Editing Lock (water navigation) (section)

==Special cases==
=== Doubled, paired or twinned locks ===
[[File:Lockport bartlett color.jpg|thumb|Doubled locks. Left lock has boat in it, right lock (center of drawing) is empty. This is on the Erie Canal at Lockport.]]
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 This facility has long been withdrawn on the English canals, although the disused paddle gear can sometimes be seen, as at [[Hillmorton]] on the [[Oxford Canal]]. Elsewhere they are still in use; a pair of twinned locks was opened in 2014 on the [[Dortmund–Ems Canal]] near [[Münster]], Germany.<ref>{{cite web|url=http://www.wna-datteln.wsv.de/projekt_wna/dek_suedstrecke/Schleusen/Zwillingsschleuse_Muenster/|title=Zwillingsschleuse Münster|language=de}}</ref>

The [[Soo Locks]] at Sault Ste. Marie include the two American locks, the MacArthur Lock which is {{cvt|800|ft|m}} long, {{cvt|80|ft|m}} wide, and {{cvt|29.5|ft|m}} deep and the Poe lock which is {{cvt|1200|ft|m}} long, {{cvt|110|ft|m}} wide, and {{cvt|32|ft|m}} deep, and the Canadian lock which is {{cvt|77|m|sp=us}} long, {{cvt|15.4|m|sp=us}} wide and {{cvt|13.5|m|sp=us}} deep. The MacArthur is used for ships which fit the smaller locks on the [[Welland Canal]], while the Poe lock accommodates the larger [[Lake freighter|lakers]] that can operate only on the upper four [[Great Lakes]]. The Canadian lock is used for recreational and tour boats.

The staircase at [[Lockport (city), New York|Lockport, New York]], was also a doubled set of locks. Five twinned locks allowed east- and west-bound boats to climb or descend the {{convert|60|ft|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 an emergency spillway and can still be seen, with the original lock gates having been restored in early 2016.<ref>{{cite web|url=https://www.governor.ny.gov/news/governor-cuomo-announces-funding-restoration-lockport-locks|title=Governor Cuomo Announces Funding For Restoration of Lockport Locks|date=17 August 2015|website=ny.gov|access-date=21 September 2018}}</ref>

===Lock flights===
[[File:Caen Hill Locks.jpg|thumb|The flight of 16 locks at [[Caen Hill locks|Caen Hill]] on the [[Kennet and Avon Canal]]]]
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.{{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}}===
[[File:Bingley Five Rise Locks 1.JPG|thumb|left|Staircase of five locks, dating from 1774, at [[Bingley Five Rise Locks|Bingley]], England<ref>{{Cite news |date=2024-03-21 |title=Bingley Five Rise Locks mark 250th anniversary |url=https://www.bbc.co.uk/news/uk-england-bradford-west-yorkshire-68617233 |access-date=2024-12-01 |work=BBC News |language=en-GB}}</ref>]] 
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.

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]].

[[File:Thorpe Top Treble instructions.jpg|thumb|upright|left|Instructions for descending the flight of three locks at Thorpe Top Treble on the [[Chesterfield Canal]]]]
Operation of a staircase is more involved than a flight. Inexperienced boaters may find operating staircase locks difficult. Key concerns 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.

One difference in using a staircase of either type (compared with a single lock, or a flight) is the optimal 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, in which keepers 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 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 unusual feats, such as 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.

===Stop locks===
When variable conditions meant that a higher water level in the new canal could not be guaranteed, then the older company would also build a stop lock (under its own control, with gates pointing towards its own canal) which could be closed when the new canal was low. This resulted in a sequential pair of locks, with gates pointing in opposite directions: one example was at Hall Green near [[Kidsgrove]], where the southern terminus of the [[Macclesfield Canal]] joined the [[Hall Green Branch]] of the earlier [[Trent and Mersey Canal]]. The four gate stop lock near Kings Norton Junction, between the [[Stratford-upon-Avon Canal]] and the [[Worcester and Birmingham Canal]] was replaced in 1914 by a pair of [[guillotine lock]] gates which stopped the water flow regardless of which canal was higher. These gates have been permanently open since nationalisation.<ref>''Birmingham's Canals'', Ray Shill, 1999, 2002, {{ISBN|0-7509-2077-7}}</ref>

===Round locks===
[[File:Agde bassin rond 3 portes.JPG|thumb|Agde Round Lock]]
The best known example of 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)|Hérault River]].<ref name=gmmidi2>{{cite web | url = http://www.tagweb.co.uk/french-waterways/0-waterways/midi.html | title = Canal du Midi | work = Afloat in France | publisher = grehanman guides | access-date = 2010-11-23}}</ref>

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 [[Allier (river)|River Allier]].<ref name=gmclall>{{cite web | url = http://www.tagweb.co.uk/french-waterways/0-waterways/loire-lateral.html | title = Canal lateral a la Loire | work = Afloat in France | publisher = grehanman guides | access-date = 2010-11-24}}</ref>

===Drop locks===
[[File:Dalmuir drop lock.jpg|thumb|[[Dalmuir]] drop lock]]
A drop lock can consist of two conventional lock chambers leading to a sump pound, or a single long chamber incorporating the sump – although the term properly applies only to the second case. As the pounds at either end of the structure are at the same height, the lock can only be emptied either by allowing water to run to waste from the sump to a lower stream or drain, or (less wastefully) by pumping water back up to the canal. Particularly in the two-chamber type, there would be a need for a bypass culvert, to allow water to move along the interrupted pound and so supply locks further down the canal. In the case of the single-chamber type, this can be achieved by keeping the lock full and leaving the gates open while not in use.<ref>{{cite web|url=http://www.gentles.info/link/Drop_Lock/Drop_Lock.htm|title=Dalmuir Drop Lock| access-date =22 October 2007 }}</ref>

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.<ref>{{cite web|url=http://www.voltimum.co.uk/news/496/infopro/Mitsubishi-helps-breath-new-life-into-important-canal-routes-.html|title=Mitsubishi helps breath new life into important canal routes|author=voltimum|date=11 December 2002| access-date =23 October 2007}}</ref> 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 (landform)|burn]].<ref>{{cite web|url=http://www.gentles.info/link/Drop_Lock/Drop_Lock.htm |title=Clydebank Drop Lock |publisher=Gentles.info |access-date=2011-08-05}}</ref>

===Very large locks===
[[File:Haven Antwerpen06.jpg|thumb|Berendrecht Lock (right) and Zandvliet Lock (left), located at the entrance to the Port of Antwerp (top) from the Scheldt (foreground)]]
[[File:Upper Mississippi River Lock & dam 6.jpg|thumb|[[List of locks and dams of the Upper Mississippi River|Upper Mississippi River]] <br> [[Lock and Dam No. 6]]]]
In 2016 the [[Kieldrecht Lock]] in the [[Port of Antwerp]] in Belgium took over the title of the world's largest lock from the [[Berendrecht Lock]] in the same port and still has the title for largest volume. In 2022 the [[IJmuiden sea lock]] serving the [[Port of Amsterdam]] became the world's largest lock by surface area. The lock is {{convert|500|m|ft|abbr=on}} long, {{convert|70|m|ft|abbr=on}} wide and has sliding lock gates creating a usable depth of {{convert|18|m|abbr=on}}. 

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 {{convert|23|m|abbr=on}}, the Leerstetten, Eckersmühlen and Hilpoltstein locks on the [[Rhine–Main–Danube Canal]] have a fall of {{convert|24.67|m|abbr=on}}, each and the [[Oskemen]] Lock on the [[Irtysh River]] in [[Kazakhstan]] has a drop of {{convert|42|m|abbr=on}}.<ref>{{cite web|url=http://www.waterwaysworld.com/latest.cgi?month=012008&start=20|title=Latest|publisher=Waterways World|access-date=2011-08-05|archive-date=2011-07-26|archive-url=https://web.archive.org/web/20110726045506/http://www.waterwaysworld.com/latest.cgi?month=012008&start=20|url-status=dead}}</ref>
<ref>{{cite web|url=https://www.portofamsterdam.com/nl/zeesluis-ijmuiden|title=Officiële opening van de grootste zeesluis ter wereld|work=Port of Amsterdam|date=26 January 2022|access-date=2022-01-22}}</ref><ref>{{cite news |last1=van den Buijs |first1=Dennis |title="Nederlanders kunnen niet rekenen": waarom Antwerpen en niet Amsterdam de grootste zeesluis ter wereld heeft |url=https://www.vrt.be/vrtnws/nl/2022/01/26/amsterdam-claimt-grootste-zeesluis-antwerpen-countert-de-nede/ |access-date=30 March 2022 |work=VRT |date=26 January 2022}}</ref>