A river system is formed by the interlink ages formed by the main river and several tributaries and distributaries joining them. Rivers usually form in a catchment area backed by a watershed dividing and collecting the rainwater. Rivers can be both perennial and non-perennial depending on the source of Origin of rivers. For instance, rivers originating from glaciers such as Brahmaputra or Tsangpo are perennial while Krishna is rain-fed hence non-perennial. However, the shaping of landforms through a river is not only dependent on the discharge of the river but also on the type of rocks that it flows on. For instance, Rivers flowing on sedimentary rocks like sandstone can erode the land easily while rivers flowing harder basaltic rocks takes longer to erode.
Processes active in shaping riverine landforms
The processes that guide the shaping of the earth’s surface depend on factors such as type of parent rock present within, climate, an abundance of active agents. For instance, a region having less rainfall will have wind as an active agent; similarly, a humid region will have rivers for shaping the landforms. The three main processes are erosion, transportation and deposition. Within erosion falls the processes of Abrasion (particles colliding with the stream floor), attrition (particles colliding with each other), hydraulic action and corrosion. Through these processes rivers actively do three types of erosion namely headward erosion (through this river gets longer), lateral erosion (it helps in making rivers wide by side cutting) and vertical erosion (deep cutting of rivers base). The transportation process includes the size of bed stream load, entrainment capacity of the river and seasonal flow. Based on three characteristics, transportation can be carried through suspension (where the load is suspended because of its less weight), traction (the bed load is heavy and carried out by huge pressure), and solution (the erodible materials are dissolved in water). When a river flows in the lower course, it loses its capacity to transport a high weight of bedload; it deposits to form landforms such as Delta. Based on deposition, rivers take various plan form views such as braided patterns, anatomising channel patterns, “anabranching” patterns so on. All these factors of transportation and deposition depend on the discharge, velocities and competence of the stream.
Landforms created in the upper course of the River
A river passes through three courses in its life cycle namely the upper course, middle course and flower course. In the upper course, the rivers are directly influenced by gravity falling from an absolute relief (watershed region), thus, having greater velocity and erosive power. Therefore, in the upper course river does vertical erosion to create deep V-shaped valleys, in this region, the river does vertical cutting rather than lateral erosion. Rivers that pass through regions of alternate hard and soft rock layers, eventually result in taking off the softer rock layer and generating waterfalls with plunge pools in mountainous regions. Rivers also cut sharp bends in valleys creating hairpin bends, and when the vertical cutting is very deep it creates I shaped valleys called Gorges. Due to the abrasion and erosion of the steam floor, smaller waterfalls are caret termed as rapids. Once the river reaches a lower gradient it creates floodplains and the streams start meandering. In the middle course of the River, natural levees are created due to overflowing and flooding of the riverbed every year. The natural levees provide an excellent place for cultivation. Apart from this, rivers in the middle course create Pools and riffles across the sides of a meandering river. As the bed load increases and the velocity of the river reduces with decreasing relative relief of the region, the river starts meandering to balance its flow. Lastly, when a river reaches its lower course, it deposits the entire suspended bed load and creates Delta. The largest delta in the world is the Ganga-Brahmaputra Delta.
Riverine landforms of India
India is a land of rivers as it consists of three major river systems namely Ganga, Brahmaputra and Indus, among which Ganga is the longest. All three rivers have a glacial source of origin and flow through north India giving birth to the Northern plains of India. The sediments brought down by these rivers from fertile alluvial plains (Khadar and Bhangar) are good for paddy and wheat cultivation. Most of the agricultural lands are present in Northern India due to the presence of three big river systems with their large catchment areas. However, the rivers of South India are non-perennial and have a seasonal flow of water, making it difficult for all year long cultivations. Farmers have to do tank irrigation in the fields of South India and the rivers are almost non-navigable. In northern India, the fertile land between two rivers is termed as Doab such as Ganga-Yamuna Doab, and these regions are very fertile for cultivations to support the huge population of India.
In summary, it can be said that River systems are the largest units of study that provide enough information on the processes active on the earth’s surface and that shape the earth’s surface. A river has three main courses namely upper, middle and lower courses, which differs in characteristics and elevations. The landforms created by rivers depend on the rock type, climatic conditions, elevation and flow velocity.