On the basis of their characteristic features, origin and manner of development, rivers are classified into the following types as:-
(a) Antecedant river :
Such rivers exist before the surface relief was impressed upon the area. E.g. Brahmaputra river.
(b) Consequent river :
These rivers flow as a consequence to the existing surface relief.
(c) Subsequent river :
The river that joins the consequent river, arising later as erosion proceeds.
(d) Insequent river:
It does not indicate any particular reason for its pattern and course of flow such as that upon homogeneous terrain.
Here the river drains in the opposite direction to the original consequent river.
Such rivers drain in the same direction as the original consequent river, but at a lower topographical level.
These rivers are independent of the geological structure of the country through which they flow. This can be explained as follows:-
At some places, old rocks may be covered under a sheet of new deposits. Any river developed on such an area will follow the surface relief of the overlying cover and will not have any relation with the older rocks lying below.
Gradual erosion removes the overlying cover and then the river flows on the older rocks below. In such cases, the river is said to be super-imposed on the older rocks below.