Difference between Perennial and Non-Perennial Rivers

Key Difference: Perennial rivers are those rivers which exhibit a continuous flow of water throughout the year except during extreme drought. On the other hand, non-perennial rivers are those rivers which have no flow for at least a part of the year.

River is a natural stream of water and tends to move in one general direction. It flows towards a sea, lake, etc. Rivers flow from a higher point to a lower point and it also collects water from some other streams many times. The characteristics of rivers are generally dependent on climate.

Perennial rivers are also known as permanent rivers. They flow throughout the year. It is indicated by the river channel which touches water table throughout the year. These rivers work extensively by eroding and deposing sediments in the channel. Groundwater and inflow from groundwater also tends to contribute in a perennial river. These are usually found in regions with humid climate where evaporation rates are much lesser than the rainfall. They may show some seasonal fluctuations in the water level but these fluctuations do not impact the flow much, and the stream flow still remains to be constant.

Periodic or non-perennial rivers are those rivers which do not have a constant flow throughout the year. It mainly consists of those rivers which flow only during the rainy season.

These are usually found in areas with arid climates where evaporation tends to be greater than precipitation. Usually, the stream flow declines on their course and they dry on occasions. At many times they are not able to even reach the sea.

Non-perennial rivers can be further classified into semi-permanent, ephemeral and episodic.

Semi-permanent are those rivers which are deprived of the flow 1 to 25 percent of time.
Ephemeral are those rivers which possess no flow 26 to 75 percent of time.
Episodic rivers are those rivers that have no flow at least 76 percent of time.

Therefore, perennial rivers are very important as they tend to support the activities dependent on the river throghout the year. They are of great importance to human, plants and animals. They are also used in irrigation and generation of hydroelectricity.

Comparison between Perennial and Non-Perennial Rivers:

	Perennial Rivers	Non-Perennial Rivers
Definition	Perennial rivers are those rivers which exhibit a continuous flow of water throughout the year except during extreme drought.	Non-perennial rivers are those rivers which have no flow for at least a part of the year.
Other name	Permanent	Periodic
Example	Himalayan River – flows from the Himalayas to the Ocean of Bay of Bengal or Indian Ocean. Ganga, Tista	Peninsular River – flows across the plan land of India. Krishna, Kaveri.
Maps	Generally, shown by blue color	Generally, shown by black color
Regions	Regions with humid climate where evaporation rates are much lesser than the rainfall.	Areas with arid climates where evaporation tends to be greater than precipitation.