FEATURES OF UPPER COURSE OF A RIVER

FEATURES OF UPPER COURSE OF A RIVER

The main features in the upper course of a river include:

  1. Gorge: This is also formed due to the deepening and narrowing of the river as a result of vertical erosion. As a result, the valley is deep and narrow with vertical sides, resulting in the formation of a gorge. A gorge may develop if a river follows a line of weakness such as a fault. An actively eroding river will carve out a gorge if it flows across a plateau which forms horizontal layers of resistant rock, leading to the formation of large and impressive gorge called Canyon.

 

  1. Rapids and Cataracts: These features are formed due to uneven resistance of hard and soft rocks which are crossed by a river. The out crop of the hard rock might cause a river to jump upstream. A minor upstream or forward jump of such water in a river is called a rapid while a jump of greater dimension is called a cataract e.g. Nile cataracts between Aswan and Khartoum.

  1. V – Shaped valley: This is formed as a result of vertical corrosion or erosion of the river. The river valley is deepened and narrow into a steep-sided V-shaped valley. The valley is widened by weathering and mass wasting which cause it to become V-shaped.

  1. Pot holes: An uneven bed of fast-flowing River causes the water to swirl the pebbles carried by this action, cut circular depressions in the river’s bed. These depressions gradually get deeper and are known as pot-holes but when they develop into large depressions, they are referred to as Plunge Pools.

 

  1. Waterfall: This feature is produced when a band of resistant rock lies across a river valley. A waterfall develops when a resistant rock overlying a less resistant rock is horizontal or vertical. The water then undercuts the softer rock leading to the receding of waterfall streams and the formation of plunge pool. Examples are Kurra falls on River Kurra near Jos (Nigeria), Victoria falls on River Zambezi, Livingstone falls on River Zaire, Niagara falls, Erin-ijesa fall, Gurara falls etc.

Importance of waterfall includes:

  • Generation of Hydro-Electric Power.
  • It can also serve as tourist centre (tourism).

  1. River capture: This is also known as river piracy or river beheading and refers to two parallel consequent rivers with tributaries separated by a more powerful river and with presence of wind gap e.g. Irrawady in India, river Ogunpa (Ibadan) in Nigeria. River capture occurs when a river through headward erosion flows into a water divide and cuts off the headwater of another weaker river.

For river capture to occur, the following must be available:

  • There must be two parallel consequent rivers separated by a divide or have a common watershed.
  • One of the rivers must be more powerful or have more erosive power than the other.
  • The valley of the more powerful river must be deeper than the other.
  • It must cut back into the headland (headward erosion) faster than the other river.

As a result of the above advantages which one river has over the other, the stronger river eats into the basin of the weaker one and beheads it. The river beheaded, is said to be captured. For example, river A cuts into a divide and beheads river B such that the water of river B now flows into A. The captured or pirated river is called misfit and the point of capture is called elbow of capture. The valley below the elbow is called wind gap or dry valley.