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== When/where invented ==
[[Canal_of_the_Pharaohs]] says "Ptolemy II was the first to solve the problem of keeping the Nile free of salt water when his engineers invented the water lock around 274/273 BC" (not sure what type) but can't see any mention here. - [[User:Rod57|Rod57]] ([[User talk:Rod57|talk]]) 23:19, 12 November 2015 (UTC)
==Templates==
I have added 2 templates to the article {{tl|refimprove}} and {{tl|tooshort}}. The latter was placed here on the talk page when it should have been on the article page, so I have removed it from here. The former has been added because for an article the size that it is, there are really very few references, and that gives a real feel of [[WP:OR|original research]]. It may be that this is all authoritative stuff, but it doesn't sound like that as there are insufficient references to support it. [[User:CalzGuy|CalzGuy]] ([[User talk:CalzGuy|talk]]) 06:49, 24 September 2016 (UTC)

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== Double Gates. ==

The locks on the Panama canal, and the big new locks in Antwerp, have two sets of gates, with a gap of about 20m. between them. Why ?

On the Kennet and Avon canal, on the upstream side of Reading, there is a lock with a rise of only about 1 foot. why ?

[[Special:Contributions/78.150.128.87|78.150.128.87]] ([[User talk:78.150.128.87|talk]]) 00:29, 15 August 2017 (UTC)

:On the K&A you are referring to [[County Lock]] which IIRC is mainly used for level control rather than hill climbing. For Panama see [[Panama Canal locks#The gates]]. [[User:Martin of Sheffield|Martin of Sheffield]] ([[User talk:Martin of Sheffield|talk]]) 08:33, 15 August 2017 (UTC)
:: County Lock is on a river section, with appreciable flow. It's alongside a weir. [[User:Andy Dingley|Andy Dingley]] ([[User talk:Andy Dingley|talk]]) 09:10, 15 August 2017 (UTC)

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== Reversion 25/1/18 ==
I've reverted the last two changes for a number of reasons.  The changes were well intentioned, but introduced a number of linguistic and factual errors.
* The essence of a lock is navigation.  Otherwise a staunch, gate or sluice would suffice.
* Please check up on the use of an apostrophe.  Plurals do not take one, only genitives.
* Control locks or stop locks are still navigation locks, otherwise they would be sluices etc.
* What are "Waaier" and "Spui" locks?  It's not an English language term I've ever seen, and there is limited explanation and no wikilink.  Are they instances of sluices?
* Please also watch the use of headings.  The highest level heading that should be used on a mainspace or talk page is level 2.

Having been rather negative so far, I will agree with you that control lock should be merged into this article and will set about doing so forthwith. [[User:Martin of Sheffield|Martin of Sheffield]] ([[User talk:Martin of Sheffield|talk]]) 13:40, 25 January 2018 (UTC)

== Merger proposal ==

I propose that [[Control lock]] be merged into [[Lock (water navigation)]].  The examples on Control lock can, if citations are found, be adequately merged into Lock.  A redirect will ensure the edit history is preserved. [[User:Martin of Sheffield|Martin of Sheffield]] ([[User talk:Martin of Sheffield|talk]]) 14:09, 25 January 2018 (UTC)

:* '''Oppose''' the proposed target is already 90K and has too many sections.  Splitting is therefore appropriate. [[user:Andrew Davidson|Andrew D.]] ([[user talk:Andrew Davidson|talk]]) 14:26, 25 January 2018 (UTC)

Some restructuring seems to be necessary. Maybe renaming the page to pound lock? and linking to the pages of the other types such as the [[control lock]]? Right now the other pages are quite hard to find and it is like the pound lock would be the only lock around.

Or even better, maybe making a page for lock that refers to the pound lock page (this page) and the other lock type pages.

I wanted to write about a lock design meant solely for the purpose to flood certain regions (these types of locks were for example used in the setting of the [[Hollandic Water Line]]) and the title of this, otherwise very well written, article got me confused.

--[[User:Danielvandermaas|Danielvandermaas]] ([[User talk:Danielvandermaas|talk]]) 18:56, 25 January 2018 (UTC)

:Have you tried [[floodgate]], [[Flood barrier]], [[Tidal barrage]] or [[sluice]]?  As the Hollandic Water Line article you referred to says: "Sluices were constructed in dikes", it does not call them locks. [[User:Martin of Sheffield|Martin of Sheffield]] ([[User talk:Martin of Sheffield|talk]]) 21:14, 25 January 2018 (UTC)

It seems that the design of door I want to describe is used for both [[control lock]]s and [[sluice]]s.

Many locks are used for both the raising/lowering of boats as well as controlling water levels. It does not seem right to split [[control lock]] and [[pound lock]] into two pages. The remark that a [[lock]]'s main or partial function can be controlling water levels (as opposed to raising boats) should probably be stated in the introduction on the current [[lock]] page.
--[[User:Danielvandermaas|Danielvandermaas]] ([[User talk:Danielvandermaas|talk]]) 08:26, 28 January 2018 (UTC)

*'''Oppose merger''' It seems to me that [[Control lock]] and [[lock (water navigation)]] are distinct topics, related topics.  Distinct topics with sufficient references, should remain standalone articles, for various reasons, including that this allows readers to put one topic's article on their watchlist, and not the other.  [[User:Geo Swan|Geo Swan]] ([[User talk:Geo Swan|talk]]) 04:49, 8 February 2019 (UTC)
:Closing, given that there seems to be there remains opposition after more than a year; no clear consensus other than, perhaps, for ''improve''. [[User:Klbrain|Klbrain]] ([[User talk:Klbrain|talk]]) 06:15, 17 April 2019 (UTC)

== Van gates ==

I have edited the section on van gates as the previous description didn't make sense. [[User:Gbm|GBM]] ([[User talk:Gbm|talk]]) 09:56, 13 February 2018 (UTC)

== Basic construction and operation ==

I suggest that the diagram in this section omits the following steps and that the text in this section doesn’t sufficiently emphasise them:

:For a boat travelling uphill, if the lock isn’t already empty, the lock will first need to be emptied
:For a boat traveling downhill, if the lock isn’t already full, the lock will first need to be filled.

Given that these steps will be required about half the time a lock is traversed, I think inclusion/greater emphasis is required.

Thoughts? [[User:Zin92|Zin92]] ([[User talk:Zin92|talk]]) 20:52, 13 June 2018 (UTC)

== Depth of locks ==
I question the statement "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)".

I think this needs reliable source because this unreliable source does not support it:
*{{cite web | title=Deepest Canal Locks in England and Wales, UK | website=Pennine Waterways | url=http://www.penninewaterways.co.uk/locks.htm | access-date=12 March 2019}}
— [[User:PBS|PBS]] ([[User talk:PBS|talk]]) 12:45, 12 March 2019 (UTC)

The following unreliaable source puts the Somerton Deep Lock at 12 feet which is deep for the Oxford canal but the canals next to the river stour have a number of locks with a similar depth (see previous unreliable reference). 
*{{cite web | title=Somerton Deep Lock No 34 | website=CanalplanAC - Canal Route Planner | date=7 February 2019 | url=//canalplan.org.uk/place/e4gk | access-date=12 March 2019}}

— [[User:PBS|PBS]] ([[User talk:PBS|talk]]) 13:13, 12 March 2019 (UTC)
:The Nicholson Guide volume 1 quotes 12 feet as the depth of Somerton Deep Lock, as does Paget-Tomlinson. I cannot find a sensible ref for the depth of Etruria top lock, so I propose removing the mention of "as-built" locks. [[User:Bob1960evens|Bob1960evens]] ([[User talk:Bob1960evens|talk]]) 13:19, 22 January 2024 (UTC)

==Uncited material in need of citations==
I am moving the following uncited material here until it can be properly supported with [[WP:INCITE|inline citations]] of [[WP:IRS|reliable]], [[WP:PSTS|secondary]] sources, per [[WP:V]], [[WP:CS]], [[WP:IRS]], [[WP:PSTS]], [[WP:BLP]], [[WP:NOR]], et al. [https://en.wikipedia.org/w/index.php?title=Lock_%28water_navigation%29&type=revision&diff=1084776730&oldid=1082460142 This diff] shows where it was in the article. [[User:Nightscream|Nightscream]] ([[User talk:Nightscream|talk]]) 14:40, 26 April 2022 (UTC) 

:Under the heading "Use of Water" there was about a page of material. With this 4/26/22 change, and to this day, 4/10/24, only two sentences remain. Many years ago, there had been an equation in the removed material. On March 13, 2016, I improved the equation, generalizing it. I won't both making such an effort again. [[Special:Contributions/24.214.166.246|24.214.166.246]] ([[User talk:24.214.166.246|talk]]) 14:36, 10 April 2024 (UTC)

{{collapse top}}
<blockquote>
==Lede section==
Since 2016, the largest lock worldwide is the [[Kieldrecht Lock]] in the [[Port of Antwerp]], Belgium.{{cn|date=April 2022}}

==Pound lock==
A ''pound lock'' is a type of lock that is used almost exclusively nowadays on [[canal]]s and [[river]]s. A pound lock has a chamber with [[floodgate|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]].{{fact|date=March 2022}}

== Use in river navigation ==
When a stretch of river is made navigable, a lock is sometimes required to bypass an obstruction such as a [[rapids|rapid]], [[dam]], or mill [[weir]] – because of the change in river level across the obstacle.{{fact|date=March 2022}}

In large scale river navigation improvements, weirs and locks are used together. A weir will increase the depth of a shallow stretch, and the required lock will either be built in a gap in the weir, or at the downstream end of an artificial ''cut'' which bypasses the weir and perhaps a shallow stretch of river below it. A river improved by these means is often called a Waterway or River Navigation (see example [[Calder and Hebble Navigation]]).{{fact|date=March 2022}}

Sometimes a river is made entirely non-tidal by constructing a ''sea lock'' directly into the estuary.{{fact|date=March 2022}}

In more advanced river navigations, more locks are required.
* Where a longer cut bypasses a circuitous stretch of river, the upstream end of the cut will often be protected by a ''[[Floodgate|flood lock]]''.
* The longer the cut, the greater the difference in river level between start and end of the cut, so that a very long cut will need additional locks along its length. At this point, the cut is, in effect, a ''canal''.{{fact|date=March 2022}}

==Use in canals==
Early completely artificial canals, across fairly flat countryside, would get round a small hill or depression by simply detouring (''contouring'') around it. As engineers became more ambitious in the types of country they felt they could overcome, locks became essential to effect the necessary changes in water level without detours that would be completely uneconomic both in building costs and journey time. Later still, as construction techniques improved, engineers became more willing to cut directly through and across obstacles by constructing long [[tunnel]]s, cuttings, [[Navigable aqueduct|aqueducts]] or embankments, or to construct even more technical devices such as inclined planes or boat lifts. However, locks continued to be built to supplement these solutions, and are an essential part of even the most modern navigable waterways.{{fact|date=March 2022}}

==Basic construction and operation==
[[File:Canal lock.svg|thumb|upright=1.5|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 [[floodgate|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.]]
{|  style="width:1px;; border:1px solid #999;"
|+ '''Principle of operation of a pound lock'''
!colspan="2"|For a boat going upstream:
|rowspan="6"|[[File:Pound lock sequence.svg|180px]]
!colspan="2"|For a boat going downstream:
|-
|valign="top" align="right" nowrap|1–2.
|valign="top"|The boat enters the lock.
|valign="top" align="right" nowrap|8–9.
|valign="top"|The boat enters the lock.
|-
|valign="top" align="right" nowrap|3.
|valign="top"|The lower gates are closed.
|valign="top" align="right" nowrap|10.
|valign="top"|The upper gates are closed.
|-
|valign="top" align="right" nowrap|4–5.
|valign="top"|The lock is filled with water from upstream.
|valign="top" align="right" nowrap|11–12.
|valign="top"|The lock is emptied by draining its water downstream.
|-
|valign="top" align="right" nowrap|6.
|valign="top"|The upper gates are opened.
|valign="top" align="right" nowrap|13.
|valign="top"|The lower gates are opened.
|-
|valign="top" align="right" nowrap|7.
|valign="top"|The boat exits the lock.
|valign="top" align="right" nowrap|14.
|valign="top"|The boat exits the lock.
|}
All pound locks have three elements:
* A watertight ''chamber'' connecting the upper and lower canals, and large enough to enclose one or more boats. The position of the chamber is fixed, but its water level can vary.
* 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.
* A set of ''lock gear'' to empty or fill the chamber as required. This is usually a simple valve (traditionally, a flat panel (paddle) lifted by manually winding a rack and pinion mechanism) which allows water to drain into or out of the chamber; larger locks may use pumps.{{fact|date=March 2022}}

The principle of operating a lock is simple. For instance, if a boat travelling downstream finds the lock already full of water:
* The entrance gates are opened and the boat moves in.
* The entrance gates are closed.
* A valve is opened, this lowers the boat by draining water from the chamber.
* The exit gates are opened and the boat moves out.{{fact|date=March 2022}}

If the lock were empty, the boat would have had to wait 5 to 10 minutes while the lock was filled. For a boat travelling upstream, the process is reversed; the boat enters the empty lock, and then the chamber is filled by opening a valve that allows water to enter the chamber from the upper level. The whole operation will usually take between 10 and 20 minutes, depending on the size of the lock and whether the water in the lock was originally set at the boat's level.{{fact|date=March 2022}}

Boaters approaching a lock are usually pleased to meet another boat coming towards them, because this boat will have just exited the lock on their level and therefore set the lock in their favour – saving about 5 to 10 minutes. However, this is not true for [[#Staircase locks|staircase locks]], where it is quicker for boats to go through in convoy.{{fact|date=March 2022}}

[[File:Canal-sequence.jpg|thumb|left|700px|<u>Operation of a canal lock</u><br/>
1–3. Boat enters 'empty' lock<br/>
4. Bottom gates are closed, bottom paddles closed, top paddles opened, lock starts to fill<br/>
5. Lock is filling with water, lifting boat to the higher level]]
{{Clear}}

==Details and terminology==
[[File:Schwabenheim Schleuse leer.jpg|thumb|A drained lock chamber]]
For simplicity, this section describes a basic type of lock, with a pair of gates at each end of the chamber and simple [[rack and pinion]] paddles raised manually by means of a detachable windlass operated by lock-keepers or the boat's shore crew. This type can be found all over the world, but the terminology here is that used on the British canals. A subsequent section explains common variations.{{fact|date=March 2022}}

===Pound===
On American canals, a pound is called a ''level''.{{fact|date=March 2022}}

===Chamber===
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".){{fact|date=March 2022}}

===Gates {{Anchor|Gates}}===
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.{{fact|date=March 2022}}

===Balance beam===
A ''balance beam'' is the long arm projecting from the landward side of the gate over the towpath. As well as providing leverage to open and close the heavy gate, the beam also balances the (non-floating) weight of the gate in its socket, and so allows the gate to swing more freely.{{fact|date=March 2022}}

===Paddle===
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.{{fact|date=March 2022}}

===Winding gear or paddle gear===
''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 lock-keeper or 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''.{{fact|date=March 2022}}

===Hydraulic paddle gear===
During the 1980s, British Waterways began to introduce a hydraulic system for operating paddles, especially those on bottom gates, which are the heaviest to operate. A metal cylinder about a foot in diameter was mounted on the balance beam and contained a small oil-operated hydraulic pump. A spindle protruded from the front face and was operated by a windlass in the usual way, the energy being transferred to the actual paddle by small bore pipes. The system was widely installed and on some canals it became very common. There turned out to be two serious drawbacks. It was much more expensive to install and maintain than traditional gear and went wrong more frequently, especially once vandals learned to cut the pipes. Even worse, it had a safety defect, in that the paddle once in the raised position could not be dropped in an emergency, but had to be wound down, taking a good deal longer. These factors led to the abandonment of the policy in the late 1990s, but examples of it survive all over the system, as it is usually not removed until the gates need replacing, which happens about every twenty years.{{fact|date=March 2022}}

=== Windlass ("lock key") ===
A ''windlass'' (also variously 'lock handle', 'iron' or simply 'key') is a detachable crank used for opening lock paddles (the word does not refer to the winding mechanism itself).{{fact|date=March 2022}}

The simplest windlass is made from an iron rod of circular section, about half an inch in diameter and two feet long, bent to make an L-shape with legs of slightly different length. The shorter leg is called the handle, and the longer leg is called the arm. Welded to the end of the arm is a square, sometimes tapered, socket of the correct size to fit onto the spindle protruding from lock winding gear.
* Socket: Traditionally, windlasses had a single socket, designed for a particular canal. When undertaking a journey through several canals with different lock-gear spindle sizes it was necessary to carry several different windlasses. A modern windlass usually has two sockets for use on different canals: the smaller is for the [[British Waterways]] standard spindle, fitted in the early 1990s almost everywhere, the larger for the gear on the [[Grand Union Canal]] north of [[Napton Junction]], which they were unable/unwilling to convert.
* 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.
* Arm: A "long throw" windlass has a longer arm so that the handle is further from the socket to give a greater leverage on stiffer paddles. If the throw is ''too long'' then the user, winding a gate paddle, risks barking their knuckles against the balance beam when the handle is at the lowest point of its arc. A sophisticated modern windlass may have an adjustable-length arm.
* Materials: Early windlasses were individually hand forged from a single piece of wrought iron by a blacksmith. More modern techniques include casting of iron or bronze, drop forging and (the most common technique) welding. Some boatmen had their windlasses 'silvered' (or chrome plated) for increased comfort and to prevent rusting. Windlasses are now only rarely plated, but a popular modern choice of metal is aluminium, whose smooth and rustproof surface has the same advantages of longevity and blister-reduction, and is also very light. One type of these, the Dunton Double, has only a single eye, but by clever tapering it will operate either size of spindle.{{fact|date=March 2022}}

=== "Turning" a lock ===
"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").{{fact|date=March 2022}}

==="Lock mooring"===
"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.{{fact|date=March 2022}}

==Variations==
Variations exist for types of locks and the terminology used for them.{{fact|date=March 2022}}

===Single gates===
Single gates are often installed on narrow canals (locks approx. {{convert|7|ft|m|disp=or}} wide).{{fact|date=March 2022}}

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. These were often fitted with a post allowing a rope to be used to stop the boat and close the gate at the same time.{{fact|date=March 2022}}

Some narrow locks (e.g. on [[Birmingham Canal Navigations]]) go even further. They have single gates at the lower end also. This speeds up passage, even though single lower gates are heavy (heavier than a single upper gate, because the lower gate is taller) and the lock has to be longer (a lower gate opens INTO the lock, it has to pass the bow or stern of an enclosed boat, and a single gate has a wider arc than two half-gates).{{fact|date=March 2022}}

=== Steel gates===
Steel gates and/or balance beams are frequently used nowadays, although all-wooden versions are still fitted where appropriate.
* Swinging gates. Even very large steel-gated locks still can use essentially the same swinging gate design as small 250-year-old locks on the English canals. On English canals, steel gates usually have wooden mitre posts as this gives a better seal.
* Sliding gates. Some low-head locks use sliding steel gates (see [[Kiel Canal]]). The sliding gates of the [[:nl:Nieuwe Meersluis|Nieuwe Meersluis]] in Amsterdam double as roadways.
* [[Caisson (lock gate)|Caisson gates]]. A kind of sliding gate that is hollow and can float. It can be constructed to withstand high heads.
* 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) [[File:Lock 10 C and O Canal.jpg|thumb|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 ([[Thames barrier|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 may be 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 [[Maeslantkering]] (huge flood gates) near [[Rotterdam]]. 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.{{fact|date=March 2022}}

=== Different paddle gear===
Some manually operated paddles do not require a detachable handle ([[windlass]]) because they have their handles ready-attached.{{fact|date=March 2022}}

On the [[Leeds and Liverpool Canal]] there is a variety of different lock gear. Some paddles are raised by turning what is in effect a large horizontal wing nut (butterfly nut) lifting a screw-threaded bar attached to the top of the paddle. Others are operated by lifting a long wooden lever, which operates a wooden plate which seals the culvert. These are known locally as "jack cloughs". Bottom gate paddles are sometimes operated by a horizontal ratchet which also slides a wooden plate sideways, rather than the more common vertical lift. Many of these idiosyncratic paddles have been "modernised" and they are becoming rare.{{fact|date=March 2022}}

On the [[Calder and Hebble Navigation]], some paddle gear is operated by repeatedly inserting a ''Calder and Hebble Handspike'' (length of 4" by 2" hardwood) into a ground-level slotted wheel and pushing down on the handspike to rotate the wheel on its horizontal axis.{{fact|date=March 2022}}

On some parts of the [[Montgomery Canal]] bottom paddles are used in place of side paddles. Rather than passing into the lock through a culvert around the side of the lock gate, the water flows through a culvert in the bottom of the canal. The paddle slides horizontally over the culvert.{{fact|date=March 2022}}

=== Composite locks===
Because the wood would swell (making the lock space smaller) or rot away, the wood was often replaced by concrete.{{fact|date=March 2022}}

=== Lock keepers===
{{Main|Lock keeper}}
Some locks are operated (or at least supervised) by professional or volunteer lock keepers. This is particularly true on commercial waterways, or where locks are large or have complicated features that the average leisure boater may not be able to operate successfully. For instance, although the Thames above Teddington (England) is almost entirely a leisure waterway, the locks are usually staffed. Only recently have boaters been allowed limited access to the hydraulic gear to operate the locks when the keeper is not present.{{fact|date=March 2022}}

=== Powered operation===
Even on smaller canals, some gates and paddles are electrically operated, particularly if the lock is regularly staffed by professional lock keepers. On the [[River Thames]] below [[Oxford]] all the locks are staffed and powered. Powered locks are usually still filled by gravity, though some very large locks use pumps to speed things up.{{fact|date=March 2022}}

=== Weigh lock===
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 weigh locks in Rochester, Syracuse, and West Troy New York. The [[Lehigh Canal]] also had weigh locks (see photo on right).{{fact|date=March 2022}}


==Special cases==
===Lock flights===
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]].{{fact|date=March 2022}}

"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.{{fact|date=March 2022}}

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.{{fact|date=March 2022}}

===Staircase locks {{Anchor|Staircase locks}}{{Anchor|Staircase lock}}===
Where a very steep gradient has to be climbed, a lock staircase is used. There are two types of staircase, "real" and "apparent".{{fact|date=March 2022}}

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. 

In an "apparent" staircase the chambers still have common gates, but the water does not pass directly from one chamber to the next, going instead via side ponds. This means it is not necessary to ensure that the flight is full or empty before starting.{{fact|date=March 2022}}

Examples of famous "real" staircases in England are [[Bingley Five Rise Locks|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 [[Grand Union Canal#The Leicester Line|Leicester Branch]] of the [[Grand Union Canal|Grand Union]].{{fact|date=March 2022}}

Operation of a staircase is more involved than a flight. Inexperienced boaters may find operating staircase locks difficult. The key worries (apart from simply being paralysed with indecision) are either sending down more water than the lower chambers can cope with (flooding the towpath, or sending a wave along the canal) or completely emptying an intermediate chamber (although this shows that a staircase lock can be used as an emergency dry dock). To avoid these mishaps, it is usual to have the whole staircase empty before starting to descend, or full before starting to ascend, apart from the initial chamber.{{fact|date=March 2022}}

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.{{fact|date=March 2022}}

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 lockkeepers at Bingley (looking after both the "5-rise" and the "3-rise") ensure 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.{{fact|date=March 2022}}

=== Doubled, paired or twinned locks ===
These terms can also (in different places or to different people) mean either a two-chamber staircase  (e.g. Turner Wood Double Locks on the [[Chesterfield Canal]]: the same canal has a three-rise staircase called Thorpe Low Treble locks), or just a flight of two locks (as at [[Thornhill Double Locks]] on the [[Calder and Hebble Navigation]]). Also, "double lock" (less often, "twin lock") is often used by novices on the English canals to mean a wide (14&nbsp;ft) lock, presumably because it is "double" the width of a narrow lock, and allows two narrow boats going in the same direction to "double up". These are properly known as broad locks.{{fact|date=March 2022}}

===Stop locks===
A "stop" lock is a (very) low-rise lock built at the junction of two (rival) canals to prevent water from passing between them.{{fact|date=March 2022}}

During the competitive years of the [[Canals of the United Kingdom|English waterways system]], an established canal company would often refuse to allow a connection from a newer, adjacent one. This situation created the [[Worcester Bar]] in [[Birmingham]], where goods had to be [[transshipment|transshipped]] between boats on rival canals only feet apart.{{fact|date=March 2022}}

Where a junction was built, either because the older canal company saw an advantage in a connection, or where the new company managed to insert a mandatory connection into its Act of Parliament, then the old company would seek to protect (and even enhance) its water supply. Normally, they would specify that, at the junction, the newer canal must be at a higher level than their existing canal. Even though the drop from the newer to the older canal might only be a few inches, the difference in levels still required a lock – called a ''stop lock'', because it was to stop water flowing continuously between the newer canal and the older, lower one. The lock would be under the control of the new company, and the gates would, of course, "point" uphill – towards the newer canal. This would protect the water supply of the newer canal, but would nevertheless "donate" a lockful of water to the older company every time a boat went through. In times of excess water, of course, the lock "bywash" would continuously supply water to the lower canal.{{fact|date=March 2022}}

Many stop locks were removed or converted to a single gate after [[nationalisation]] in 1948. Hall Green stop lock remains, but as a single lock: the extra lock was removed because the lowering of the T&M's summit pound (to improve Harecastle Tunnel's "air draught" – its free height above the water level) meant that the T&M would always be lower than the Macclesfield. The Hall Green Branch is now considered to be an extension of the Macclesfield Canal, which now meets the T&M at [[Hardings Wood Junction]] (just short of the Harecastle Tunnel north portal).{{fact|date=March 2022}}

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]], built 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.{{fact|date=March 2022}}

===Round locks===
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.{{fact|date=March 2022}}

===Drop locks===
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).{{fact|date=March 2022}}

===Flood locks===
A ''flood lock'' is to prevent a river from flooding a connected waterway. It is typically installed where a canal leaves a river. At normal river levels, the lock gates are left open, and the height of the canal is allowed to rise and fall with the height of the river.{{fact|date=March 2022}}

However, if the river floods beyond a safe limit for the canal, then the gates are closed (and an extra lock created) until the river drops again. Since this is a true lock it is possible for boats to leave the canal for the flooded river despite the difference in water levels (though this is not likely to be wise) or (more sensibly) to allow boats caught out on the flood to gain refuge in the canal.{{fact|date=March 2022}}

Note that if the canal is simply a navigation cut connecting two stretches of the same river, the flood lock will be at the upstream end of the cut (the downstream end will have a conventional lock).{{fact|date=March 2022}}

Flood locks which have been used only as flood ''gates'' (see below) are often incapable of reverting to their former purpose without refurbishment. That is, where only outer gates are ever closed (probably because a waterway is not a true commercial one, and therefore there is no financial imperative for a boat to venture out onto a flooded river) inner gates soon suffer from lack of maintenance. A good example is on the [[Calder and Hebble Navigation]], where structures referred to in the boating guides as "Flood Locks" are clearly only capable of being used for flood-prevention, not for "penning" boats to or from the river in flood.{{fact|date=March 2022}}

===Flood gates===
{{main|Flood gate}}
A ''flood gate'' or ''stop gate'' is the cheaper equivalent of a flood lock. Only one set of gates exist, and so when the river is higher than the canal, the gates are closed and navigation ceases. These are quite common in the French inland waterways system. Flood gates may also be used to sub-divide long [[canal pound]]s or protect, in case of bank collapse, the surrounding area if this is lower than the water level of the canal. They are commonly found at the ends of long embankments and at aqueducts. These gates are often overlooked because they lack balance beams and are only a little higher than normal canal level.{{fact|date=March 2022}}

=== Bi-directional gates and locks ===
Where a lock is tidal (i.e. one side of the lock has water whose level varies with the tide) or where a canal meets a river whose level may vary, the water on the tidal or river side (the "downstream" side) may rise above the water on the normal "upper" side. The "upstream" pointing doors will then fail to do their job, and will simply drift open. To prevent water flowing the wrong way through the lock, there will need to be at least one set of gates pointing in the "wrong" direction. If it is desirable that boats can use the lock in these circumstances, then there needs to be a full set of gates pointing towards the tidal or river side. The usual method is to have gates pointing in opposite directions at both ends of the chamber (alternatively, the "paired stop lock" arrangement of two separate sequential locks pointing in opposite directions would work here – but would require an extra chamber). If navigation is not required (or impossible) at one "extreme" (e.g. allow navigation above mid-tide, but just prevent the canal emptying at low tide) then it is only necessary to have one set of bi-directional gates.{{fact|date=March 2022}}

===Tidal locks===
A sea lock is one that connects a canal or river directly with an estuary or ocean.  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.{{fact|date=March 2022}} Examples:
* ''A canal joining a river whose levels are always lower than the canal.'' All that is needed is an ordinary lock, with the gates pointing up the canal. The lock is used normally so long as the tide is high enough to float boats through the lower gates. If near low tide the lock becomes unusable, then the gates can be barred (and simply become a "reverse flood gate", holding water in the canal). This arrangement also applies to some sea locks (e.g. [[Bude Canal]]).
* ''A canal joining a river which is normally below it, but which can rise above it (at very high tides, or after heavy rain).'' One pair of gates can be made bidirectional, i.e. the inward-pointing gates would be supplemented by a pair pointing out to the river. When the river is higher than the canal, the normal gates would just drift open, but the additional pair of gates can be closed to protect the canal, and prevent navigation to the river. In effect, we have simply added a flood gate.
* ''As above, but where it is safe to navigate even when the river is higher than the canal''. The lock will be fully bidirectional (two pairs of oppositely pointing gates at each end) to allow boats to pass at any normal river levels. At extreme low or high tides unsuitable for navigation, the appropriate sets of gates are barred to prevent passage.{{fact|date=March 2022}}

===Inlet locks===
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]].{{fact|date=March 2022}}

===Very large locks===
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.{{fact|date=March 2022}}

The [[List of locks and dams of the Upper Mississippi River|29 locks]] on the [[Mississippi River]] are typically {{convert|600|ft|m}} long while tug and barge combinations are as much as {{convert|1200|ft|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.{{fact|date=March 2022}}

The gates of a [[Guillotine lock]] work in a way similar to a sluice gate, but most [[Lock (water transport)|canal lock]] gates are hinged to swing like doors.{{fact|date=March 2022}}

==== Hiram M. Chittenden Locks ====
Every November, the large lock of the [[Hiram M. Chittenden Locks]] (better known locally as the "Ballard Locks" in reference to the [[Ballard, Seattle, Washington|Seattle neighborhood]] they are located in) was emptied for maintenance, as seen in the November 2004 pictures below. This provides an opportunity to visualize how a lock works without the water obscuring the bottom of the lock. For reference, the picture far left shows the lock in operation, with a tug and a barge (loaded with sand and gravel) waiting for the gates to open. In the bottom left corner of the picture may be seen the cut-out in the side wall that contains the gate when open.{{fact|date=March 2022}}

The lock has three pairs of gates, one pair at each end and one pair in the middle so that half the length of the lock can be used when the whole length is not required, thus saving water. The barely visible person walking along the bottom of the lock in the second picture gives an indication of the vast size of this lock. In both pictures of the end gates, the string of [[penstock]] openings are visible along the sides at the bottom. The water entering and leaving the lock flows by gravity through these openings. It requires around 15 minutes to fill or empty the lock.{{fact|date=March 2022}}
<gallery mode=packed>
Hiram M. Chittenden Locks-3.JPG|[[Hiram M. Chittenden Locks]]: tug and barge in lock when full.
Locks-1.jpg|Lock emptied for maintenance – low water end of the lock.
Locks-3.jpg|Lock emptied for maintenance – centre pair of gates.
Locks-2.jpg|Lock emptied for maintenance – high water end of the lock.
</gallery>

=== Van gate ===
This type of gate was a Dutch invention in the early 19th century. The Van gate has the special property that it can open in the direction of high water solely using water pressure. This gate type was primarily used to purposely flood certain regions, for instance in the case of the [[Hollandic Water Line]]. Nowadays this type of gate can still be found in a few places, for example in [[Gouda, South Holland|Gouda]].{{fact|date=March 2022}}

The design of a Van gate is shown in the image on the lower right. When the tube connecting the separate chamber with the high water level side of the sluice is closed and the connection with the low water level side opened, the water level in the separate chamber will drop to the level on the low water level side of the sluice. The surface area of the gate separating the chamber from the high water level side of the sluice is larger than that of the gate closing the sluice. This results into a net force that opens up the sluice.{{fact|date=March 2022}}

==History and development==
===Dams and weirs===
In ancient times river transport was common, but rivers were often too shallow to carry anything but the smallest boats. Ancient people discovered that rivers could be made to carry larger boats by making [[dam]]s to raise the water level. The water behind the dam deepened until it spilled over the top creating a [[weir]]. The water was then deep enough to carry larger boats. This dam building was repeated along the river, until there were "steps" of deep water.{{fact|date=March 2022}}

===Flash locks===
{{Main|Flash lock}}
The development of dams and weirs created the problem of how to get the boats between these "steps" of water. An early and crude way of doing this was by a [[flash lock]]. A flash lock consisted essentially of a small opening in the dam, which could be quickly opened and closed. On the Thames in England, this was closed with vertical posts (known as rymers) against which boards were placed to block the gap.

When the gap was opened, a torrent of water would spill out, carrying a "downstream" boat with it, or allowing an "upstream" boat to be man hauled or winched through against the flow. When the boat was through, the opening would be quickly closed again. The "gate" could also be opened to release a 'flash' downstream to enable grounded boats to get off shoals, hence the name.{{fact|date=March 2022}}

This system was used extensively in [[History of China#Ancient China|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.{{fact|date=March 2022}}

===Staunch===
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.{{fact|date=March 2022}}

===Turf-sided lock===
Both these locks are in the canalised river section of the canal and so are over supplied with water.{{fact|date=March 2022}}

==Use of water==
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.{{fact|date=March 2022}}

===Design===
When planning a canal, the designer will attempt to build a summit level with a large [[reservoir (water)|reservoir]], or one supplied by an artificial watercourse from a distant source, or one as long as possible (to act as its own reservoir) or which cuts across as many springs or rivers as possible (or all of these).  Driving the summit level through a deep cutting or tunnel may cut through the water table as well as underground sources of water.{{fact|date=March 2022}}

===Pumping===
Where it is clear that natural supply will not be sufficient to replenish the summit level at the rate that water will be used (or to allow for unexpected periods of drought) the designer may plan for water to be back-[[pump]]ed back up to the summit from lower down. Such remedies may of course be installed later, when poor planning becomes apparent, or when there is an unforeseeable increase in traffic or [[Wikt:dearth|dearth]] of rain. On a smaller scale, some local pumping may be required at particular points (water is continually recycled through some locks on the [[Kennet and Avon canal]]).{{fact|date=March 2022}}

===Water saving basins=== 
A way of reducing the water used by a lock is to give it one or multiple reservoirs, whose levels are intermediate between the upper and lower pounds. These reservoirs can store the water drained from the lock as a boat descends, and release it to fill the next time a boat ascends. This saves half the amount of water lost downhill in each fill–empty cycle. Generally these reservoirs are called "saving basins".{{fact|date=March 2022}}

Installing a single side pond will save 1/3 of the water, whereas three side ponds will save 60% of the water: the first 1/5 of the water goes into the top pond, the 2nd 1/5 into the middle pond, the 3rd 1/5 into the bottom pond – and 2/5 is wasted at each passage (assuming the area of each pond equals the area of the lock). The formula for <math>n</math> side ponds of optimal altitude and depth, with area of each pond, <math>a_p</math>, and area of the lock, <math>a_l</math>, is:

<math>\frac{\text{water used with side ponds}}{\text{water used without side ponds}}=1-\frac{n}{n+1+a_l/a_p}</math>.

For example, the Hindenburg-lock (in [[Hanover|Hannover]], Germany, built 1919–1928) has two lock chambers of 225 m length, each of which would use 42,000 m<sup>3</sup> of water for a full locking cycle. Due to the use of 10 water saving basins, only 10,500 m<sup>3</sup> 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.{{fact|date=March 2022}}

Side ponds were also installed on the [[Grand Union Canal]] and the [[Coventry Canal]], among others. Most 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|date=March 2012}} 
A notable survival is at the four-lock staircase at [[Watford Locks|Watford Gap]].
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.{{fact|date=March 2022}}

==Alternatives==
As well as the "static" approaches mentioned earlier (various types of contouring, excavating, and spanning), there were many ingenious "dynamic" solutions, mostly variations on the boat lift or the inclined plane. These tend to be more expensive to install and operate, but offer faster transit and waste less water.{{fact|date=March 2022}}

===Inclined plane===
{{Main|Canal inclined plane}}
An inclined plane consists of a cradle (to hold a barge) or caisson (a box full of water in which a barge can float) which moves on rails sideways up a slope from one waterway to the other. Since the box is "wet" (filled with water), [[Archimedes' principle]] ensures that the caisson always weighs the same, regardless of the size of boat being carried (or even if it contains only water). This makes for easy counterbalancing by a fixed weight or by a second caisson. The motive power may be steam or hydraulic, or may come from overbalancing the top caisson with extra water from the upper waterway.{{fact|date=March 2022}}

===Boat lift===
{{Main|Boat lift}}
The [[Falkirk Wheel]], the world's first rotating boat lift, acts as the centrepiece of the restoration of the [[Forth and Clyde]] and [[Union Canal (Scotland)|Union Canals]]. The Wheel replaced a flight of locks which formerly connected the canals and which were filled in<!--not a mistake--> in 1930. It was the winning design in a competition to design a new lock. Visitors can now take a boat trip on the Wheel and be lifted over {{convert|100|ft|m}} in a few minutes compared to the time it took when the original lock staircase operated.{{clarify|if you don't specify what that former time was, the clause is useless.|date=February 2018}}

The Victorian [[Anderton Boat Lift]], the world's first vertical boat lift, linking the [[Trent and Mersey Canal]] and the [[River Weaver]] in [[Cheshire]], was reopened in 2002. The world's highest boat lift in [[Strépy-Thieu boat lift|Strépy-Thieu]] in Belgium raises or lowers {{convert|1,350|t}} boats by {{convert|73.15|m|ft}}.{{fact|date=March 2022}}

Another 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]]. Its dual lifts are the highest [[hydraulic]] boat lifts in the world, rising {{convert|19.8|m|ft|abbr=on}}. This was a considerable accomplishment when conventional locks usually only had a {{convert|2|m|ft|abbr=on}} rise. Each lift has a capacity of {{convert|1,300|t}}. The basins are {{convert|140|ft|m}} long, {{convert|33|ft|m}} wide and {{convert|9|ft|10|in|m}} deep. The vertical distance lifted is {{convert|65|ft|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.{{fact|date=March 2022}}

====Marine railway====
A [[marine railway]] is similar to a [[canal inclined plane]] in that it moves boats up or down a slope on rails. However, the vessel is carried in a dry carrying frame, or cradle, rather than in a water-filled caisson. The principle is based on the [[patent slip]], used for hauling vessels out of the water for maintenance.{{fact|date=March 2022}}

In operation, a boat is navigated into the carrying frame, which has been lowered into the water. The boat is secured to the cradle, possibly by raising slings under the hull using [[hydraulic]]s, and the cradle is hauled out of the water and up the hill with a cable. At the top of the slope, the cradle is lowered into the upper waterway, and the boat released. As the boat is not floating, [[Archimedes' principle]] does not apply, so the weight lifted or lowered by the device varies – making counterbalancing (by dead weights or a second boat carriage) more difficult.{{fact|date=March 2022}}

In some locations, such as the [[Big Chute Marine Railway]] on the [[Trent-Severn Waterway]], in [[Ontario]], Canada, a marine railway was installed as a temporary measure at the planned site of a flight of conventional locks. In this and several other cases, the locks were never built, and the marine railway continued to serve on a permanent basis.  Where there is a steep rise in the land a marine railway may be more effective than multiple locks, such as on the [[Elbląg Canal]].{{fact|date=March 2022}}

===Diagonal lock===
This concept in lock design has yet to be installed on any waterway. It is basically a shaft lock with a diagonal shaft. The proposal is for a long tube of reinforced concrete, of a size to accommodate the boats being lifted, to be built on the slope between the upper and lower levels. The bottom of the tube is sealed with a strong watertight door, but there is a single pair of conventional lock gates at the top, installed a boat's length from the far wall of the tube. The change in level is achieved by filling the tube with water from the top pound, or by draining. The vessel floats on the surface of the water, with a guide float or [[Pontoon (boat)|pontoon]], shaped to fit the tube, floating alongside to keep it clear of the walls. Side ponds, piped from the main tube, are incorporated to save water. In replacing a traditional flight or staircase of locks, a considerable time saving is anticipated. It differs from the similar [[caisson lock]] design in that the boat does not have to be carried in a submerged chamber.{{fact|date=March 2022}}

=== A combined system: Three Gorges Dam ===
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.{{fact|date=March 2022}}

==Ship sizes named after locks==
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]].{{fact|date=March 2022}}
<!-- * [[Suezmax]] Comment out Suezmax as the Suez has no locks... -->
</blockquote>
{{collapse bottom}}

== Dester13 ==

Fork99 we need to discuss. I was trying to put Canal Lock on the article but you then revert it. Canal Lock is an alternate term for “Lock (water navigation)” and it’s not a bad problem with no grammar errors. As i speak i have it saw Canal Lock article before it was deleted by admin in Wikipedia. So we here to add that sure. Reply? [[User:Dester13|Dester13]] ([[User talk:Dester13|talk]]) 22:13, 16 June 2023 (UTC)

:@[[User:Dester13|Dester13]]: As I said in my edit summary, the sentence you edited already discussed that this is in relation to canals. There’s no need to make the sentence a [[tautology (language)|tautology]]. Also, there’s been similar discussions on other articles you’ve edited. [[User:Fork99|Fork99]] ([[User talk:Fork99|talk]]) 22:24, 16 June 2023 (UTC)
::Okay then Fork99. But i swear that i just seen Canal Lock article in the past years before being deleted by admin, so it just only have Lock (water navigation) article then I may have to add it there. I agree. [[User:Dester13|Dester13]] ([[User talk:Dester13|talk]]) 23:15, 16 June 2023 (UTC)
:::I don’t understand exactly what you mean, but if you mean that there were articles at the present redirects [[Canal lock]] or [[Canal Lock]], there is no need for duplicate articles on Wikipedia, see the pages at [[Wikipedia:MERGEREASON]] and [[Wikipedia:Redirect]]. Those redirects were created at least a decade or more ago. [[User:Fork99|Fork99]] ([[User talk:Fork99|talk]]) 00:23, 17 June 2023 (UTC)
::::While this not i want to say Fork99. I just want to put Canal Lock in the Lock (water navigation) article because i seen “Canal Lock” page in the past years before being removed by admin, and it’s another term for that. There is no reason for grammar errors and wording unclears sure. Reply to me if it right? I swear.

=== Ending Message ===
We wish that i want to put Canal Lock term at this article after it deleted by admin in past years. [[User:Dester13|Dester13]] ([[User talk:Dester13|talk]]) 01:11, 17 June 2023 (UTC)

:I’m sorry, what? Firstly, correct if I’m wrong, but are you using a translator program from your presumably native language to English to edit on the English Wikipedia? If so, there are lots of Wikipedias in different languages (see this link: [[List of Wikipedias#Basic list|List of Wikipedias]]). Secondly, a lock (water transport) can also refer to a river lock, not just a canal lock. This is explained in this article’s lead. [[User:Fork99|Fork99]] ([[User talk:Fork99|talk]]) 01:37, 17 June 2023 (UTC)
::While okay than. I will add River Lock in this article instead of Canal Lock Fork99. I sorry sure. [[User:Dester13|Dester13]] ([[User talk:Dester13|talk]]) 14:17, 17 June 2023 (UTC)
:::No. Specific typing does not create a new term. A 'Ball' is not also known as a 'Red Ball'. [[User:MrOllie|MrOllie]] ([[User talk:MrOllie|talk]]) 14:23, 17 June 2023 (UTC)
::::Dude MrOllie. I’m agree with Fork99. The sentence “Secondly, a lock (water transport) (diverted into water navigation) can also refer to a river lock” tells me to add River Lock refer in this article instead of Canal Lock. I’m right sure so i decide to put River Lock on it. [[User:Dester13|Dester13]] ([[User talk:Dester13|talk]]) 16:28, 17 June 2023 (UTC)
:::::You are misreading Fork99's comment. [[User:MrOllie|MrOllie]] ([[User talk:MrOllie|talk]]) 16:40, 17 June 2023 (UTC)
::::::@[[User:Dester13|Dester13]]: As I said in a different discussion at [[Talk:Apostrophe#Dester13]], please STOP using Google Translate. If you genuinely believe that “canal lock” is the same as a “lock”, or for that matter, ANY word on ANY article, please use the article’s talk page (such as this one) to ask a native speaker of English. For example: “I’m not a native speaker of English, but does the word ‘lock’ in the article need the clarification that it’s also a ‘canal lock’? If so, can someone add this to the article for me please?”
::::::We do not need to have this same conversation over multiple articles more than once (see [[Talk:Apostrophe#Dester13]], [[Talk:Volcanic plateau#Dester13]], [[Talk:Cities: Skylines#Dester13]], [[Talk:Railway track#Dester13]]).
::::::As I said in other discussions, machine translation of languages is very difficult. Without further context, a computer would not understand that an English ‘ball’ could refer to either ‘a formal dance party’ OR ‘a usually round-shaped object that is usually used in various sports’. I’m sure that your native language (like any language, including English) has similar homonyms, homophones and linguistic aspects that a native English speaker would find difficult to learn and understand. [[User:Fork99|Fork99]] ([[User talk:Fork99|talk]]) 19:51, 17 June 2023 (UTC)
:::::::Well well, another user has taken Dester to [[WP:ANI|ANI]] and gotten Dester and their other accounts all blocked for sockpuppetry, among other things. Hopefully that’s the last of that. [[User:Fork99|Fork99]] ([[User talk:Fork99|talk]]) 10:03, 18 June 2023 (UTC)