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RIVERS AND RIVER TRAINING METHODS


#1

rivers and river training methods

general
rivers have always played an important role in human development and in shaping civilisations.
primary function of a river is the conveyance of water and sediment. besides serving as a
source of water supply for domestic, irrigation, and industrial consumption, rivers have been
useful in providing facilities for navigation, recreation, hydropower generation, and waste disposal.
rivers, except when flowing through well-defined narrow sections confined by high and stiff
banks, have also generally caused problems of flooding, change of course, banks erosion etc.
the structure and form of rivers including plan-forms, channel geometry (i.e., crossectional
shape of river), bed form, and profile characteristics together form what is termed
river morphology. the morphology of river changes considerably on account of natural causes.
besides, changes made by man in an attempt to harness a river strongly influences behaviour
of the river.

12.2. classification of rivers

rivers can be classified as follows:
(i) based on variation of discharge in river, as
(a) perennial rivers,
(b) non-perennial rivers,
© flashy rivers, and
(d) virgin rivers.
(ii) based on stability of river, as
(a) stable rivers,
(b) aggrading rivers, and
© degrading rivers.

perennial rivers
perennial rivers obtain their water from melting snow for the larger part of any year besides
getting rain water during the rainy season. being snow-fed, perennial rivers carry significant
flow all through the year.

12.2.2. non-perennial rivers

non-perennial rivers are not snow-fed rivers and, hence, get completely dried up or carry
insignificant flow during the summer season. they get their supplies only during the monsoon
as a result of rains in their catchment areas.

12.2.3. flashy rivers

in case of flashy rivers, the river stage rises and falls in a very short period of a day or two due
to the steep flood hydrograph. a small flow may, however, continue for sometime.

12.2.4. virgin rivers

in arid regions, waters of some rivers may get completely lost due to evaporation and percolation.
such rivers become completely dry much before they join another river or sea, and are called
virgin rivers.

12.2.5. stable rivers

when the alignment of a river channel, river slope, and river regime are relatively stable and
show little variation from year to year except that the river may migrate within its permanent
banks (i.e., khadirs) (fig. 12.1), the river is talked to be stable. however, changes in bed and
plan-forms of a stable river do take place, but these are small.

12.2.9. rivers in flood plains

after the boulder stage, a river enters the alluvial plains. the bed and banks are now made up
of sand and silt. the bed slope and the velocity of flow in the river are much smaller than those
of boulder rivers. the cross-section of the river is decided by the sediment load and the erodibility
of the bed and banks of the river. a typical cross-section of a river with a flood plain is shown
in fig. 12.1. the sediment transported by such rivers is predominantly of the same type as the
material forming the channel bed. during high floods, these rivers inundate very large areas
and cause considerable damage to life, property, and crops. such rivers are also called alluvial
rivers.

12.2.10. tidal rivers

all rivers ultimately meet the sea. in the reach of a river just upstream of the sea, there would
occur periodic changes in water levels due to tides. this reach of the river is called tidal river
and receives sea water during flood tides and raises its level. during ebb tides, the river water
level is lowered. the length of the river reach affected by tidal effects depends on the river
slope, the tidal range, discharge, river configuration etc.

12.2.11. delta rivers

a river, before becoming a tidal river, may split into number of branches due to very flat bed
slopes resulting in shoal formation and braiding of the channel. this part of the river reach is
called delta river. the delta river indicates a stage, rather than a type of river.

12.2.12. straight rivers

in the straight reaches of a river, its section has the shape of a trough and maximum velocity
of flow occurs in the middle of the section. it is very difficult to find the straight reach of an
alluvial river over large lengths. alluvial rivers seldom run straight through a distance greater
than ten times the river width (1). even in the apparent straight reaches, the line of maximum
depth - commonly known as talweg moves back and forth from one khadir (permanent bank)
to another khadir.
rivers and river training methods 409

12.2.13. meandering rivers

on account of the slight asymmetry of flow in alluvial rivers, there is a tendency for such
rivers to vary their plan-forms into bends which eventually result in a meandering pattern
(fig. 12.2). the term meandering has been derived from the great menderes river in turkey
which follows a winding or intricate course (fig. 12.2). rivers having such meandering patterns
are known as meandering rivers which, in plan, comprise a series of bends of alternate curvature.
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#2

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