Trialling a new approach to beach renourishment in Poole Bay – a programme of fieldwork by the Borough of Poole Coast Protection Team, and the Environment Agency 2018 report on the trial.
Lead Authority
Borough of Poole
Budget
£230,000
Start date
February 2015
Last updated
20 March 2018
Before and After images compare the beach in February and July 2015
Project Summary
The Nearshore Beach Replenishment Trial, endorsed and funded by the Environment Agency both locally and nationally, tested a new approach to beach renourishment in Poole Bay. The concept was to make use of locally dredged sediment and place it near the shore, allowing the prevailing waves and tidal currents to move material toward and along the beach. A similar approach, has been used widely in the Netherlands and more recently in Denmark. The trial was the first of its kind in the UK.
After 15 months, some material had renourished the beach but both a larger quantity of source material and more time would be needed demonstrate long-term viability of this technique. The success of the technique elsewhere would depend on site-specific conditions.
Overview: the area shown in the detail map is marked in red.
Overview: the area shown in the detail map is marked in red.
Detail map: approx 30,000 cu.m. of dredged material was placed as close as possible to site A on a set grid pattern.
Detail map: approx 30,000 cu.m. of dredged material was placed as close as possible to site A on a set grid pattern.
© Crown Copyright and/or database rights. Reproduced by permission of the Controller of Her Majesty’s Stationery Office and the UK Hydrographic Office
Method
The Marine Management Organisation granted the licence to allow the placing of sand in the sea. The works were undertaken between the 9th and 14th February 2015, when 30,000m³ of sand was placed on the sea bed approximately 400m offshore at Canford Cliffs Chine, in water between 5-8m deep.
Poole Harbour Commissioners provided the sand from maintenance dredging of Poole Harbour entrance, thereby recycling beach material back into the system, rather than dumping it offshore at a disposal site.
The trial site was selected owing to its position at the up-
Seven survey sets were collected by the Channel Coast Observatory over time. Each set consisted of a topographic survey of the beach and a bathymetric survey of the sea bed. Fluorescent sediment tracer studies were also undertaken to establish a link between the sediment deposited on the sea bed and the beach. An Acoustic Doppler Current Profiler (ADCP) measured the speed, direction and turbidity of water currents using sound waves.
The Results
- A short report on the trial’s aims & methods was produced by the project team in July 2016
- The Environment Agency published their final report in March 2018.
Winter trials of sand recycling on Poole’s beaches 2013/14
An earlier (Nov 2013) coast protection trial carried out by the same team sought to assess the volume of wind blown sand and the possibility of recycling sand on Poole’s beaches.
A metre deep hole was dug in the sand east of Flaghead Chine beach, and it was anticipated that the naturally occurring build-
Unfortunately the severe storms of Dec 2013 and Jan 2014 effectively put paid to the trial, removing significant quantities of sand from the system and bringing beach levels down to that of the metre deep trial hole dug out east of Flaghead Chine beach. The beach was monitored and it was hoped another trial could be arranged for a future date.
What could the trial have revealed?
This was a ‘learn-
We had hoped to assess:
- how much sand had migrated back to Flaghead Chine
- how much had been retained by Shore Road beach
- whether it is economically viable to use nature to help provide a long-
term and sustainable approach to managing our wide, sandy beaches.
Note: in the image above, the darker the red the greater the erosion. Blue represents areas of accretion (the accumulation of sand) recorded between 2007 and the present day; the darker the blue the greater the levels of accretion.