This article provides a paragraph on rivers.
Rivers have always played an important role in shaping civilisation. Besides supplying water, rivers also provide means of transportation, recreation, hydropower generation and waste disposal. However, rivers have also generally caused problems of flooding, change of course resulting in migration of people, loss of properties, etc.
Rivers can be classified in the following ways:
(i) Based on the variation of discharge in a river, it may be either:
(a) Perennial river, if it obtains its water from melting snow for the larger part of the year and, therefore, carries significant flow throughout the year, or
(b) Non-perennial river which gets its supplies only during the monsoon season as a result of rains in its catchment areas and may get completely dried up during summer season.
(ii) Based on the stability of a river, it may be either:
(a) Stable river in which case its slope and regime show little variation from year to year, or
(b) Non-stable river, if it has a tendency to either aggrade or degrade. Rivers aggrade when sediment load entering a river reach is more than its sediment-carrying capacity. Therefore, part of the sediment load gets deposited in that reach.
Such a river is known as aggrading river in that reach. On the other hand, when sediment load being carried by river is less than its capacity and the river bed is erodible under the river flow conditions, the river flow picks up the material from the river bed. Such a river is called degrading river.
(iii) Based on the plan-form of a river, it can be:
a) Straight,
b) Meandering, and
c) Braided.
Straight reaches of an alluvial river for a large length are rare. Alluvial rivers have a tendency to vary their plan-forms into bends which eventually result in a meandering pattern (Fig. 9.1). When a river flows in two or more channels around alluvial islands, it is called a braided river.
(iv) Based on the location of the reach under consideration, a river may be called:
(a) Mountainous river, if the reach is in the mountains and hills,
(b) Flood plain river, if the river is in flood plains, and
(c) Tidal river when the river reach is located just upstream of the sea.