River landscapes are the result of many natural processes. These processes are carried out by water and thus depends on the intensity of the water flow. There are two types of river landforms
Erosional landform
When river water leaves a place with high speed it takes away the sediments of a place. Thus these landforms are generally found on the upper course of the river where water flow is too high. There are many types of erosional landforms and we will discuss them in detail.
Waterfall and Gorges
Waterfall is the dropping of river water from a certain height. Waterfall forms when hard rocks are exposed and soft rocks are positioned below it. The erosion of soft rock occurs quickly and it forms a step. Further erosion forms a undercut below the hard rock and hard rocks looks like an overhang.
Water falling from certain height puts hydraulic pressure abrade the surface on the base of the rock making a plunge pool. This process of erosion of soft rock continue till it becomes weak enough to hold the hard rock and finally the hard rock collapses. The water starts retreating upstream and formation of gorges takes place.
V – Shaped Valley
The less power of the river in the upper course of the river give way to vertical erosion and there is no movement of material in the form of suspension, instead, this material is moved forward with the help of traction and saltation. This movement of material from the sides of the river form a v shaped valley. The river tends to bend from the areas where the rocks are hard and can’t be eroded easily.
Erosional and Depositional Landforms
Meanders
River gains more water as the river creates its path to the middle course and at this time the river has lot of energy which helps in carrying the sediments in suspension and it help in further erosion of the banks of the river. The river gets wide due to lateral erosion and when river flows over a flat land, it develops huge bends called meanders.Most of the water is exerted towards the outside as the water goes around a bend. The presence of less friction increases its speed and therefore supports more erosion through abrasion and hydraulic action.
The undercut is formed on the river bank due to lateral erosion on the outer side of the bend which gradually forms river cliff.
The less amount of water on the inner side of the bend of a meander which decreases the speed of water. Now, water loses energy and deposit the sediments and material the river brought with it and thus forms a gentle slope. This deposition of sediment keeps building up and forms slip-off slope or river beach.
Meanders are formed both by erosional and depositional erosions. Meander is not a landform, instead it is a type of channel pattern.
Depositional landforms
Floodplains
Floodplain is a major landform formed due to depositional erosion. When stream channel breaks, large sized materials are deposited. Material like silt, sand and clay are fine and small in size and are thus carried away by slow moving water and are deposited over the river bed. An active flood plain is a river bed made of river deposits. An inactive floodplain lies above the bank and contains flood deposits and channel deposits.
Levees
When there is an increase in the volume of water in the lower course of a downstream river and flood like conditions have formed, it leads to the creation of Levees.
- The eroded sediments are transported from upstream to downstream.
- The flooding of river causes the spreading out of sediments across the floodplains.
- The river loses its energy and the largest material is deposited on the sides of the river banks while the smaller sediments moves further away.
- After repeated flooding and deposition of sediments, the height of the river banks increases which creates a higher river bank making natural protection against floods in future.
Factors that affect the change in landform
1. Geology – The presence of different types of material ranging from soft material that easily give passage to the water to hard material which blocks the path of the river forcing it to find other way plays an important role in the formation of landform.
2. Climate – The hot climate induces evaporation process and affect the volume of water in a river. Similarly, the rivers can overflow in rainy season making different kinds of landforms.
3. Human – The human activities like construction of dams affect the flow of water and also the sediments that are brought with it. Too much interference of human activities can negatively affect the structure of landforms.