Dredging: what is it, how do we do it, and why?
Updated: Oct 19, 2021
We’ve talked before about how important the UK’s waterways are to construction, and The Rothen Group is dedicated to maintaining them to the best possible standard. Thanks to our diverse fleet of vessels, we are capable of undertaking a range of different marine engineering works to help achieve this.
With over 2,000 miles of canals and rivers in the UK, 11,000 miles of coastline, and thousands of private and commercial marinas, plus lakes, ponds, reservoirs and wetlands, keeping canals and rivers clear of naturally deposited sediments is a critical part of canal maintenance, and the importance of dredging activity should not be underestimated.
What does dredging mean?
Dredging is defined as the removal of sediments and debris from the bottom of bodies of water, including rivers, canals, and lakes. It involves managing the effects of climate change through flood and drought, coastal erosion, and the pressure of increasing urbanisation. Sediment removal is necessary due to the natural process of sand and silt washing downstream and building up along key chokepoints, such as river banks.
The type of work required can vary depending on whether operators are carrying out canal dredging or river dredging. The best way to categorise dredging is to split it into the two underlying reasons: economic and environmental. Below is more information on these two dredging examples:
UK dredging is often focused on maintaining or increasing the depth of navigation channels, to allow safe passage of boats. This is because vessels require a certain amount of water to float, and a buildup of sediment will prevent a boat from being able to effectively navigate a waterway. The amount of heavy goods transported on canals and rivers makes them massively important to the UK’s economy, which is why maintenance dredging projects so crucial.
The sediments which are found in river channels and canals can be potentially harmful to wildlife and people, especially in and around cities or industrial areas. If pollutants are introduced into waterways, such as from sewer overflows, then sediments can become contaminated and present a danger to water-dwelling life.
As well as minimising the risk of pollutants, removing sediment can have a positive impact on biodiversity by allowing more light to reach the water bed. This can encourage fish spawning grounds, and generally lead to a healthier waterway.
How to dredge a canal
The process of dredging a canal is more technical and precise than it may appear at first. Care must be taken to not damage the bed of the canal/ river as the excavator drags along the bottom. Often, canal beds are sealed with puddling clay to prevent leakage, which must remain intact for the canal to be functional. There can also be culverts and underground services to be taken into consideration.
A rough step-by-step guide is as follows:
1. Mobilise boats/kit to site
2. Use a digger or crane to excavate material out. These usually have special clamshell grabs or buckets on designed to let some water pass through, but retain the majority of silt/deposits in the bucket. There are usually plans to indicate the water depths, or a bathymetric survey to highlight silt deposits
3. Place silt into a hopper or crane barge
4. Move to the discharge site
5. Use a discharge machine, which can be a crane on a barge or a separate digger on the bank, to dig out silt from the hopper. This silt can be placed into lorries to be taken off site. Silt can be dried on land to be used as a natural fertiliser, providing it isn’t contaminated
For challenging dredging operations, the best course of action is to engage with dredging contractors such as The Rothen Group, who can bring a wealth of experience to the project.
Depending on availability, The Rothen Group can mobilise within 24-28 hours. This depends on a number of factors, such as location and complexity of the project, and a team of experts are always on-hand to help manage logistics and act quickly.
Canal dredging equipment
A ‘dredger’ can take many forms, with different sized kits for various situations, including different levels of access to sites, or varying dredging requirements. This includes:
· A long reach excavator (operating from the bank)
· A long reach excavator (operating from a boat)
· An excavator on a pontoon with jack legs
· A crane or grab barge with a clamshell bucket
· An amphibious digger
Effectively, anything that is able to ‘scoop’ material from the water and move it elsewhere can be used for dredging work.
Dredging is not limited to certain locations or habitats. It needs to be done wherever there is likely to be a build-up of material in water. In cities this might be because the water is slower moving, but in rural areas there may be more vegetation, which acts as a natural silt trap.
The Rothen Group’s experience
Dredging is a significant part of The Rothen Group’s work. Alongside the sizable fleet it has at its disposal, the company also has a wealth of experience to draw upon.
We’ve completed work for the Environment Agency (EA) and the Canal & River Trust (C&RT), along a variety of different waterways, from the River Ouse to inner-city canals. We’ve used diggers, pontoons, and crane boats to undertake projects with a host of different goals - be it environmental, aesthetic, or practical in nature, such as canal clearance ahead of winter stoppage works.
Crucially, we are able to get permits and marine licenses from the EA and C&RT, ensuring that projects are completed in a safe, efficient, and environmentally conscious way.
Cost of dredging a canal
The cost of canal dredging in the UK, or any other type of waterway, is dependent on a significant number of factors. The complexity of the project, site access, location, and many more contribute to the overall price, which makes it impossible to provide a definitive figure.
Anyone who is looking to engage The Rothen Group’s services should get in touch to discuss individual projects’ needs, allowing us to generate a quote that is specific to their unique circumstances.
If you have any further questions about dredging, or would like to know more about the services The Rothen Group can offer, please contact us on 01827 215715, or email firstname.lastname@example.org