Dredging

Nationally, we spend £6.5 million annually on dredging (2023 figures).

Of the £6.5 million budget, about £3 million is allocated to the routine dredging of river navigations that need regular works every year or two to maintain them (such as Gloucester & River Severn, Weaver Navigation, Yorks & NE river navigations, and others) plus other fixed annual costs.

The rest is allocated to mainline and spot dredging of canals (which generally only need dredging much less frequently – perhaps every 20 years or more).

Canal dredging can be defined as “Mainline” or “Spot” work. Mainline dredging is the large-scale removal of silt and debris from several kilometres of the canal to meet a bed level bespoke to each canal. The dredger will slowly move along the canal for several weeks, removing all material that doesn’t meet the designed bed level.

Spot dredging is smaller in scale and aims to tackle areas with large deposits of silt in otherwise deep enough canals. These can often be found near feeder outfalls, around width restrictions, on river navigations or downstream of lock bywashes. They take far less time to dredge but can still be costly depending on access, the quality of the sediment and what we can do with it.

We run a cyclical survey programme that revisits every kilometre of our 3,000km network at least once every six to eight years. These surveys show us if that kilometre meets or fails our target channel profile (based on the published dimensions). This alone doesn’t generally result in dredging; we review the surveys to determine how much blockage is in a kilometre and where the issues are. We also use customer complaints as a way of prioritising what failing sections are causing the most issues. The location of issues and the amount of blockage will decide whether a canal is mainline dredged or spot dredged.

To report a dredging issue, please use our national enquiries page: Ways to contact us | Canal & River Trust (canalrivertrust.org.uk)

You can find the maximum craft dimensions for each waterway here: Waterway dimensions

These dimensions will help you decide if your boat can navigate a waterway. Please note that we do not / cannot guarantee that our waterways will meet these dimensions at all times; they are for guidance only. We have used these dimensions to create a trigger profile that we compare to our survey results to determine if we need to carry out a mainline dredge or not. If we decide to dredge, we then dredge deeper than the target profile – typically to around 15% deeper. However, this varies based on the original dimensions of the canal and any following repairs. If a canal has suffered a series of leaks, for example, then the hard bed depth might be shallower than the rest of the canal due to clay repairs or a new liner.

We do not guarantee a minimum depth for mooring anywhere except at access points for facilities (water points, lock landings, visitor moorings, etc). Where mooring rings or bollards are present, it is reasonable to expect there to be sufficient depth to moor.

We especially do not accept responsibility for depth at private moorings. Your agreement with us should state this. If you are on commercial moorings (where you pay an operator such as the landowner), then they will have the responsibility for maintaining your mooring, not the Trust.

Your mooring may benefit from the dredging we carry out in the central channel. If we are dredging in the area, then we can include you / your commercial mooring manager in consultation as a stakeholder so that you can take advantage of any cost savings by delivering your work alongside ours.

Third-party-owned and operated marinas are expected to maintain their own water depth. However, if you rent waterspace from us then there are certain processes that must be followed to ensure that the works are carried out in a safe and compliant manner. Dredging can be risky to people, assets and the environment if incorrectly carried out – it's one of the reasons why it can be so expensive for us to do. Some risks include using excavators near bank protection of unknown stability; accidentally excavating the liner and causing leaks; dissolved oxygen risks to fish and other aquatic wildlife; and release of contaminants or pollution to other watercourses. Any works must be carried out by a competent contractor and have a full methodology and risk assessment completed and approved via your Business Boating contacts. Further information can be found on our Business Boating pages.

Our framework contractors are Land & Water Services and Ebsford Environmental, and there are other contractors who have worked on canals and rivers who may be able to carry out works on your behalf.

We have compiled a list of dredging contractors who have completed works on our waterways. This list is not exhaustive and there may be other contractors who can complete this work: Inland Dredging Companies.

We will evaluate the severity of the dredging requirement against our existing programme. Where we can see from both the complaint and our surveys that we need to dredge, it will go onto our long list. In some very rare circumstances, we may need to dredge urgently (i.e. for flood prevention or safety), but often small spot dredging would be programmed for two to three years, and larger scale projects would be included in the upcoming three or five-year programme (where the need is demonstrated to be greater than other locations). All other dredging requirements would sit prioritised but unprogrammed. We review this long list every year and speak with regional colleagues to ensure that the proposed programme reflects the most urgent local needs and benefits as many customers as possible.

Dredging plant and operators are expensive to maintain, and we need many different types of kits for our different waterways. We can’t afford to have kit sitting idle for long periods when not in use, and a full-time national roving specialist team would look very similar to our Framework Contract – and that’s not how our teams work; they are more locally based. Because the contractors use their equipment and teams to work for other clients as well as us, they can provide them to us when needed for less than the cost of maintaining them ourselves.

It is something we keep under review, along with methods of dredging as part of our strategy. In addition, we use a long-term framework contract so we can be assured of the capability of the contractors involved. Dredging can be risky to people, assets and the environment if incorrectly carried out. Some risks include using excavators near bank protection of unknown stability, dissolved oxygen risks to fish and other aquatic wildlife, and release of contaminants or pollution to other watercourses. Any contractor who is successful in tendering with us has to prove that they can carry out work safely and sensitively.

If you’re on a river navigation, it’s very important to remember that the flow of the river means the outside of a bend is deeper. It’s very possible that the centre of the channel is a lot shallower than the published dimensions. This is also true on canals and is why we ask boaters not to moor on bends as it causes difficulties for boats navigating past (see more in our Boaters Handbook).

It’s also important to remember that whilst we do have published dimensions, these are a guide. Given the size and nature of the network, it is not possible for us to ensure that these dimensions are met at all times in all places. We do plan dredging works to target those areas most in need of work to achieve these dimensions based on our surveys and customer feedback, but it is not always possible to respond to these issues quickly. Most customers do not encounter difficulties within the central channel on a canal.

There isn’t a straightforward answer to this. The two big costs in dredging are mobilising (getting the team and equipment there) and disposing of the sediment. Where we have a small job that can be done by an excavator and deposited straight to the banks, this would be much cheaper and easier to do than a larger job requiring lots of tugs, hoppers and excavators with the sediment going offsite.

So, what causes these variations? If we can easily access the water with an excavator, if we have to pay for access, if the sediment is clean enough to go onto the banks, if it’s a large or long job, if it requires specialist equipment, if we need to pay landowners to deposit or spread sediment on their land. Balancing all of these elements means we generally find costs in the region of £100/m3 to £200m3. With some of our larger jobs coming in at as much as 10,000m3, it’s easy to see how costs stack up.