More to moor?

This is the second in a series of features about dredging the canals, the hows and whys, and a bit of waterway history. This time we take a look at the navigational constraints on developing more casual towpath moorings: factors we have to take into account when planning our dredging projects.

London winter moorings London winter moorings

In our previous post Dredge to the Edge we looked at the physical constraints that restrict us dredging to create more casual mooring along the towpath side of the canal. This time we’re going to consider the navigational constraints that prevent us from creating moorings in places that those with an uninitiated eye might think were suitable.

To do a quick recap, canals are generally built in a dish shape with the edges being much shallower than the main navigable channel. If you dredge to the edge to create a deeper area for mooring, problems can be caused which could result in water loss the collapse of towpath wash walls or even the collapse of the towpath itself. The new deeper mooring areas could also leak and potentially cause a breach, especially where the canal has been built on an embankment. So, what other factors do we have to consider?

There are more boats registered on our waterways now than at the height of the Industrial Revolution. Some places are very popular indeed and prone to congestion. We would all like more places to moor where there’s such high demand, particularly at key visitor attractions and cities such as London, Oxford and Bath.

Moored boats at King's Cross in London King's Cross, London

Location, location, location

The first and most obvious limitation to creating moorings to meet demand is the finite length of waterway available. Today there are 2,000 miles of waterway in our care and just under 34,500 licensed boats (2019/2020 annual report). On the face of it you would have thought that there would be plenty of room for everyone, but naturally some places are more popular than others.

Attractions, good transport links, urban areas where people have taken to living on boats as a way of dealing with high property prices, popular destinations for days out, eating out, or even going shopping, can all cause congestion and difficulties for people trying to find a mooring for up to 14 days.

In some areas such as London, even with double mooring as a norm, it can be difficult to find a mooring spot. But due to sky-high land values, the cost of construction, and lack of available sites, simply creating mooring basins or digging new stretches of canal to create moorings is not possible.

How about all those redundant canal docks from the past? Can’t they be brought back into use? Many are already in use as long-term moorings, but others never belonged to the canal companies in the first place, having been built by canal carriers and other businesses who either had raw materials brought in by boat, or finished goods delivered. When these businesses ceased trading, land was sold off and basins filled in, disappearing under car parks, warehousing, offices, and housing. Many along the Paddington arm and the Grand Union in London were used as refuse tips. (If this interests you, then look up the history of Sabey’s of Paddington).

Archive map showing a former canal dock that has now disappeared Archive map of a former canal dock

In high-demand areas it is important to have as much of the towpath length of the canal available for casual mooring as possible. But it is neither desirable, nor possible, for every metre of canal to be used. We don’t want to spend all our time boating very slowly on tickover past very long lines of moored boats, and there are some places that should always remain ‘no mooring’ for very good reasons.

Navigational safety

Adequate space without moorings should be left either side of bridges to improve sightlines through the bridge and to create space for boats to safely pass or wait their turn to pass through. There needs to be sufficient space left on the approach to locks for at least one boat (or two in the case of broad canals) to set down crew, work the passage through the lock, and pick up crew again. Space at lock landings is especially crucial for boaters travelling solo. There also needs to be sufficient room either end of a tunnel for craft to pass and wait their turn.

Winding and water control

Mooring opposite a winding hole prevents other boaters from turning. Mooring in front of marina entrances, canal junctions, and mooring basins can prevent boats from entering and leaving. The canal may look wide enough in your opinion but you have to leave at least the full length of the maximum length of boat able to use the canal, and a good five or more extra metres, to allow ease of turning, especially in windy conditions.

Less obvious ‘no mooring’ areas include in front of weirs and submerged sluices used for water control. Boats obstructing weirs and sluices can contribute to flooding, and mooring next to a sluice or weir can be dangerous. The force of the water can stick the boat to the side and prevent it from rising as flood waters rise.

Mooring on bends

Very few canals were built in a dead straight line. Rivers invariably bend. Some waterways bend extravagantly, such as the South Oxford Canal as it hugs the contour line around the hills. Boats don’t bend. Depending on the length of boat there are many places where it is not a good idea to moor.

Mooring on the outside of a bend makes it difficult for passing craft to see what is coming from the opposite direction. Mooring on an inside bend reduces the width of the navigable channel. Add a river current to either of these and collisions become inevitable if craft are inconsiderately moored. This is particularly important where water space is shared with unpowered craft such as canoeing and rowing clubs.

Two diagrams showing the boats moored on the inside and the outside of a bend Diagram of the problems caused by mooring on bends

Doubling up

Doubling or breasting up of narrow boats is a way of increasing capacity in popular spots and one that we encourage. Sharing the space and avoiding unusable gaps increases capacity.

But not everywhere is suitable and this comes down to the width and design of the canal. Remember that canals are usually built in a dish shape and the deeper channel is generally slightly closer to the towpath. If you moor too many craft, or craft that are too wide, on the towpath this reduces the amount of deeper water for other boats to pass, resulting in craft running aground. The offside is invariably much shallower than people think, sometimes just a few inches if it’s a soft bank.

Wash wall and batter

Our Waterway Dimensions document refers to the maximum size of craft recommended for each section of waterway. The ‘minimum open channel’ is derived from this and is centred around the ‘navigation line’. They both refer to the maximum recommended size of craft that can navigate the canal, not necessarily what can pull into the side. 

Some canals are dish shaped, some have a wash wall, and some of them have an angled shape called a batter: the depth available for mooring towpath side will never be as deep as the minimum open channel. This is something that needs to be considered when buying a boat. If your draft is close to, or on the maximum of the minimum open channel, you won’t be able to moor up close to the towpath edge.

A cross section diagram of a typical canal with a wash wall at the towpath edge A cross section diagram of a typical canal

Pontoons

Some people suggest that adding a pontoon to the towpath edge would increase the depth available for casual mooring by effectively moving the mooring more into the main channel. This is a potential solution where the channel is very wide but that is not the case in many places, especially where moorings already exist on the offside of the canal.

Pontoons are the best solution on rivers, where not only are the soft banks too shallow, but water levels can vary enormously from summer low flows to flooding. Pontoons are expensive and require regular maintenance to remain safe. The average life of a pontoon is around 30 to 40 years if well maintained, so replacement costs do also have to be factored in. When only £1 out of every £5 to maintain the canals comes from boaters’ licence fees, meeting the cost of mooring pontoons would need to be financed somehow. There is no easy or cheap solution to finding more places to moor.

All of the factors above have to be taken into account when considering where best to try and create or improve new casual or short-stay moorings. In the next post we’ll look at how we actually go about preparing a dredging project to improve moorings, as well as maintain the minimum open channel.

Last date edited: 18 December 2020

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