My Science School

Water, left to its own devices, always flows from its highest point to its lowest, until the two points are on the same level. If a canal sloped as it climbed a hill, its water would simply flow to the bottom. One solution is to bore a tunnel through the hill, so that the canal can continue on a level course, but sometimes this is too costly or geologically impossible. Building locks can solve this problem.

Canals are waterways channels, or artificial waterways, for water conveyance, or to service water transport vehicles. They may also help with irrigation. It can be thought of as an artificial version of a river.

In most cases, the engineered works will have a series of dams and locks that create reservoirs of low speed current flow. These reservoirs are referred to as slack water levels, often just called levels.

A canal is also known as a navigation when it parallels a river and shares part of its waters and drainage basin, and leverages its resources by building dams and locks to increase and lengthen its stretches of slack water levels while staying in its valley. In contrast, a canal cuts across drainage divide atop a ridge, generally requiring an external water source above the highest elevation.

Many canals have been built at elevations towering over valleys and other water ways crossing far below. Canals with sources of water at a higher level can deliver water to a destination such as a city where water is needed. The Roman Empire’s aqueducts were such water supply canals.

Caen Hill Locks are a flight of 29 locks on the Kennet and Avon Canal, between Rowde and Devizes in Wiltshire, England. The 29 locks have a rise of 237 feet in 2 miles (72 m in 3.2 km) or a 1 in 44 Gradient. The locks come in three groups: the lower seven locks, Foxhangers Wharf Lock to Foxhangers Bridge Lock, are spread over 3?4 mile (1.2 km); the next sixteen locks form a steep flight in a straight line up the hillside and are designated as a scheduled monument. Because of the steepness of the terrain, the pounds between these locks are very short. As a result, fifteen of them have unusually large sideways-extended pounds, to store the water needed to operate them. A final six locks take the canal into Devizes. The locks take 5–6 hours to traverse in a boat.

A lock consists of two gates across the canal, with mechanisms for opening them on the towpath.

To climb to a higher level of the canal, a boat enters the first lock gate, which is closed behind it.

Paddles in the second lock gate are opened so that water can flow in, gradually raising the level of water in the lock.

When the water ahead is level with that in the lock, the gates are opened and the boat can move on.

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For thousands of years, people have transported heavy goods along waterways. The first canals were probably built to join existing navigable rivers. In the fifteenth century, the Aztec city of Tenochtitlan had a sophisticated series of canals, providing transport for goods and people. Venice, in Italy, although a smaller city, was also built on a system of canals rather than roads. However, the golden age of canal-building probably came with the Industrial Revolution, when there was an enormous need for cheap and easy ways to carry the goods made in factories to the nearest port. Canal boats, powered at first by a horse on the towpath and later by coal-fired steam engines, could carry enormous loads much more conveniently than horse drawn carts on bumpy roads.

The British canal system of water transport played a vital role in the United Kingdom’s Industrial Revolution at a time when roads were only just emerging from the medieval mud and long trains of packhorses were the only means of "mass" transit by road of raw materials and finished products. The UK was the first country to develop a nationwide canal network.

The canal system dates to Roman Britain, but was largely used for irrigation or to Link Rivers. The navigable water network in the British Isles grew as the demand for industrial transport increased. It grew rapidly at first, and became an almost completely connected network covering the south, Midlands, and parts of the North of England and Wales. There were canals in Scotland, but they were not connected to the English canals or, generally, to each other (the main exception being the Monkland Canal, the Union Canal and the Forth and Clyde Canal which connected the River Clyde and Glasgow to the River Forth and Edinburgh). As building techniques improved, older canals were improved by straightening, Embankments, cuttings, tunnels, aqueducts, inclined planes, and boat lifts, which together snipped many miles and locks, and therefore hours and cost, from journeys. However, there was often fierce opposition to the building.

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The earliest bridges were probably tree trunks across streams or flat slabs of rock. Gradually, people learned to span wider rivers and ravines by supporting the bridge in the middle. Since then, engineers have devised ways of spanning very wide distances.

There are many different types of bridges although typically their structures can be traced back to one of the seven main types. It is the way in which the vertical/horizontal stresses are managed which dictates the structure of different bridges. In some cases the deck area will be the load-bearing element while in others it will be the towers. There are also designs that transmit tension through bridge cables which allow a degree of flexibility for different terrains.

Beam Bridge

A beam bridge is one of the simplest types of bridge. A perfect example being a basic log bridge – something you may see while out on a country walk. The deck area traditionally consists of wood plank or stone slabs (often referred to as a clapper bridge). These are supported either side by two beams running between abutments/piers. Very often you will find other beams, positioned in between the main beams, offering additional support and stability. The area over which people or vehicles travel will be a simple decking positioned vertically across the underlying beams. This is often referred to as a “simply supported” structure. There is no transfer of stress which you see in arch structures and other types of bridges.

Truss Bridge

The truss bridge has been around for literally centuries and is a load-bearing structure which incorporates a truss in a highly efficient yet very simple design. You will notice an array of different variations of the simple truss bridge but they all incorporate triangular sections. The role of these triangular elements is important because they effectively absorb tension and compression to create a stressed structure able to accommodate dynamic loads. This mixture of tension and compression ensures the structure of the bridge is maintained and the decking area remains uncompromised even in relatively strong winds.

Cantilever Bridge

When the first cantilever bridge was designed it was seen as a major engineering breakthrough. The bridge works by using cantilevers which may be simple beams or trusses. They are made from pre-stressed concrete or structural steel when used to accommodate traffic. When you consider that the horizontal beams making up the cantilever arm are only supported from one side it does begin to sound a little dangerous. However, the two cantilever arms are connected by what is known as the “suspended span” which is effectively a centrepiece which has no direct support underneath. The bridge load is supported through diagonal bracing with horizontal beams as opposed to typical vertical bracing. Extremely safe and very secure, the design of cantilever bridges is one which still lives on today.

Suspension Bridges

The structure of a stereotypical suspension bridge looks very simple but the design is extremely effective. The deck of the suspension bridge is the load-bearing element of the structure. This is held in place by vertical suspenders which support the cables. The suspension cables extend out beyond each side of the bridge and are anchored firmly into the ground. It will depend upon the size of the bridge but a number of towers will be installed to hold up the suspension cables. Any load applied to the bridge is transformed into tension across the suspension cables which are the integral part of the structure. As there is some “give” in the suspension cables this can translate into slight, but measured, bridge movement in difficult weather conditions.

Cable stayed bridge

A cable stayed bridge is dependent upon towers/pylons which are the load-bearing element of the structure. Cables are connected from the pylons to the deck below. Either directly from the top of the tower or at different points of the column. When connected at different points of the column this creates a fan like pattern. This is the feature many people associate with cable stayed bridges. This type of structure tends to be used for distances greater than those achieved with a cantilever bridge design but less than a suspension bridge. One of the main issues with this type of bridge is that the central connection of the cables can place horizontal pressure on the deck. Therefore, the deck structure needs to be reinforced to withstand these ongoing pressures.

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From the earliest times, humans and animals have created track ways along well-used routes, but it was the Romans who were the first to set about road-building in a systematic manner. The Roman Empire stretched from North Africa to Scotland. In order to govern successfully, the occupying forces needed to be able to reach trouble spots quickly. Roman roads were built so that armies could march rapidly for hundreds of miles.

A top level of paving stones gave a smooth surface for carts and marching armies. Roman roads were made in layers. First the route was cleared of large stones and boulders. Then the bed of the road was levelled with sand. The Romans tried to build straight roads as far as possible. Straight roads were easier to march along and reduced the risk of ambush, as the view was clear in both directions.

Roman road system outstanding transportation network of the ancient Mediterranean world, extending from Britain to the Tigris-Euphrates river system and from the Danube River to Spain and northern Africa. In all, the Romans built 50,000 miles (80,000 km) of hard-surfaced highway, primarily for military reasons.

The first of the great Roman roads, the Via Appia (Appian Way), begun by the censorAppius Claudius Caecus in 312 BCE, originally ran southeast from Rome 162 miles (261 km) to Tarentum (now Taranto) and was later extended to the Adriatic coast at Brundisium (now Brindisi). The Long Branch running through Calabria to the Straits of Messina was known as the Via Popilia. By the beginning of the 2nd century BCE, four other great roads radiated from Rome: the Via Aurelia, extending northwest to Genua (Genoa); the Via Flaminia, running north to the Adriatic, where it joined the Via Aemilia, crossed the Rubicon, and led northwest; the Via Valeria, east across the peninsula by way of Lake Fucinus (Conca del Fucino); and the Via Latina, running southeast and joining the Via Appia near Capua. Their numerous feeder roads extending far into the Roman provinces led to the proverb “All roads lead to Rome.”

The Roman roads were notable for their straightness, solid foundations, cambered surfaces facilitating drainage, and use of concrete made from pozzolana (volcanic ash) and lime. Though adapting their technique to materials locally available, the Roman engineers followed basically the same principles in building abroad as they had in Italy. In 145 BCE they began the Via Egnatia, an extension of the Via Appia beyond the Adriatic into Greece and Asia Minor, where it joined the ancient Persian Royal Road.

In northern Africa the Romans followed up their conquest of Carthage by building a road system that spanned the south shore of the Mediterranean. In Gaul they developed a system centred on Lyon, whence main roads extended to the Rhine, Bordeaux, and the English Channel. In Britain the purely strategic roads following the conquest were supplemented by a network radiating from London. In Spain, on the contrary, the topography of the country dictated a system of main roads around the periphery of the peninsula, with secondary roads developed into the central plateaus.

The Roman road system made possible Roman conquest and administration and later provided highways for the great migrations into the empire and a means for the diffusion of Christianity. Despite deterioration from neglect, it continued to serve Europe throughout the Middle Ages, and many fragments of the system survive today.

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