The Havant, Portsmouth and Gosport Group have developed a new shingle tracer study
technique using Radio-Frequency Identification (RFID) technology to track pebbles
moving around the East Solent coastline.
The pebbles are collected from the study area, drilled and a tag inserted, before
being measured and deployed back onto the beach. Each tracer pebble has a unique
identification number, and can be detected up to a metre deep within the beach without
the need to dig up the pebble.
The study is being carried out to supplement the South West Hayling Island Beach
£1,500 was provided by SCOPAC to assist with the preparation costs of the tracer
Clive Moon reports…
A total of 2,300 tracer pebbles have now been deployed around the Hayling and Portsea
Island open coast as part of an ongoing study to confirm the long-term sediment pathways
in the East Solent. The deployment locations include the nourished beach at Eastoke,
either side of the Langstone Entrance Channel and the Southsea frontage (Figure 1).
At Eastoke the tracers will be used in conjunction with volumetric analysis to improve
the understanding of losses from the nourished frontage.
At the Langstone Harbour entrance the tracers will be used to identify the rate and
direction of material from the open coast of Portsea and Hayling Island, into the
At Southsea Memorial the tracers will be used to confirm the path taken by material
placed on the upper beach to counter coastal erosion.
Eastoke deployment 1 - results to date
On Hayling Island, 10% of the original batch of 300 tracers deployed in September
2010 were detected in June 2011 after 9 months active in the beach. The tracers have
moved west between 25 and 1900 metres and continue to move in a westerly direction
towards the Langstone Harbour entrance channel.
Eastoke deployment 2 - results to date
Of the 1,000 tracers deployed immediately after the 2011 beach recycling operation
at Eastoke, 24% were detected after nearly three months active in the beach. The
tracers remain largely on the nourished frontage, and are following the anticipated
pattern of sediment transport. The tracers deployed at the drift divide have dispersed
in both directions along the nourished frontage but the centre of the mass of tracers
remains near the deployment location, whereas the batches placed further away from
the drift divide show a clearer pattern of movement downdrift in both directions.
Langstone Harbour entrance channel - results to date
On the Hayling Island side of the Langstone Harbour channel, 14% of the 250 tracers
deployed in January at Gunner Point were detected in the latest sweep. The tracers
continue to move westwards into the Langstone Harbour entrance channel.
The deployment on the west side of the Langstone Harbour entrance is returning interesting
results already, showing that sediment does bypass the Fort Cumberland outfall, initially
thought to act as a permanent obstruction to sediment moving along the Eastney spit.
Southsea deployments - results to date
Tracer pebbles have been deployed at the Southsea Memorial (between Southsea Castle
and Clarence Pier). These pebbles are currently moving in the anticipated east to
west direction as outlined in the SCOPAC Sediment Transport Study.
Still, the tracer pebbles deployed between Southsea Castle and South Parade Pier
are moving in a west to east direction which is not the assumed direction of drift
outlined in the SCOPAC Sediment Transport Study. Longer term monitoring of the tracer
pebbles will deduce if this is a seasonal variation or whether the drift is consistently
west to east.
A towed RFID antenna array has been constructed to assist in detecting a larger number
of tracer pebbles in one sweep (photo right). In addition, the handheld antenna
has had additional batteries installed to increase the survey duration between recharges.
The tracer pebbles can be detected up to a 1 metre depth. Those tracer pebbles
not recovered will either be buried too deep in the beach or will be taken offshore.
The study is programmed to finish in March 2012.
SCOPAC has awarded the Havant, Portsmouth and Gosport Group a further £4,000 for
2012-2013 to undertake additional sediment tracer study trials.