Lock (water transport)

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Canal lock and lock-keeper's cottage on the Aylesbury Arm of the Grand Union Canal at Marsworth in Hertfordshire, England
Lock on the River Neckar at Heidelberg in Germany



Pound lock[edit]


A pound lock is a type of lock that is used almost exclusively nowadays on canals and rivers. A pound lock has a chamber (the pound)[citation needed] with gates at both ends that control the level of water in the pound. In contrast, an earlier design with a single gate was known as a flash lock.

Pound locks were used in medieval China during the Song Dynasty (960–1279 AD), having been pioneered by the government official and engineer Qiao Weiyo in 984.[1] They replaced earlier double slipways that had caused trouble and are mentioned by the Chinese polymath Shen Kuo (1031–1095) in his book Dream Pool Essays (published in 1088),[2] and fully described in the Chinese historical text Song Shi (compiled in 1345):[3]

The distance between the two locks was rather more than 50 paces, and the whole space was covered with a great roof like a shed. The gates were 'hanging gates'; when they were closed the water accumulated like a tide until the required level was reached, and then when the time came it was allowed to flow out.

The water level could differ by 4 feet (1.2 m) or 5 feet (1.5 m) at each lock and in the Grand Canal the level was raised in this way by 138 feet (42 m).[3]

In medieval Europe a sort of pound lock was built in 1373 at Vreeswijk, Netherlands.[4] This pound lock serviced many ships at once in a large basin. Yet the first true pound lock was built in 1396 at Damme near Bruges, Belgium.[4] A famous civil engineer of pound locks in Europe was the Italian Bertola da Novate (c. 1410–1475), who constructed 18 of them on the Naviglio di Bereguardo (part of the Milan canal system sponsored by Francesco Sforza) between the years 1452 and 1458.[5]

Use of locks in river navigations[edit]

Locks on the Rideau Canal, Entrance Valley, near Parliament Hill, Ottawa, Canada




In more advanced river navigations, more locks are required.


Use of locks in canals[edit]

Locks of the Panama Canal during construction, 1913.


Basic construction and operation[edit]

A plan and side view of a generic, empty canal lock. A lock chamber separated from the rest of the canal by an upper pair and a lower pair of mitre gates. The gates in each pair close against each other at an 18° angle to approximate an arch against the water pressure on the "upstream" side of the gates when the water level on the "downstream" side is lower.
Principle of operation of a pound lock
For a boat going upstream: Pound lock sequence.svg For a boat going downstream:
1–2. The boat enters the lock. 8–9. The boat enters the lock.
3. The lower gates are closed. 10. The upper gates are closed.
4–5. The lock is filled with water from upstream. 11–12. The lock is emptied by draining its water downstream.
6. The upper gates are opened. 13. The lower gates are opened.
7. The boat exits the lock. 14. The boat exits the lock.

All pound locks have three elements:

  • A gate (often a pair of "pointing" half-gates) at each end of the chamber. A gate is opened to allow a boat to enter or leave the chamber; when closed, the gate is watertight.


  • The entrance gates are opened and the boat moves in.
  • The entrance gates are closed.
  • The exit gates are opened and the boat moves out.



Operation of a canal lock
1-3. Boat enters 'empty' lock
4. Bottom gates are closed, bottom paddles closed, top paddles opened, lock starts to fill
5. Lock is filling with water, lifting boat to the higher level

Details and terminology[edit]

an empty lock chamber



The rise is the change in water-level in the lock. The two deepest locks on the English canal system are Bath deep lock[6][7] on the Kennet and Avon Canal and Tuel Lane Lock on the Rochdale Canal, which both have a rise of nearly 20 feet (6.1 m). Both locks are amalgamations of two separate locks, which were combined when the canals were restored to accommodate changes in road crossings. The deepest "as-built" locks in England are considered to be Etruria Top Lock on the Trent and Mersey Canal and Somerton Deep Lock on the Oxford Canal: both have a rise of about 14 ft (4.3 m). Again, sources vary as to which is the deepest, and in any case Etruria has been deepened over the years to accommodate subsidence. A more typical rise (in England) would be 7–12 feet (2.1–3.7 metres) (though even shallower ones can be encountered). By comparison, the Carrapatelo and Valeira locks on the Douro river in Portugal, which are 279 feet (85 m) long and 39 feet (12 m) wide, have maximum lifts of 115 feet (35 m) and 108 feet (33 m) respectively.[8] The two Ardnacrusha locks near Limerick on the Shannon navigation in Ireland have a rise of 100 feet (30 m). The upper chamber rises 60 feet (18 m) and is connected to the lower chamber by a tunnel, which when descending does not become visible until the chamber is nearly empty.[9]


A pound is the level stretch of water between two locks (also known as a reach).[10] On American canals, a pound is called a level.


The chamber is the main feature of a lock. It is a watertight (masonry, brick, steel or concrete) enclosure which can be sealed off from the pounds at both ends by means of gates. The chamber may be the same size (plus a little manoeuvring room) as the largest vessel for which the waterway was designed; sometimes larger, to allow more than one such vessel at a time to use the lock. The chamber is said to be "full" when the water level is the same as in the upper pound; and "empty" when the level is the same as in the lower pound. (If the lock has no water in it at all, perhaps for maintenance work, it might also be said to be empty, but it is more usually described as "drained" or "de-watered".)


The cill exposed in the deep Pont de Flandre lock on the Canal Saint-Denis, Paris
Top gate of a lock, showing the balance beams and paddle winding gear
200-year-old paddle gear on the Wiener Neustädter Kanal, Austria
Water conservation gear on the Birmingham Canal Navigations

The cill is a narrow horizontal ledge protruding a short way into the chamber from below the upper gates. Allowing the rear of the boat to "hang" on the cill is the main danger one is warned to guard against when descending a lock, and the position of the forward edge of the cill is usually marked on the lock side by a white line. The edge of the cill is usually curved, protruding less in the centre than at the edges. In some locks, there is a piece of oak about 9 in (23 cm) thick which protects the solid part of the lock cill. On the Oxford Canal it is called a Babbie; on the Grand Union Canal it is referred to as the cill Bumper.

Gates [edit]

Gates are the watertight doors which seal off the chamber from the upper and lower pounds. Each end of the chamber is equipped with a gate, or pair of half-gates, made of oak or elm (or now sometimes steel). The most common arrangement, usually called miter gates, was invented by Leonardo da Vinci, sometime around the late 1400s.[11] When closed, a pair meet at an angle like a chevron pointing upstream and only a very small difference in water-level is necessary to squeeze the closed gates securely together. This reduces any leaks from between them and prevents their being opened until water levels have equalised. If the chamber is not full, the top gate is secure; and if the chamber is not completely empty, the bottom gate is secure (in normal operation, therefore, the chamber cannot be open at both ends). A lower gate is taller than an upper gate, because the upper gate only has to be tall enough to close off the upper pound, while the lower gate has to be able to seal off a full chamber. The upper gate is as tall as the canal is deep, plus a little more for the balance beam, winding mechanism, etc.; the lower gate's height equals the upper gate plus the lock's rise.

Balance beam[edit]



A paddle – sometimes known as a slacker, clough, or (in American English) wicket – is the simple valve by which the lock chamber is filled or emptied. The paddle itself is a sliding wooden (or nowadays plastic) panel which when "lifted" (slid up) out of the way allows water to either enter the chamber from the upper pound or flow out to the lower pound. A gate paddle simply covers a hole in the lower part of a gate; a more sophisticated ground paddle blocks an underground culvert. There can be up to 8 paddles (two gate paddles and two ground paddles at both upper and lower ends of the chamber) but there will often be fewer. For a long period since the 1970s it was British Waterways policy not to provide gate paddles in replacement top gates if two ground paddles existed. The reason for this was given as safety, since it is possible for an ascending boat to be swamped by the water from a carelessly lifted gate paddle. However, without the gate paddles the locks are slower to operate and this has been blamed in some places for causing congestion. Since the late 1990s the preferred method has been to retain or re-install the gate paddles and fit 'baffles' across them to minimise the risk of inundation.

On the old Erie Canal, there was a danger of injury when operating the paddles: water, on reaching a certain position, would push the paddles with a force which could tear the windlass (or handle) out of one's hands, or if one was standing in the wrong place, could knock one into the canal, leading to injuries and drownings.[12]

Winding gear or paddle gear[edit]

Winding gear is the mechanism which allows paddles to be lifted (opened) or lowered (closed). Typically, a square-section stub emerges from the housing of the winding gear. This is the axle of a sprocket ("pinion") which engages with a toothed bar ("rack") attached by rodding to the top of the paddle. A member of the boat's shore crew engages the square socket of their windlass (see below) onto the end of the axle and turns the windlass perhaps a dozen times. This rotates the pinion and lifts the paddle. A pawl engages with the rack to prevent the paddle from dropping inadvertently while being raised, and to keep it raised when the windlass is removed, so that the operator can attend to other paddles. Nowadays it is considered discourteous and wasteful of water to leave a paddle open after a boat has left the lock, but in commercial days it was normal practice. To lower a paddle the pawl must be disengaged and the paddle wound down with the windlass. Dropping paddles by knocking the pawl off can cause damage to the mechanism; the paddle gear is typically made of cast iron and can shatter or crack when dropped from a height. In areas where water-wastage due to vandalism is a problem, (for example the Birmingham Canal Navigations), paddle mechanisms are commonly fitted with vandal-proof locks (nowadays rebranded "water conservation devices") which require the boater to employ a key before the paddle can be lifted. The keys are officially known as "water conservation keys", but boaters usually refer to them as T-keys, from their shape; handcuff keys because the original locks, fitted on the Leeds and Liverpool Canal, resembled handcuffs; Leeds and Liverpool Keys after that canal; or simply Anti-Vandal Keys.

Hydraulic paddle gear[edit]


Windlass ("lock key")[edit]

Collection of lock windlasses. Note: rakes are for clearing trash out of the lock.



  • Handle: The handle is long enough for a two-handed grip and is far enough from the socket to give enough leverage to wind the paddle up or down. There may be a freely rotating sleeve around the handle to protect the hands from the friction of rough iron against skin.

On the Chesapeake and Ohio Canal, the lockkeepers were required to remove the windlasses from all lock paddles at night, to prevent unauthorized use.[13]

"Turning" a lock[edit]

"Turning" a lock can simply mean emptying a full lock, or filling an empty one ("We entered the lock, and it only took us five minutes to turn it"). It is used more often to refer to a lock being filled or emptied for the benefit of someone else ("The lock was turned for us by a boat coming the other way") and sometimes the opposite ("The lock was set for us, but the crew of the boat coming the other way turned it before we got there").

Swell or Swelling[edit]

A swell was caused by opening suddenly the paddle valves in the lock gates, or when emptying a lock.[14] To help boats leave (downstream) a lock, the locksman would sometimes open the paddles to create a swell, which would help "flush" the boat out of the lock. In one case, a boatsman asked for a back swell, that is, open and shut the paddles a few times to create some waves, to help him get off the bank where he was stuck.[15] If boats ran aground (from being overloaded) they sometimes asked passing crews to tell the upstream lock to give them an extra heavy swell, which consisted of opening all the paddles on the lock gate, creating a surge that affected the whole pound below.[16]

On the Erie Canal, some loaded boats needed a swell to get out of the lock, particularly lumber boats, being top heavy, would list to one side and get stuck in the lock, and needed a swell to get them out. Some lockkeepers would give a swell to anyone to help them on the way, but some would ask for money for the swell.[14]

The Erie Canal management did not like swelling, since it 1. Used too much water lowering the water on the pound above sometimes causing boats to run aground, 2. it raised the water level on the pound below causing some boats to strike bridges or get stuck.[14]

"Lock mooring"[edit]

"Lock mooring" was a commonly used method of navigating into a lock by a barge travelling upstream. The barge would be directed to the slack water to one side of the lock gates and as the volume of water decreased as the lock emptied the barge or boat is effectively sucked out of the slack water into the path of the lock gates. The effort required to navigate the barge or boat into the mouth of the lock was therefore substantially reduced.

Snubbing posts[edit]

Snubbing a boat to keep it from hitting the downstream gates. Note the rope wrapped around the snubbing post.

On horse-drawn and mule-drawn canals, snubbing posts were used to slow or stop a boat in the lock. A 200-ton boat moving at a few miles an hour could destroy the lock gate. To prevent this, a rope was wound around the snubbing post as the boat entered the lock. Pulling on the rope slowed the boat, due to the friction of the rope against the post.[17] A rope 2 1/2 inches in diameter and about 60 feet long was typically used on the Erie Canal to snub a boat in a lock.[18]

One incident, which took place in June 1873 on the Chesapeake and Ohio Canal, involved the boat the Henry C. Flagg and its drunk captain. That boat was already leaking; the crew, having partially pumped the water out, entered Lock 74, moving in front of another boat. Because they failed to snub the boat, it crashed into and knocked out the downstream gates. The outrush of water from the lock caused the upstream gates to slam shut, breaking them also, and sending a cascade of water over the boat, sinking it. This suspended navigation on the canal for 48 hours until the lock gates could be replaced and the boat removed from the lock.[19]


A series of photos of the Canadian Locks in Sault Ste. Marie to illustrate a drop of about 22 ft (6.7 m) in a lock.

Variations exist for types of locks and the terminology used for them.

  • Single gates on narrow canals (locks approx. 7 feet (2.1 m) wide)
    • On most English narrow canals, the upper end of the chamber is closed by a single gate the full width of the lock. This was cheaper to construct and is quicker to operate with a small crew, as only one gate needs to be opened.
    • A few narrow locks imitate wide locks in having paired gates at both ends. An example is the Bosley Lock Flight on the Macclesfield Canal.
  • Steel gates. Steel gates and/or balance beams are frequently used nowadays, although all-wooden versions are still fitted where appropriate.
    • Sliding gates. Some low-head locks use sliding steel gates (see Kiel Canal).
    • Guillotine gates. Some locks have vertically moving steel gates — these are quite common on river navigations in East Anglia. Sometimes just one of the pairs of swinging gates is replaced by a guillotine: for instance at Salterhebble Locks, where space to swing the balance beams of bottom gates of the lowest lock was restricted by bridge widening. On the River Nene most locks have this arrangement as in time of flood the top mitre gates are chained open and the bottom guillotines lifted so that the lock chamber acts as an overflow sluice. Guillotine gates are also used on the downstream side of larger locks such as the 23m Bollène lock on the River Rhône, the aperture being large enough for a boat to travel under it.
    • Vertically rotating gates (American usage: Drop gates)
      Example of a lock with a drop gate (Lock 10) on the Chesapeake and Ohio Canal
      are gates which, when open, lie flat on the canal bed and which close by lifting (London Flood Barrier). Some of these were installed on the Chesapeake and Ohio Canal in the congested 7 Locks area since they could be operated by one man and also could speed up traffic.
    • Rotating-sector gates. Some of these work very like traditional swinging gates, but with each gate in the form of a sector of a cylinder. They close by rotating out from the lock wall and meeting in the centre of the chamber. Water is let in or out by opening the gates slightly: there are no paddles or other lock gear. The lock at Limehouse Basin, which gives access to the River Thames, is an example. A dramatically large one can be seen at the Rotterdam flood defences (huge flood gates). There is a different type at the sea lock on the Ribble Link: this is a rising sector gate, which has a horizontal axis: the gate drops to the bed of the river to allow boats to pass.
  • Alternate paddle gear
    • Some manually operated paddles do not require a detachable handle (windlass) because they have their handles ready-attached.
  • Composite locks. To economise, especially where good stone would be prohibitively expensive or difficult to obtain, composite locks were made, i.e. they were constructed using rubble or inferior stone, dressing the inside walls of the lock with wood, so as not to abrade the boats. This was done, for instance, on the Chesapeake and Ohio Canal with the locks near the Paw Paw Tunnel[20] and also the Chenango Canal[21] Because the wood would swell (making the lock space smaller) or rot away, the wood was often replaced by concrete.
  • Fish Ladders. The construction of locks (or weirs and dams) on rivers obstructs the passage of fish. Some fish such as trout and salmon go upstream to spawn. Measures such as a fish ladder are often taken to counteract this.
  • Weigh lock.
A weigh lock on the Lehigh canal

A weigh lock is a specialized canal lock designed to determine the weight of barges to assess toll payments based upon the weight and value of the cargo carried. The Erie Canal had a weigh locks in Rochester, Syracuse, and West Troy New York. The Lehigh Canal also had weigh locks (see photo on right).

Special cases[edit]

Lock flights[edit]


Loosely, a flight of locks is simply a series of locks in close-enough proximity to be identified as a single group. For many reasons, a flight of locks is preferable to the same number of locks spread more widely: crews are put ashore and picked up once, rather than multiple times; transition involves a concentrated burst of effort, rather than a continually interrupted journey; a lock keeper may be stationed to help crews through the flight quickly; and where water is in short supply, a single pump can recycle water to the top of the whole flight. The need for a flight may be determined purely by the lie of the land, but it is possible to group locks purposely into flights by using cuttings or embankments to "postpone" the height change. Examples: Caen Hill locks, Devizes.

"Flight" is not synonymous with "Staircase" (see below). A set of locks is only a staircase if successive lock chambers share a gate (i.e. do not have separate top and bottom gates with a pound between them). Most flights are not staircases, because each chamber is a separate lock (with its own upper and lower gates), there is a navigable pound (however short) between each pair of locks, and the locks are operated in the conventional way.

However, some flights include (or consist entirely of) staircases. On the Grand Union (Leicester) Canal, the Watford flight consists of a four-chamber staircase and three separate locks; and the Foxton flight consists entirely of two adjacent 5-chamber staircases.

Staircase locks [edit]

Staircase of five locks, dating from 1774, at Bingley, England

Where a very steep gradient has to be climbed, a lock staircase is used. There are two types of staircase, "real" and "apparent".

A "real" staircase can be thought of as a "compressed" flight, where the intermediate pounds have disappeared, and the upper gate of one lock is also the lower gate of the one above it. However, it is incorrect to use the terms staircase and flight interchangeably: because of the absence of intermediate pounds, operating a staircase is very different from operating a flight. It can be more useful to think of a staircase as a single lock with intermediate levels (the top gate is a normal top gate, and the intermediate gates are all as tall as the bottom gate). As there is no intermediate pound, a chamber can only be filled by emptying the one above, or emptied by filling the one below: thus the whole staircase has to be full of water (except for the bottom chamber) before a boat starts to ascend, or empty (except for the top chamber) before a boat starts to descend. By building a pair of such lock sets (one used to climb and the other to descend) these difficulties are avoided, as well as enabling a greater traffic volume and reduced wait times.


Examples of famous "real" staircases in England are Bingley and Grindley Brook. Two-rise staircases are more common: Snakeholme Lock and Struncheon Hill Lock on the Driffield Navigation were converted to staircase locks after low water levels hindered navigation over the bottom cill at all but the higher tides — the new bottom chamber rises just far enough to get the boat over the original lock cill. In China, the recently completed Three Gorges Dam includes a double five-step staircase for large ships, and a ship lift for vessels of less than 3000 metric tons. Examples of "apparent" staircases are Foxton Locks and Watford Locks on the Leicester Branch of the Grand Union.

Instructions for descent of treble staircase, Chesterfield Canal


One striking difference in using a staircase of either type (compared with a single lock, or a flight) is the best sequence for letting boats through. In a single lock (or a flight with room for boats to pass) boats should ideally alternate in direction. In a staircase, however, it is quicker for a boat to follow a previous one going in the same direction. Partly for this reason staircase locks such as Grindley Brook, Foxton, Watford and Bratch are supervised by lockkeepers, at least during the main cruising season, they normally try to alternate as many boats up, followed by down as there are chambers in the flight.

As with a flight, it is possible on a broad canal for more than one boat to be in a staircase at the same time, but managing this without waste of water requires expertise. On English canals, a staircase of more than two chambers is usually staffed: the lockkeeper at Bingley (looking after both the "5-rise" and the "3-rise") has worked there for more than 20 years and ensures that there are no untoward events and that boats are moved through as speedily and efficiently as possible. Such expertise permits miracles of boat balletics: boats travelling in opposite directions can pass each other halfway up the staircase by moving sideways around each other; or at peak times, one can have all the chambers full simultaneously with boats travelling in the same direction.

Doubled, paired or twinned locks[edit]

Locks can be built side by side on the same waterway. This is variously called doubling, pairing, or twinning. The Panama Canal has three sets of double locks. Doubling gives advantages in speed, avoiding hold-ups at busy times and increasing the chance of a boat finding a lock set in its favour. There can also be water savings: the locks may be of different sizes, so that a small boat does not need to empty a large lock; or each lock may be able to act as a side pond (water-saving basin) for the other. In this latter case, the word used is usually "twinned": here indicating the possibility of saving water by synchronising the operation of the chambers so that some water from the emptying chamber helps to fill the other. This facility has long been withdrawn on the English canals, although the disused paddle gear can sometimes be seen, as at Hillmorton on the Oxford Canal.

The once-famous staircase at Lockport, New York was also a doubled set of locks. Five twinned locks allowed east- and west-bound boats to climb or descend the 60 feet (18 m) Niagara Escarpment, a considerable engineering feat in the nineteenth century. While Lockport today has two large steel locks, half of the old twin stair acts as a spillway and can still be seen (without lock gates).


Stop locks[edit]






It should be noted that the newer canal was not always at a higher level than the one it joined. For instance, there is a very shallow lock at Autherley Junction, where the 1835 Birmingham and Liverpool canal (now part of the Shropshire Union Canal) met the older Staffordshire and Worcestershire Canal, build in 1772. The Nicholson guide shows that a boater travelling south along the newer canal locks "up" before turning north or south onto the older Staffordshire and Worcestershire Canal - so the Shropshire Union Canal gains a small lockful of water each time a boat passes. However, the gain is tiny since the level difference is so small that it is sometimes possible to open both gates at once.

Round locks[edit]

Agde Round Lock

There are several examples where locks have been built to a round plan, with more than two exits from the lock chamber, each serving a different water level. Thus the lock serves both as a way of changing levels and as a junction. The circular plan of the lock allows boats within it to rotate to line up with the appropriate exit gate.

The best known example of such a round lock is the Agde Round Lock on the Canal du Midi in France. This serves as a lock on the main line of the canal and allows access to the Hérault River.[11]

A second French round lock can be found in the form of the, now disused, Écluse des Lorraines, connecting the Canal latéral à la Loire with the River Allier.[23]

Drop locks[edit]

Dalmuir drop lock

A drop lock allows a short length of canal to be lowered temporarily while a boat passes under an obstruction such as a low bridge. During canal restoration, a drop lock may be used where it is impractical or prohibitively expensive to remove or raise a structure that was built after the canal was closed (and where re-routing the canal is not possible).


While the concept has been suggested in a number of cases, the only example in the world of a drop lock that has actually been constructed is at Dalmuir on the Forth and Clyde Canal in Scotland.[25] This lock, of the single chamber type, was incorporated during the restoration of the canal, to allow the replacement of a swing bridge (on a busy A road) by a fixed bridge, and so answer criticisms that the restoration of the canal would cause frequent interruptions of the heavy road traffic. It can be emptied by pumping - but as this uses a lot of electricity the method used when water supplies are adequate is to drain the lock to a nearby burn. A series of pictures showing the operation of the lock can be seen here.[26]

Flood locks[edit]





Flood gates[edit]

Main article: Flood gate
Bi-directional flood gates on the canal Schoten-Dessel, Belgium
Flood gate or Stop gate (American usage) on Chesapeake and Ohio Canal. When a flood threatened, boards were put in the lock to divert waters from the canal prism to the Potomac river. Note winch house on top for the boards.


Bi-directional gates and locks[edit]

Bi-directional gates at one chamber end of a tidal lock (located in Veurne on the canal Nieuwpoort - Duinkerke)


Two types of bidirectional locks at the end of the Marne-Rhine Canal in the Independent Port of Strasbourg

A sea lock is one that connects a canal or river directly with an estuary or ocean. All sea locks are tidal.

Tidal locks[edit]

Sea lock at Bude, Cornwall

A tidal lock is generally any lock that connects tidal with non-tidal water. This includes a lock between a tidal river and the non-tidal reaches, or between a tidal river and a canal, or a sea lock. However, the term usually refers specifically to a lock whose method of operation is affected by the state of the tide. Examples:


Inlet Locks[edit]

Inlet lock (left) from feeder canal, regulates water from the Potomac river into the C&O canal. Lift lock (right) allows boats to continue up the canal in a normal fashion.

An inlet lock is to regulate water from a feeder canal or a river into the main canal. In some cases, the inlet lock may double as a lift lock to allow boats into the river slackwater. Note that in the example on the right, the feeder canal was originally George Washington's Little Falls Skirting Canal which was part of the Potomac Company's canals, later re-purposed as a feeder canal for the Chesapeake and Ohio Canal.

Very large locks[edit]

Berendrecht Lock (right) and Zandvliet Lock (left), located at the entrance to the Port of Antwerp (top) from the Scheldt (foreground)
Barges at a lock on the Mississippi River

The world's largest lock is the Berendrecht Lock, giving access to the Port of Antwerp in Belgium. The lock is 500 m (1,600 ft) long, and 68 m (223 ft) wide and drops 13.5 m (44 ft), and has four sliding lock gates. The size of locks cannot be compared without considering the difference in water level that they are designed to operate under. For example, the Bollène lock on the River Rhône has a fall of at least 23 m (75 ft) and the Oskemen Lock on the Irtysh River in Kazakhstan has a drop of 42 m (138 ft).[27] The total volume of water to be considered in any lock equals the product of its length, breadth and the difference in water levels. Lock staircases are used in an attempt to reduce the total volume of water required in relation to the amount of useful work done. The useful work done relates to the weight of the vessel and the height it is lifted. When a vessel is lowered the consumption of potential energy of the water consumed is considered. An alternative to locks is a boat lift; facilities of this type, e.g. the Anderton boat lift or the Strépy-Thieu boat lift in Belgium, do not rely on the consumption of water as the primary power source, are powered by motors and are designed to consume a minimum amount of water.

The 29 locks on the Mississippi River are typically 600 feet (180 m) long while tug and barge combinations are as much as 1,200 feet (370 m) long consisting of as many as 15 barges and one tug. In these cases, some of the barges are locked through, using partially opened lock valves to create a current to pull the un-powered barges out of the lock where they are tied up to wait for the rest of the barges and the tug to pass through the lock. It can take as much as an hour and a half to pass the lock.

Hiram M. Chittenden Locks[edit]



History and development[edit]

Dams and weirs[edit]


Flash locks[edit]



This system was used extensively in Ancient China and in many other parts of the world. But this method was dangerous, and many boats were sunk by the torrent of water. Since this system necessarily involved lowering the level in the pound, it was not popular with millers who depended on a full head of water to operate their equipment. This led to constant battles, both legal and physical, between the navigation and milling interests, with rivers being closed to navigation if there was any shortage of water. It was mainly this conflict, which led to the adoption of the pound lock in medieval China, as this means that relatively little water is consumed by navigation.


A more sophisticated device was the staunch or water gate, consisting of a gate (or pair of mitred gates) which could be closed (and held shut by water pressure) when the river was low, to float vessels over upstream shallows at times of low water. However, the whole upstream head of water had to be drained (by some auxiliary method approaching modern sluices) before a boat could pass. Accordingly they were not used where the obstacle to be passed was a mill weir.

Pound lock[edit]

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

Turf-sided lock[edit]

A turf-sided lock is an early form of canal lock design that uses earth banks to form the lock chamber, subsequently attracting grasses and other vegetation, instead of the now more familiar and widespread brick, stone, or concrete lock wall constructions. This early lock design was most often used on river navigations in the early 1700s before the advent of canals. The sides of the turf-lock are sloping so, when full, the lock is quite wide. Consequently, this type of lock needs more water to operate than vertical-sided brick- or stone-walled locks. On British canals and waterways most turf-sided locks have been subsequently rebuilt in brick or stone, and so only a few good examples survive, such as at Garston Lock, and Monkey Marsh Lock, on the Kennet and Avon Canal.[29]

Use of water[edit]

The main problem caused by locks is that, each time a lock goes through one fill-empty cycle, a lockful of water (tens of thousands up to millions of litres) is released to the lower pound. In more simplistic terms, on a canal where only one boat will fit into a lock, a boat travelling from the summit pound to the lowest pound is accompanied on its journey by one 'personal' lockful of water. A boat going the other way also transfers a lockful of water from the summit pound to the lowest pound. To prevent the canal from running dry, some method must be used to ensure that the water supply at the canal summit is constantly replenished at the rate that the water is being drained downwards. This is, of course much more of a problem on an artificial canal crossing a watershed than on a river navigation.





Water saving basins[edit]

Disused side pond at Atherstone on the Coventry Canal, England


Diagram of water saving basins (descending)
Diagram of water saving basins (ascending)

For example the Hindenburg-lock (in Hannover, Germany, built 1919–1928) has two lock chambers of 225 m length, each of which would use 42,000 m³ of water for a full locking cycle. Due to the use of 10 water saving basins, only 10,500 m³ of water are used. A more recent example is the Rhine–Main–Danube Canal with 13 saving locks out of a total of 16 locks.


Map showing extended intermediate pounds at Caen Hill locks

On English canals, these reservoirs are called "side ponds". The Droitwich Canal, reopened in 2011, has a flight of three locks at Hanbury which all have operational side ponds.[32] Side ponds were also installed on the Grand Union Canal and the Coventry Canal, among others. They are now out of use, and in some cases have been filled in, because British Waterways considered that it was too easy to misuse them and flood the surrounding area.[citation needed] On some flights of locks with short intermediate pounds, the pounds are extended sideways — in effect to provide a reservoir to ensure that the pound does not run dry (in case, for instance, the lock below leaks more than the lock above). These extended intermediate pounds are sometimes confused with side ponds.



Inclined plane[edit]

Main article: Canal inclined plane
Boat in cradle, at the top of inclined plane on the Morris Canal.


There are no working waterway inclined planes in the UK at the moment, but the remains of a famous one can be seen at Foxton in Leicestershire on the Leicester arm of the Grand Union Canal. The plane enabled wide-beam boats to bypass the flight of ten narrow locks, but failure to make improvements at the other end of the arm and high running costs led to its early demise.[33] There are plans to restore it, and some funding has been obtained.[34]

Marine railway[edit]




Boat lift[edit]

Main article: Boat lift



Another famous derivative is the Peterborough lift lock which is a boat lift located on the Trent Canal in the city of Peterborough, Ontario, Canada and is Lock 21 on the Trent-Severn Waterway.

The dual lifts are the highest hydraulic boat lifts in the world, rising 19.8 m (65 ft). This was a considerable accomplishment when conventional locks usually only had a 2 m (6.6 ft) rise. Each lift has a capacity of 1,300 tonnes.

The basins are 140 feet (43 m) long, 33 feet (10 m) wide and 9 feet 10 inches (3.00 m) deep. The vertical distance lifted is 65 feet (20 m). The Trent-Severn has another similar lift lock at Kirkfield, with basins of the same dimension, but which lifts over a smaller vertical distance.

Caisson lock[edit]

Operation of caisson lock
Main article: Caisson lock

Around 1800 the use of caisson locks was proposed by Robert Weldon for the Somerset Coal Canal in England. In this underwater lift, the chamber was 80 ft long and 60 ft (18 m) deep and contained a completely enclosed wooden box big enough to take a barge. This box moved up and down in the 60 ft (18 m) deep pool of water. Apart from inevitable leakage, the water never left the chamber, and using the lock wasted no water. Instead, the boat entered the box and was sealed in by the door closing behind it, and the box itself was moved up or down through the water. When the box was at the bottom of the chamber, it was under almost 60 feet (18 m) of water – at a pressure of three atmospheres, in total. One of these "locks" was built and demonstrated to the Prince Regent (later George IV), but it had various engineering problems and the design was not put into use on the Coal Canal.[35][36]

Hydro-pneumatic canal lift[edit]

Possibly inspired by Weldon's caisson lock, William Congreve in 1813 patented a "hydro-pneumatic double balance lock" in which two adjacent locks containing pneumatic caissons could be raised and lowered in counterbalance by the movement of compressed air from one caisson to the other. In about 1817 the Regents Canal Company built one of these locks at the site of the present-day Camden Lock, north London. Here the motivation was, again, water supply problems. The company insisted on various modifications to Congreve's design; the resulting installation proved to be unsatisfactory, and was soon replaced by conventional locks.[37][38]

Diagonal lock[edit]


The "Diagonal Lock Advisory Group" has identified several sites in Britain where the new design could be installed, either on new waterways or canals under restoration.[39] Projects under consideration include the restoration of the Lancaster Canal to Kendal and the proposed new branch of the Grand Union Canal between Bedford and Milton Keynes.

Three Gorges Dam model view. A pair of five locking steps is at center with a ship lift to the left

A combined system - the Three Gorges Dam[edit]

At the Three Gorges Dam on the Yangtze River (Chang Jiang) in China there are two stairsteps of five large ship locks (each 300 m long and 35 m wide) for ten-thousand-tonne ships. In addition to this there will be a boat lift (a large elevator) capable of moving a three-thousand-ton ship vertically in one motion. The locks and the boat lift provide a total lift of up to 113 metres.

Ship sizes named after locks[edit]

Locks restrict the maximum size of ship able to navigate a waterway, and some key canals have given rise to the name of standard ship sizes, such as the Panamax and the Seawaymax.

See also[edit]


  1. ^ Needham, Volume 4, Part 3, 350-351
  2. ^ Needham, Volume 4, Part 3, 351-352.
  3. ^ a b Needham, Volume 4, Part 3, 351.
  4. ^ a b Needham, Volume 4, Part 3, 357.
  5. ^ Needham, Volume 4, Part 3, 358.
  6. ^ "Second Lock". Images of England. Retrieved 4 September 2006. 
  8. ^ "Final Report of the International Commission for the Study of Locks". Google Books. Retrieved 20 May 2013. 
  9. ^ "The ESB lock at Ardnacrusha". Irish Waterways History. Retrieved 2012-03-23. 
  10. ^ "Reach". Oxford English Dictionary (Second ed.). Oxford, England: Oxford University Press. 1989. ...the portion of a canal between two locks, having a uniform level 
  11. ^ a b "Lock". UXL Encyclopedia of Science. Retrieved 2013-06-20. 
  12. ^ Garrity, Richard (1977). Canal Boatman My Life on Upstate Waterways. Syracuse, NY: Syracuse University Press. p. 38. ISBN 0-8156-0139-5. 
  13. ^ Unrau P. 336
  14. ^ a b c Garrity, Richard (1977). Canal Boatman My Life on Upstate Waterways. Syracuse, NY: Syracuse University Press. p. 39. ISBN 0-8156-0139-5. 
  15. ^ Kytle, Elizabeth. Home on the Canal. Seven Locks Press, 1983. p. 207
  16. ^ Garrity, Richard. p. 40
  17. ^ Kytle, Elizabeth. Home on the Canal. 1996. ISBN 0801853281, P. 133
  18. ^ Garrity, Richard. p. 41
  19. ^ http://www.nps.gov/history/history/online_books/choh/unrau_hrs.pdf P. 812
  20. ^ Kytle, Elizabeth. Home on the Canal. Seven Locks Press, 1983, ISBN 0-932929-13-5 P. 71-72
  21. ^ Edwin C. Bearss. "The Composite Locks". [US Department of the Interior, National Park Service]. Retrieved 2013-05-24. , p. 15
  22. ^ Birmingham's Canals, Ray Shill, 1999, 2002, ISBN 0-7509-2077-7
  23. ^ "Canal lateral a la Loire". Afloat in France. grehanman guides. Retrieved 2010-11-24. 
  24. ^ "Dalmuir Drop Lock". Retrieved 22 October 2007. 
  25. ^ voltimum. "Mitsubishi helps breath new life into important canal routes". Retrieved 23 October 2007. 
  26. ^ "Clydebank Drop Lock". Gentles.info. Retrieved 2011-08-05. 
  27. ^ "Latest". Waterways World. Retrieved 2011-08-05. 
  28. ^ Frank Gardner Moore "Three Canal Projects, Roman and Byzantine." American Journal of Archaeology, 54, (1950), 97-111 (99)
  29. ^ "British Waterways 'Waterscape' website". Retrieved 11 January 2011. 
  30. ^ "Study of Additional Combinations of Lock Water Saving Basins for Proposed Post-Panamax Locks at the Panama Canal". Autoridad del Canal de Panamá. 23 April 2004. Retrieved 13 July 2008. 
  31. ^ Jackson, Eric (17 September 2006). "Environmental defense of Torrijos". The Panama News. Retrieved 13 July 2008. 
  32. ^ Smithett, Robin (April 2012). "A bit on the side". Waterways World. ISSN 0309-1422. 
  33. ^ Nicholson Waterways Guide, Volume 3, Harper Collins Publishers, ISBN 0-00-713666-8
  34. ^ "Foxton Inclined Plane Trust: Restoration". Fipt.org.uk. Retrieved 2011-08-05. 
  35. ^ "The Somerset Coal Canal". Bath Royal Literary and Scientific Institution. Retrieved 6 October 2006. 
  36. ^ "History of the Caisson Lock On the Somersetshire Coal Canal". The Somersetshire Coal Canal (Society). Retrieved 6 October 2006. 
  37. ^ "Congreve's Hydro-Pneumatic Canal Lift - A Humbug!". London Canals. Retrieved 25 September 2013. 
  38. ^ Faulkner, Alan (2005): The Regent’s Canal: London’s Hidden Waterway. Waterways World Ltd. ISBN 1-870002-59-8.
  39. ^ Fogarty, Terry (2008). "Diagonal Lock How It Works". Retrieved 18 June 2008. 

External links[edit]