Table of Contents
Fluvial Landforms
Fluvial Landforms: Fluvial topography refers to the landforms created by flowing water. Fluvial landforms include, for instance, waterfalls, oxbow lakes, valleys, and deltas. The fluvial process results in the formation of two distinct landforms. It includes fluvial erosion and fluvial depositional landforms. From minor features like rills to significant continental-scale morpho-hydrological units like huge rivers and their drainage basins, fluvial landforms span a vast array of proportions.
Approximately 68% of the land on Earth is drained by rivers that empty into the oceans. The river’s source is typically located in an area of upland terrain with a slope for runoffs. As a result, the uplands serve as the rivers’ catchment areas, and the mountain crest serves as the watershed from which the streams descend. The subsequent stream is the first stream that forms as a result of the slope. Several tributaries from either side join the stream as it wears down the surface. In fluvial geomorphology, the drainage basin or watershed is a key landscape component.
Running water is regarded as the most significant geomorphic factor in causing the degradation of the ground surface in humid locations that get heavy rainfall. Running water consists of two parts. One is a sheet-like overland flow on the overall ground surface.
The majority of water-induced landforms that are the result of erosion are linked to rivers that are active and young and flow through terrain with a steep gradient. As a result of ongoing erosion, stream channels with steep slopes gradually become smoother and lose velocity over time, which encourages active deposition. Streams flowing across steep slopes could be related to depositional forms.
River Course
1. Youth
During this stage, there are few streams that are poorly integrated and flow over the old slopes.
The resulting valley is deep, narrow, and clearly V-shaped, with either no floodplains or extremely small floodplains. Downcutting outweighs lateral corrosion in importance. Marshes, swamps, and lakes along the broad, flat stream divide. During this stage, notable features like gorges, canyons, waterfalls, rapids, and river capture are developed.
2. Mature
Streams are plentiful at this point and are well integrated. Vertical corrasion typically gives way to lateral corrasion. Due to active bank erosion, the valleys are still V-shaped but wider and deeper. Trunk streams are wide enough to have wider floodplains within which streams may flow in meanders constrained within the valley. Young marshes and swamps as well as vast, level inter stream habitats vanish. The stream splits abruptly. Rapids and waterfalls vanish. The hallmarks of this stage are meandering and sliding down slopes.
3. Old
Sediments weigh down the river as it flows downstream across a wide, level plain. Although lateral erosion of the banks continues, vertical erosion practically stops at this point. Older tributaries are scarce and have a mild gradient. Streams freely meander across wide floodplains. There are lakes, bogs, and marshes along the vast, flat divides. The majority of the landscape is at or just above sea level at this stage due to the dominance of accretionary structures.
This stage is characterised by floodplains, oxbow lakes, natural levees, and deltas, among other things.
Fluvial Erosive Action Effects
- Rocks are eroded by the force of flowing water, which is hydration.
- Weathering is caused by a chemical reaction known as corrosion or solution.
- When materials are being carried, attrition refers to the wear and tear that occurs when they roll into one another and collide.
- Rocks are worn down by corrosion or abrasion caused by a heavy river load striking them.
- Vertical erosion known as downcutting: is the eroding of a stream’s base (downcutting leads to valley deepening).
- The eroding of a stream’s side walls is known as lateral erosion (leads to valley widening).
- Headward erosion is the erosion of a stream channel’s origin, which moves the origin back from the stream’s flow direction and lengthens the stream channel as a result.
- Gorges, canyons, waterfalls, rapids, and river capture are examples of fluvial eroded landforms.
- The mechanical loosening and sweeping away of materials by river water is known as hydraulic action. It mostly happens by rushing into rock crevices and cracks and eroding them.
- The primary waterway braiding into several, smaller channels A braided river or channel is made up of a network of river channels that are divided by tiny, frequently transient islands known as braid bars. Rivers with low slopes and/or high sediment loads frequently have braided streams.
Fluvial Landforms Types
There are two types of Fluvial Landforms:
- Fluvial Erosional Landforms
- Fluvial Depositional Landforms
Erosional Landforms Fluvial
1. River Valleys
A river valley is an extensive ground depression through which a stream travels throughout the entirety of its course. As the erosional cycle progresses, the valley develops several profiles. The valley is deep, and narrow, and has steep, wall-like sides and a convex slope when it is young. Most of the erosional action in this area is vertical down-cutting in nature. This valley has a typical “V”-shaped valley profile. The valley floor flattens as the cycle reaches maturity and the lateral erosion becomes noticeable. With a broad base and a concave slope, the valley profile now takes on a characteristic “U” shape.
2. Georges
These valleys are called “I-shaped valleys” because they form an “I” shape when their sides are nearly parallel to one another. A gorge is a deep valley that is narrow and has steep, straight sides. The breadth of a gorge is about equal at both its top and bottom. Hard rocks are where gorges are formed.
Example: Indus Gorge in Kashmir
3. Potholes
Potholes, which are typically cylindrical in shape, are kettle-like tiny depressions in the rocky river valley bottoms. Sandstones and granites, which are examples of coarse-grained rocks, are where potholes typically occur. When caught in water eddies or whirling water, grinding tools (rock fragments, such as boulders and angular rock pieces) begin dancing in a circular motion and drill and grind the rock beds of valleys like a drilling machine. This process is known as potholing or pothole-drilling. Thus, they create tiny holes that eventually get larger as the aforementioned action is repeated. The potholes continue to become deeper and wider.
4. Gulleys/Rills
An incised water-worn channel known as a gulley is typical of semi-arid regions. It develops when water that overflows from the land rushes down a slope, particularly after a lot of rain, and is condensed into rills that then combine and widen to form a gulley. Examples: the ravines of Chambal Valley in Central India.
5. Ox-Bow Lake
The outer curve of a meander can occasionally be increased by vigorous erosion to the point where the inner ends of the loop are close enough to the main river to become an isolated water body. In due course, these bodies of water turn into swamps. In the Indo-Gangetic plains, Ganga’s southerly movement has left a number of ox-bow lakes to the north of the river’s current route.
6. Incised Meanders
Normally, erosion is concentrated in streams that move quickly over steep grades.
on the stream channel’s floor. Additionally, compared to streams flowing on low and mild slopes, lateral erosion on the sidewalls of valleys is less for streams flowing on steep gradients. Active lateral erosion causes streams moving over mild slopes to take a winding or sinuous paths. Where stream slopes are fairly mild, meandering streams frequently cross floodplains and delta plains. However, hard rocks can also have meanders that are carved quite deeply and broadly. Incised or entrenched meanders are the name given to these meanders.
7. River Terraces
River terraces are levels that represent former floodplain or valley floor levels. They could be terraces made of stream deposits or bedrock surfaces devoid of any alluvial cover. River terraces are essentially a result of erosion since a stream’s vertical erosion into its own depositional floodplain causes them to form.
Such terraces may be numerous and vary in height, showing the levels of an earlier river bed. When the river terraces are found at the same elevation on both banks of the rivers, they are referred to as paired terraces.
8. Peneplain
This describes an undulating, featureless plain that is dotted with small, remnant hills made of hardy rocks. In periods of prolonged tectonic stability, the peneplain is designed to suggest the portrayal of a close-to-final (or penultimate) stage of river erosion.
Erosional Landforms Diagram
Here is the diagram for various Erosional Landforms:
Depositional Landforms
Stream velocity and the amount of river load have an impact on how much sediment is deposited by a stream. As a result of being compelled to leave more cargo to settle, streams with lower stream velocity have less carrying power. Increased sediment load in downstream sections of rivers is caused by (i)accelerated rate of erosion in source catchment areas as a result of deforestation; (ii) supply of glacio-fluvial materials; (iii) supply of additional sediment load by tributary streams; and (iv) gradual increase in stream sediment load as a result of rill and gully erosion.
1. Delta
A delta is an area of alluvium near the mouth of a river where more material is dumped there than can be taken away. A network of channels is created by splitting the river into two or more channels (distributaries), which may then split again and again.
2. Meanders
A river channel’s pronounced curve or loop is referred to as a meander. The term “cliff-slope side” refers to the outer bend of a meander that is marked by severe erosion and vertical cliffs. The slope on this side is concave. The inner side of the loop is known as the slip-off side and is characterised by deposition and a mild convex slope. The meanders may have wavy, horse-shoe, ox-bow, or bracelet-shaped morphologies.
3. Alluvial Fans and Cones
A stream’s velocity drops because of a reduced gradient as it departs the mountains and descends to the plains. As a result, near the foothills, it sheds a significant amount of the stuff it was carrying from the mountains. This material is deposited in a conical shape, resembling a series of continuous fans. They are referred to as alluvial fans. These fans can be seen all over the north Indian plains, at the foothills of the Himalayas.
4. Natural Levees, Floodplains, and Point Bars
A floodplain is created through deposition, much as valleys are created by erosion. A significant river-depositing landform is a floodplain. When a stream channel changes from a flat surface to a slight slope, larger items are deposited first. As a result, fine-grained materials like sand, silt, and clay are typically carried by relatively slow-moving streams in kinder channels that are typically found in the plains, where they are then dumped over the bed and during flooding above the bed. The active floodplain is a bed of river deposits. Over the bank, there is an inactive floodplain.
There are essentially two types of deposits in the inactive floodplain above the banks: flood deposits and channel deposits. Up plains, channels occasionally reverse direction and move laterally, leaving cut-off routes that gradually fill in.
Coarse deposits can be found in such locations, which are built up over flood plains by abandoned or cut-off channels. Silt and clay, which are considerably finer materials, are carried by the flood deposits of water spills. The term “delta plains” refers to the flood plains in a delta.
5. Doab
The area of land that is situated where two rivers converge. Doab is a name for the “tongue” or tract of land located between two converging rivers that is used in South Asia, mainly in India and Pakistan.
Depositional Landforms Diagram
Here is the diagram for various Depositional Landforms:
Fluvial Landforms UPSC
- The highest waterfall in India is Kunchikal Falls, which is a cascade waterfall with numerous steps that are generated by the Varahi river in the Shimoga region of Karnataka (455 m).
- India’s tallest plunge waterfall is Nohkalikai Falls (340 m). It is located near Cherrapunji.
- The second-highest plunge waterfall in India is Jog or Gersoppa Falls, which is located in Karnataka on the Sharavati River (a tributary of the Cauvery).
- The highest waterfall in the world, Angel Falls in Venezuela, rises 979 metres and plunges 807 metres.
- The second-highest waterfall in the world is Tugela Falls (948 m), located in the Drakensberg mountains of South Africa.
A UPSC aspirant should be well versed with the topic of the Evolution of various Landforms like Glacial, Fluvial, and Aeolian. This topic of geography holds immense importance from both Prelims and Mains point of View. The details in the article would help candidates preparing for UPSC 2023.
Fluvial Landforms FAQs
Q) What is Fluvial Topography?
Ans. Fluvial topography refers to the landforms created by flowing water.
Q) What are the three stages of the River Course?
Ans. There are three stages of the river course-Young, Mature and Old.
Q) What is a gorge?
Ans. A gorge is a deep valley that is narrow and has steep, straight sides. The breadth of a gorge is about equal at both its top and bottom.
Q) What is an example of a gorge?
Ans. Indus Gorge in Kashmir
Q) What is a Delta?
Ans. A delta is an area of alluvium near the mouth of a river where more material is dumped there than can be taken away. Example: Sundarban Delta.
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