Preston Tracer Study

Dave Picksley, Environment Agency and Sacha Neill, Eastern Solent Coastal Partnership: £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 Eastern Solent Coastal Partnership 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.

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.

Pebble preparation is now underway with 600 native pebbles collected from site ready for water-jetting and tagging with RFID tags. It is anticipated that the tracer pebbles will be deployed this winter and will be surveyed over the course of a year. The results of any tracer pebble movement will be linked to hydrodynamic conditions during analysis reporting and will inform future beach management activities and further understanding of localised coastal processes.