lock (water transport)
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A lock is a device used for raising and lowering
boat A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size, shape, cargo or passenger capacity, or its ability to carry boats. Small boats are typically found on inl ...
s,
ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...
s and other
watercraft Any vehicle used in or on water as well as underwater, including boats, ships, hovercraft and submarines, is a watercraft, also known as a water vessel or waterborne vessel. A watercraft usually has a propulsive capability (whether by sail, ...
between stretches of water of different levels on river and canal
waterway A waterway is any navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other languages. A first distinction is necessary b ...
s. The distinguishing feature of a lock is a fixed chamber in which the water level can be varied; whereas in a
caisson lock The caisson lock is a type of canal lock in which a narrowboat is floated into a sealed watertight box and raised or lowered between two different canal water levels. It was invented in the late 18th century as a solution to the problem posed ...
, a
boat lift A boat lift, ship lift, or lift lock is a machine for transporting boats between water at two different elevations, and is an alternative to the canal lock. It may be vertically moving, like the Anderton boat lift in England, rotational, like ...
, or on a
canal inclined plane An inclined plane is a type of cable railway used on some canals for raising boats between different water levels. Boats may be conveyed afloat, in caissons, or may be carried in cradles or slings. History Inclined planes have evolved over the ...
, it is the chamber itself (usually then called a caisson) that rises and falls. Locks are used to make a
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
more easily navigable, or to allow a
canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flo ...
to cross land that is not level. Later canals used more and larger locks to allow a more direct route to be taken.


Pound lock

A ''pound lock'' is most commonly used on
canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flo ...
s and
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
s today. A pound lock has a chamber with
gates Gates is the plural of gate, a point of entry to a space which is enclosed by walls. It may also refer to: People * Gates (surname), various people with the last name * Gates Brown (1939-2013), American Major League Baseball player * Gates McFadde ...
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 first used in China during the
Song Dynasty The Song dynasty (; ; 960–1279) was an imperial dynasty of China that began in 960 and lasted until 1279. The dynasty was founded by Emperor Taizu of Song following his usurpation of the throne of the Later Zhou. The Song conquered the rest ...
(960–1279 AD), having been pioneered by the Song politician and naval engineer Qiao Weiyue in 984.Needham, Volume 4, Part 3, 350-351. They replaced earlier double
slipway A slipway, also known as boat ramp or launch or boat deployer, is a ramp on the shore by which ships or boats can be moved to and from the water. They are used for building and repairing ships and boats, and for launching and retrieving small ...
s that had caused trouble and are mentioned by the Chinese
polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose knowledge spans a substantial number of subjects, known to draw on complex bodies of knowledge to solve specific pro ...
Shen Kuo (1031–1095) in his book '' Dream Pool Essays'' (published in 1088),Needham, Volume 4, Part 3, 351–52. and fully described in the Chinese historical text ''Song Shi'' (compiled in 1345):Needham, Volume 4, Part 3, 351.
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 or at each lock and in the Grand Canal the level was raised in this way by . In medieval Europe a sort of pound lock was built in 1373 at
Vreeswijk Vreeswijk is a former village and municipality in the Dutch province of Utrecht. The municipality merged with Jutphaas in 1971, and is now the southern half of the town of Nieuwegein. The former village was located on the Lek River, near wher ...
, Netherlands.Needham, Volume 4, Part 3, 357. 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 Bruges ( , nl, Brugge ) is the capital and largest city of the province of West Flanders in the Flemish Region of Belgium, in the northwest of the country, and the sixth-largest city of the country by population. The area of the whole city a ...
, Belgium. The
Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...
Bertola da Novate (c. 1410–1475) constructed 18 pound locks on the Naviglio di Bereguardo (part of the
Milan Milan ( , , Lombard: ; it, Milano ) is a city in northern Italy, capital of Lombardy, and the second-most populous city proper in Italy after Rome. The city proper has a population of about 1.4 million, while its metropolitan city h ...
canal system sponsored by
Francesco Sforza Francesco I Sforza (; 23 July 1401 – 8 March 1466) was an Italian condottiero who founded the Sforza dynasty in the duchy of Milan, ruling as its (fourth) duke from 1450 until his death. In the 1420s, he participated in the War of L'A ...
) between 1452 and 1458.Needham, Volume 4, Part 3, 358.


Basic construction and operation

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. 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. 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. 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, where it is quicker for boats to go through in convoy.


Details and terminology


Rise

The ''rise'' is the change in water-level in the lock. The two deepest locks on the English canal system are Bath deep lock on the Kennet and Avon Canal and Tuel Lane Lock on the Rochdale Canal, which both have a rise of nearly . 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 The Oxford Canal is a narrowboat canal in central England linking the City of Oxford with the Coventry Canal at Hawkesbury (just north of Coventry and south of Bedworth) via Banbury and Rugby. Completed in 1790, it connects to the River Thames ...
: both have a rise of about . Again, sources vary as to which is the deepest, and in any case Etruria has been deepened over the years to accommodate subsidence. By comparison, the Carrapatelo and Valeira locks on the
Douro The Douro (, , ; es, Duero ; la, Durius) is the highest-flow river of the Iberian Peninsula. It rises near Duruelo de la Sierra in Soria Province, central Spain, meanders south briefly then flows generally west through the north-west part o ...
river in Portugal, which are long and wide, have maximum lifts of and respectively. The two Ardnacrusha locks near Limerick on the Shannon navigation in Ireland have a rise of . The upper chamber rises and is connected to the lower chamber by a tunnel, which when descending does not become visible until the chamber is nearly empty.


Pound

A '' pound'' is the level stretch of water between two locks (also known as a ''reach'').


Cill

The ''cill'', also spelled ''sill'', 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 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 center than at the edges. In some locks, there is a piece of oak about 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. Some canal operation authorities, primarily in the United States and Canada, call the ledge a ''miter sill'' (mitre sill in Canada).Merriam-Webster Dictionary, definition of miter sill
Retrieved Jan. 28, 2015.


Photo gallery

File:Canal Saint-Denis-Ecluse N°1-Le petit bief.JPG, The cill exposed in the deep Pont de Flandre lock on the
Canal Saint-Denis The Canal Saint-Denis is a canal in Paris that is in length. The canal connects the Canal de l'Ourcq, at a point north-northwest of the Bassin de la Villette in the 19th arrondissement, with the suburban municipalities of Saint-Denis and Auberv ...
, Paris File:JesusGreenLock-Cambridge.jpg, Top gate of a lock, showing the balance beams and paddle winding gear File:ZSchützmechanik.jpg, 200-year-old paddle gear on the Wiener Neustädter Kanal, Austria File:BCN water conservation lock.jpg, Water conservation gear on the
Birmingham Canal Navigations Birmingham Canal Navigations (BCN) is a network of canals connecting Birmingham, Wolverhampton, and the eastern part of the Black Country. The BCN is connected to the rest of the English canal system at several junctions. It was owned and opera ...
File:Lock gate cogs, Montgomery Canal - geograph.org.uk - 1806427.jpg, Lock gate controls on a
canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flo ...


Gates

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 An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
or
elm Elms are deciduous and semi-deciduous trees comprising the flowering plant genus ''Ulmus'' in the plant family Ulmaceae. They are distributed over most of the Northern Hemisphere, inhabiting the temperate and tropical-montane regions of North ...
(or now sometimes steel). The most common arrangement, usually called ''miter gates'', was invented by
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially res ...
sometime around the late 15th century.


Paddle

On the old
Erie Canal The Erie Canal is a historic canal in upstate New York that runs east-west between the Hudson River and Lake Erie. Completed in 1825, the canal was the first navigable waterway connecting the Atlantic Ocean to the Great Lakes, vastly reducing t ...
, 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.


Windlass ("lock key")

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


Swell or swelling

A ''swell'' was caused by opening suddenly the paddle valves in the lock gates, or when emptying a lock. To help boats traveling downstream exit 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. 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. 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. The Erie Canal management did not like swelling for two reasons. First, it used too much water lowering the water on the pound above sometimes causing boats to run aground. In addition, it raised the water level on the pound below causing some boats to strike bridges or get stuck.


Snubbing posts

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. A rope 2½ inches (6.3 cm) in diameter and about 60 feet (18 meters) long was typically used on the Erie Canal to snub a boat in a lock. 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.


Variations


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 The Paw Paw Tunnel is a canal tunnel on the Chesapeake and Ohio Canal (C&O) in Allegany County, Maryland. Located near Paw Paw, West Virginia, it was built to bypass the Paw Paw Bends, a stretch of the Potomac River containing five horseshoe-sha ...
. and also the Chenango Canal


Powered operation

On large modern canals, especially very large ones such as
ship canal A ship canal is a canal especially intended to accommodate ships used on the oceans, seas, or lakes to which it is connected. Definition Ship canals can be distinguished from barge canals, which are intended to carry barges and other vessel ...
s, the gates and paddles are too large to be hand operated, and are operated by
hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...
or
electric Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
al equipment. On the Caledonian Canal the lock gates were operated by man-powered capstans, one connected by chains to open the gate and another to draw it closed. By 1968 these had been replaced by hydraulic power acting through steel rams.


Fish ladders

The construction of locks (or weirs and dams) on rivers obstructs the passage of fish. Some fish such as lampreys,
trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', '' Salmo'' and '' Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salm ...
and
salmon Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus ''Salmo'') and North Pacific (genus '' Oncorhy ...
go upstream to spawn. Measures such as a
fish ladder A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as move ...
are often taken to counteract this. Navigation locks have also potential to be operated as fishways to provide increased access for a range of biota.


Special cases


Doubled, paired or twinned locks

Locks can be built side by side on the same waterway. This is variously called ''doubling'', ''pairing'', or ''twinning''. The
Panama Canal The Panama Canal ( es, Canal de Panamá, link=no) is an artificial waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean and divides North and South America. The canal cuts across the Isthmus of Panama and is a condui ...
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. The Belgian Compan
SBE Engineering
worked on this project. 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 Hillmorton is a suburb of Rugby, Warwickshire, England, around south-east of Rugby town centre, forming much of the eastern half of the town. It is also a ward of the Borough of Rugby. Hillmorton was historically a village in its own right, b ...
on the
Oxford Canal The Oxford Canal is a narrowboat canal in central England linking the City of Oxford with the Coventry Canal at Hawkesbury (just north of Coventry and south of Bedworth) via Banbury and Rugby. Completed in 1790, it connects to the River Thames ...
. Elsewhere they are still in use; a pair of twinned locks has been opened in 2014 on the Dortmund-Ems Canal near
Münster Münster (; nds, Mönster) is an independent city (''Kreisfreie Stadt'') in North Rhine-Westphalia, Germany. It is in the northern part of the state and is considered to be the cultural centre of the Westphalia region. It is also a state di ...
, Germany. The once-famous staircase at
Lockport, New York Lockport is both a city and the town that surrounds it in Niagara County, New York. The city is the Niagara county seat, with a population of 21,165 according to 2010 census figures, and an estimated population of 20,305 as of 2019. Its name d ...
, was also a doubled set of locks. Five twinned locks allowed east- and west-bound boats to climb or descend the 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.


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 The Stratford-upon-Avon Canal is a canal in the south Midlands of England. The canal, which was built between 1793 and 1816, runs for in total, and consists of two sections. The dividing line is at Kingswood Junction, which gives access to the ...
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.


Round locks

The best known example of such a round lock is the
Agde Round Lock The Agde Round Lock (french: L'Écluse Ronde d'Agde) is a canal lock on the Canal du Midi that connects to the Hérault River in Agde France. It is almost unique because it is round, which allows a boat to turn around, and the fact that it has th ...
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. 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 The Canal latéral à la Loire (, "canal parallel to the Loire") was constructed between 1827 and 1838 to connect the Canal de Briare at Briare and the Canal du Centre at Digoin, a distance of . It replaced the use of the river Loire, which wa ...
with the River Allier.


Drop locks

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. 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 Dalmuir (; gd, Dail Mhoire) is an area northwest of Glasgow, Scotland, on the western side of Clydebank, and part of West Dunbartonshire Council Area. The name is a lowland Scots derivation of the Gaelic meaning Big Field. The area was ori ...
on the
Forth and Clyde Canal The Forth and Clyde Canal is a canal opened in 1790, crossing central Scotland; it provided a route for the seagoing vessels of the day between the Firth of Forth and the Firth of Clyde at the narrowest part of the Scottish Lowlands. This allowe ...
in Scotland. 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 burn is an injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or ultraviolet radiation (like sunburn). Most burns are due to heat from hot liquids (called scalding), solids, or fire. Burns occur ma ...
.


Very large locks

The world's largest lock was, until 2016, the Berendrecht Lock, giving access to the
Port of Antwerp The Port of Antwerp-Bruges is the port of the City of Antwerp. It is located in Flanders (Belgium), mainly in the province of Antwerp but also partially in the province of East Flanders. It is a seaport in the heart of Europe accessible to ...
in Belgium. In 2016 the Kieldrecht Lock in the same port became the largest. The lock is long, wide, drops , 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 Bollène (; Provençal: ''Bouleno'') is a commune in the Vaucluse department in the Provence-Alpes-Côte d'Azur region in southeastern France. Geography Bollène is a commune located in the north of the Vaucluse department next to the juncti ...
lock on the
River Rhône A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wa ...
has a fall of at least , the Leerstetten, Eckersmühlen and Hilpoltstein locks on the
Rhine–Main–Danube Canal The Rhine–Main–Danube Canal (German: ''Rhein-Main-Donau-Kanal''; also called Main-Danube Canal, RMD Canal or Europa Canal), is a canal in Bavaria, Germany. Connecting the Main and the Danube riv ...
have a fall of , each and the
Oskemen Oskemen ( kk, Өскемен, translit=Öskemen ), or Ust-Kamenogorsk (russian: Усть-Каменого́рск), is the administrative center of East Kazakhstan Region of Kazakhstan. Population: Name The city has two official names. In th ...
Lock on the Irtysh River in
Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbeki ...
has a drop of .


History and development


Pound lock

The natural extension of the staunch was to provide an upper gate (or pair of gates) to form an intermediate "pound" which was all that need be emptied when a boat passed through. This type of lock, called a pound lock was known in Imperial China and Europe. Pound locks were first used in medieval China during the
Song Dynasty The Song dynasty (; ; 960–1279) was an imperial dynasty of China that began in 960 and lasted until 1279. The dynasty was founded by Emperor Taizu of Song following his usurpation of the throne of the Later Zhou. The Song conquered the rest ...
(960–1279 AD). The Songshi or History of the Song Dynasty, volume 307, biography 66, records how Qiao Weiyue, a high-ranking tax administrator, was frustrated at the frequent losses incurred when his grain barges were wrecked on the
West River West River may refer to: Rivers Canada *West River (Antigonish, Nova Scotia) in Antigonish County, Nova Scotia * West River (Pictou, Nova Scotia) in Pictou County, Nova Scotia * West River (Halifax, Nova Scotia) in Sheet Harbour, Nova Scotia * West ...
near
Huai'an Huai'an (), formerly called Huaiyin () until 2001, is a prefecture-level city in the central part of Jiangsu province in East China, Eastern China. Huai'an is situated almost directly south of Lianyungang, southeast of Suqian, northwest of Yan ...
in
Jiangsu Jiangsu (; ; pinyin: Jiāngsū, alternatively romanized as Kiangsu or Chiangsu) is an eastern coastal province of the People's Republic of China. It is one of the leading provinces in finance, education, technology, and tourism, with its ca ...
. The soldiers at one double slipway, he discovered, had plotted with bandits to wreck heavy imperial barges so that they could steal the spilled grain. In 984 Qiao installed a pair of sluice-gates two hundred and fifty feet apart, the entire structure roofed over like a building. By siting two staunch gates so close to one another, Qiao had created a short stretch of canal, effectively a pound-lock, filled from the canal above by raising individual wooden baulks in the top gate and emptied into the canal below by lowering baulks in the top gate and raising ones in the lower.


Turf-sided lock

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 18th century before the advent of canals in Britain. 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 Garston Lock () is a lock on the Kennet and Avon Canal. It is near the M4 motorway and near Reading, England. Garston Lock was built between 1718 and 1723 under the supervision of the engineer John Hore of Newbury, and this stretch of the river ...
, and
Monkey Marsh Lock Monkey Marsh Lock is a lock on the Kennet and Avon Canal, at Thatcham, Berkshire, England. Monkey Marsh Lock was built between 1718 and 1723 under the supervision of the engineer John Hore of Newbury. The canal is administered by Canal & River T ...
, on the Kennet and Avon Canal.


Use of water


Water saving basins

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.


Alternatives


Inclined plane

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 Grand Union Canal in England is part of the British canal system. It is the principal navigable waterway between London and the Midlands. Starting in London, one arm runs to Leicester and another ends in Birmingham, with the latter ...
. 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. There are plans to restore it, and some funding has been obtained.


Caisson lock

Around 1800 the use of caisson locks was proposed by Robert Weldon for the
Somerset Coal Canal The Somerset Coal Canal (originally known as the Somersetshire Coal Canal) was a narrow canal in England, built around 1800. Its route began in basins at Paulton and Timsbury, ran to nearby Camerton, over two aqueducts at Dunkerton, through a ...
in England. In this underwater lift, the chamber was long and deep and contained a completely enclosed wooden box big enough to take a barge. This box moved up and down in the 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 of water – at a pressure of , in total. One of these "locks" was built and demonstrated to the Prince Regent (later
George IV George IV (George Augustus Frederick; 12 August 1762 – 26 June 1830) was King of the United Kingdom of Great Britain and Ireland and King of Hanover from the death of his father, King George III, on 29 January 1820, until his own death ten y ...
), but it had various engineering problems and the design was not put into use on the Coal Canal.


Hydro-pneumatic canal lift

Possibly inspired by Weldon's caisson lock,
William Congreve William Congreve (24 January 1670 – 19 January 1729) was an English playwright and poet of the Restoration period. He is known for his clever, satirical dialogue and influence on the comedy of manners style of that period. He was also a mi ...
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.


Shaft lock

Looking superficially similar to the caisson lock is the shaft lock. Shaft locks consist of a deep shaft with conventional upper gates. The lower gates are reached through a short tunnel. The gates only close off this approach tunnel so do not have to reach the full height of the lock. Notable examples have been built at Saint Denis (Paris, France), Horin (near Melnik, Czech Republic) and Anderten (Hannover Germany). The shaft lock at Minden has a fall of and has eight tanks linked in pairs to the lock chamber. As the lock is emptied water is run into each chamber in turn, for filling the water is released from the chambers thus saving the waste of a complete lockfull of water. An earlier attempt at a shaft lock had been made at Trollhättan in Sweden on the line of the present Göta canal. The fall would have been , astonishing in 1749. However the approach tunnel proved to be unusable in times of flood and the shaft lock was replaced by a 2-rise staircase in 1768.


Diagonal lock

This is similar to a shaft lock, but having the shaft built on an incline. Boats are moored to floating bollards which guide them along the shaft as it fills or empties. 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. Projects under consideration include the restoration of the
Lancaster Canal The Lancaster Canal is a canal in North West England, originally planned to run from Westhoughton in Lancashire to Kendal in south Cumbria ( historically in Westmorland). The section around the crossing of the River Ribble was never complete ...
to Kendal and the proposed new branch of the
Grand Union Canal The Grand Union Canal in England is part of the British canal system. It is the principal navigable waterway between London and the Midlands. Starting in London, one arm runs to Leicester and another ends in Birmingham, with the latter ...
between
Bedford Bedford is a market town in Bedfordshire, England. At the 2011 Census, the population of the Bedford built-up area (including Biddenham and Kempston) was 106,940, making it the second-largest settlement in Bedfordshire, behind Luton, whilst ...
and Milton Keynes.


See also

* Canal Safety Gates * Water slope *
Control lock A control lock, guard lock or stop lock differs from a normal canal lock in that its primary purpose is controlling variances in water level rather than raising or lowering vessels. A control lock may also be known as a tide lock where it is used t ...


References


External links


Deepest Canal Locks in England


– ''this demonstration shows guillotine-type gates for clarity''
Interactive lock game
for students with single and double flight locks and lesson plans
Video footage of the unique Drop Lock at Dalmuir on the Forth & Clyde Canal
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