Dredger Borr Busy with the River Parrett Trials

Image source: Somerset Drainage Boards Consortium - Phil Brewin
Image source: Somerset Drainage Boards Consortium – Phil Brewin

Van Oord’s water injection dredger Borr is currently working on the River Parrett, testing new methods of dredging Somerset’s rivers.

The dredging trials, funded by Somerset Rivers Authority, are being delivered by the Parrett Internal Drainage Board and their contractors Van Oord.

During the three-week trials, dredging will be carried out between Westonzoyland Pumping Station and Burrowbridge. The trials will provide valuable information on how effective water injection dredging can be at getting silt moving down to Bridgwater Bay and preserving the River Parrett’s capacity.

According to Cllr John Osman, SRA chairman, the new methods could offer Somerset big benefits. “If done at the right times, in the right places, they could be much cheaper, more effective, and better for the environment, local residents and farmers.”

How does water injection dredging work?

The water injection dredging is a cost-effective, hydrodynamic dredging technique for maintaining the depth of a river. Water injection dredger injects large volumes of water at a low pressure into the sediment, using pumps with a series of nozzles on a horizontal jetbar.

This fluidises the sediment by effectively overcoming the cohesion in fine-grained soils or internal friction of coarse-grained soils. The fluidised sediment then remains close to the river or channel bed, flowing down to deeper areas.

Staying close to the bed creates a density current that then, either by the force of gravity or through a natural or artificially created slope, flows downwards to deeper water. This all occurs with a minimum of disturbance to the equilibrium of the ecosystem.

In this way, instead of mechanical transportation, nature takes care of the sediment transport, making Water Injection Dredging under certain conditions a very cost-efficient dredging technique.