Trialling a new approach to beach replenishment in Poole Bay

The Environment Agency has presented a report of the trial tests of a new approach to beach replenishment at Poole Bay.

The report revealed results of a year-long programme of fieldwork to monitor the behaviour of sand deposited in the nearshore zone off Canford Cliffs in Poole Bay.

The technique of replenishing beaches by deposition sand in the nearshore (sub-tidal) area is widely used in the Netherlands, but the project in Poole Bay was the first trial of the method in the UK. The material used was from maintenance dredging in Poole Harbour and thus was beneficial use of sediment that would otherwise have been dumped at sea.

The trial included 30,000m3 of material dredged from Poole Harbour that was deposited on the seabed approximately 350m offshore of Shore Road, Canford Cliffs. Hopper dredger Magni-R was used to discharge sand at the deposition site

Some 14 months after deposition, the mounds remained distinct features, approximately 2m high. The sediment had remained in situ, with a net loss of only ~1,000m3 (~3%) since deposition. Such small net volumes of sediment change are difficult to identify even from high precision bathymetric and topographic surveys, said EA in the report.

Although a sediment transport connection between the nearshore and the adjacent beach was proved (that is, nearshore deposition can replenish the beach), it remains difficult to assess the long-term fate of the material.

It is likely that both a larger quantity of material and more time are needed for sediment dispersal at this site to demonstrate long-term viability of nearshore replenishment as an alternative to traditional methods.

The Poole Bay nearshore beach replenishment trial monitoring was commissioned under the Flood and Coastal Erosion Risk Management Research and Development Programme (Project SC130035), funded by Defra, the Environment Agency and the Welsh Government, with additional contributions from the Borough of Poole, New Forest District Council (Channel Coastal Observatory) and SCOPAC (Standing Conference on Problems Associated with the Coastline).

To access the full report, please click here.

Photo: Dredger Magni-R in Poole Harbour/Photo courtesy of Poole Beaches´╗┐