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Lock (water transport)
Encyclopedia
A lock is a device for raising and lowering boats between stretches of water of different levels on river and canal waterway
s. The distinguishing feature of a lock is a fixed chamber in which the water level can be varied; whereas in a caisson lock
, a boat lift
, or on a canal inclined plane
, it is the chamber itself (usually then called a caisson
) that rises and falls.
Locks are used to make a river
more easily navigable, or to allow a canal
to take a reasonably direct line across land that is not level.
s and river
s. A pound lock has a chamber (the pound
) with gates
at both ends that control the level of water in the pound. In contrast, an earlier design with a single gate was known as a flash lock
.
Pound locks were used in ancient China
during the Song Dynasty
(960–1279 AD), having been pioneered by the government official and engineer Qiao Weiyo
in 984. They replaced earlier double slipways that had caused trouble and are mentioned by the Chinese polymath Shen Kuo
(1031–1095) in his book Dream Pool Essays
(published in 1088), and fully described in the Chinese historical text
Song Shi (compiled in 1345):
The water level could differ by 4 or 5 feet at each lock and in the Grand Canal the level was raised in this way by 138 feet (42.1 m).
In medieval Europe
a type of pound lock was first built in 1373 at Vreeswijk
, Netherlands
. This pound lock serviced many ships at once in a large basin, yet the true pound lock (i.e. one for a small basin) came in 1396 with the one built at Damme
near Bruges
. A famous civil engineer of pound locks in Europe was the Italian
Bertola da Novate (c. 1410-1475), who constructed 18 of them on the Naviglio di Bereguardo (part of the Milan
canal system sponsored by Francesco Sforza) between the years 1452 and 1458.
, or mill weir
— because of the change in river level across the obstacle.
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
).
The lowest lock on a navigable river separates the tidal and non-tidal stretches. Sometimes a river is made entirely non-tidal by constructing a sea lock directly into the estuary.
In more advanced river navigations, more locks are required.
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, aqueduct
s 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.
All pound locks have three elements:
The principle of operating a lock is simple. For instance, if a boat travelling downstream finds the lock already full of water:
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.
paddles raised manually by means of a detachable windlass operated by 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.
on the Kennet and Avon Canal
and Tuel Lane Lock
on the Rochdale Canal
, which both have a rise of nearly 20 feet (6.1 m). Both locks are amalgamations of two separate locks, which were combined when the canals were restored to accommodate changes in road crossings. The deepest "as-built" locks in England are considered to be Etruria Top Lock on the Trent and Mersey Canal
or Somerton Deep Lock on the Oxford Canal
, both of which have a rise of about 14 ft (4.3 m). Again, sources vary as to which is the deepest and in any case Etruria has been deepened over the years to accommodate subsidence. A more typical (English) rise would be 7–12 feet (though even shallower ones can be encountered).
The cill is a narrow horizontal ledge protruding a short way into the chamber from below the upper gates. Allowing the rear of the boat to "hang" on the cill is the main danger one is warned to guard against when descending a lock, and the position of the forward edge of the cill is usually marked on the lock side by a white line. The edge of the cill is usually curved, protruding less in the centre than at the edges.
In some locks, there is a piece of oak about 9” 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.
or elm
(or now sometimes steel
). The most common arrangement, usually called mitre gates, was invented in 1440 in Italy by Philippe Marie Visconti. 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 completely 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.
) 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 has been British Waterways policy not to provide gate paddles in replacement top gates if two ground paddles exist. The reason for this has been safety, since it is possible for an ascending boat to be swamped by the water from a carelessly lifted gate paddle. However, this makes the locks slower to operate and has been blamed in some places for causing congestion. Since the late 1990s the preferred method has been to retain the gate paddles and fit 'baffles' across them to minimise the risk of inundation.
), 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.
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.
Loosely, a flight of locks is simply a series of locks in close-enough proximity to be identified as a single group. For many reasons, a flight of locks is preferable to the same number of locks spread more widely: crews are put ashore and picked up once, rather than multiple times; transition involves a concentrated burst of effort, rather than a continually interrupted journey; a lock keeper may be stationed to help crews through the flight quickly; and where water is in short supply, a single pump can recycle water to the top of the whole flight. The need for a flight may be determined purely by the lie of the land, but it is possible to group locks purposely into flights by using cuttings or embankments to "postpone" the height change. Examples: Caen Hill locks, Devizes
.
"Flight" is not synonymous with "Staircase" (see below). A set of locks is only a staircase if successive lock chambers share a gate (i.e. do not have separate top and bottom gates with a pound between them). Most flights are not staircases, because each chamber is a separate lock (with its own upper and lower gates), there is a navigable pound (however short) between each pair of locks, and the locks are operated in the conventional way.
However, some flights include (or consist entirely of) staircases. On the Grand Union (Leicester) Canal, the Watford flight consists of a four-chamber staircase and three separate locks; and the Foxton flight consists entirely of two adjacent 5-chamber staircases.
When a very steep gradient has to be climbed, a lock staircase is used. There are two types of staircase. 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 "loss" of the intermediate pounds, operating a staircase is very different from operating a flight. It can be more useful to think of a staircase as a single lock with intermediate levels (the top gate is a normal top gate, and the intermediate gates are all as tall as the bottom gate). As there is no intermediate pound, a chamber can only be filled by emptying the one above, or emptied by filling the one below: thus the whole staircase has to be full of water (except for the bottom chamber) before a boat starts to ascend, or empty (except for the top chamber) before a boat starts to descend. By building a pair of such lock sets (one used to climb and the other to descend) these difficulties are avoided, as well as enabling a greater traffic volume and reduced wait times.
In an "apparent" staircase the chambers still have common gates, except in the case of Bratch
Locks on the Staffordshire and Worcestershire Canal
, 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
include 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 three thousand metric tons. Examples of "apparent" staircases include Foxton Locks
and Watford Locks
on the Leicester Branch of the Grand Union
.
The absence of intermediate pounds in a "real" staircase of locks causes the staircase to use more water to transfer boats between levels than an ordinary flight does . An "apparent" staircase does not suffer from this problem and indeed this is the main reason for their design.
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 tidal 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 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) it is obvious that 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 lock-keepers, at least during the main cruising season and the normal rule they apply is 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 lock keeper at Bingley (looking after both the "5-rise" and the "3-rise") has worked there for more than 20 years and ensures that there are no untoward events and that boats are moved through as speedily and efficiently as possible. Such expertise permits miracles of boat balletics: it is possible for boats travelling in opposite directions to pass each other halfway up the staircase by moving sideways around each other; or at peak times, to have all the chambers full simultaneously with boats travelling in the same direction.
north of Harecastle Tunnel
. Doubling gives advantages in speed: avoiding hold-ups at busy times; or increasing the chance of a boat finding a lock set in its favour. Also, there can be water savings: the locks may be of different sizes, so that a small boat does not need to empty a large lock; or each lock may be able to act as a side pond (water-saving basin) for the other. In this latter case, the word used is usually "twinned": here indicating the possibility of saving water by synchronising the operation of the chambers so that some water from the emptying chamber helps to fill the other. This facility has long been withdrawn on the English canals, although the disused paddle gear can sometimes be seen, as at Hillmorton on the Oxford Canal
.
The once-famous staircase at Lockport, New York
was also a doubled set of locks. Five twinned locks allowed east- and west-bound boats to climb/descend the 60 feet (18.3 m) Niagara Escarpment
— a considerable engineering feat in the nineteenth century. While Lockport today has two large steel locks, half of the old twin stair acts as a spillway and can still be seen (without lock gates).
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 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.
A "stop" lock is a (very) low-rise lock built at the junction of two (rival) canals to prevent water from passing between them.
During the competitive years of the 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 transshipped
between boats on rival canals only feet apart.
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.
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.
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).
It should be noted that the "new canal must be higher" rule is not cast-iron. For instance: the very shallow lock at Autherley Junction
, where the 1835 Birmingham and Liverpool canal (now part of the Shropshire Union Canal
) met the older (1772) Staffordshire and Worcestershire Canal
. The Nicholson guide shows that a boater coming south down the "Shroppie" locks "up" before turning north or south onto the older S & W Canal - so the Shroppie (the newer 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.
The best known example of such a round lock is the Agde Round Lock
on the Canal du Midi
in France
. This both 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
with the River Allier.
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
on the Forth and Clyde Canal
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 series of pictures showing the operation of the lock can be seen here. A similar arrangement is due to be built as part of the Droitwich Canal
restoration.
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.
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).
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.
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 pounds 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.
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.
A sea lock is one that connects a canal or river directly with an estuary or ocean. All sea locks are tidal.
A tidal lock is generally any lock that connects tidal with non-tidal water. This includes a lock between a tidal river and the non-tidal reaches, or between a tidal river and a canal, or a sea lock. However, the term usually refers specifically to a lock whose method of operation is affected by the state of the tide. Examples:
The world's largest lock is the Berendrecht Lock, giving access to the Port of Antwerp
in Belgium
. The lock is 500 metres (1,640 ft) long, and 68 metres (223 ft) wide and drops 13.5 m, and has four sliding lock gates. The size of locks cannot be compared without considering the difference in water level that they are designed to operate under. For example, the Bollène
lock on the River Rhône has a fall of at least 23 m and the Oskemen
Lock on the Irtysh River in Kazakhstan
has a drop of 42 m. The total volume of water to be considered in any lock equals the product of its length, breadth and the difference in water levels. Lock staircases are used in an attempt to reduce the total volume of water required in relation to the amount of useful work done. The useful work done relates to the weight of the vessel and the height it is lifted. When a vessel is lowered the consumption of potential energy of the water consumed is considered. An alternative to locks is a boat lift
; facilities of this type, e.g. the Anderton boat lift
or the Strépy-Thieu boat lift
in Belgium
, do not rely on the consumption of water as the primary power source, are powered by motors and are designed to consume a minimum amount of water.
The Welland Canal
is a ship canal in Canada, that runs 42 km (26.1 mi) from Port Colborne, Ontario on Lake Erie
to Port Weller, Ontario on Lake Ontario
. A major part of the St. Lawrence Seaway, the canal allows ships to avoid Niagara Falls
by traversing the Niagara Escarpment
.
Approximately 40,000,000 tonnes of cargo is carried through the Welland Canal annually by over 3,000 ocean and lake vessels. It allows goods from notable cities like Toronto
, Detroit, Cleveland and Chicago
along with other heavily industrialized areas of the United States and Canada to be shipped via ocean-going vessels for international delivery.
The completion of the Welland Canal
made the Trent-Severn Waterway
(which links Lake Ontario with Lake Huron) all but obsolete as a commercial traffic route for Great Lakes navigation.
The canal's Lake Erie (southern) terminus, at Port Colborne, is 99.5 m (326.5 feet) higher in elevation than the Lake Ontario (northern) terminus at Port Weller. The canal comprises eight lift locks, each 24.4 m (80 ft) wide by 233.5 m (766 ft) long. Due to the Garden City Skyway, the maximum ship height allowed is 35.5 m (116.5 ft). All other crossings are movable bridges (lift or Bascule) or tunnels. The maximum permissible vessel length is 225.5 m (740 ft). It takes ships an average of 11 hours to traverse the canal's length.
The 29 locks on the Mississippi River
are typically 600 feet (180 m) long while tug and barge combinations are as much as 1,200 feet (360 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.
(better known locally as the "Ballard Locks" in reference to the Seattle neighborhood
they are located in) was emptied for maintenance, as seen in the pictures below. This provided 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.
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.
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.
. 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 rimers) 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 manhauled 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.
This system was used extensively in Ancient China and in many other parts of the world. But this method was dangerous and many boats were sunk by the torrent of water. Since this system necessarily involved lowering the level in the pound, it was not popular with millers who depended on a full head of water to operate their equipment. This led to constant battles, both legal and physical, between the navigation and milling interests, with rivers being closed to navigation if there was any shortage of water. It was mainly this conflict which led to the adoption of the pound lock in medieval China, as this means that relatively little water is consumed by navigation.
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
, Medieval Europe, and possibly the Roman
s as indirect evidence suggests. Note the change in terminology: on a British Canal, it is the section of canal between locks that is called a pound.
, and Monkey Marsh Lock
, on the Kennet and Avon Canal
.
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 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
).
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".
For example the Hindenburg-lock (in Hannover
, Germany, built 1919-1928) has two lock chambers of 225 m length, each of which would use 42,000 m³ of water for a full locking cycle. Due to the use of 10 water saving basins, only 10,500 m³ of water are used. A more recent example is the Rhine–Main–Danube Canal with 13 saving locks out of a total of 16 locks.
Water saving basins are incorporated in proposals to augment the capacity of the Panama Canal
, but the scheme is controversial because the mixing of salt and fresh water in the basins will allow brackish water into Gatun Lake
, a source of drinking water and a wildlife reserve.
On English canals, these reservoirs are called "side ponds". They were installed on the Grand Union Canal
and the Coventry Canal
, among others. They are now out of use, and in some cases have been filled in, because British Waterways considered that it was too easy to misuse them and flood the surrounding area. 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.
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.
There are no working waterway inclined planes in the UK at the moment, but the remains of a famous one can be seen at Foxton in Leicestershire on the Leicester arm of the Grand Union Canal
. The plane enabled wide-beam boats to bypass the flight of ten narrow locks, but failure to make improvements at the other end of the arm and high running costs led to its early demise. There are plans to restore it, and some funding has been obtained.
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 "dry" (in a 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.
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 hydraulics, 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.
In some locations, notably 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.
, the world's first rotating boat lift, acts as the centrepiece of the restoration of the Forth and Clyde and Union Canal
s. The spectacular "Wheel" presents the 21st century's solution to replacing a flight of locks which formerly connected the canals and which were filled-in in 1930. The Falkirk Wheel 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 100 feet (30.5 m) in a few minutes compared to the time it took when the original lock staircase operated.
The Victorian Anderton Boat Lift
, the world's first vertical boat lift, linking the Trent and Mersey Canal
and the River Weaver
in Cheshire
, has recently been restored. The world's highest boat lift of Strépy-Thieu
in Belgium
raises or lowers 1,350 tonnes boats by 73.15 metres.
Another famous derivative is the Peterborough lift lock
which is a boat lift
located on the Trent Canal in the city of Peterborough, Ontario
, Canada
and is Lock 21 on the Trent-Severn Waterway
.
The dual lifts are the highest hydraulic boat lifts in the world, rising 19.8 m (65 ft). This was a considerable accomplishment when conventional locks usually only had a 2 m (7 ft) rise. Each lift has a capacity of 1,300 tonnes.
The basins are 140 feet (43 m) long, 33 feet (10 m) wide and 9 feet 10 inches (3.0 m) deep. The vertical distance lifted is 65 feet (20 m). The Trent-Severn has another similar lift lock at Kirkfield, with basins of the same dimension, but which lifts over a smaller vertical distance.
Around 1800 the use of caisson locks was proposed by Robert Weldon for the Somerset Coal Canal
in England. In this underwater lift, the chamber was 80 ft long and 60 ft (18.3 m) deep and contained a completely enclosed wooden box big enough to take a barge. This box moved up and down in the 60 ft (18.2 m) deep pool of water. Apart from inevitable leakage, the water never left the chamber, and using the lock wasted no water. Instead, the boat entered the box and was sealed in by the door closing behind it, and the box itself was moved up or down through the water. When the box was at the bottom of the chamber, it was under almost 60 feet (18.3 m) of water – at a pressure of three atmospheres, in total. One of these "locks" was built and demonstrated to the Prince Regent
(later George IV
), but it had various engineering problems and the design was not put into use on the Coal Canal. However, 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. Even though the change in level is much lower than that would have been the case in Somerset, the system was soon replaced by conventional locks. No commercially successful example has ever been built.
, 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 discredited caisson lock
design in that the boat does not have to be carried in a submerged chamber.
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
to Kendal
and the proposed new branch of the Grand Union Canal between Bedford
and Milton Keynes
on the Yangtze River
(Chang Jiang) in China there are two stair-steps 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.
and the Seawaymax
.
Waterway
A waterway is any navigable body of water. Waterways can include rivers, lakes, seas, oceans, and canals. In order for a waterway to be navigable, it must meet several criteria:...
s. The distinguishing feature of a lock is a fixed chamber in which the water level can be varied; whereas in a caisson lock
Caisson lock
A caisson lock is a type of canal lock in which a narrowboat is enclosed in a sealed box and raised or lowered between two water levels. It was intended primarily as a water-saving measure, but also to save construction costs when compared with other engineering solutions. It was capable of...
, a boat lift
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 and the canal inclined plane....
, or on a canal inclined plane
Canal inclined plane
An inclined plane is a system 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. It can be considered as a specialised type of cable railway....
, it is the chamber itself (usually then called a caisson
Caisson (engineering)
In geotechnical engineering, a caisson is a retaining, watertight structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships. These are constructed such that the water can be pumped out, keeping the working...
) that rises and falls.
Locks are used to make a river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
more easily navigable, or to allow a canal
Canal
Canals are man-made channels for water. There are two types of canal:#Waterways: navigable transportation canals used for carrying ships and boats shipping goods and conveying people, further subdivided into two kinds:...
to take a reasonably direct line across land that is not level.
Pound lock
A pound lock is a type of lock that is used almost exclusively nowadays on canalCanal
Canals are man-made channels for water. There are two types of canal:#Waterways: navigable transportation canals used for carrying ships and boats shipping goods and conveying people, further subdivided into two kinds:...
s and river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s. A pound lock has a chamber (the pound
Canal pound
A canal pound, aka reach, is the stretch of level water impounded between two canal locks. Canal pounds can vary in length from the non-existent, where two or more immediately adjacent locks form a lock staircase, to many miles....
) with gates
Floodgate
Floodgates are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and canals, or they may be designed to stop water flow entirely as part of a levee or...
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
Flash lock
Early locks were designed with a single gate, known as a flash lock or staunch lock. The earliest European references to what were clearly flash locks were in Roman times....
.
Pound locks were used in ancient China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
during the Song Dynasty
Song Dynasty
The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a...
(960–1279 AD), having been pioneered by the government official and engineer Qiao Weiyo
Technology of the Song Dynasty
The Song Dynasty provided some of the most significant technological advances in Chinese history, many of which came from talented statesmen drafted by the government through imperial examinations....
in 984. They replaced earlier double slipways that had caused trouble and are mentioned by the Chinese polymath Shen Kuo
Shen Kuo
Shen Kuo or Shen Gua , style name Cunzhong and pseudonym Mengqi Weng , was a polymathic Chinese scientist and statesman of the Song Dynasty...
(1031–1095) in his book Dream Pool Essays
Dream Pool Essays
The Dream Pool Essays was an extensive book written by the polymath Chinese scientist and statesman Shen Kuo by 1088 AD, during the Song Dynasty of China...
(published in 1088), and fully described in the Chinese historical text
Twenty-Four Histories
The Twenty-Four Histories is a collection of Chinese historical books covering a period from 3000 BC to the Ming Dynasty in the 17th century. The whole set contains 3213 volumes and about 40 million words...
Song Shi (compiled in 1345):
The distance between the two locks was rather more than 50 paces, and the whole space was covered with a great roof like a shed. The gates were 'hanging gates'; when they were closed the water accumulated like a tide until the required level was reached, and then when the time came it was allowed to flow out.
The water level could differ by 4 or 5 feet at each lock and in the Grand Canal the level was raised in this way by 138 feet (42.1 m).
In medieval Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
a type of pound lock was first built in 1373 at Vreeswijk
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....
, Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
. This pound lock serviced many ships at once in a large basin, yet the true pound lock (i.e. one for a small basin) came in 1396 with the one built at Damme
Damme
Damme is a municipality located in the Belgian province of West Flanders, six kilometres northeast of Brugge . The municipality comprises the city of Damme proper and the towns of Hoeke, Lapscheure, Moerkerke, Oostkerke, Sijsele, Vivenkapelle, and Sint-Rita. On 1 January 2006, the municipality had...
near Bruges
Bruges
Bruges is the capital and largest city of the province of West Flanders in the Flemish Region of Belgium. It is located in the northwest of the country....
. A famous civil engineer of pound locks in Europe was the Italian
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
Bertola da Novate (c. 1410-1475), who constructed 18 of them on the Naviglio di Bereguardo (part of the Milan
Milan
Milan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...
canal system sponsored by Francesco Sforza) between the years 1452 and 1458.
Use of locks in river navigations
A lock is required when a stretch of river is made navigable by bypassing an obstruction such as a rapid, damDam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
, or mill weir
Weir
A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...
— because of the change in river level across the obstacle.
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
Calder and Hebble Navigation
The Calder and Hebble Navigation is a Broad inland waterway in West Yorkshire, England, which has remained navigable since it was opened.-History:...
).
The lowest lock on a navigable river separates the tidal and non-tidal stretches. Sometimes a river is made entirely non-tidal by constructing a sea lock directly into the estuary.
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 flood lockFloodgateFloodgates are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and canals, or they may be designed to stop water flow entirely as part of a levee or...
. - 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.
Use of locks in canals
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...
s, cuttings, aqueduct
Aqueduct
An aqueduct is a water supply or navigable channel constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose....
s 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.
Basic construction and operation
| For a boat going upstream: | For a boat going downstream: | ||
|---|---|---|---|
| 1–2. | The boat enters the lock. | 8–9. | The boat enters the lock. |
| 3. | The lower gates are closed. | 10. | The upper gates are closed. |
| 4–5. | The lock is filled with water from upstream. | 11–12. | The lock is emptied by draining its water downstream. |
| 6. | The upper gates are opened. | 13. | The lower gates are opened. |
| 7. | The boat exits the lock. | 14. | The boat exits the lock. |
All pound locks have three elements:
- A 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
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 pinionRack and pinion
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby...
paddles raised manually by means of a detachable windlass operated by 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.
Rise
The rise is the change in water-level effected by the lock. The two deepest locks on the English canal system are Bath deep lockBath Locks
Bath Locks are a series of locks situated on the Kennet and Avon Canal, at Bath, England.Bath Bottom Lock, which is numbered as No 7 on the canal is the meeting with the River Avon just south of Pulteney Bridge...
on the Kennet and Avon Canal
Kennet and Avon Canal
The Kennet and Avon Canal is a waterway in southern England with an overall length of , made up of two lengths of navigable river linked by a canal. The name is commonly used to refer to the entire length of the navigation rather than solely to the central canal section...
and Tuel Lane Lock
Tuel Lane Lock
Tuel Lane Lock is a canal lock, situated on the Rochdale Canal in Sowerby Bridge. With a fall of , it is the deepest lock in the United Kingdom.-History:...
on the Rochdale Canal
Rochdale Canal
The Rochdale Canal is a navigable "broad" canal in northern England, part of the connected system of the canals of Great Britain. The "Rochdale" in its name refers to the town of Rochdale, Greater Manchester, through which the canal passes....
, which both have a rise of nearly 20 feet (6.1 m). Both locks are amalgamations of two separate locks, which were combined when the canals were restored to accommodate changes in road crossings. The deepest "as-built" locks in England are considered to be Etruria Top Lock on the Trent and Mersey Canal
Trent and Mersey Canal
The Trent and Mersey Canal is a in the East Midlands, West Midlands, and North West of England. It is a "narrow canal" for the vast majority of its length, but at the extremities—east of Burton upon Trent and west of Middlewich—it is a wide canal....
or Somerton Deep Lock on the Oxford Canal
Oxford Canal
The Oxford Canal is a narrow canal in central England linking Oxford with Coventry via Banbury and Rugby. It connects with the River Thames at Oxford, to the Grand Union Canal at the villages of Braunston and Napton-on-the-Hill, and to the Coventry Canal at Hawkesbury Junction in Bedworth just...
, both of which have a rise of about 14 ft (4.3 m). Again, sources vary as to which is the deepest and in any case Etruria has been deepened over the years to accommodate subsidence. A more typical (English) rise would be 7–12 feet (though even shallower ones can be encountered).
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 either end 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 less-confusing terms for this are "drained" or "de-watered".)Cill
In some locks, there is a piece of oak about 9” thick which protects the solid part of the lock cill. On the Oxford Canal it is called a Babbie; on the Grand Union Canal it is referred to as the cill Bumper.
Gates
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 oakOak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
or elm
Elm
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The dozens of species are found in temperate and tropical-montane regions of North America and Eurasia, ranging southward into Indonesia. Elms are components of many kinds of natural forests...
(or now sometimes steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
). The most common arrangement, usually called mitre gates, was invented in 1440 in Italy by Philippe Marie Visconti. 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 completely full, the top gate is secure; and if the chamber is not completely empty, the bottom gate is secure (in normal operation, therefore, the chamber cannot be open at both ends). A lower gate is taller than an upper gate, because the upper gate only has to be tall enough to close off the upper pound, while the lower gate has to be able to seal off a full chamber. The upper gate is as tall as the canal is deep, plus a little more for the balance beam, winding mechanism, etc.; the lower gate's height equals the upper gate plus the lock's rise.
Balance beam
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.Paddle
A paddle – sometimes known as a slacker, clough, or (in American EnglishAmerican English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....
) 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 has been British Waterways policy not to provide gate paddles in replacement top gates if two ground paddles exist. The reason for this has been safety, since it is possible for an ascending boat to be swamped by the water from a carelessly lifted gate paddle. However, this makes the locks slower to operate and has been blamed in some places for causing congestion. Since the late 1990s the preferred method has been to retain the gate paddles and fit 'baffles' across them to minimise the risk of inundation.
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 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 NavigationsBirmingham Canal Navigations
Birmingham Canal Navigations is a network of navigable canals connecting Birmingham, Wolverhampton, and the eastern part of the Black Country...
), 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
Leeds and Liverpool Canal
The Leeds and Liverpool Canal is a canal in Northern England, linking the cities of Leeds and Liverpool. Over a distance of , it crosses the Pennines, and includes 91 locks on the main line...
, resembled handcuffs, "Leeds and Liverpool Keys" after that canal, or simply Anti-Vandal Keys.
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.Windlass ("lock key")
A windlass (also known as a '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).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 WaterwaysBritish WaterwaysBritish Waterways is a statutory corporation wholly owned by the government of the United Kingdom, serving as the navigation authority in England, Scotland and Wales for the vast majority of the canals as well as a number of rivers and docks...
standard spindle, fitted in the early 1990s almost everywhere, the larger for the gear on the Grand Union CanalGrand Union CanalThe Grand Union Canal in England is part of the British canal system. Its main line connects London and Birmingham, stretching for 137 miles with 166 locks...
north of Napton Junction, which they were unable 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 tender hands of a novice boater from the blisters which can be caused by the friction of a rough iron handle turning against soft 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.
"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")."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.Variations
Variations exist for types of locks and the terminology used for them.- Single gates on narrow canals (locks approx. 7 feet / 2.1 m wide)
- On most English narrow canals, the upper end of the chamber is closed by a single gate the full width of the lock. This was cheaper to construct and is quicker to operate with a small crew, as only one gate needs to be opened.
- Some narrow locks (e.g. on Birmingham Canal NavigationsBirmingham Canal NavigationsBirmingham Canal Navigations is a network of navigable canals connecting Birmingham, Wolverhampton, and the eastern part of the Black Country...
) 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). - A few narrow locks imitate wide locks in having paired gates at both ends (e.g. Bosley, on the Macclesfield CanalMacclesfield CanalThe Macclesfield Canal is a canal in east Cheshire, England, one of the six that make up the Cheshire Ring.-Route:The canal runs from Marple Junction at Marple, where it joins the Upper Peak Forest Canal, , southwards , before arriving at Bosley.Having descended the 12 Bosley Locks over the course...
)
- 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 CanalKiel CanalThe Kiel Canal , known as the Kaiser-Wilhelm-Kanal until 1948, is a long canal in the German state of Schleswig-Holstein.The canal links the North Sea at Brunsbüttel to the Baltic Sea at Kiel-Holtenau. An average of is saved by using the Kiel Canal instead of going around the Jutland Peninsula....
). - Guillotine gates. Some locks have vertically moving steel gates — these are quite common on river navigations in East AngliaEast AngliaEast Anglia is a traditional name for a region of eastern England, named after an ancient Anglo-Saxon kingdom, the Kingdom of the East Angles. The Angles took their name from their homeland Angeln, in northern Germany. East Anglia initially consisted of Norfolk and Suffolk, but upon the marriage of...
. 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 NeneRiver NeneThe River Nene is a river in the east of England that rises from three sources in the county of Northamptonshire. The tidal river forms the border between Cambridgeshire and Norfolk for about . It is the tenth longest river in the United Kingdom, and is navigable for from Northampton to The...
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 sluiceSluiceA sluice is a water channel that is controlled at its head by a gate . For example, a millrace is a sluice that channels water toward a water mill...
. 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 are gates which, when open, lie flat on the canal bed and which close by lifting (London Flood Barrier).
- Rotating-sector gates. Some of these work very like traditional swinging gates, but with each gate in the form of a sector of a cylinder. They close by rotating out from the lock wall and meeting in the centre of the chamber. Water is let in or out by opening the gates slightly: there are no paddles or other lock gear. The lock at Limehouse BasinLimehouse BasinThe Limehouse Basin in Limehouse, in the London Borough of Tower Hamlets provides a navigable link between the Regent's Canal and the River Thames, through the Limehouse Basin Lock. A basin in the north of Mile End, near Victoria Park connects with the Hertford Union Canal leading to the River Lee...
, which gives access to the River ThamesRiver ThamesThe River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...
, is an example. A dramatically large one can be seen at the RotterdamRotterdamRotterdam is the second-largest city in the Netherlands and one of the largest ports in the world. Starting as a dam on the Rotte river, Rotterdam has grown into a major international commercial centre...
flood defences (huge flood gates). There is a different type at the sea lock on the Ribble LinkRibble LinkThe Millennium Ribble Link is a Linear Water Park and new navigation which links the once-isolated Lancaster Canal in Lancashire, England to the River Ribble...
: this is a rising sector gate, which has a horizontal axis: the gate drops to the bed of the river to allow boats to pass.
- Alternate paddle gear
- Some manually operated paddles do not require a detachable handle (windlassWindlassThe windlass is an apparatus for moving heavy weights. Typically, a windlass consists of a horizontal cylinder , which is rotated by the turn of a crank or belt...
) because they have their handles ready-attached. - On the Leeds and Liverpool CanalLeeds and Liverpool CanalThe Leeds and Liverpool Canal is a canal in Northern England, linking the cities of Leeds and Liverpool. Over a distance of , it crosses the Pennines, and includes 91 locks on the main line...
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. - On the Calder and Hebble NavigationCalder and Hebble NavigationThe Calder and Hebble Navigation is a Broad inland waterway in West Yorkshire, England, which has remained navigable since it was opened.-History:...
, 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. - On some parts of the Montgomery CanalMontgomery CanalThe Montgomery Canal , known colloquially as "The Monty", is a partially restored canal in Powys, in eastern Wales, and in northwest Shropshire, in western England...
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.
- Some manually operated paddles do not require a detachable handle (windlass
- Lock keepers. Some locks are operated (or at least supervised) by professional 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.
- Powered operation. On large modern canals, especially very large ones such as ship canalShip canalA ship canal is a canal especially constructed to carry ocean-going ships, as opposed to barges. Ship canals can be enlarged barge canals, canalized or channelized rivers, or canals especially constructed from the start to accommodate ships....
s, the gates and paddles are too large to be hand operated, and are operated by hydraulic or electrical equipment. 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 ThamesRiver ThamesThe River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...
below OxfordOxfordThe city of Oxford is the county town of Oxfordshire, England. The city, made prominent by its medieval university, has a population of just under 165,000, with 153,900 living within the district boundary. It lies about 50 miles north-west of London. The rivers Cherwell and Thames run through...
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.
- Fish Ladders. The construction of locks (or weirs and dams) on rivers obstructs the passage of fish. Some fish such as troutTroutTrout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
and salmonSalmonSalmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
go upstream to spawn. Measures such as a fish ladderFish ladderA fish ladder, also known as a fishway, fish pass or fish steps, is a structure on or around artificial barriers to facilitate diadromous fishes' natural migration. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps into the waters on...
are often taken to counteract this.
- Weigh lock. A weigh lockWeigh lockA weigh lock is a specialized canal lock designed to determine the weight of barges in order to assess toll payments based upon the weight and value of the cargo carried. This requires that the unladen weight of the barge be known....
is a specialized canal lock designed to determine the weight of barges in order to assess toll payments based upon the weight and value of the cargo carried.
Lock flights
Devizes
Devizes is a market town and civil parish in Wiltshire, England. The town is about southeast of Chippenham and about east of Trowbridge.Devizes serves as a centre for banks, solicitors and shops, with a large open market place where a market is held once a week...
.
"Flight" is not synonymous with "Staircase" (see below). A set of locks is only a staircase if successive lock chambers share a gate (i.e. do not have separate top and bottom gates with a pound between them). Most flights are not staircases, because each chamber is a separate lock (with its own upper and lower gates), there is a navigable pound (however short) between each pair of locks, and the locks are operated in the conventional way.
However, some flights include (or consist entirely of) staircases. On the Grand Union (Leicester) Canal, the Watford flight consists of a four-chamber staircase and three separate locks; and the Foxton flight consists entirely of two adjacent 5-chamber staircases.
Staircase locks
In an "apparent" staircase the chambers still have common gates, except in the case of Bratch
Bratch
The Bratch is an area of Wombourne in Southern Staffordshire, England, noted for its industrial heritage and as a way station for walkers, riders and cyclists...
Locks on the Staffordshire and Worcestershire Canal
Staffordshire and Worcestershire Canal
The Staffordshire and Worcestershire Canal is a narrow navigable canal in the English Midlands, passing through the counties of Staffordshire and Worcestershire....
, 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
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
include Bingley
Bingley Five Rise Locks
Bingley Five Rise Locks is a staircase lock on the Leeds and Liverpool Canal at Bingley . As the name implies, a boat going up the lock is lifted in five stages.-Description:...
and Grindley Brook
Grindley Brook
Grindley Brook is a small village in Shropshire, England, on the A41 trunk road around 1.5 miles north west of the market town of Whitchurch. It is the most northerly settlement in Shropshire and borders directly onto Cheshire, and is within the civil parish of Whitchurch Rural.It is also the name...
. Two-rise staircases are more common: Snakeholme Lock
Snakeholme Lock
Snakeholme Lock is a brick chamber canal lock on the Driffield Navigation, in the East Riding of Yorkshire, England. It is notable in being a staircase lock, but only the upper lock is still used.-Location:...
and Struncheon Hill Lock
Struncheon Hill Lock
Struncheon Hill Lock was built as a later addition to the Driffield Navigation in the East Riding of Yorkshire, England. It improved access to the next section of water during low tide conditions, and is the first lock...
on the Driffield Navigation
Driffield Navigation
The Driffield Navigation is an waterway, through the heart of the Holderness Plain to the market town of Driffield, East Riding of Yorkshire, England. The northern section of it is a canal, and the southern section is part of the River Hull. Construction was authorised in 1767, and it was fully...
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
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, the recently completed Three Gorges Dam
Three Gorges Dam
The Three Gorges Dam is a hydroelectric dam that spans the Yangtze River by the town of Sandouping, located in the Yiling District of Yichang, in Hubei province, China...
includes a double five-step staircase for large ships, and a ship lift for vessels of less than three thousand metric tons. Examples of "apparent" staircases include Foxton Locks
Foxton Locks
Foxton Locks are ten canal locks consisting of two "staircases" each of five locks, located on the Leicester line of the Grand Union Canal about 5 km west of the Leicestershire town of Market Harborough and are named after the nearby village of Foxton....
and Watford Locks
Watford Locks
Watford Locks is a group of seven locks on the Leicester Line of the Grand Union Canal, in Northamptonshire, England, famous for the Watford Gap service area....
on the Leicester Branch of the Grand Union
Grand Union
- Transport :* Grand union, a four-way, double track rail junction often found on tram systems* Grand Union Canal, a waterway running from London to Birmingham in the United Kingdom...
.
The absence of intermediate pounds in a "real" staircase of locks causes the staircase to use more water to transfer boats between levels than an ordinary flight does . An "apparent" staircase does not suffer from this problem and indeed this is the main reason for their design.
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) it is obvious that 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 lock-keepers, at least during the main cruising season and the normal rule they apply is 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 lock keeper at Bingley (looking after both the "5-rise" and the "3-rise") has worked there for more than 20 years and ensures that there are no untoward events and that boats are moved through as speedily and efficiently as possible. Such expertise permits miracles of boat balletics: it is possible for boats travelling in opposite directions to pass each other halfway up the staircase by moving sideways around each other; or at peak times, to have all the chambers full simultaneously with boats travelling in the same direction.
Doubled, paired or twinned locks
Locks can be built in parallel (i.e. side by side). This can be called doubling, pairing, or twinning. There are several examples (in this case called "double locks") on the Trent and Mersey CanalTrent and Mersey Canal
The Trent and Mersey Canal is a in the East Midlands, West Midlands, and North West of England. It is a "narrow canal" for the vast majority of its length, but at the extremities—east of Burton upon Trent and west of Middlewich—it is a wide canal....
north of Harecastle Tunnel
Harecastle Tunnel
Harecastle Tunnel is a canal tunnel on the Trent and Mersey Canal at Kidsgrove in Staffordshire. It is made up of two separate, parallel, tunnels described as Brindley and the later Telford after the engineers that constructed them. Today only the Telford tunnel is navigable...
. Doubling gives advantages in speed: avoiding hold-ups at busy times; or increasing the chance of a boat finding a lock set in its favour. Also, there can 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
Oxford Canal
The Oxford Canal is a narrow canal in central England linking Oxford with Coventry via Banbury and Rugby. It connects with the River Thames at Oxford, to the Grand Union Canal at the villages of Braunston and Napton-on-the-Hill, and to the Coventry Canal at Hawkesbury Junction in Bedworth just...
.
The once-famous staircase at Lockport, New York
Lockport (city), New York
Lockport is a city in Niagara County, New York, United States. The population was 21,165 at the 2010 census. The name is derived from a set of Erie canal locks within the city. Lockport is the county seat of Niagara County and is surrounded by the town of Lockport...
was also a doubled set of locks. Five twinned locks allowed east- and west-bound boats to climb/descend the 60 feet (18.3 m) Niagara Escarpment
Niagara Escarpment
The Niagara Escarpment is a long escarpment, or cuesta, in the United States and Canada that runs westward from New York State, through Ontario, Michigan, Wisconsin and Illinois...
— a considerable engineering feat in the nineteenth century. While Lockport today has two large steel locks, half of the old twin stair acts as a spillway and can still be seen (without lock gates).
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
Chesterfield Canal
The Chesterfield Canal is in the north of England and it is known locally as 'Cuckoo Dyke'. It was opened in 1777 and ran 46 miles from the River Trent at West Stockwith, Nottinghamshire to Chesterfield, Derbyshire...
: 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
Calder and Hebble Navigation
The Calder and Hebble Navigation is a Broad inland waterway in West Yorkshire, England, which has remained navigable since it was opened.-History:...
). Also, "double lock" (less often, "twin lock") is often used by novices on the English canals to mean a wide (14 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.
Stop locks
During the competitive years of the English waterways system
Canals of the United Kingdom
The canals of the United Kingdom are a major part of the network of inland waterways in the United Kingdom. They have a colourful history, from use for irrigation and transport, through becoming the focus of the Industrial Revolution, to today's role for recreational boating...
, an established canal company would often refuse to allow a connection from a newer, adjacent one. This situation created the Worcester Bar in Birmingham
Birmingham
Birmingham is a city and metropolitan borough in the West Midlands of England. It is the most populous British city outside the capital London, with a population of 1,036,900 , and lies at the heart of the West Midlands conurbation, the second most populous urban area in the United Kingdom with a...
, where goods had to be transshipped
Transshipment
Transshipment or Transhipment is the shipment of goods or containers to an intermediate destination, and then from there to yet another destination....
between boats on rival canals only feet apart.
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.
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
Kidsgrove
Kidsgrove is a town in the borough of Newcastle-under-Lyme, Staffordshire, England, near the border with Cheshire. It forms part of The Potteries Urban Area in North Staffordshire, along with Stoke-on-Trent and Newcastle-under-Lyme. It has a population of 24,112...
, where the southern terminus of the Macclesfield Canal
Macclesfield Canal
The Macclesfield Canal is a canal in east Cheshire, England, one of the six that make up the Cheshire Ring.-Route:The canal runs from Marple Junction at Marple, where it joins the Upper Peak Forest Canal, , southwards , before arriving at Bosley.Having descended the 12 Bosley Locks over the course...
joined the Hall Green Branch
Hall Green Branch
The Hall Green Branch of the Trent and Mersey Canal is a canal in east Cheshire, England. It runs for one mile from Kidsgrove to Hall Green, where it makes an end-on junction with the Macclesfield Canal at Hall Green Stop Lock....
of the earlier Trent and Mersey Canal
Trent and Mersey Canal
The Trent and Mersey Canal is a in the East Midlands, West Midlands, and North West of England. It is a "narrow canal" for the vast majority of its length, but at the extremities—east of Burton upon Trent and west of Middlewich—it is a wide canal....
. The four gate stop lock near Kings Norton Junction, between the Stratford-upon-Avon Canal
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 Grand Union Canal...
and the Worcester and Birmingham Canal
Worcester and Birmingham Canal
The Worcester and Birmingham Canal is a canal linking Birmingham and Worcester in England. It starts in Worcester, as an 'offshoot' of the River Severn and ends in Gas Street Basin in Birmingham. It is long....
was replaced in 1914 by a pair of guillotine lock
Guillotine lock
A guillotine lock is a type of canal lock. The lock itself operates on the same principle as any normal pound lock, but is unusual in that each gate is a single piece, usually of steel, that slides vertically upwards when opened to allow a boat to traverse underneath...
gates which stopped the water flow regardless of which canal was higher. These gates have been permanently open since nationalisation.
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
Hardings Wood Junction
Hardings Wood Junction is a canal junction near Kidsgrove, Staffordshire, England and the point at which the Macclesfield Canal joins the Trent and Mersey Canal....
(just short of the Harecastle Tunnel north portal).
It should be noted that the "new canal must be higher" rule is not cast-iron. For instance: the very shallow lock at Autherley Junction
Autherley Junction
Autherley Junction is the name of the canal junction where the Shropshire Union Canal terminates and meets the Staffordshire and Worcestershire Canal near to Oxley, north Wolverhampton, West Midlands, England....
, where the 1835 Birmingham and Liverpool canal (now part of the Shropshire Union Canal
Shropshire Union Canal
The Shropshire Union Canal is a navigable canal in England; the Llangollen and Montgomery canals are the modern names of branches of the Shropshire Union system and lie partially in Wales....
) met the older (1772) Staffordshire and Worcestershire Canal
Staffordshire and Worcestershire Canal
The Staffordshire and Worcestershire Canal is a narrow navigable canal in the English Midlands, passing through the counties of Staffordshire and Worcestershire....
. The Nicholson guide shows that a boater coming south down the "Shroppie" locks "up" before turning north or south onto the older S & W Canal - so the Shroppie (the newer canal) gains a small lockful of water each time a boat passes. However, the gain is tiny since the level difference is so small that it is sometimes possible to open both gates at once.
Round locks
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, but also as a junction. The circular plan of the lock allows boats to rotate within the lock, in order to line up with the appropriate exit gate.The best known example of such a round lock is the Agde Round Lock
Agde Round Lock
The Agde Round Lock 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 three sets of lock gates, each with a different water level...
on the Canal du Midi
Canal du Midi
The is a long canal in Southern France . The canal connects the Garonne River to the on the Mediterranean and along with the Canal de Garonne forms the Canal des Deux Mers joining the Atlantic to the Mediterranean. The canal runs from the city of Toulouse down to the Étang de Thau...
in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. This both 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
Canal latéral à la Loire
The Canal Latéral à la 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 196 km. It replaced the use of the River Loire which had reliability problems arising from winter floods and summer droughts...
with the River Allier.
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 mooted 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).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
Dalmuir is an area on the western side of Clydebank, in West Dunbartonshire, Scotland.-Location:It is neighboured by the village of Old Kilpatrick, the Mountblow and Parkhall areas of Clydebank, as well as the town centre...
on the Forth and Clyde Canal
Forth and Clyde Canal
The Forth and Clyde Canal crosses Scotland, providing a route for sea-going vessels between the Firth of Forth and the Firth of Clyde at the narrowest part of the Scottish Lowlands. The canal is 35 miles long and its eastern end is connected to the River Forth by a short stretch of the River...
in Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
. This lock, of the single chamber type, was incorporated during the restoration of the canal, to allow the replacement of a swing bridge (on a busy A road) by a fixed bridge, and so answer criticisms that the restoration of the canal would cause frequent interruptions of the heavy road traffic. It can be emptied by pumping - but as this uses a lot of electricity the method used when water supplies are adequate is to drain the lock to a nearby burn. A series of pictures showing the operation of the lock can be seen here. A similar arrangement is due to be built as part of the Droitwich Canal
Droitwich Canal
The Droitwich Canal is a synthesis of two canals in Worcestershire, England; the Droitwich Barge Canal and the Droitwich Junction Canal. The Barge Canal is a broad canal which opened in 1771 linking Droitwich Spa to the River Severn at Hawford Mill, Claines...
restoration.
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.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.
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).
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
Calder and Hebble Navigation
The Calder and Hebble Navigation is a Broad inland waterway in West Yorkshire, England, which has remained navigable since it was opened.-History:...
, 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.
Flood gates
Bi-directional gates and locks
A sea lock is one that connects a canal or river directly with an estuary or ocean. All sea locks are tidal.
Tidal locks
- 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 CanalBude CanalThe Bude Canal was a canal built to serve the hilly hinterland in the Devon and Cornwall border territory in the United Kingdom, chiefly to bring lime-bearing sand for agricultural fertiliser. The Bude Canal system was one of the most unusual in Britain....
). - 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.
Very large locks
Port of Antwerp
The port of Antwerp, in Belgium, is a port in the heart of Europe accessible to capesize ships. Antwerp stands at the upper end of the tidal estuary of the Scheldt. The estuary is navigable by ships of more than 100,000 Gross Tons as far as 80 km inland. The inland location means that the port...
in Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
. The lock is 500 metres (1,640 ft) long, and 68 metres (223 ft) wide and drops 13.5 m, 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
Bollène is a commune in the Vaucluse department in the Provence-Alpes-Côte d'Azur region in southeastern France.-References:*...
lock on the River Rhône has a fall of at least 23 m and the Oskemen
Oskemen
Oskemen and Ust-Kamennaya , is the capital of the East Kazakhstan Province. It is served by the Ust-Kamenogorsk Airport.-History:...
Lock on the Irtysh River in Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
has a drop of 42 m. 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
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 and the canal inclined plane....
; facilities of this type, e.g. the Anderton boat lift
Anderton Boat Lift
The Anderton Boat Lift near the village of Anderton, Cheshire, in north-west England provides a vertical link between two navigable waterways: the River Weaver and the Trent and Mersey Canal....
or the Strépy-Thieu boat lift
Strépy-Thieu boat lift
The Strépy-Thieu boat lift lies on a branch of the Canal du Centre in the municipality of Le Rœulx, Hainaut, Belgium. With a height difference of between the upstream and downstream reaches, it is the tallest boat lift in the world, and will remain so until the Three Gorges dam boat lift in...
in Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
, do not rely on the consumption of water as the primary power source, are powered by motors and are designed to consume a minimum amount of water.
The Welland Canal
Welland Canal
The Welland Canal is a ship canal in Canada that extends from Port Weller, Ontario, on Lake Ontario, to Port Colborne, Ontario, on Lake Erie. As a part of the St...
is a ship canal in Canada, that runs 42 km (26.1 mi) from Port Colborne, Ontario on Lake Erie
Lake Erie
Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...
to Port Weller, Ontario on Lake Ontario
Lake Ontario
Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north and southwest by the Canadian province of Ontario, and on the south by the American state of New York. Ontario, Canada's most populous province, was named for the lake. In the Wyandot language, ontarío means...
. A major part of the St. Lawrence Seaway, the canal allows ships to avoid Niagara Falls
Niagara Falls
The Niagara Falls, located on the Niagara River draining Lake Erie into Lake Ontario, is the collective name for the Horseshoe Falls and the adjacent American Falls along with the comparatively small Bridal Veil Falls, which combined form the highest flow rate of any waterfalls in the world and has...
by traversing the Niagara Escarpment
Niagara Escarpment
The Niagara Escarpment is a long escarpment, or cuesta, in the United States and Canada that runs westward from New York State, through Ontario, Michigan, Wisconsin and Illinois...
.
Approximately 40,000,000 tonnes of cargo is carried through the Welland Canal annually by over 3,000 ocean and lake vessels. It allows goods from notable cities like Toronto
Toronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...
, Detroit, Cleveland and Chicago
Chicago
Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...
along with other heavily industrialized areas of the United States and Canada to be shipped via ocean-going vessels for international delivery.
The completion of the Welland Canal
Welland Canal
The Welland Canal is a ship canal in Canada that extends from Port Weller, Ontario, on Lake Ontario, to Port Colborne, Ontario, on Lake Erie. As a part of the St...
made the Trent-Severn Waterway
Trent-Severn Waterway
The Trent–Severn Waterway is a Canadian canal system formerly used for industrial and transportation purposes and now for recreational and tourism purposes, connecting Lake Ontario at Trenton to the Georgian Bay portion of Lake Huron at Port Severn...
(which links Lake Ontario with Lake Huron) all but obsolete as a commercial traffic route for Great Lakes navigation.
The canal's Lake Erie (southern) terminus, at Port Colborne, is 99.5 m (326.5 feet) higher in elevation than the Lake Ontario (northern) terminus at Port Weller. The canal comprises eight lift locks, each 24.4 m (80 ft) wide by 233.5 m (766 ft) long. Due to the Garden City Skyway, the maximum ship height allowed is 35.5 m (116.5 ft). All other crossings are movable bridges (lift or Bascule) or tunnels. The maximum permissible vessel length is 225.5 m (740 ft). It takes ships an average of 11 hours to traverse the canal's length.
The 29 locks on the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
are typically 600 feet (180 m) long while tug and barge combinations are as much as 1,200 feet (360 m) long consisting of as many as 15 barges and one tug. In these cases, some of the barges are locked through, using partially opened lock valves to create a current to pull the un-powered barges out of the lock where they are tied up to wait for the rest of the barges and the tug to pass through the lock. It can take as much as an hour and a half to pass the lock.
Hiram M. Chittenden Locks
In November 2004 one of the Hiram M. Chittenden LocksHiram M. Chittenden Locks
The Hiram M. Chittenden Locks are a complex of locks that sit at the west end of Salmon Bay, part of Seattle's Lake Washington Ship Canal. They are known locally as the Ballard Locks after the neighborhood to their north...
(better known locally as the "Ballard Locks" in reference to the Seattle neighborhood
Ballard, Seattle, Washington
Ballard is a neighborhood located in the northwestern part of Seattle, Washington. To the north it is bounded by Crown Hill, ; to the east by Greenwood, Phinney Ridge and Fremont ; to the south by the Lake Washington Ship Canal; and to the west by Puget Sound’s Shilshole Bay. The neighborhood’s...
they are located in) was emptied for maintenance, as seen in the pictures below. This provided 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.
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
Penstock
A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydraulic turbines and sewerage systems. It is a term that has been inherited from the technology of wooden watermills....
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.
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 damDam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
s to raise the water level. The water behind the dam deepened until it spilled over the top creating a weir
Weir
A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...
. 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.
Flash locks
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 means of a flash lockFlash lock
Early locks were designed with a single gate, known as a flash lock or staunch lock. The earliest European references to what were clearly flash locks were in Roman times....
. 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 rimers) 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 manhauled 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.
This system was used extensively in Ancient China and in many other parts of the world. But this method was dangerous and many boats were sunk by the torrent of water. Since this system necessarily involved lowering the level in the pound, it was not popular with millers who depended on a full head of water to operate their equipment. This led to constant battles, both legal and physical, between the navigation and milling interests, with rivers being closed to navigation if there was any shortage of water. It was mainly this conflict which led to the adoption of the pound lock in medieval China, as this means that relatively little water is consumed by navigation.
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, in order 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 the a boat could pass. Accordingly they were not used where the obstacle to be passed was a mill weir.Pound lock
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, Medieval Europe, and possibly the Roman
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....
s as indirect evidence suggests. Note the change in terminology: on a British Canal, it is the section of canal between locks that is called a pound.
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 1700s before the advent of canals. The sides of the turf-lock are sloping so, when full, the lock is quite wide. Consequently, this type of lock needs more water to operate than vertical-sided brick- or stone-walled locks. On British canals and waterways most turf-sided locks have been subsequently rebuilt in brick or stone, and so only a few good examples survive, such as at Garston LockGarston 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 is now administered by British Waterways and known as the...
, and Monkey Marsh Lock
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 British Waterways...
, on the Kennet and Avon Canal
Kennet and Avon Canal
The Kennet and Avon Canal is a waterway in southern England with an overall length of , made up of two lengths of navigable river linked by a canal. The name is commonly used to refer to the entire length of the navigation rather than solely to the central canal section...
.
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.Design
When planning a canal, the designer will attempt to build a summit level with a large 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).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-pumpPump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
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 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
Kennet and Avon Canal
The Kennet and Avon Canal is a waterway in southern England with an overall length of , made up of two lengths of navigable river linked by a canal. The name is commonly used to refer to the entire length of the navigation rather than solely to the central canal section...
).
Water saving basins
For example the Hindenburg-lock (in Hannover
Hanover
Hanover or Hannover, on the river Leine, is the capital of the federal state of Lower Saxony , Germany and was once by personal union the family seat of the Hanoverian Kings of Great Britain, under their title as the dukes of Brunswick-Lüneburg...
, Germany, built 1919-1928) has two lock chambers of 225 m length, each of which would use 42,000 m³ of water for a full locking cycle. Due to the use of 10 water saving basins, only 10,500 m³ of water are used. A more recent example is the Rhine–Main–Danube Canal with 13 saving locks out of a total of 16 locks.
Water saving basins are incorporated in proposals to augment the capacity of the Panama Canal
Panama Canal
The Panama Canal is a ship canal in Panama that joins the Atlantic Ocean and the Pacific Ocean and is a key conduit for international maritime trade. Built from 1904 to 1914, the canal has seen annual traffic rise from about 1,000 ships early on to 14,702 vessels measuring a total of 309.6...
, but the scheme is controversial because the mixing of salt and fresh water in the basins will allow brackish water into Gatun Lake
Gatun Lake
Gatun Lake is a large artificial lake situated in the Republic of Panama; it forms a major part of the Panama Canal, carrying ships for of their transit across the Isthmus of Panama....
, a source of drinking water and a wildlife reserve.
Grand Union Canal
The Grand Union Canal in England is part of the British canal system. Its main line connects London and Birmingham, stretching for 137 miles with 166 locks...
and the Coventry Canal
Coventry Canal
The Coventry Canal is a navigable narrow canal in the Midlands of England.It starts in Coventry and ends 38 miles north at Fradley Junction, just north of Lichfield, where it joins the Trent and Mersey Canal...
, among others. They are now out of use, and in some cases have been filled in, because British Waterways considered that it was too easy to misuse them and flood the surrounding area. 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.
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.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' principleArchimedes' principle
Archimedes' principle relates buoyancy to displacement. It is named after its discoverer, Archimedes of Syracuse.-Principle:Archimedes' treatise On floating bodies, proposition 5, states that...
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.
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
Grand Union Canal
The Grand Union Canal in England is part of the British canal system. Its main line connects London and Birmingham, stretching for 137 miles with 166 locks...
. 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.
Marine railway
Canal inclined plane
An inclined plane is a system 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. It can be considered as a specialised type of cable railway....
in that it moves boats up or down a slope on rails. However, the vessel is carried "dry" (in a carrying frame, or cradle) rather than in a water-filled caisson. The principle is based on the patent slip
Patent slip
The patent slip or Marine Railway was invented by Scot Thomas Morton in 1818 as a cheaper alternative to a dry dock for ship repair. It consisted of an inclined plane, which extended well into the water, and a wooden cradle onto which a ship was floated...
, used for hauling vessels out of the water for maintenance.
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 hydraulics, 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
Archimedes' principle
Archimedes' principle relates buoyancy to displacement. It is named after its discoverer, Archimedes of Syracuse.-Principle:Archimedes' treatise On floating bodies, proposition 5, states that...
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.
In some locations, notably the Big Chute Marine Railway
Big Chute Marine Railway
Big Chute Marine Railway is a boat lift at Lock 44 of the Trent-Severn Waterway in Ontario, Canada. It works on an inclined plane to carry boats in individual cradles over a change of height of about...
on the Trent-Severn Waterway
Trent-Severn Waterway
The Trent–Severn Waterway is a Canadian canal system formerly used for industrial and transportation purposes and now for recreational and tourism purposes, connecting Lake Ontario at Trenton to the Georgian Bay portion of Lake Huron at Port Severn...
, in Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, 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.
Boat lift
The Falkirk WheelFalkirk Wheel
The Falkirk Wheel is a rotating boat lift located in Scotland, UK,connecting the Forth and Clyde Canal with the Union Canal, opened in 2002. It is named after the nearby town of Falkirk which is in central Scotland...
, the world's first rotating boat lift, acts as the centrepiece of the restoration of the Forth and Clyde and Union Canal
Union Canal (Scotland)
The Union Canal is a 31.5-mile canal in Scotland, from Lochrin Basin, Fountainbridge, Edinburgh to Falkirk, where it meets the Forth and Clyde Canal.-Location and features:...
s. The spectacular "Wheel" presents the 21st century's solution to replacing a flight of locks which formerly connected the canals and which were filled-in in 1930. The Falkirk Wheel 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 100 feet (30.5 m) in a few minutes compared to the time it took when the original lock staircase operated.
The Victorian Anderton Boat Lift
Anderton Boat Lift
The Anderton Boat Lift near the village of Anderton, Cheshire, in north-west England provides a vertical link between two navigable waterways: the River Weaver and the Trent and Mersey Canal....
, the world's first vertical boat lift, linking the Trent and Mersey Canal
Trent and Mersey Canal
The Trent and Mersey Canal is a in the East Midlands, West Midlands, and North West of England. It is a "narrow canal" for the vast majority of its length, but at the extremities—east of Burton upon Trent and west of Middlewich—it is a wide canal....
and the River Weaver
River Weaver
The River Weaver is a river, navigable in its lower reaches, running in a curving route anti-clockwise across west Cheshire, northern England. Improvements to the river to make it navigable were authorised in 1720 and the work, which included eleven locks, was completed in 1732...
in Cheshire
Cheshire
Cheshire is a ceremonial county in North West England. Cheshire's county town is the city of Chester, although its largest town is Warrington. Other major towns include Widnes, Congleton, Crewe, Ellesmere Port, Runcorn, Macclesfield, Winsford, Northwich, and Wilmslow...
, has recently been restored. The world's highest boat lift of Strépy-Thieu
Strépy-Thieu boat lift
The Strépy-Thieu boat lift lies on a branch of the Canal du Centre in the municipality of Le Rœulx, Hainaut, Belgium. With a height difference of between the upstream and downstream reaches, it is the tallest boat lift in the world, and will remain so until the Three Gorges dam boat lift in...
in Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
raises or lowers 1,350 tonnes boats by 73.15 metres.
Another famous derivative is the Peterborough lift lock
Peterborough Lift Lock
The Peterborough Lift Lock 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....
which is a boat lift
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 and the canal inclined plane....
located on the Trent Canal in the city of Peterborough, Ontario
Peterborough, Ontario
Peterborough is a city on the Otonabee River in southern Ontario, Canada, 125 kilometres northeast of Toronto. The population of the City of Peterborough was 74,898 as of the 2006 census, while the census metropolitan area has a population of 121,428 as of a 2009 estimate. It presently ranks...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and is Lock 21 on the Trent-Severn Waterway
Trent-Severn Waterway
The Trent–Severn Waterway is a Canadian canal system formerly used for industrial and transportation purposes and now for recreational and tourism purposes, connecting Lake Ontario at Trenton to the Georgian Bay portion of Lake Huron at Port Severn...
.
The dual lifts are the highest hydraulic boat lifts in the world, rising 19.8 m (65 ft). This was a considerable accomplishment when conventional locks usually only had a 2 m (7 ft) rise. Each lift has a capacity of 1,300 tonnes.
The basins are 140 feet (43 m) long, 33 feet (10 m) wide and 9 feet 10 inches (3.0 m) deep. The vertical distance lifted is 65 feet (20 m). The Trent-Severn has another similar lift lock at Kirkfield, with basins of the same dimension, but which lifts over a smaller vertical distance.
Caisson lock
Around 1800 the use of caisson locks was proposed by Robert Weldon for the Somerset Coal Canal
Somerset Coal Canal
The Somerset Coal Canal was a narrow canal in England, built around 1800 from basins at Paulton and Timsbury via Camerton, an aqueduct at Dunkerton, Combe Hay, Midford and Monkton Combe to Limpley Stoke where it joined the Kennet and Avon Canal...
in England. In this underwater lift, the chamber was 80 ft long and 60 ft (18.3 m) deep and contained a completely enclosed wooden box big enough to take a barge. This box moved up and down in the 60 ft (18.2 m) deep pool of water. Apart from inevitable leakage, the water never left the chamber, and using the lock wasted no water. Instead, the boat entered the box and was sealed in by the door closing behind it, and the box itself was moved up or down through the water. When the box was at the bottom of the chamber, it was under almost 60 feet (18.3 m) of water – at a pressure of three atmospheres, in total. One of these "locks" was built and demonstrated to the Prince Regent
Prince Regent
A prince regent is a prince who rules a monarchy as regent instead of a monarch, e.g., due to the Sovereign's incapacity or absence ....
(later George IV
George IV of the United Kingdom
George IV was the King of the United Kingdom of Great Britain and Ireland and also of Hanover from the death of his father, George III, on 29 January 1820 until his own death ten years later...
), but it had various engineering problems and the design was not put into use on the Coal Canal. However, in about 1817 the Regents Canal Company built one of these locks at the site of the present-day Camden Lock
Camden Lock
Camden Lock, or Hampstead Road Locks is a twin manually-operated lock on the Regent's Canal in Camden Town, London Borough of Camden. The sign on each of the twin locks reads "Hampstead Road Lock 1"...
, north London. Here the motivation was, again, water supply problems. Even though the change in level is much lower than that would have been the case in Somerset, the system was soon replaced by conventional locks. No commercially successful example has ever been built.
Diagonal lock
This new concept in lock design has yet to be installed on any waterway. 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 pontoonPontoon (boat)
A pontoon is a flotation device with buoyancy sufficient to float itself as well as a heavy load. A pontoon boat is a flattish boat that relies on pontoons to float. Pontoons may be used on boats, rafts, barges, docks, floatplanes or seaplanes. Pontoons may support a platform, creating a raft. A...
, 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 discredited caisson lock
Caisson lock
A caisson lock is a type of canal lock in which a narrowboat is enclosed in a sealed box and raised or lowered between two water levels. It was intended primarily as a water-saving measure, but also to save construction costs when compared with other engineering solutions. It was capable of...
design in that the boat does not have to be carried in a submerged chamber.
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
Lancaster Canal
The Lancaster Canal is a canal in the north of England, originally planned to run from Westhoughton in Lancashire to Kendal in south Cumbria...
to Kendal
Kendal
Kendal, anciently known as Kirkby in Kendal or Kirkby Kendal, is a market town and civil parish within the South Lakeland District of Cumbria, England...
and the proposed new branch of the Grand Union Canal between Bedford
Bedford
Bedford is the county town of Bedfordshire, in the East of England. It is a large town and the administrative centre for the wider Borough of Bedford. According to the former Bedfordshire County Council's estimates, the town had a population of 79,190 in mid 2005, with 19,720 in the adjacent town...
and Milton Keynes
Milton Keynes
Milton Keynes , sometimes abbreviated MK, is a large town in Buckinghamshire, in the south east of England, about north-west of London. It is the administrative centre of the Borough of Milton Keynes...
A combined system - the Three Gorges Dam
At the Three Gorges DamThree Gorges Dam
The Three Gorges Dam is a hydroelectric dam that spans the Yangtze River by the town of Sandouping, located in the Yiling District of Yichang, in Hubei province, China...
on the Yangtze River
Yangtze River
The Yangtze, Yangzi or Cháng Jiāng is the longest river in Asia, and the third-longest in the world. It flows for from the glaciers on the Tibetan Plateau in Qinghai eastward across southwest, central and eastern China before emptying into the East China Sea at Shanghai. It is also one of the...
(Chang Jiang) in China there are two stair-steps 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
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 and the canal inclined plane....
(a large elevator
Elevator
An elevator is a type of vertical transport equipment that efficiently moves people or goods between floors of a building, vessel or other structures...
) capable of moving a three thousand ton ship vertically in one motion. The locks and the boat lift provide a total lift of up to 113 metres.
Ship sizes named after locks
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 PanamaxPanamax
Panamax and New Panamax are popular terms for the size limits for ships traveling through the Panama Canal. Formally, the limits and requirements are published by the Panama Canal Authority titled "Vessel Requirements"...
and the Seawaymax
Seawaymax
The term Seawaymax refers to vessels which are the maximum size that can fit through the canal locks of the St. Lawrence Seaway.Seawaymax vessels are in length, wide, and have a draft of and a height above the waterline of . A number of lake freighters larger than this size cruise the Great...
.
See also
- Canal poundCanal poundA canal pound, aka reach, is the stretch of level water impounded between two canal locks. Canal pounds can vary in length from the non-existent, where two or more immediately adjacent locks form a lock staircase, to many miles....
- Flash lockFlash lockEarly locks were designed with a single gate, known as a flash lock or staunch lock. The earliest European references to what were clearly flash locks were in Roman times....
- Pound lock
- SluiceSluiceA sluice is a water channel that is controlled at its head by a gate . For example, a millrace is a sluice that channels water toward a water mill...
External links
- Deepest Canal Locks in England
- Interactive simulation of lock operation – this demonstration shows guillotine-type gatesGuillotine lockA guillotine lock is a type of canal lock. The lock itself operates on the same principle as any normal pound lock, but is unusual in that each gate is a single piece, usually of steel, that slides vertically upwards when opened to allow a boat to traverse underneath...
for clarity - Interactive lock game for students with single and double flight locks and lesson plans