11.5 Canalization and navigation canals
11.5.1 CanalizationA free-flowing river can be canalized by a series of barrages with naviga-
tion locks. Canalization becomes necessary from the navigation point of
view if the free-flowing river has too shallow a depth and too high a veloc-
ity to permit navigation.
The advantages of canalization are as follows: the opportunity to
develop multipurpose utilization of water resources; sufficient depth for
navigation throughout the year, even at times of low river flows; reduced
flow velocities; increased width of waterways; safer and cheaper naviga-
tion; often the reduced need for bank protection and its maintenance
(compared with regulated rivers). The main disadvantages are the high
capital cost, the need for protection of adjacent land, drainage problems,
the delay of traffic passing through locks, the possible deposition of sedi-
ments at the upstream end and possible winter régime complications.
The upper reaches of most of the major navigable rivers are canal-
ized or in the process of being canalized. The heights of individual steps in
the cascade of barrages, i.e. the difference of water levels, varies greatly
according to hydrological, morphological, and geological conditions, but is
usually between 5 and 15 m.
11.5.2 Navigation canalsNavigation canals can be used to bypass a river section that is difficult to
navigate and can be used in conjunction with a single barrage or several
barrages spaced wider apart than in the case of river canalization. Further-
more, they are an essential part of inland navigation where they connect
two watersheds. They require suitably shaped intakes, often a separate
flow regulation structure, and navigation locks.
The position and layout of canals can – within the traffic and geologi-
cal constraints – be adapted to general transport, land-use and industrial
demands. The canal is usually appreciably shorter than a canalized river
which, together with low (or zero) flow velocities, aids navigation in both
directions. Their main disadvantage is use of land, and disruption of com-
munications; thus when planning a canal, maximum use should be made of
existing rivers, as far as their canalization is feasible.
Navigation canals can have a fall in one direction only or in both
directions with a top water reservoir. They may connect two river systems
or branch off a navigable waterway to give access to an industrial centre.
The crossing of a canal with a navigable river, the branching of a canal