Dredging with spray jets

Welcome to my blog, I hope it will give you an insight into the variety of work that a Trust Environmental Scientist gets involves with. I mainly deal with water quality and waste issues and this can range from working on national issues (such as Water Framework Directive) to more local issues (I tend to cover canals and rivers in Worcestershire, Gloucestershire and South Wales).

At the moment I am involved in a lot of planning, for next year’s projects.

One project is to undertake water injection dredging along the River Avon in February 2014, to move sediment that has built up behind lock gates. We will use a specialist dredger with adjustable spray bars, which pushes jets of water into the sediment that needs moving, to re-suspend it. The natural flow of river water then carries the sediment away. The photo shows the dredger in action.

We have used the system successfully along the River Severn. As the dredger is highly manoeuvrable, it's able to access the sometimes inaccessible mounds of sediment. It is also is a much cheaper option than taking the sediment away to landfill.

As the work involves the temporary suspension of sediment, the project manager, ecologist and I attended a meeting with the Environment Agency to discuss the works. The meeting went well and so we can continue planning for a February start date.

One of the main issues that the EA wished to discuss, was the potential impact the dredging could have on water quality. We have agreed to undertake dissolved oxygen monitoring during the work, to ensure it remains at healthy levels. Dissolved oxygen is needed by fish and invertebrates that live in the river. 

I now have to write a monitoring programme for the dredging contractors to use, as they will be undertaking some of the monitoring work for us. It will detail the sampling frequency during the day, sampling locations, threshold levels for dissolved oxygen and what to do if dissolved oxygen levels begin to fall. 

I'll update you on the works in February.

Last date edited: 5 December 2013

About this blog

Sara has been with the Trust for 17 years, working in the environment team. She is a senior environmental scientist and will cover waste and water quality issues. She works closely with the South Wales and Severn Waterway team but her work will also pick up national issues, such as the Water Framework Directive.


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