Editing Canal (section)

==Features==
At their simplest, canals consist of a trench filled with water. Depending on the [[stratum]] the canal passes through, it may be necessary to [[canal lining|line]] the cut with some form of watertight material such as clay or concrete. When this is done with clay, it is known as [[Puddling (engineering)|puddling]].

Canals need to be level, and while small irregularities in the lie of the land can be dealt with through cuttings and embankments, for larger deviations other approaches have been adopted. The most common is the [[pound lock]], which consists of a chamber within which the water level can be raised or lowered connecting either two pieces of canal at a different level or the canal with a river or the sea. When there is a hill to be climbed, flights of many locks in short succession may be used.

Prior to the development of the pound lock in 984&nbsp;AD in China by Chhaio Wei-Yo<ref>{{Harvnb|Hadfield|1986|p=22.}}</ref> and later in Europe in the 15th century, either [[flash lock]]s consisting of a single gate were used or ramps, sometimes equipped with rollers, were used to change the level. Flash locks were only practical where there was plenty of water available.

Locks use a lot of water, so builders have adopted other approaches for situations where little water is available. These include [[boat lift]]s, such as the [[Falkirk Wheel]], which use a [[caisson (water transport)|caisson]] of water in which boats float while being moved between two levels; and [[canal inclined plane|inclined planes]] where a caisson is hauled up a steep railway.

To cross a stream, road or valley (where the delay caused by a flight of locks at either side would be unacceptable) the valley can be spanned by a [[navigable aqueduct]] – a famous example in Wales is the [[Pontcysyllte Aqueduct]] (now a [[UNESCO]] [[List of World Heritage Sites of the United Kingdom|World Heritage Site]]) across the valley of the [[River Dee (Wales)|River Dee]].

Another option for dealing with hills is to tunnel through them. An example of this approach is the [[Harecastle Tunnel]] on the [[Trent and Mersey Canal]]. Tunnels are only practical for smaller canals.

Some canals attempted to keep changes in level down to a minimum. These canals known as [[contour canal]]s would take longer, winding routes, along which the land was a uniform altitude. Other, generally later, canals took more direct routes requiring the use of various methods to deal with the change in level.

Canals have various features to tackle the problem of water supply. In cases, like the Suez Canal, the canal is open to the sea. Where the canal is not at sea level, a number of approaches have been adopted. Taking water from existing rivers or springs was an option in some cases, sometimes supplemented by other methods to deal with seasonal variations in flow. Where such sources were unavailable, [[reservoirs]]&nbsp;– either separate from the canal or built into its course&nbsp;– and [[back pumping]] were used to provide the required water. In other cases, water pumped from mines was used to feed the canal. In certain cases, extensive "feeder canals" were built to bring water from sources located far from the canal.

Where large amounts of goods are loaded or unloaded such as at the end of a canal, a [[canal basin]] may be built. This would normally be a section of water wider than the general canal. In some cases, the canal basins contain [[wharf]]s and cranes to assist with movement of goods.

When a section of the canal needs to be sealed off so it can be drained for maintenance [[stop planks]] are frequently used. These consist of planks of wood placed across the canal to form a dam. They are generally placed in pre-existing grooves in the canal bank. On more modern canals, "guard locks" or gates were sometimes placed to allow a section of the canal to be quickly closed off, either for maintenance, or to prevent a major loss of water due to a canal breach.

===Canal falls===
A ''canal fall'', or canal drop, is a vertical drop in the canal bed.<!-- Sharma 2016, p. 643 --> These are built when the natural ground slope is steeper than the desired canal gradient.<!-- Sharma 2016, p. 643 --> They are constructed so the falling water's kinetic energy is dissipated in order to prevent it from [[hydrodynamic scour|scouring]] the bed and sides of the canal.<!-- Sharma 2016, p. 643 --><ref name="Sharma 2016">{{cite book |last1=Sharma |first1=S. K. |title=Irrigation Engineering and Hydraulic Structures |date=2016 |publisher=S Chand and Company |location=New Delhi |isbn=978-93-525-3377-0 |url=https://books.google.com/books?id=WkRxDwAAQBAJ |access-date=31 July 2023}}</ref>{{rp|643}}

A canal fall is constructed by [[cut and fill]].<!-- Sharma 2016, p. 643 --> It may be combined with a regulator, bridge, or other structure to save costs.<!-- Sharma 2016, p. 644 --><ref name="Sharma 2016"/>{{rp|643–4}}

There are various types of canal falls, based on their shape.<!-- Sharma 2016, p. 644 --> One type is the [[ogee]] fall, where the drop follows an s-shaped curve to create a smooth transition and reduce [[turbulence]].<!-- Sharma 2016, p. 644 --> However, this smooth transition does not dissipate the water's kinetic energy, which leads to heavy scouring.<!-- Sharma 2016, p. 644 --> As a result, the canal needs to be reinforced with concrete or masonry to protect it from eroding.<!-- Sharma 2016, p. 644 --><ref name="Sharma 2016"/>{{rp|644}}

Another type of canal fall is the vertical fall, which is "simple and economical".<!-- Sharma 2016, p. 646 --> These feature a "cistern", or depressed area just downstream from the fall, to "cushion" the water by providing a deep pool for its kinetic energy to be [[diffusion|diffused]] in.<!-- Sharma 2016, p. 646 --> Vertical falls work for drops of up to 1.5&nbsp;m in height, and for discharge of up to 15 cubic meters per second.<ref name="Sharma 2016"/><!-- Sharma 2016, p. 646 -->{{rp|646}}

<gallery mode="packed" heights="135">
File:Caen.hill.locks.in.devizes.arp.jpg|alt=A series of approximately 20 black lock gates with white ends to the paddle arms and wooden railings, each slightly higher than the one below. On the right is a path and on both side's grass and vegetation.|The flight of 16 consecutive locks at [[Caen Hill Locks|Caen Hill]] on the [[Kennet and Avon Canal]], [[Wiltshire]]
File:Pontcysyllte aqueduct arp.jpg|[[Llangollen Canal|The Llangollen Canal]] traverses [[Pontcysyllte Aqueduct|the longest and highest aqueduct]] in [[Denbighshire]], Wales, United Kingdom 
File:Canal of korinth greece.jpg|The [[Corinth Canal]] seen from the air
File:Miami and Erie Canal Lock photographs - DPLA - a4f6bf1bdcffd61c72c1a077104f91ed (page 1).jpg|Miami and Erie Canal Lock in Ohio, United States
</gallery>