Posted on December 22, 2016
TRIALS of different dredging methods on the River Parrett have produced promising initial results, according to the Somerset Rivers Authority.
Tests of water injection dredging and agitation dredging and sophisticated monitoring, were carried out on sections of river between Westonzoyland Pumping Station and Burrowbridge.
The tests were carried out for the SRA by the Parrett Internal Drainage Board and contractors Van Oord over three weeks in November and early December.
The tests were then continued for a further two weeks upstream to Burrowbridge thanks to encouragement by early analyses of data.
Cllr John Osman, chairman of Somerset Rivers Authority, said: “We agreed to the IDB’s request for further trials because different methods of dredging potentially offer Somerset big benefits.
“Work done at the right times, in the right places, could be much cheaper, more effective, and better for the environment, local residents and farmers.
“Evidence so far suggests that we’re on the right lines – and no detrimental effects have been observed.
“But we need to keep getting the most useful experience and information that we can. So even though the dredging vessel has now gone, we’ll keep on monitoring throughout the winter. We need to understand not just the immediate effects of different dredging techniques, but what happens along the Parrett in the weeks and months afterwards.”
In water injection dredging, the idea is that river water is pumped through an injection bar positioned just above the bed of the Parrett and aimed at soft silts so they become super-saturated and travel, in a layer of their own, on an outgoing tide, where they disperse into the natural system.
Iain Sturdy, chief engineer at the Parrett IDB, said: “We have found that water injection dredging is capable of moving large volumes of material from the bed of the channel very quickly indeed. Further scouring also occurred after our dredging because of heavy rain at the end of November. If we can turn that kind of event to our advantage, and get natural forces to work for us, that’s potentially a very interesting development and one that we’re going to look out for and monitor.”
There have also been positive results from agitation dredging which again sees silt carried out by the tide before it disperses.
Now work is taking place to see how the process can be further optimised.
Cllr Osman added: “I went out to see the trials for myself and I know that the Parrett IDB and the contractors Van Oord worked very hard. I’d like to thank them for all their efforts so far. It’s important work and I look forward to seeing more results.”
Source: Somerset County Gazette
