tracer pebble study. 

The objectives of the study are:

  • To highlight the movement of sediment between Preston Beach rock groyne and Bowleaze Cove (west);
  • To investigate whether there is any evidence of change to the littoral drift pathways along Preston Beach since the SCOPAC (2004) and SCOPAC (2012) STS;
  • To explore the location of any transient drift divides.

Figure 1: Sediment transport pathways around Weymouth Bay taken from the updated SCOPAC Sediment Transport study (SCOPAC STS, 2012)

The Coastal Partners tracer study method utilises radio-frequency identification (RFID) technology to track the movement of material along the beach frontage. The system comprises of three main components; passive induced transponder (PIT) tags which broadcast a unique ID number when detected; an antenna/reader used to scan the beach and a data logger used to store the ID number and recorded location.

See Tracer Pebble Studies for further detail on the technique used.

The plan is for up to 6 deployments to be placed along the CCO monitoring profile lines at Preston Beach:

  • Deployments between the rock groyne to the southern end of Preston Beach and Overcombe: To ascertain longshore drift rates and direction between these two locations. The current understanding is that there is a weak north-eastwards drift which may be subject to periodic drift reversals;
  • One deployment between Overcombe and Bowleaze Cove (west): To understand whether material is accumulating down-drift at Bowleaze Cove.

Update June 2019: Approximately 600 tracer pebbles were prepared by the Coastal Partners during the winter of 2018/19. These were deployed in January 2019 and will be monitored for one year. There has been a good recovery rate for the larger Radio Frequency Identification (RFID) tags. Following issues with the frequency of the smaller Radio Frequency Identification Tags, additional small tracer pebbles will be made up to be re-deployed in the summer time. Findings will confirm sediment transport pathways which will inform future beach management activities at Preston beach.