Presentation for Southern Coastal Group

Sediment Tracer Study

The River Hamble to Portchester Coastal Flood & Erosion Risk

Management Strategy

David Picksley – Coastal Engineer

• Introduction to the study

• Method

• Deployment sites

• Results to date

• Future monitoring

• Questions

Introduction to the tracer study

• Native pebbles tagged and deployed at specific locations

• Periodic surveys of the deployment site to detect tagged pebbles and track movement

• Used to examine small scale sediment transport studies around localised areas or structures

• Present case study to inform the coastal processes report for the RHPS (Fareham & Gosport)

Pebbles laid out in a

tray ready to be jetted

Method

Native pebbles collected from potential deployment sites

Side View

Plan View

Example RFID tags

Radio-frequency identification (RFID) is the wireless non-contact use of

radio-frequency electromagnetic fields to transfer data

‘Life expectancy’ of

approximately 50 years

• Tagged pebbles then catalogued

Each pebble:

• Numbered

• Weighed

• Photographed

• X, Y & Z axis measurements recorded

Deployment sites

©2013 Google ·

TerraMetrics

1

2

3

Stokes Bay Lee-on-the-Solent Solent Breezes

Example deployment locations

500 pebbles deployed in 5 batches of 100 at each of the 3 deployment sites

during March 2013

Pebbles deployed at MSL along existing Regional Monitoring profile lines

Results to date

Pebbles deployed in March 2013

1st survey after 1 week

2nd survey after 4 weeks (April 2013)

3rd survey after 12 weeks (May 2013)

4th survey after 24 weeks (August 2013)

Survey extents increased proportionally for each successive survey

Location Detection Rates (%)

Survey 1

March

Survey 2

April

Survey 3

May

Survey 4

August

Solent Breezes 14.6 9.8 11.8 11.6

Lee-On-The-Solent 17.8 5.2 13.6 11

Stokes Bay 13.8 9.4 13 13.8

SOLENT BREEZES

LEE ON THE SOLENT

STOKES BAY

Lee-on-the-Solent

•Notable movement of pebbles to the east at all deployments

•Pebbles free to move beyond rock groyne structures in to adjacent groyne bays

•Results suggest there is continuous sediment transport along this frontage,

predominately from west to east.

Tracer study findings

Solent Breezes

•General trend for westerly movement towards the Solent Breezes holiday park, for

deployments 1, 2 and 3. Easterly movement at deployment 5.

•The slipway at the caravan site may be acting as a potential barrier. No pebbles

were found west of this point.

• Pebbles have moved in both directions at deployment 4 (possible drift divide near

this location)

•Movement of pebbles to the east at deployment site 1 & 2, adjacent to River Alver

outlet, suggests strong easterly current around this headland

•Evidence for offshore transport of material as pebbles transported offshore within

River Alver tidal delta.

•Pebble movement both east and west along central Stokes Bay beach frontage.

•Lifeboat station slipway may act as a barrier to sediment transport further east

Stokes Bay

Note:

Prolonged period of easterly winds after initial deployments may have

influenced early survey results

Future Monitoring

• Next survey planned for March 2014

- one year after initial deployments

• Additional 500 pebbles already tagged and available for

future deployments as and when necessary

• Current working with Phd student at Sussex University

Questions or Comments?