Sediment Tracer Studies Phase I, East Solent
Minor funds contribution 2010-11 \ Havant, Portsmouth & Gosport Coastal Partnership: £1,500
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 were 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 tags do not rely on battery power and should work for 50 years.
See www.escp.org.uk/tracer-pebble-studies for further detail on the technique used.
The study was carried out to supplement the South West Hayling Island Beach Management Study. £1,500 was provided by SCOPAC to assist with the preparation costs of the tracer pebbles.
Sediment Tracer Report (PDF, 2Mb)
Clive Moon reported…
“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 channel.
- 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
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
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
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.
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. 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 Coastal Partnership a further £4,000 to undertake additional sediment tracer study trials in 2012-2013.