Stages of a River
A river passes through three stages — upper, middle and lower course. Erosion is active in the steep upper course, while deposition is active in the flatter lower course. Each stage produces different landforms. Along its course, a river carries out three main processes: erosion, transport and deposition.
Erosional Landforms
In the upper course, vertical erosion deepens the channel to form a narrow, steep V-shaped valley, rapids and interlocking spurs on either side of the valley. A waterfall forms where a band of hard rock lies over soft rock; the soft rock erodes faster, forming a deep plunge pool below, and the waterfall slowly retreats upstream. Lata Kinjang Waterfall in Perak is one Malaysian example.
In the middle course, lateral erosion becomes dominant and produces meanders, with a steep river cliff on the outer bank and a gentle slip-off slope on the inner bank. Over time the meanders grow more curved.
Depositional Landforms
In the lower course, the slow river deposits material to form a fertile flood plain, levees along the channel, and an oxbow lake when a meander neck is cut off. At the mouth, fine deposits build a delta, which is good for farming, such as the Kelantan River delta used for growing rice.
Remember
Upper — erosion (V-valley, waterfall); middle — meanders; lower — deposition (flood plain, oxbow lake, delta).