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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] |
