Lock (water navigation)

A lock is a special device used to help boats, ships, and other small water vehicles move between areas of water that are at different heights on rivers and canals. It works by having a fixed chamber where the water level can be raised or lowered. This allows boats to travel up or down when there is a difference in water level.

Locks make it easier for boats to travel on rivers that change height or to cross land that isn’t flat by using canals. Over time, people have built bigger and more locks in canals to create shorter, more direct routes for travel by water.

History

Ancient Egypt

In Ancient Egypt, river locks were likely part of the Canal of the Pharaohs. Engineers from the time of Ptolemy II are said to have been the first to create a way to keep the Nile River free of salt water. They did this by inventing the lock around 274–273 BC.

Ancient China

From 960 to 1279 CE, a new kind of lock was developed in China. This lock had an upper gate to create a small section of the canal. This section, called a pound lock, made it easier to move boats through. It was first used during the Song dynasty. Records show that a tax official named Qiao Weiyue faced problems with his grain ships getting wrecked on the West River near Huai'an in Jiangsu. In 984, Qiao built a pair of gates close together, creating a short stretch of canal that could be filled and emptied to move boats safely.

Medieval Europe

In 1385, a kind of pound lock was built at Vreeswijk, in the Netherlands. This lock could handle many ships at once in a large basin. The first true European pound lock was built in 1396 at Damme near Bruges, Belgium. An Italian builder named Bertola da Novate constructed 18 pound locks on the Naviglio di Bereguardo between 1452 and 1458. This was part of the Milan canal system supported by Francesco Sforza.

Basic operation

Locks help boats move between stretches of water that are at different heights. A lock has three main parts:

• A chamber that connects two parts of a canal and can hold one or more boats. The chamber stays in one place, but the water level inside can change.
• A gate at each end of the chamber. When open, a boat can enter or leave; when closed, the gate keeps water from leaking out.
• Lock gear that lets water flow in or out of the chamber. This is often a simple valve or a panel that is lifted by turning a handle.

The way a lock works is quite simple. If a boat is going downstream (to lower water), the chamber is first filled with water. Then the upstream gate opens, the boat enters, and the gate closes. Next, water drains out until the level matches the water below. Finally, the downstream gate opens, and the boat leaves. Going upstream is the opposite process. The whole trip usually takes between 10 and 20 minutes, depending on the lock’s size and the water level when the boat arrives.

Historic lock designs

Historic lock designs are old ways of building locks that are no longer used for new locks. These designs have been replaced by newer and better ones.

Caisson lock

Main article: Caisson lock

Around 1800, a man named Robert Weldon suggested using caisson locks for the Somerset Coal Canal in England. In this design, there was a special box that could move up and down in water. The box was big enough to hold a boat. When the box was at the bottom, it was under a lot of water pressure. One of these boxes was shown to a prince, but it had some problems and was never used for the canal.

Composite material locks

Sometimes, people used cheaper materials to build locks. They used rubble or weaker stone and covered the inside walls with wood to protect the boats. This was done on some canals in America.

Hydro-pneumatic canal lift

A man named William Congreve created a lock design in 1813 that used air pressure to move locks up and down. One of these was built in London, but it did not work well and was replaced with regular locks.

Inclined plane

An inclined plane allowed wider boats to pass without needing many narrow locks. However, it was expensive and not used for long. There are plans to bring one back to working condition.

Shaft lock

Shaft locks look a bit like caisson locks but have a deep shaft with gates at the top. The bottom gates are reached through a tunnel. Some famous shaft locks are in France, the Czech Republic, and Germany. One in Minden, Germany, has eight water tanks that help save water when the lock is used.

Turf-sided lock

A turf-sided lock is an old type of lock made from earth banks covered in grass. These locks were used in the early 1700s but were later replaced with brick or stone locks. Only a few of these old locks are left.

Types of lock

Basic Pound lock

A pound lock is most commonly used on canals and rivers today. It has a chamber with gates at both ends that control the water level.

Pound locks were first used in China during the Song dynasty (960–1279 CE). They replaced earlier designs that had caused trouble.

Composite Pond locks

Diagonal lock

This is similar to another type of lock, but built on an incline. Boats are guided along as the water level changes.

Drop locks

A drop lock can have two lock chambers or a single long chamber. The water level at either end is the same, so the lock can only be emptied by letting water run away or by pumping it back up.

The only example of a drop lock in the world is at Dalmuir on the Forth and Clyde Canal in Scotland.

Doubled, paired or twinned locks

Locks can be built side by side on the same waterway. This is called doubling, pairing, or twinning.

The Panama Canal has three sets of double locks. Having locks side by side helps avoid delays and can save water.

The Soo Locks include two American locks and one Canadian lock. They help ships move between different sizes of locks and waterways.

Round locks on intersecting canals

A well-known example of a round lock is the Agde Round Lock on the Canal du Midi in France. It allows access to the Hérault River.

Lock flights

A flight of locks is a series of locks close together. This makes travel easier and more efficient.

Staircase locks

When a very steep slope must be climbed, a lock staircase is used. Operating a staircase lock can be more complicated, and it often requires a lock keeper to help manage the water levels and boat movements.

Tidal locks

Marina Locks

In areas with big tides, locks can help marinas keep fixed slips instead of needing floating slips.

Sea Locks

Locks are also used where strong currents would otherwise occur because of tides on either side of a barrier. The lock in the Canso Canal is an example.

Terminology

The cill, also called a sill, is a narrow ledge inside a lock chamber. It helps keep boats safe when moving between water levels. Fish sometimes have trouble passing locks, so special passages called fish ladders help them swim upstream.

Locks have strong, watertight doors called gates to keep water in the right place. These gates are usually made of steel today. Some locks use devices called paddles to move water in and out.

A pound is a flat stretch of water between two locks. On big modern canals, machines control the gates and paddles instead of people.

The rise is how much the water level changes in a lock. Some locks have very big rises, like nearly 20 feet (6.1 m).

On older canals, special posts helped slow down boats entering locks. This prevented accidents.

A swell is a small wave made by quickly opening and closing lock gates. Lock workers sometimes made swells to help boats move easier.

Some canals have special water storage areas called side ponds to save water.

On some canals, lock workers had to remove tools called windlasses at night to keep locks safe.

Largest locks

This section lists some of the biggest locks around the world. The size of a lock depends on the difference in water level it can handle. For example, the Bollène lock on the River Rhône can manage a drop of at least 23 metres, while locks on the Rhine–Main–Danube Canal can handle about 25 metres.

In 2016, the Kieldrecht Lock in the Port of Antwerp in Belgium became the largest lock by volume. Then, in 2022, the IJmuiden sea lock in the Port of Amsterdam became the largest by surface area. This lock is 500 metres long, 70 metres wide, and 18 metres deep.

Photo gallery

• A gate in the Hatton flight in England.
• Iroquois Lock on the Saint Lawrence Seaway
• Model of early river pound lock, constructed in Lankheet water park, Netherlands.
• The turf-sided Monkey Marsh Lock on the Kennet & Avon Canal at Thatcham.
• The cill exposed in the deep Pont de Flandre lock on the Canal Saint-Denis, Paris.
• The balance beams typical of many locks on the Upper Thames at Eynsham Lock, Eynsham, Oxfordshire, England. Visible on the gates are the paddle winding gears, used to operate the sluice gates.
• Top gates of Jesus Lock, a beam lock on the River Cam in Cambridge, England.
• 200-year-old paddle gear on the Wiener Neustädter Kanal, Austria.
• Water conservation gear on the Birmingham Canal Navigations.
• Lock gate controls on a canal.
• Caversham Lock on the River Thames, with its chamber nearly filled. Visible on top of the gates are the hydraulic mechanisms that raise and lower the sluices in their raised position. To the right is one of two pedestals which are used to operate the gates and sluices, as well as the lock cottage.