Tracer Pebble Studies - Hill Head

A small-scale beach tracer study was carried out over a six-month period along the Hill Head frontage in October 2016. The study proved valuable the monitoring of movement of additional beach material placed on the frontage to prevent the continued loss of beach in front of the old sea wall.


Figure showing the location of the deployment sites at Hill Head, indicated by the yellow star


Deployments

On the 7th October 2016 a total of 46 tracer pebbles were deployed at two pre-defined locations on the site adjacent to Hill Head Sailing Club (See figure below). Deployment of the tracers occurred after a small-scale beach recharge to groyne bays 1 to 5 in September/October 2016. At both locations pebbles were deployed at approximate Mean Sea Level (MSL) 0.16 mODN to ensure a comparable scattering around each release point.

 Figures: Deployments at the two sites at Hill Head


Results

Retrieval surveys were carried out between October 2016 and April 2017. Detection rates between the two deployment sites varied greatly but generally retrieval rates have remained fairly steady after a sharp initial decrease in the number of pebbles found between the first and second survey. On average, location 2 had 20% higher retrieval rates than location 1.

The pebbles had been painted red to test the ability for visual monitoring together with electronic detection. However, it is thought that many of the pebbles were picked up by passers-by and taken away from the site! This could explain why a number of the pebbles were not found again after deployment. Subsequent studies have not used painted pebbles!

Click here to see the results of the Hill Head study full details of this study, including the results from the retrieval surveys can be found in the following report.