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deep well defined beds and wider flood plains and develop zig-zag courses. On
the other hand, in the boulder stage, the river flows through wide shallow beds
and interlaced channels and develops a straighter course. During floods, the
boulders, shingles and gravels are transported downstream but as the flood
subsides, the materials get deposited in heaps. The water, then, unable to shift
these heaps, go round them and channel often wanders in new direction,
attacking the banks and consequently widening the bed.
Rivers in the alluvial plains
From the hills, the rivers flowing through a definite channel tends to have a fairly
flat and level bottoms, but very few rivers remain straight for a long
distance and follow a zig zag path called meanders. These are actually
complex formations curved out by lateral movements of the river flow. A single
bend has a concave outer bank where the current is faster and erosion
predominates, and a convex inner bank, where the slower water deposits more
alluvium. As the river flows there could be successive meanders. Sometimes
meander will curve so much that it becomes a complete loop, cutting off the
meander core and resulting in the formation of an oxbow lake.
All the rivers are characterized by several dynamic components like current,
type of flow and its discharge, erosion, transportation of materials and
deposition. Although erosion, transportation and deposition all occur
simultaneously, rivers are often described by their dominant process. A river
that is aggrading is carrying a load greater than its capacity and therefore
depositing alluvium to its channel. By contrast, a degrading river is one that is
piling up alluvium and thus eroding the channel. A river that is in dynamic
equilibrium between erosional and depositional forces is called graded or stable.
No river is stable throughout its profile although the tendency of the river flow is
to attain the stage of equilibrium. In general, the rivers in the upper reaches are
mostly degrading whereas in the low land reaches they are aggrading type.
Near the oceans where the rivers release all the transported materials are very
flat, often take the shape of delta, fans out through number of
distributaries. This is the deltaic part of the river. This is extremely dynamic,
almost opposite to the dendritic pattern in the catchment area of the river where
