Canal
Canal man-made open water channel. There are two categories of canals, conveyance canals and navigation canals. Conveyance canals are dug to carry water for irrigation, drainage or power, while navigation canals are constructed for navigational purposes. Both types of canals are often used for river navigation. Canals may connect two natural waterways.
Canals were probably first built for irrigation but with the improvement of technology, especially with the invention of lock (water), they have been constructed for navigation. Canals have dramatically reduced voyage distances for ships, as Suez Canal (completed in 1869), and Panama Canal (1914). Canals are also constructed to join two rivers to improve waterways, eg the Rhine-Marne canal.
In canal construction, the availability of water, topography (variations in land and water level, slope etc) are the most important parameters. Conveyance canals are usually narrow, carry water with high velocity, and are earth lined. As a result, they are subjected to both erosion and siltation. Depending on the situation, the soil condition of the bed and the bank can be lined, and the sides may be given protection against erosion. However, barge or ship canals are usually constructed completely lined with bank protection facilities.
In Bengal, it is reported that irrigation canal construction started 3,000 years ago. From that time till now the construction of conveyance canal is being practised throughout the country. Systematic canal network (both lined and unlined) may be seen in different irrigation projects, currently executed and managed by the bangladesh water development board, such as ganges-kobadak irrigation project (G-K Project), Meghna-Dhonagoda Irrigation Project, Tista Project, and Muhuri Irrigation Project. Several regulators, navigation locks, fish pass etc have been constructed on different canals.
The loop-cuts of a number of small meandering rivers eg the sangu and the gumti can be cited as examples of navigation canals. madaripur beel route was excavated between 1905 and 1915 across the Madaripur Beel to connect the arial khan, Old Kumar and madhumati rivers. This opened a new navigation route connecting Dhaka and Narayanganj with Khulna. All navigation canals of the country are unlined. However, at places they have been provided with some bank protection facilities. [HS Mozaddad Faruque]
