Work of River – The Most Active Agent of Gradation

Upper Course

(i) The gradient is very steep which makes the river flow very fast, so its velocity is at its maximum. Erosion is maximum due to the fast flow.

(ii) Its carrying capacity is high; therefore, it transports the eroded materials.

(iii) The load and volume of the river is less, the deposition is minimum.

(iv) Rivers form the following features-gorge, canyon, waterfall, rapids, cascades and U-shaped valleys.

(b) Middle or Mature Stage of the River

(i) The volume and load of the river increases. The gradient reduces, hence the velocity of the river decreases. As the velocity decreases and the load of the river is more, its carrying (transporting) capacity reduces. Deposi­tion increases as the carrying capacity of the river reduces.

(ii) River causes erosion, transportation and deposition.

(iii) The river forms a broad valley.

(iv) It flows sluggishly.

(v) It forms a number of features such as alluvial fan, flood plain, levees, meanders and ox-bow lakes.

(c) Lower Course or the Old Stage of the River.

(i) The volume or load of the river is maximum. Gradient here is minimum hence the flow of the river is very slow. Due to reduced velocity the carrying capacity of the river is very less and hence deposition is maximum.

(ii) The river is passive as it flows very sluggishly.

(iii) The river forms a flat valley.

(iv) It forms ox-bow lakes and delta mainly, e.g., Sundarbans delta. Some rivers form estuaries.