The course of a river may be divided into three distinct parts:

• the upper or the mountain course (in the stage of youth)
• the middle or Valley course (in the stage of maturity)
• the lower or plain course (in the stage of old age)

Erosion and transportation are the main activities of a river in the upper course.

In the mountainous course, a river passes through a steep slope. Its water, therefore, rushes down with great speed. Under such a condition the water can dig the river bed very deeply and carries or pools down heavy boulders and pebbles.

V-SHAPED VALLEYS: A river has a deep and narrow channel in this stage. Moreover, some of the rocks over which a river flows are very hard, while the others are soft. As a result of this, the river course is not smooth. The deep and steep-sided river valley is V-shaped here. Both erosion and transportation are active at this stage.

GORGES: Sometimes, the river flows through very hard rocks. In that situation the two sides of the river become so steep that they become almost vertical. The formation is known as Gorge. There are many gorges on the upper course of the Brahmaputra, the Indus, and the Ganges. Again when river flows through dry desert its bed becomes very deep and the two sides become vertical. The river valley takes the shape of I instead of V.

INTERLOCKING SPURS: As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs, which look a bit like the interlocking parts of a zip.

RAPIDS and CATARACTS: When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form.  Due to the unequal resistance of hard and soft Rocks traversed by a river the outcrop of a band of hard rock may cause a river to jump or fall down stream. Thus, rapids are formed. Similar false of Greater dimensions are also referred to as cataracts.

WATERFALLS: Waterfalls commonly form where water rushes down steep hillsides in upland areas. They are typical of the upper valley but can be found in the rivers lower courses. This typically occurs in areas where alternating bands of rock, made up of soft and hard rock, form the bedrock. Some types of rocks (shale, for example) wear away more easily than others (such as sandstone or limestone).

Waterfalls form when waterfalls onto soft rock after flowing over hard rock. Falling water and rock particles erode the soft rock below, forming a plunge pool. Processes of erosion, such as hydraulic action, abrasion and corrasion further erode the plunge pool and the back wall of the waterfall, undercutting the hard rock above. Eventually, the hard rock will no longer be supported and it will collapse. The waterfall continues to retreat leaving behind a steep-sided gorge.

RIVER CAPTURE: a natural process which is more active in the youthful stage of the valley development because the streams are actively engaged in head-ward erosion and valley lengthening. The stronger and more powerful streams (in terms of channel gradient, stream velocity and discharge and kinetic energy) capture the upper courses of weak and sluggish streams.

 There are four major evidences of river capture. The elbow of capture denotes the point where the course of the captured stream has been diverted to the course of the captor stream. Generally, the elbow of capture denotes sharp turn in the course of a river almost at right angle. The water gap denotes the deep and narrow valley in the form of a gorge formed by the captor stream through headward erosion across the ridge. Wind gap (col) is the dry portion of the beheaded stream just below the elbow of capture. The misfit or under-fit stream is the lower course of the captured stream. It is called misfit because of the fact that the former valley of the captured stream becomes too large and wide for the beheaded stream because of substantial decrease in the volume of water due to diversion of its water to the captor stream.

Conclusion:

 India has many rivers at the youthful stage originating in Himalayas. The evolution of various landforms due to the high pace of rivers has its impacts on the geography, economy and people. With climate change, the rate of melting of glaciers is high leading to changes in river water flow. Thus, it is imperative to understand the river geomorphology.