A         Locks

Fundamental to the ability of any navigation to rise or fall was the use of lock-gates to hold one stretch of water at a higher level than an adjoining section.

Single (or "flash") lock-gates were in use by the 1st century BC (Chien-Lu Dam and canals near Nanyang) but may have been used earlier (in the valley of the Euphrates, or the port of Sidon) for irrigation and sluicing purposes.

In Europe, the lock was developed initially to overcome two specific problems: a desire to allow boats to enter a drainage and navigable water system which was protected by dykes, and the need to increase the depth of water available for the navigation of rivers. For the former use they were originally of the single lifting gate portcullis type, while staunches or weirs with removable wooden boards sufficed for the latter, boats sailing up or down the river on the "flash" of water released when the boards were removed. The earliest single-gate locks were built in the Low Countries at Nieuwpoort and in Italy on the river Mincio at Governolo in the late 12th century, though there had probably been river staunches in Flanders earlier in the century.⁹ At the end of the 14th century the opening of the Stecknitz Canal in Germany (1398) was the first summit canal in Europe, a progression made possible by the use of single locks.

The main problem with "flash" locks and single gates was that they used large volumes of water unless the levels on either side of the gate was equal. Two lock-gates placed close together made a huge saving in water and time in lock-use. This, the "pound" or "chamber" lock, originated in China by the 10th century AD and may have been in use in the Netherlands by the 14th century. A basin between the gates was capable of holding one or more boats. The chamber lock radically reduced water usage. The first recorded example (1373) in Europe was at Vreeswijk (Netherlands), where the canal from Utrecht entered the river Lek.¹⁰ The use of the lock in more upland canal schemes was pioneered in 15th-century Italy with the building of a lock in Milan in 1420.

For very large steep sites the lower gate of one lock might form the upper gate of another. A Chinese text of 1072 mentions a staircase pair of locks.¹¹ In Europe they were first used in France, when the Canal du Briare (France) opened in 1642, 39 years after the first plans had been drawn up (A History of Technology, 3, 460-3). In staircase locks, the upper gate of the lowest lock also forms the lower gate of the second lock, and so on up the flight. This method of construction reduced costs but caused hold-ups when boats working in opposite directions needed to use the locks. More importantly, from a canal engineering viewpoint, they were inefficient users of water, and canals on which they were built often had water-supply problems.

The two greatest of these early lock staircases are the eight lock rises at Fonserannes (Béziers) on the Canal du Midi (France) and at Banavie (Neptune's Staircase) on the Caledonian Canal (Scotland, UK). The Rideau Canal in Canada also made considerable use of staircase locks, with a great eight-lock rise at Ottawa. Technology transfer from the Caledonian Canal led to the seven-lock flight at Berg on the Göta Canal (Sweden), where Thomas Telford was consultant, using his Caledonian Canal drawings as the basis for the Göta's Locks.¹² In his turn Telford had learnt from the engineering of the Canal du Midi, for in his library at the Institution of Civil Engineers in London are copies of the two older books (1778 and 1804) on the Canal du Midi with annotations in Telford's hand on them.¹³

A major improvement in the design of locks was the mitre gate. Because of the stresses involved, a single wooden gate restricted the width of lock which could be constructed. The mitre gate, where two gates meet at an angle on the centre line of the lock, increases the width of lock it is possible to build. The mitre gate was probably introduced in Italy by Bertola da Novate, though the earliest drawings are by Leonardo da Vinci and date from the late 15th century.

The early locks built in China and Italy were of stone, but elsewhere turf-sided locks were often used, where the section of lock between the gates consisted of sloping turf-covered sides. Vertical wooden guides were used to stop boats from sticking to these sloping sides. Such locks used larger amounts of water than conventional stone locks owing to leakage. They can still be found on the River Kennet Navigation in England and on the Grossefehn-Kanal near Emden (Germany). Wood was also used for the construction of locks, and a wooden lock survives from the old Maryinsk Canal (1810) in Vitegra (Russia).

A feature developed on French canals in the 17th century was the ground paddle, or sluice built into the stonework of the lock, which controlled the flow of water from the upper to the lower level. Previously locks had been emptied and filled by sluices in the gate. This restricted the depth of to which a lock could be built, as the water flowing through the gate paddle into a deep lock would flood the boat using the lock. By placing the sluices and their channels into the structure of the lock, water could be fed into the bottom of the lock without the possibility of flooding boats.

When the Canal du Midi was built, the side walls of the locks were built curved, making the centre of the lock wider than the gates. It was thought that this would counteract the forces tending to push out the side walls of the locks when the lock was empty. This disregarded the fact that when the lock was full the water provided a similar, but reversed, force, and consequently locks are better built with straight sides. However, several canals were built with curved lock sides, including the Canal de Castille in Spain (1790s) and the original Saimaa Canal in Finland (1845-56).

Water supply was the canal engineer's main problem, and there are hints in the documentation that the Grand Canal in China used side ponds to save water. Side ponds were built such that their level was half-way between the upper and lower levels of the lock. When emptying, the first half of the locking water could then be fed into the side pond, and this water could be used subsequently for filling the first half of the lock. Many European 18th- and 19th-century locks, such as the flight at Devizes on the Kennet and Avon Canal, were built with side ponds between locks.

In central and eastern Europe, double-width locks were sometimes constructed which allowed two boats to lock through together. Single-width gates were provided and these were offset, to the right at one end of the lock and to the left at the other. The first boat entered the lock and then moved over to allow a second boat to enter. The first use of such locks may have been on the Finow-Kanal (Germany) when it was rebuilt in the 1830s. They can also be found on other canals in Germany and on the Labe and Vltava in the Czech Republic.

Towards the end of the 19th century there was a growth of interest in canal engineering in Europe as more canals were planned and built. To reduce costs and to decrease the time taken to pass through them, locks were designed and built deeper than previously. This would have caused excessive stresses with mitre gates, so the shaft lock was successfully developed. In these, the lower end of the lock was enclosed by a wall, boats entering and leaving through a hole in the lower part of the wall. Both mitre gates and vertical lifting gates were used to seal this. Shaft locks, because of their depth, used large quantities of water. To reduce this usage chambers were built into the side walls of the locks which acted as side ponds. Up to five or six chambers could be used, one above the other on each side of the lock.

The earliest known (but unsuccessful) shaft lock was built on the line of the uncompleted trans-Sweden canal at Trollhättan in 1754. This was on the Karls Grav and had a fall of no less than 16m. Unfortunately the shaft-lock proved unusable in flood-time owing to insufficient height in the entrance tunnel, and in 1768 it was replaced by a staircase pair of locks.¹⁴

Improvements in lock design have continued throughout this century, with different types of gate design appearing. These have included gates which lift and rotate, increasing headroom under the raised gate, gates which slide to one side, gates which lower either sliding vertically or are hinged at the bottom, and sector and segment gates which are curved and thus distribute stresses more evenly. Gates are also now used for emptying and filling locks, doing away with the necessity for sluices and paddle gear.

S I T E S

a       Single-gate locks

An important non-canal site in the evolution of the single-gate lock is the port of Sidon (2nd century BC or earlier); there are still extant Phoenician harbour works there, where rock-cut grooves (one still remaining) indicate the former existence of four sluice-gates, probably for flushing the harbour. These could well go back to the 8th-12th centuries BC.¹⁵

i	Nile to Red Sea Canal Lock (Egypt), rebuilding by Pharaoh Ptolemy II (Philadelphus), c 285 BC.
Grading: 1. ***; 2. ***; 4. ***. Total: 9
	Diodorus Siculus wrote of this 97km canal that the Pharaoh: "... in the most suitable spot constructed an ingenious kind of lock. This he opened, whenever he wished to pass through, and quickly closed again, a contrivance which usage proved to be highly successful."16

ii	Magic Canal (China) (see "Contour canals").
Grading: 1. **; 2. ***; 4. *. Total: 6

iii	Duckerschleuse, Stecknitz Canal (Germany) Single- gate flash-type lock.
Grading: 1. *; 2. **; 3. **; 4. *. Total: 6
	Eight kilometres north of Lauenburg, a town with a long tradition of inland water transport, on the Elbe, 30km east of Hamburg (Germany), the lock is close to the village of Witeeze. Alongside the lock is the lock-keeper's house. As boats only used the lock infrequently, the lock-keeper was also a farmer. The house is now used as a cafe and guest- house. The lock is currently under restoration. To gain access to the site, it is necessary to cross the Elbe-Trave Canal, which replaced the Stecknitz Canal in 1900, at Witeeze Lock. This, and the other locks on the canal, was built to the Hotropp design. Water is used to operate the gates by counterbalances and the sluices are activated by air, and also compressed by water flowing from the upper level to the lower. Other associated sites include the Palm-Schleuse in Lauenburg, a circular chamber lock capable of accepting several of the small Stecknitz canal barges at one time. This lock was built in 1724 on the site of an earlier single- gate lock. It is named after Herr Palm, who was the local miller (the mill is next to the lock) and lock-keeper (see "Summit-level canals" for other details of this waterway).

b       Double-gate locks

i	Grand Canal (China), 984 AD.
Grading: 1. ***; 2. ***; 4. ***. Total: 9
	The first recorded double-gate or pound lock in the world was built at the northern end of the Shan-yang Yun-Tao section between the Yangtze and Huai-yin in AD 984 by Chhiao Wei-Yo, Assistant Commissioner of Transport for Huainan.17

ii	The Conca di Viarenna, Via Arena, Milan (Italy), c 1400.
Grading: 1. ***; 2. ***; 4.*. Total: 7
	In 1179-1209 a water-supply and irrigation canal was built over the 50 km from an intake on the river Ticino (running from Lake Maggiore) to the Po, southwards to Abbiategrasso and east to the south side of Milan. In 1269 this was enlarged and made navigable as the Naviglio Grande. In 1386 work began on the new cathedral that was being built with marble from quarries near Lake Maggiore. Boats were raised the 2m to the level of the city moat by stopping the flow of the Naviglio Grande at the most convenient times and raising its level to that of the moat with stop planks. The boats passed into the moat and on to a short canal to the cathedral site. When the boats had passed, stop planks were used to cut off the moat and reopen the Naviglio Grande. The procedure was reversed to allow boats to return. A staunch (single-lock gate) was then provided at the entrance to the linking canal at Viarenna, and later a second at the junction between the moat and the Naviglio Grande, to replace the stop planks. The engineers Filippo da Modena and Fioravante da Bologna created Italy's first pound lock (one of the first in Europe) by bringing the two lock gates nearer together to reduce water consumption. A second pound lock was built on the enlarged old moat by 1445 (now renamed the Naviglio Interno). The various sections of the Naviglio Interno have now either been culverted or filled in.

c       Lock staircases

i	Rogny Staircase, Canal de Briare (France), 1605-10. [Figure 1]
Grading: 1. **; 2. **; 3. **; 4. **. Total: 8
	The first staircase flight of locks in Europe is situated 130km south of Paris, 15km NE of Briare. From the point of view of technological innovation, this is a more important flight of locks than those on the Canal du Midi (see below). The canal was supplied with water from two lakes which fed its summit level. The flight of seven "staircase" locks at Rogny was at the northern end of this; they have straight sides and are fitted with ground paddles. When the latter were introduced to the United Kingdom (on the Newry Canal in Northern Ireland) the locks were described as "after the French pattern." These original locks were bypassed at the end of the 19th century and they remain as substantial structures.

Figure 1 The large early 17th century lock staircase at Rogny, Canal de Briare (France)

ii	Fonserannes (Béziers) Staircase, Canal du Midi (France), 1665-81.
Grading: 1. **; 2. **; 3. **; 4. ***. Total: 9
	Original eight-rise staircase on the Canal du Midi (see section on "Technologically significant canals"), built 1665-81. The upper six locks are still in use and the lower two, below a later diversion of the canal, are used occasionally. Most traffic now uses the new "water-slope," completed in 1983.

iii	"Neptune's Staircase," Caledonian Canal (Scotland, UK), 1803-11.
Grading: 1. *; 2. *; 3. ***; 4. **. Total: 7
	This 60-mile canal was designed to carry sailing ships, up to 170ft by 40ft, through the Great Glen of Scotland. Thomas Telford was principal, with William Jessop as consulting engineer. Telford had assembled a specialist construction team and the scale of the work set a precedent with the large use of construction railways and three steam engines for pumping. With the large lakes on the summit level of the canal there was no shortage of water. The locks were therefore placed in groups to save expense: at Bonavie was built the "Neptune's Staircase" of eight locks, at Fort Augustus five, at Muirtown another four, and double locks at Corpach and Laggan. The locks were designed for a navigable depth of 20ft, but the canal itself did not reach a depth of 17ft until 1847. The locks remain in substantially their original condition and are all still in active use on the Caledonian Canal (see Paget-Tomlinson 1978, 106).

d       Earth-sided locks

These represent an early and primitive type of lock used on river navigations that have sometimes survived in use into the modern period.

i	Garston Lock, Burghfield, Kennet Navigation, England (UK), c 1854.
Grading: Grading: 3. ***. Total: 3
	This is a conserved turf-sided lock, originally built in 1715-23 as part of the Kennet Navigation from Reading to Newbury. The survival of parts of a timber substructure indicate a rebuilding in c 1767 to a length of 37m and a width of 5.8m (with a lift of 2.5m) so that it could accommodate "Newbury" barges. It was absorbed as part of the arterial Kennet and Avon Canal and rebuilt as a smaller (27.6m long and 4.6-5.2m wide) turf-sided lock, revetted with slate, in c 1854. The lock was brought back into operation after conservation in 1993-94.18

e       Wooden-sided locks

Another primitive type of lock that has remained in use intermittently.

i	Wooden-sided lock at Vitegra (Russia).
Grading: 3. ***. Total: 3
	350km ENE of St Petersburg, on the southern shore of Lake Onega. This is the last remaining lock of the 39 built (size given as 74m by 10.3m) on the Maryinsk Canal, dating from 1810. The canal, which linked Lake Onega with Tcherepovetz, was repeatedly reconstructed and was awarded the Grand Gold Medal at the 1903 Paris International Exhibition as an outstanding example of Russian engineering. In the 1960s the canal was rebuilt to much larger standard and reopened in 1964.

f       Mitre-gated lock chambers

Single tall and heavy gates both restricted the width of a lock chamber and were heavy to move. The introduction of double mitre-gates, which were kept closed by the pressure against them, became universal.

i	Spaarndam (The Netherlands), early mitre-gated chamber lock, 1572.
Grading: 2. *; 3. *. Total: 2
	This is the site, 15km west of Amsterdam, of a chamber lock which possibly used mitre gates and was built in 1572. The lock allowed passage between the river Spaarne and the Haarlemmer (which was eventually drained by the Cruquis pumping engine). It is possibly on the site of an earlier lock dating from the mid-14th century. Also in the village are flood control sluices, a later stone-built lock, and a large modern lock. It is possibly worth considering because of the location's long history of hydraulic engineering. There were earlier structures here, and today there are two more recent locks close to the site.

g       Shaft locks

i	Saint Denis Lock, central Paris (France), 1892.
Grading: 2. **; 3. **. Total: 4
	This was the first successful shaft lock. The Saint Denis Canal was rebuilt c 1892 to accommodate the deeper boats which were being built for the recently dredged Seine. The number of locks was reduced, and in one place a single lock, with a fall of 10m, replaced four older ones. This was the first shaft lock to be built, the lower end of the lock being traversed by a masonry bridge, which was also used to contain the water in the lock when the single gate fitted against it.19

ii	Horin Lock, near Melnik (Czech Republic), 1905.
Grading: 2. **; 3. *. Total: 3
	This is an early shaft lock with offset gates, later to become a common feature. This lock, located close to the confluence of the Labe and Vltava rivers, is a shaft lock dating from 1905. It has twin lower gates which form a straight seal against the bridge section across the lower mouth of the lock. The lock gates are offset to allow two boats to use the lock simultaneously.

iii	Anderten Lock, Hannover (Germany).
Grading: 2. *; 3. ***. Total: 4
	This shaft lock and associated complex, 5km east of Hannover, on the Mitteland-Kanal, built c 1930, raises the canal to its summit level. There are two locks, 225m by 12m, side-by-side. Five chambers, one above the other, are built into each lock side to conserve water. A water pumping station to feed the summit level is also built on the site. This lock, with its large size and water economy measures, represents the direction in which waterway engineering has proceeded up to the present.20

 

B         Inclined planes

The idea for transporting boats over dry land must have grown out of the necessity in ancient times of having primitive rough portages around rapids on rivers, or to connect two arms of the sea across an isthmus. The Greeks called this a diolkos, and one of the earliest and largest, with a paved way, rails, and terminal slipways, was at Corinth (see below).

Differences of height on a canal line could also be overcome by pulling boats up ramps between varying levels of water, which overcame many of the water-supply problems generated by heavy lockage.

It was realized in China at an early date that if the ramp of a spillway was made to slope at a reasonably gentle gradient it would be possible to drag canal boats up and over it to the higher level. In this manner the double slipway was developed. This consisted of a pair of inclined stonework aprons over which boats were hauled, in China generally with the use of capstans, from a waterway at one level to a waterway at another. In 1696 Lecomte described the use of one as follows:

At the end of the Canal they have built a double Glasis, or sloping Bank of Freestone, which uniting at the point, extends itself on both sides down to the Surface of the Water. When the barque is in the lower Channel they hoist it up by the help of several Capstans to the plane of the first Glacis, so far, till being raised to the Point, it falls back again by its own Weight along the second Glacis, into the Water of the upper Channel, where it skuds away during a pretty while, like an Arrow out of a Bow; and they make it descend after the same manner proportionably. I cannot imagine how these Barques, being commonly very long and heavy laden, escape being split in the middle, when they are poised in the Air on this Acute angle ...

Passages of the slipway only took 2.5-3 minutes and European observers considered them much preferable to conventional pound locks, since it was also possible to construct them at a quarter of the expense.²¹

There was probably an indigenous development of the double slipway in Europe. This, the overtoom, was in use in the Netherlands by 1148, when there were two examples in use on the Nieuwe Rhijn Canal near Utrecht; there was probably another at Spaarndam in 1220 and elsewhere in Europe at Ypres in 1298.

The next stage in development was for rope-hauled short inclines to convey boats in wheeled cradles as had been used on the Corinth diolkos. In Italy a particularly well known one was that erected in 1437 at Lizzafusina or Zafosina on the river Brenta at Fusina near Venice (see below).²²

It was gradually realized that larger inclined planes could be used in very hilly country to overcome large changes in level, initially with the use of very small boats. In such situations the alternative would have been the use of great flights of locks, expensive to build, slow to use, and requiring large amounts of water. The other, less common alternative, was a boat lift (see below).

A Sardinian-born engineer, Daviso de Arcort, was the first to design such long inclines on small "tub-boat" canals in hill country. He probably knew of existing short Italian inclines from first-hand knowledge of from books such as Leone Battista Alberti's De re aedificatoria (1485) or Cornelius Meijer's L'Arte de restituire a Roma la tralasciata navigatione (1685). In 1767 he began the construction of three inclined planes on a canal from Drumglass collieries, County Tyrone (Ireland), towards the river Blackwater. The eminent British engineers John Smeaton and his assistant William Jessop suggested that these inclines should be made double and counterbalanced. Davis Ducart (as de Arcort was known in Ireland) then substituted cradles on rails rather than the rollers on wooden ramps he had previously built. Even with these crucial innovations these inclines were abandoned largely unused.

The first successful modern inclined planes were those used in Shropshire (UK) from 1788 onwards. The international evolution of the canal inclined plane is a good example of international and intercontinental technology transfer. In 1795 a small inclined plane based on the Ketley type was built at Hadley, Massachusetts (USA), and in 1796 the American engineer Robert Fulton published his Improvements in Canal Navigation, partly based on his study of the Coalbrookdale planes. François de Recicourt, a French military and civil engineer, had a translation of Fulton's book produced in 1799. Fulton visited France from 1797 to 1801 and the French engineers Bossu and Solages built one incline and a lift at Le Creusot between 1801 and 1806.²³

The underground incline at Worsley (Manchester), on the Bridgewater Canal in Britain, was built at the end of the 19th century and linked the main canal tunnel level with one of the other three levels which served the coal mine. It was particularly important for the way it was reported on, and because it caught the international imagination.

In 1824 the Pennsylvania Society sent the engineer William Strickland to Great Britain to study railway construction, and it was subsequently that the astonishing Allegheny Portage Tramroad was built as part of a composite railway and canal link, with no less than ten powered inclined planes. Later in the 19th century engineers from abroad studied the Morris Canal inclined planes in the USA and built canals with inclined planes in Poland and Japan.

S I T E S

i	Corinth diolkos (Greece), early 6th century BC.
Grading: 1. ***; 2. **; 3. **; 4. *. Total: 8
	This was not strictly a canal line, but it did involve the movement of ships inland, pioneering the use of boat or ship cradles, and so it is included in this list. The diolkos was a stone-paved ship-railway with slipways at either end that traversed the 4 miles across the Isthmus of Corinth and remained in use until the 9th century AD. A roadway of stone blocks had very broad and shallow grooves of 5ft 6in gauge with an inner edge 4ft 11in apart. There was a passing place on a curve with double tracks. Ships were carried on wheeled cradles running in these stone-way grooves. Remains of part of the track have been excavated. Stone-track railways of later date are not uncommon; one of the more complete ran the 10 miles from granite quarries at Haytor on Dartmoor down to the navigable river Teign (Devon, England).24

ii	Double-slipways on the Chinese Canals.
Grading: 1. ***; 2. **; 4. **. Total: 8
	Some were still in operation in 1934 (see section on the Grand Canal in "Technologically Significant Canals"). The specific site location of well preserved remains need to be established.

iii	Short incline at Lizzafusina, or Zafosina, on the River Brenta dam, near Venice (Italy).
Grading: 1. **; 2. ***. Total: 5
	This dam stopped the river waters from silting-up the salt water of the Venetian lagoon. Boats were transported over the dam on a short incline, positioned on two strong cradles on wheels, drawn up by a rope passing over an axle which was worked by a horse gin. The surviving illustrations show a double-incline without any evident means of counterbalancing. The wheels of the cradle ran in grooves, as at Corinth, rather than the later use of upstanding rails.25

iv	The three inclines built by Daviso de Arcort near Coalisland, County Tyrone, Northern Ireland (UK), 1767-77.
Grading: Grading: 1. **; 2. ***; 3. *. Total: 6
	The first was on the Drumglass colliery canal 862m from Coalisland basin with a rise of 16.7m; the second was 772m further on at Drumreagh House, with a rise of 20m. The third was just west of Farlough Lake, with a rise of 21m. The inclines were originally to be single water-wheel powered ramps, but there proved to be insufficient water and so counterbalanced railed inclines were substituted with horse gins to help the 2-tonne boats over the sills. Little traffic passed the inclines and they were abandoned in 1787. There may have been insufficient water for the working of the upper canal or the inclines may have been too steep for effective counterbalanced working. Substantial remains of these first long inclines, the first also fitted with upstanding rails, and the first to be worked by counterbalanced working, can still be seen. They were also important for sowing the idea of canal inclined planes in Britain and Ireland as the Industrial Revolution was starting.26

v	Hay Inclined Plane, Ironbridge Gorge Museum, Shropshire (UK). [Figure 2]
Grading: 1. *; 2. ***; 3. ***; 4. *. Total: 8
	The first successful modern inclined-plane was that built by the Shropshire ironmaster William Reynolds in 1788 at Ketley near the modern town of Telford in 1788, with a vertical lift of 22.25m. It was counterbalanced, loaded boats descending on cradles running on rails. The first steam-powered inclines were then constructed by the same builder on the adjacent Shrewsbury Canal, which opened in 1791-92, the greatest having a rise of 63m.27 This, the Hay inclined plane leading down the side of the Severn Gorge, has been re-railed and forms part of the Ironbridge Gorge Museum (a World Heritage site). Detailed drawings were made by French engineers and disseminated widely.

Figure 2 The 1790s Hay inclined plane at the Ironbridge Gorge World Heritage site, England (UK)

vi	Underground incline, Worsley, Bridgewater Canal, Manchester (UK).
Grading: 1. **; 2. *; 3. *; 4. **. Total: 6
	Deep coal-mining tunnels were built from the end of the Bridgewater Canal from its inception in 1759. By 1795 this level of underground waterways and one 32m above it extended for 24km. They may not have been the first underground mining canals in Britain but they attracted many visitors from home and abroad, who helped to spread the idea of canal mines widely and who also reported on this underground inclined plane.28 The idea for the inclined plane was put forward by the originating mining engineer, John Gilbert, and construction took place between September 1795 and October 1797. It was sited on a 1 in 4 incline following a sloping bed of gritstone 4km from the surface entrance of the mining canals and was 138m long with the upper part consisting of a double railway 5.8m wide. At peak capacity it was capable of handling 30 boats each way in an 8-hour shift, a total weight of around 915 tonnes. The incline was abandoned in 1822 with the exhaustion of the upper shallow seams, but substantial remains survive underground.29

vii	Allegheny Portage Railroad, Pennsylvania (USA), 1831-34.
Grading: 1. ***; 2. *; 3. ***; 4. *. Total: 8
	The 394 miles of the Pennsylvania Main Line was a unique composite canal and railway line linking Philadelphia and Pittsburgh, opened between 1826 and 1834. Built over mountainous terrain, and only made possible by the extensive use of steam-powered inclines, it was even more astonishing an innovation than the pioneering Erie Canal itself. Both passengers and goods could travel the whole distance without transshipment by the use of sectional boats that could be divided into three or four units. The 132km eastern section was operated as a horse and locomotive railway, but the 60km central section consisted of the Allegheny Portage Railroad with five steam-assisted counterbalance inclines reaching up and over Allegheny Mountain. Sylvester Welch built the railway over a 712m summit in three years. The Pennsylvania canals were a crucial step in establishing the industrial might of the most powerful nation on earth.30

viii	Elblag Canal (Poland), an outstanding example of a canal still in operation with multiple 19th-century inclined planes.
Grading: 1. *; 3. ***; 4. *. Total: 5
	Between 1844-60 in what was then East Prussia, the Oberland or Elbing (now Elblag) Canal ran from the Frisches Haff (near Elblag) and the Geerich lake to Osterode. The canal originally had four counterbalanced inclined planes with waterwheel-powered assistance. In 1881 a fifth inclined plane with water-turbine power replaced five of the seven locks. 60-tonne barges have now been replaced by the regular use of passenger tour-boats. The original four inclines of 20-24.5m in rise were designed after study of America's Morris Canal.31

ix	Biwako Canal Inclines, Kyoto (Japan), 1885-90.
Grading: 1. *; 2. ***; 3. *. Total: 5
	The Biwako Canal is an outstanding example of intercontinental technology transfer. The designer, Sakuro Tanabe, toured the USA (including the inclines of the Morris Canal) to study current practice in canal engineering and hydro-electric practice. It has one of the world's first hydro-electric power stations and in many ways is the climax to the building of 19th-century small canals.32 The canal connected Lake Biwa (Biwako) to Kyoto via the counterbalanced Keage Incline. This has double-track inclines of 2.5m gauge. The incline descended 36m towards the City of Kyoto in a length of 555m on a gradient of 6.48%.33 The twin steel-built boat cradles and the incline are preserved. There was also a second incline.

 

C         Boat lifts

Some mid-18th century canals such as the Bridgewater in England used vertical haulage of loaded containers to overcome differences in level. The idea of lifting an actual boat from one canal level to another seems to have evolved separately in both England and Germany at the end of the 18th century.

The first recorded boat lift was constructed in 1788-89 on the short Churprinz Canal at Halsbrücke in Saxony (Germany). This was for small 2.5-tonne boats and involved the use of a five-fold manual tackle. The lift continued in use until 1868 (see "Sites" below).³⁴

The more sophisticated experimental lifts built in the last decade of the 19th century in Britain were generally unsuccessful. These included deep shaft locks with caissons and boat cradles supported on pillars supported by floats immersed in under-lift tanks.³⁵

Subsequent lifts have been largely successful. In the early 1830s the Grand Western Canal in the south-west of England was opened with no less than seven counterbalanced twin-chamber lifts and operated successfully until 1867 (see "Sites" below).³⁶

Hydraulically operated lifts were the big success stories of the late 19th and early 20th centuries. Edwin Clark (1814-94) was the engineer behind their development, and it was his designs that have led to the widespread practical use of the lift. In 1846 Robert Stephenson appointed him to be superintending engineer to the Britannia and Conwy Tubular Bridges, the wrought-iron tubes of which were raised using hydraulic presses. In 1857 he became engineer to the Thames Graving Dock Limited, for which he designed a graving dock in which the ships to be repaired were lifted from the water by hydraulic presses. In 1866 he lectured on this, by which time the lift had been working for about seven years and had raised 1055 ships with an average tonnage of 686 tonnes.

A connection was made between the Weaver River Navigation and the Trent and Mersey (at Anderton, Cheshire, UK) using a 15.35m lift to Edwin Clark's design with two counterbalanced troughs. The hydraulic cylinders extended 21.35m below each tank. The lift was set in operation by removing some centimetres of water from the lower caisson. The speed of operation was controlled by transferring the hydraulic fluid through a 0.127m pipe from below one caisson to the other. The descending caisson became immersed in the canal water and for the last 1.22m had to be assisted by a steam-powered hydraulic accumulator. Boats of 102 tonnes could be raised in the 22.88m by 4.73m tanks. In 1904 the lift was converted to electrical operation because of chemical corrosion of the rams.³⁷

Edwin Clark, his brother Latimer, and John Standfield went on to design a series of lifts on the European mainland in conjunction with the well known French engineering works, SA des anciens établissements Cail. Les Fontinettes lift was built to replace five locks in northern France in 1880-88 and could raise large 300-tonne barges in caissons 38.6m by 5m (see "Sites" below).³⁸

During this important example of technology transfer to the European continent several developments were made on this larger lift that were to be important in later examples. Edwin Clark decided that the lift pits should be kept dry which did away with the necessity for the troughs to be moved for the final short distance by a hydraulic accumulator. A structural innovation was the introduction of masonry towers which supported the troughs at their centre-points and also supported the operator's cabin.

The hydraulic presses for operating the rams were made of cast-iron at Anderton and were designed to be of such at Les Fontinettes. However, on 26 April 1882, the side of one of the Anderton presses blew out during operation and so the Les Fontinettes presses were made of steel with a thin lining of copper. Water-turbines also provided the extra power needed to operate the lift and blow the seals on the gates.³⁹

The last lifts to be built under the auspices of Messrs Clark, Standfield & Clark were the unequalled concentration of four added to the Canal du Centre; the first was built simultaneously with the Les Fontinettes Lift and opened on 4 June 1888. The building of the last three was delayed and they were opened in August 1917.⁴⁰

Three other hydraulically operated lift schemes illustrate intercontinental technology transfer. The British engineer James Brunlees proposed a ship railway across the Central American isthmus in 1872. This was to take vessels of at least 1220 tonnes on six rails holding 60 four-wheel bogies. Propulsion would be by steam-powered rack-locomotives and ships would be got out of the water and returned to it by hydraulic lifts. This scheme was never built. H G C Ketchum, who had worked with Brunlees, then proposed a 27.4km ship-railway across the Chignecto peninsula that would save a 800km sea journey around Nova Scotia for shipping travelling from the eastern seaboard of the USA to the Gulf of St Lawrence. Ships of up to 2032 tonnes would be positioned over a gridiron and carrying cradle in a lifting dock at either end of the railway. The gridiron would then be raised by 20 hydraulic rams and presses and the ship on its cradle hauled on to the railway. The Chigneto Marine Transport Railway Company was formed in England by James Brunlees and Edwin Clark in 1883 and over half the work of construction was completed between 1888 and July 1891, when the company ran out of money. Remains of the formation survive.⁴¹

There followed the construction of two successful lifts on the Trent Canal in Ontario (Canada). These were constructed at Peterborough in 1896-1902 and in 1900-07 at Kirkfield. These followed on from earlier designs but are significant for being an example of intercontinental technology transfer. The still-operating Peterborough Lift, with a rise of 19.5m, was the highest hydraulic lift built.⁴²

The next lifts moved away from the technology of having twin caissons counterbalanced by hydraulic pressure. Both of the next types - counterweighted and those using floats - were foreshadowed by early experiments: Woodhouse in the former case and Rowland and Pickering or Bossu and Solages in the latter case.

The Henrichenburg Lift in Germany was built between 1894 and 1899 to give access to Dortmund from the Dortmund-Ems Canal. This raised large 950-tonne craft through vertical rises of 14.5m. Five floats in a row beneath the caisson rose or fell in their respective pits as the water-level was changed. An experimental English lift had first used the system in 1796.⁴³

An international competition for boat-lift design took place in 1902. A jury of international experts, including Sir Vernon Harcourt, considered over 200 designs for boat lifts to be used on the proposed Danube-Oder-Elbe Canal. Although the canal was not built (it is still being promoted), the designs became the inspiration for many of the boat lifts that were built subsequently.⁴⁴

In Britain chemicals in the canal water caused problems with the hydraulic operation of the pioneering Anderton Lift, and in 1903-08 its system of operation was altered. The steam-power that had operated the accumulator was replaced by electricity. Over the next few years the hydraulic rams were taken out and each caisson was then operated separately by electric power assisted by counterweights.

S I T E S

i	Churprinz Canal Lift, Halsbrücke, Saxony (Germany), built 1788-89. [Figure 3]
Grading: 1. ***; 2. **; 3. **. Total: 7
	The Churprinz Canal ran for 5.3km on the bank of the Freiberger Mulde river in order to carry ore to the Halsbrücke smelting works from the Churprinz-Friedrich-August mine adit. The whole operation was labour-intensive, with 2.5-tonne boats being towed by two men, a third man on the boat steering with a pole. The river was crossed on the level with the stone-built lifthouse entered through an arch on one bank. This was a rectangular chamber 5.5m wide and 17m long up which boats were lifted by a five-fold tackle into the upper level of the canal. Bad weather and high water in the river could disrupt the working of the lift but it continued in use until 1868. The substantial remains of the lift are still extant.45

ii	Grand Western Canal Lifts, Devon (UK), designed by James Green and built in 1832-35.
Grading: 1. **; 2. *; 3. **. Total: 6
	The first successful twin-chamber counter-balanced canal lifts; in use until 1867. The biggest of the lifts rose 13m and there are substantial remains at Nynehead lift (7.32m). Two counterbalanced iron tanks were suspended by pulleys within a masonry framework.46 A lift important to the evolution of canal lifts (but not on a canal) was the ship lift at the Thames Graving Docks, Royal Victoria Dock, Woolwich, London, designed by Edwin Clark and built in c 1859. The lift was sited in a channel connecting the Royal Victoria Dock at Woolwich and the Pontoon Dock that lay on its south side and was the first of all the lifts using hydraulic power to lift vessels.

iii	Anderton Canal Lift, Weaver Navigation/Trent and Mersey Canal, Cheshire (UK), designed by Edwin Clark and built in 1872-75.
Grading: 1. ***; 2. ***; 3. **. Total: 8
	This is important for being the first hydraulic canal lift and the first of a series of large late 19th and early 20th century lifts based upon it. Boats are carried through a lift of 15.35m in one of two tanks or caissons: 22.9m x 4.73m x 1.53m, encased within an iron framework. Each caisson, weighing 244 tonnes with its water, was originally supported in the centre by a 0.915m diameter iron ram extending downwards into a cast-iron hydraulic press with a 0.127m diameter pipe originally connecting it to the press beneath the second caisson. 0.1525m of water removed from the lower caisson were enough to start the lower caisson falling, its descent being controlled by the rate of flow of the water in the interconnecting 0.127m pipe. Since 1908 each caisson has been operated independently by electric power and two rows of counterbalance weights. The lift has been conserved as an ancient monument and is being restored to use.47

Figure 3 The 18th century Churprinz canal lift at Halsbrücke (Germany)

iv	Les Fontinettes Lift, Neufosse Canal linking the Pas de Calais ports to the Canal de St Quentin (France), 1883-88.
Grading: 2. **; 3. ***. Total: 5
	The first large continental European lift, it bypassed no less than five old locks on a flight dating from 1760. The rise was rather less than Anderton but the capacity was much greater: 38.5m long, 305-tonne Freycinet standard barges drawing 1.8m of water. The design was that largely adopted on future lifts with central towers steadying great steel tanks that were cantilevered out from each side of the central rising column. The old locks were kept in case of breakdown but the lift was so successful that it carried 11,161 boats in 1905. A single large lock replaced the structure in daily use in 1967 and it remains as an industrial monument.48

v	Canal du Centre Lifts (Belgium), 1888-1917.
Grading: 1. **; 2.*; 3. ***. Total: 6
	The difference in levels between the two ends of the canal was 89.45m and there were two distinct sections of the waterway, one of 13 km having five locks with a total rise of 23.26m and the other of 8km with a rise of 66.19m. To overcome part of the latter rise the 15.4m high La Louvière lift was opened in 1888, with the other three lifts of 16.93m rise opening in 1917. The first lift was designed by M P Nolet, an engineer at the Société Cockerill, Seraing, employed by Clark, Standfield & Clark. The framework of this lift was lattice girders rather than the masonry of Les Fontinettes. This unique concentration of lifts carried boats of 404 tonnes. All four of the Canal du Centre lifts have been replaced in use by the 73.15m Strepy Lift but are to be preserved.49 The lifts form part of an integrated industrial landscape, with the early continental European coal-mining at Bois-du-Luc, recommended as being of world significance by the TICCIH Board.

vi	Peterborough and Kirkfield Canal Lifts, Trent-Severn Waterway, Ontario (Canada), 1896-1902 & 1900-07.
Grading: 1.*; 3. **. Total: 4
	These followed on from earlier designs but are significant for being an example of intercontinental technology transfer. The still operating Peterborough Lift, with a rise of 19.5m, was the highest hydraulic lift built. It was also one of the world's largest concrete structures at the time of its completion: more than 19,890m2 of concrete were poured. The commercial success of this link between the Great Lakes was impaired by there only being money available to build two small-scale inclined planes at two further changes of level. The second lift, at Kirkfield, illustrates the progression to a lighter steel structure. A large lock and bigger incline have now allowed more intensive use of the lifts, which are conserved with the canal by Parks Canada.50

vii	Henrichenburg Lift (Germany), 1899.
Grading: 1.*; 3. ***. Total: 4
	Situated on the Dortmund-Ems Canal, the site dates from 1899, when the first boatlift was built. The tank of this lift is supported on five flotation cylinders fitted underneath. It soon proved inadequate to cope with the volume of traffic and a shaft lock with side chambers was built close by in 1914. By the 1960s, boats had increased in size, so a new lift was built, this time with just two flotation cylinders. This in turn has been supplemented in 1989 by a new shaft lock, capable of accommodating a 2000- tonne push-tow unit. This complex of structures illustrates the rapid development in scale of 19th and 20th century waterways and could be considered for any designation as a group.51

 

D         Earthworks

The civil engineering of the artificial waterways had to develop in order to allow the line of water channel to be conveyed over undulating countryside.

Because of the problems in moving the large volumes of earth required and the difficulty in understanding soil stability, large embankments did not feature on the earliest canals. It also accounts to some extent for the use by the Romans of aqueducts, rather than earthworks, for their water supply systems.

By the late 18th century, engineers began to overcome these problems. One of the greatest of the early embankments was at Burnley, on the Leeds and Liverpool Canal (UK), where the canal is carried 1km over the valleys of the rivers Brun and Calder at a height of over 12m. The section of the Leeds and Liverpool Canal between Burnley and Wigan, built between 1796 and 1816, features eight large embankments and shows the confidence then being discovered by canal engineers.

The British engineer Thomas Telford was involved in three notable early uses of large-scale earthworks. These are, first, the approach embankments to the Pontcysyllte Aqueduct on the Ellesmere Canal, Wales (UK), dating from 1795-1805 (see "Aqueducts" and "Technologically significant canals") and, secondly, the great embankment at Shelmore and the nearby Tyrley (Woodseaves) Cutting, Shropshire (UK). The third of his works noted here is the Smethwick Cutting, a 3660m cutting up to 20m deep on Telford's low-level line for the Birmingham Canal, one of the greatest excavations to that date in Britain.⁵²

The construction of the great ship canals - Manchester, Kiel, and Panama - saw the mechanization of earth movement and the ability to construct the vast cuttings on those canals. The largest embankment to be built on a conventional canal was the Raguser Dam, Brandenburg (Germany) on the Havel-Oder Canal. Opened in 1914, it carries the canal some 28m above the valley of the river Raguser. The embankment has a cross-section of 2800m2 and contains around 1 million m3 of earth.⁵³

 

E         Reservoirs

A most important aspect of canal engineering is the adequate supply of water. The height of a canal's summit level is dictated by the method of supplying water. Early canals, such as the 1398 Stecknitz Canal (Germany), had low summit levels, which were supplied with water directly from lakes, rivers, and streams. The Canal de Briare (France) of 1642 was also supplied from existing water supplies, but the water supply to the Canal du Midi (1681) came from dams and water feeders built specifically for that purpose (see "Dams").

Large European ecclesiastical and monastic estates of the Middle Ages had sufficient resources and need for a moderate development of waterway transport, and the first recorded navigation dam survives from this period.

S I T E S

i	Alresford Dam and 200-acre (80ha) reservoir, Itchen River Navigation, (UK).
Grading: 1. ***; 2. **; 3. **. Total: 7
	The earthen dam is overgrown but still holds 24.3ha of water. This was the first known navigation dam in the world.54 Seven hundred years ago the area around Winchester, the early medieval capital of England, was prosperous because of its wool and cloth industries. In 1189 Godfrey de Lucy, Bishop of Winchester, decided to improve the commercial potential of the area by making the river Itchen navigable along its entire length between Alresford and Southampton Water. This work required the construction of a series of flash locks whose subsequent operation depended on a supply of water in excess of the river's natural flow. Bishop de Lucy therefore constructed a reservoir just to the north of Alresford which stores the water of two small streams (see "Dams").

ii	Reservoir on the Grand Canal (China), c 1411.
Grading: 1. **; 2. **; 3. ***. Total: 7
	A reservoir with a 1 mile long dam on the Kuang River, north of Ningyang. This is the second known recorded navigation dam in the world, built around 1411.55 (see "Dams" and "Technologically significant canals").

iii	Canal du Midi reservoirs and feeder system (France). [Figure 4]
Grading: 1. **; 2. ***; 3. ***; 4. **. Total: 10
	The Canal du Midi was a summit-level canal with a heavy lockage requiring a large quantity of water. To the north of the canal's summit, suitable sources of water were found in the rivers of the Montagne Noire. Pierre-Paul Riquet planned a 42km long feeder system in 1661. The only drawback was that more water than was needed was available in the winter, and less in the summer. He therefore took the logical step of building a reservoir to store the surplus winter run-off for use during the following summer. The dam of St Ferréol was built across the river Laudot about 2 miles south-east of Revel. Later, a second dam was required, the stone Lampy Dam, built by the canal engineer Garripuy in 1777-81 (see "Dams").

Figure 4 Low-level outlet tunnel in the base of the large earthwork reservoir dam of Saint Ferréol, Canal du Midi (France), 1667-71

 

F         Water pumps

Water usage on canals with heavy lockage could be enormous and might easily outstrip the water supply available from gravity feeders. The use of pumps goes back to at least the end of the 11th century AD, when there are Chinese references dated 1098 and 1120 to batteries of hand-pumps built to supply water to summit levels and probable references to pumps mounted on pontoons that were used to pump water back at pound locks.⁵⁶ The Archimedean screw was extensively used on canals, not so much for water supply as for ensuring dry conditions when construction or maintenance work was being undertaken.

On the first canals of the Industrial Revolution at the end of the 18th and the beginning of the 19th century power pumps began to become fairly common: they were powered by water-wheels and steam engines. Two of the more significant early examples are listed below. Two more steam-engine houses have significant remains at Smethwick on the Birmingham Canal mainline (see "Technologically significant canals").

During the later part of the 19th century, manual and animal- powered pumps used for maintenance purposes were replaced by steam-driven reciprocating and centrifugal ones. Generally, Archimedean screws were used for water supply where there was only a low head to overcome, such as on river navigations. At Locquinol on the river Sambre (northern France), an electrically powered screw pump is still in operation. It was formerly driven by a steam-powered beam engine which is preserved on site.

On the Mitteland Canal, in Germany, there are impressive late water-pumping systems at Minden (c 1914), and at Anderton, Hannover (c 1930).⁵⁷

S I T E S

i	Crofton pumping station, Kennet and Avon Canal (UK), begun in 1800.
Grading: 1. *; 2. *; 3. ***. Total: 5
	This pumping station was intended to supply the summit level of the Kennet and Avon barge canal that runs across southern England. The brick-built engine house with its separate iron-bound chimney stands above the canal near the village of Great Bedwyn and not far from Hungerford. It houses the only Boulton & Watt engine still doing the work for which it was originally installed. Built in 1812, it is the oldest working steam engine in the world. There was also an earlier Boulton & Watt engine which began work here in 1809. Both were low-pressure engines, fitted with Watt's parallel-motion linkage and his patent separate condenser. The 1812 engine was converted to high-pressure working in 1844, and a Sims engine was installed to replace that of 1809. The latter was rebuilt in 1905 when new Lancashire boilers were added. The Sims engine worked until 1952 and the 1812 one until 1958, when the top 6m had to be removed from the chimney and the steam-engine pumping was replaced by electric pumps. Restoration of the steam-pumps began in 1968 and both steam engines have been regularly operated since 1971, the 1812 engine raising 1 tonne of water at a stroke.

ii	Claverton water-powered pumping station, Kennet and Avon Canal (UK), 1813.
Grading: 1. *; 3. ***. Total: 4
	This installation lifts water 16m from the river Avon to the Kennet and Avon Canal. A tall Bath-stone building houses the original beam-worked bucket pumps with the smaller wheelhouse alongside. There was originally a breast waterwheel 7.6m (25ft) wide and 5.58m (18ft 4in) dia In 1858 this was replaced by two 4.73m (15ft 6in) dia waterwheels on a single shaft, each 3.36m (11ft) wide. A small diesel pump replaced them in 1952, but restoration began in 1969 and the waterwheel pumps are now run on a regular basis.59 There was a third pumping station on the Kennet and Avon Canal and the remains of this are now within the World Heritage site of the Georgian City of Bath. The ornamental stone chimney of this former pumping station is situated halfway down the six-lock (formerly seven) flight leading to the river Avon. The old steam-engine house is at the bottom of the flight. The World Heritage site at Bath also includes two iron arch bridges (7m and 9.15m in span) over the canal cast at Ironbridge in 1800 and sited in the 18th-century Sydney Gardens and adjacent to the elegant classical canal offices which straddle the canal on a bridge.

 

G         Aqueducts

A canal used a natural resource, water, as the medium of its transport way. Deep natural obstacles needed to be bridged by large structures, including a waterproofing medium. Until the 19th century the technology of building masonry walls and arches was better understood than the science of soil mechanics, which was required to design stable earthworks. Before the advent of steam-powered machinery aqueducts were more practical to build than large earthworks. Such structures bridging natural watercourses also ensured the separation of the artificial water-economy of the canal from the natural land drainage and considerably eased the water management of the artificial navigation.

Non-navigable aqueduct bridges, often of considerable size and length, were common in antiquity. One of the first recorded was built by King Sennacherib of Assyria (c 705-681 BC) on the 50-mile long water-supply canal to his capital at Nineveh from springs at Bavian. This Jerwan aqueduct was 305m long and 11.9m wide and an inscription was excavated in the present century that read "I caused a canal to be dug to the meadows of Nineveh. I spanned a bridge of white stone blocks. These waters I caused to pass over it."⁶⁰

The Romans built huge lengths of high arches carrying channels waterproofed with hydraulic mortar. Some 1600 million litres of water daily poured into Rome through eleven great aqueducts. Across low-lying land, particularly outside towns, an aqueduct had to be raised high enough to give a sufficient "head" to the supply, and the use of arches both removed a potential barrier to communication and lessened the amount of stone required for construction. The water-channels above the arches varied from 0.46m to 1.2m wide and from 0.6m to 2.4m high.

The Aqua Marcia (144 BC) actually forms part of a three-deck aqueduct at the Porta San Lorenzo gate into Rome; the arches of the gate also carry the Aqua Tepula (127 BC) and the Aqua Julia (33 BC) aqueducts. Probably the finest Roman aqueduct is the 72km of the Aqua Claudia, built by the Emperors Caligula and Claudius to bring water from Subiaco to Rome. Part of its length is on solid masonry and for 15.3km it is borne on lofty arches, some over 30m high, great lengths of which remain in the Campagna. It is joined 3 miles from Rome by the Anio Novus (AD 38), 99km in length.

Technology transfer over the large extent of the Roman Empire was especially noteworthy. The Pont du Gard (c AD 14) at Nîmes (France), which is on the World Heritage List, was part of a 40km long aqueduct to bring water from the neighbourhood of Uzès. The aqueduct bridge itself has a triple arcade carried 47km above the river Gard and is 270m long, of largely unmortared masonry. The double arcade of the aqueduct at Segovia (Spain), dating from c AD 10 and also on the World Heritage List, is another of the more remarkable water-supply bridges spread throughout the Roman Empire.⁶¹

Such water-supply, irrigation, water-power, and dual-purpose aqueducts continued to be built into the modern period and have had a significant influence on those built primarily for navigation.

It is arguable that the birthplace of highly engineered canals in the modern period was in 15th-century Italy. A navigable canal aqueduct was built on the Martesana Canal from the river Adda to Milan between 1462 and 1470. The Canal du Midi was the largest civil-engineering enterprise of its time and by 1661 a large 9.15m (30ft) span aqueduct had been built on its line at Répudre. The Duke of Bridgewater, inspired by a visit to this canal, planned the first major canal of the world's first Industrial Revolution. This included a three-arched aqueduct carrying the canal 11.6m above the navigable river Irwell, the central arch being 19.2m (38ft) in span.⁶²

Waterproofing varied, with the earlier continental European examples often using hydraulic mortar whereas most British examples used vast amounts of puddled clay - an unstable waterlogged mass.

The scale and monumental character of the masonry aqueduct developed considerably in the first new national integrated transport network that served England's first Industrial Revolution and produced such superb masonry structures as the Lune, Dundas, and Marple Aqueducts.

Iron as a constructional material for girder bridges was used by the ancient Chinese by AD 1000, and in the modern period first for large arches of wrought iron, as at Kirklees, Yorkshire (UK), and then cast iron over the river Severn at Ironbridge, Shropshire (UK) in 1779 (part of the World Heritage site). It was only a matter of time before the material was applied in aqueducts.

The world centre of the iron trade at the beginning of the 19th century was Merthyr Tydfil, Wales (UK), which successively had the two largest ironworks of the 19th century. It was here in 1793 that a two-deck water-power aqueduct was constructed with the lower deck and trough made of iron: the Pont y Cafnau. A sketch of this appeared in the sketchbook of the Shropshire ironmaster William Reynolds in 1794, when he was working on the first large-scale navigable aqueduct made out of iron at Longdon-on-Tern in Shropshire in conjunction with Thomas Telford. This project led on to Jessop and Telford's Pontcysyllte Aqueduct with its 307m long and 38.4m high iron trough, the loftiest navigable canal aqueduct ever built. On the way were several aqueducts that combined cast-iron and hydraulic lime in their waterproofing, such as Chirk and the Edinburgh and Union Canal aqueducts.

The USA had aqueducts that served its developing New World economy, cheaply built in timber with a limited life-span but which enabled the local economy to develop and thrive via accessible cheap transport. Some of these were of great length, and the immense weight of the water carried ensured that these were not simple wooden troughs but had strong lateral reinforcement. One of the Delaware and Hudson Canal aqueducts designed by John Roebling and completed in 1847 survived after conversion to a road bridge. It is the earliest wire-cable suspension "bridge" in the world to retain its principal original elements.⁶³

In the 20th century reinforced concrete became the standard material used for large-scale canal aqueducts. Notable are the reinforced-concrete aqueduct at Minden (Germany) of 1914, which crosses the valley of the Weser (375m long and Europe's longest canal aqueduct)⁶⁴ and the remains of the unfinished concrete aqueduct (1939) which was to cross the Elbe at Magdeburg, and which it is currently proposed to complete. This may mean that the existing remains will be removed.

S I T E S

i	River Molgora Aqueduct, Martesana Canal, near Milan (Italy).
Grading: 1. ***; 2. ***; 3. ***; 4. *. Total: 10
	In 1462-70 Bertola da Novate, engineer to the Duke of Milan, built his second large navigable canal (29km long) eastwards from Milan to near the river Adda at Groppello, then north for 8km to its intake at Trezzo. It had a small three-arched aqueduct over the river Molgora; the river Lambro was also culverted under this canal, which also had two staunch or flash locks. There are remains of this waterway.65

ii	Répudre Aqueduct, Canal du Midi (France), 1665-81.
Grading: 1. *; 2. ***; 3. ***; 4. **. Total: 9
	The whole line and the scale and sophistication of all its engineering works were an inspiration to succeeding canal engineers in the Industrial Revolution. Other aqueducts over the Orbiel and Cesse rivers were designed by the French military engineer Sébastien Vauban and built by Antoine Niquet on the Canal du Midi in 1686.66

iii	Pontcysyllte Aqueduct, Ellesmere Canal, Wales (UK), 1795-1805. [Figure 5]
Grading: 1. ***; 2. ***; 3. ***; 4. *. Total: 10
	One of the heroic monuments that symbolizes the world's first Industrial Revolution and its transformation of technology. Thomas Telford, the Ellesmere Canal "general surveyor and agent," was working under William Jessop, the most prolific engineer of the British canal mania. The relative roles of these two engineers in the design is not totally clear.67 The construction of this landmark, the highest navigable canal aqueduct built, led to the formation and consolidation of a team important to the subsequent development of civil engineering on such large projects as the Caledonian Canal. The decision to build such a high deck, and in the new civil-engineering medium of cast-iron, was a bold one. The canal surface is carried 38m over the river Dee on an iron-arched deck, 313m long, comprised of nineteen spans of 13.6m (44ft 6in). The 3.6m (11.8ft) wide trough is carried on successive spans of four arched ribs spanning between slender masonry piers, which are partly hollow and taper to 3.96m (13ft) by 2.29m (71ft) at their summit. The southern approach embankment was one of the largest earthworks built up to this time.68 Other aqueducts linked to the genesis of this structure might also be associated in any designation. Pont y Cafnau was a cast-iron aqueduct whose construction was authorized in 1793 in order to carry both a water-supply channel and a horse-worked railway into what was the largest ironworks in the world by the early 19th century at Cyfarthfa, Merthyr Tydfil, Wales (UK). A sketch of this done in 1794 survives in William Reynolds's sketchbook. Also in this collection of papers is a sketch made by Telford of a design for a high iron aqueduct made in 1794. Reynolds was the ironmaster who was experimenting, together with Thomas Telford, in 1795 on the first iron canal aqueduct to be designed. This Longdon-upon-Tern aqueduct is a protected monument 57m long, with four spans of 14.5m (47ft 8in), and a trough 2.7m (9ft) wide and 0.9m (3ft) deep. One month before it was completed in 1796 a much smaller single-span iron canal aqueduct was built by the engineer Benjamin Outram (William Jessop's business partner) on the Derby Canal (demolished 1971).69 On the Ellesmere Canal, near Pontcysyllte, the earlier Chirk Aqueduct had a cast-iron base to the water-channel, and Telford went on to advise a further group of three very large aqueducts with cast-iron channels on the Glasgow and Edinburgh Union Canal in Scotland (see the section on "Technologically significant canals").

Figure 5 The huge cast-iron aqueduct of Pontcysyllte, Wales, 1795-1805

iv	Delaware River Aqueduct, Lackawaxen, Pike County, Pennsylvania (USA).
Grading: 1. **; 2. *; 3. **; 4. *. Total: 7
	The ambitious Pennsylvania Main Line (see "Inclined planes") of 1826-34 entered Pittsburgh at its western end by passing over a 348m long wooden-trough aqueduct over the Allegheny River. The pioneering engineer John Roebling replaced it in 1845 with a new one of seven 49.4m (162ft) spans reinforced by wire suspension cables.70 In 1847 two rivers formerly crossed by the Delaware and Hudson Canal on the level were given two of the four new aqueducts commis- sioned from Roebling by the canal company.71 The Delaware River aqueduct survived after conversion to a private road bridge and was carefully restored in the 1980s and conserved as a National Historic Site. This is the earliest wire-cable suspension bridge in the world to retain its principal original elements.72 The bridge runs from Pennsylvania into Minisink Ford, Sullivan County, New York. There are four spans of 43m (141ft 5in) from the centre of one 2.9m (9ft 6in) wide suspension tower to the next. The stone piers and abutments carried the 2.6m (8ft 6in) deep trough 9.5m above the level of the river. The wooden floor of the trough was held by wrought-iron hangers from the suspension cables that were largely hidden in the side-bracing for the wooden canal trough, with the two towing paths being almost at the level of the top of the low suspension pylons.73 Barges of 132 tonnes used the canal from 1852.

9      C Singer, A History of Technology, 3, 442.
10      T Telford, "Canals," The Edinburgh Encyclopedia, 15, 209-315: Edinburgh, 1830.
11      C Hadfield, op.cit., 23.
12      C Hadfield, Waterways Sights to See, 41: Newton Abbot, 1976.
13      L T C Rolt, From Sea to Sea: The Canal du Midi, 5: London, 1973.
14      C Hadfield, op.cit.,1986, 55.
15      J Needham, Science and Civilisation in China, 4.III, 350-51.
16      C Hadfield, op.cit., 1986, 17; Hahn et al., op.cit., 3.
17      J Needham, op.cit., 350-51. Chhiao Wei-Yo was Assistant Commissioner of Transport for Huainan in AD 983 at the beginning of the Sung Dynasty. He was concerned with the barge traffic problem at the northern end of the Shan-yang Yun-Tao section of the Pien or Grand Canal between the Yangtze and Huai-yin. Exasperated with the thefts of tax-grain made possible by the high casualty rate of ships crossing the double slipways, the Sung Shih says that in AD 984: "Chhiao Wei-Yo therefore first ordered the construction of two gates (tou men) at the third dam along the West River (near Huai-yin). The distance between the two gates was rather more than 50 paces [250ft], and the whole space was covered over with a great roof like a shed. The gates were "hanging" or portcullis gates (hsuan men); [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."
18      P A Harding, An Archaeological Survey and Watching Brief at Garston Lock, Kennet and Avon Canal, Industrial Archaeology Review, 17.2, Spring 1995, 159-70.
19      Annales des Ponts et Chaussées, July 1893, 44; Transactions of the Institution of Civil Engineers, 115.2, 1892-93, 429-31.
20      Personal communication, Michael Clarke.
21      J Needham, op.cit., 363-64.
22      Ibid., 364-65, and D Tew, Canal Inclines and Lifts, 3: Gloucester, 1984.
23      C Hadfield, op.cit., 1986, 71.
24      J Needham, op.cit., 364.
25      D Tew, op.cit., 3.
26      Ibid., 5-7.
27      C Hadfield, op.cit., 71.
28      G Jars, Metallurgische Reisen zur Untersuchung und Beobachtung de vornehmsten Eisen-, Stahl-, Blech-, und Steinkohlenwerke in Deutschland, Schweden, Norwegen, England und Schotland von Jahr 1757 bis 1769: Berlin, 1777-85; J M Dutens, Mémoires sur les travaux publics de l'Angleterre: Paris, 1819; H Fournel & I Dyèvre, Mémoires sur les canaux souterrains et sur les houillères de Worsley près Manchester: Paris, 1842.
29      P K Roberts, Boat Levels Associated with Mining: I. Coal Mining, Industrial Archaeology Review, 5.2, Spring 1981, 85-95.
30      C Hadfield, op.cit., 1986, 305-7; Hahn et al., op.cit., 24-5.
31      C Hadfield, op.cit., 1986, 136-37.
32      B Trout, The Biwako Canal, Waterways News, 77, February 1978, 4-5.
33      G J Thompson, Japan's Biwa Canal: All-Purpose Water Utilization, American Canals, 83, November 1992, 4-7.
34      D Tew, op.cit., 1984, 62.
35      Ibid., 62-67.
36      Ibid., 72-74.
37      Ibid., 75-77.
38      Ibid., 77-78.
39      Ibid., 78-80.
40      Ibid., 78-79.
41      C Hadfield, op.cit., 1986, 351-53.
42      R Greenhill, The Peterborough lift lock, in D Newell and R Greenhill, Survivals: Aspects of Industrial Archaeology in Ontario, 209-26: Boston, 1989.
43      C Hadfield, op.cit., 1986, 135-36.
44      Correspondence from Ing. Jaroslav Kube_ (Czech Republic).
45      C Hadfield, op.cit., 1986, 62.
46      N Crowe, English Heritage Book of Canals, 36: London, 1994; C Hadfield, op.cit., 1976, 11.
47      W J Sivewright, Civil Engineering Heritage: Wales & Western England, 195-96: London, 1986.
48      D Tew, op.cit., 77-78.
49      Ibid., 78-79.
50      As 42.
51      E Schinkel, Altes Schiffshebewerk Henrichenburg: Dortmund, 1992.
52      Mackenzie Archive, Institution of Civil Engineers, London.
53      H-J Uhlemann, Berlin und die Murkischen Wasserstrassen: Hamburg, 1994.
54      N Smith, A History of Dams, 164-5: London, 1971.
55      J Needham, op.cit., 313-19. The idea for an entirely new section of canal on the main north-south link of the Grand Canal was conceived in AD 1275. This, the Hui Thung Ho (Union Link Channel) was built southwards from the existing Grand Canal to cross the northern course of the Yellow River at right-angles. It was implemented in 1289 by the magistrate of Shou-chang, Han Chung-Hui, and another astronomer, Shih Pien-Yuan. The latter did the actual survey. Chang Khung-Sun and a Mongol, Loqsi, were the engineers in charge of the work, which was completed within the year. It had 31 locks (mu chha) in a distance of some 250 li (about 80 miles) and had the popular name Chha Ho. It crossed a newly diminished branch of the Yellow River at a point south of Tung-a in western Shantung and reached as far as An-Shan near Tung-phing, where it met the northern end of the summit level completed six years before. On the way it incorporated the short canal, the Chhing Chi Tu, which had been built by Hsun Hsien in AD 352. The important summit section of the completed 1035 mile new line of the Grand Canal was itself the work of a Mongol military engineer, Oqruqui, in 1283 and the following years. It had been built in accordance with plans drawn up by Kuo Shou-Ching and the canal was conveyed through a cutting 30ft deep. The canal was known as the Chi Chou Ho and at its northern end connected with the Chhing Chi Tu of AD 352 and at its southern end, at Chi-ning, with the Huan Kung Kou, built in AD 369 for the campaigns of Marshal Huan Wen. The summit level of the 1280s was 138ft above sea level and always caused problems for the overall use of the canal, so that the parallel sea-trade prospered. As a consequence the central and most difficult parts of the Grand Canal were remodelled to a high level of efficiency in 1411. This was carried out by Sung Li, an engineer who had trained at the Imperial University and been the Minister of Works, at the proposal of the Assistant Administrator of Chi-ning, Phan Cheng-Shu. He was advised by "an old countryman" (probably an irrigation-worker) of Wen-shang, Pai Ying, who showed how the waters of the Wen and Kuang Rivers could be used more effectively. Pai Ying suggested that a new 1 mile long bund or dam be constructed on the latter north of Ning-yang to form a reservoir which would always keep the canal full, with the aid of a forking lateral canal from the former, and these major works were successfully completed in 200 days by a force of 165,000 men. Sung Li also installed four small reservoirs near the canal itself, known as "water boxes" (shui kuei). These may have been the first side pounds. They were repaired and enlarged in 1540 and 1616.
56      C Hadfield, op.cit., 1986, 23.
57      Personal communication, Michael Clarke.
58      C Hadfield, op.cit., 1976, 9.
59      Ibid., 10 & W J Sivewright, op.cit., 114-15.
60      T F Hahn et al., op.cit., 3.
61      B Fletcher, A History of Architecture on the Comparative Method, 17th edition, ed R A Cordingley, 235-36; London, 1967.
62      E W Paget-Tomlinson, The Complete Book of Canal and River Navigations, 29: Wolverhampton, 1978.
63      D H Shayt, Pennsylvania, in B Trinder (ed), The Blackwell Encyclopedia of Industrial Archaeology, 561: Oxford, 1992; C Hadfield, op.cit., 1986, 307.
64      Informationen zum Wasserstrassenkreuz Minden, Wasser und Schiffahrtsamt Minden.
65      C Hadfield, op.cit., 1986, 34-35.
66      Ibid., 43.
67      C Hadfield & A W Skempton, William Jessop, Engineer.
68      W J Sivewright, op.cit., 36-7.
69      Ibid., 179-80.
70      C Hadfield, op.cit., 1986, 307.
71      Ibid., 298.
72      D H Shayt, op.cit., 561.
73      J H Burns (ed), Recording Historic Structures, 8, 150, 225: Washington, 1989.