3 Distinct Sections of River Profile | Geography

The first part of the river profile is known as the Upper Course or Mountainous Course or youthful stage. Second part of river profile is known as Valley Stage or mature stage or Middle Course. Third part  of river profile is known as Plain Stage or old age or Lower Course. The river course from source to its mouth is known as River Valley which may attain a depth ranging from some meters to 500 meters and even more than that.

1. The Upper Course of the River:

It starts from the source of river. River flows from steep gradients to low gradients. In this part velocity of river water is high, erosion and friction power is also high. River carries the debris formed by weathering. Various stones roll on the sea bed and moreover friction between these moving rocks results in formation of round shape rocks. Gravitational Pull and Rain water plays an important role at this part/stage of river.

Rain water starts flowing downwards because of gravitational pull. Because of ‘down cutting’ erosion process at this stage various landforms are formed. The process of ‘land form’ formation is high in areas having soft rocks and in mountains rocks are hard therefore down cutting is possible. Down cutting forms tight steep-side valleys and gorges.

(i) Gorges/Canyons:

Rivers like Satluj, Indus, Brahmaputra, Gandak, Kosi etc. form gorges in Himalayan mountains. In dry areas, canyons are formed by rivers. Canyons like letter “I” and these are steep and narrow. Canyon made by Colorado river in U.S.A. is one of the finest examples. This is the largest canyon of world. It is 480 kilometers long, 1828 kilometers deep and 6 to 16 kilometers wide.

(ii) V-Shaped Valley:

Mostly the rivers formed ‘V’ shape valleys. Because of high rainfall, along with down cutting erosion, sides are also eroded. Due to this narrow valleys look like letter ‘V’ with the passage of time they become wider. We can easily understand this process from the figure.

(iii) Water Falls:

River water flowing through a steep gradient area and falls from vertical gradient at high speed/velocity is known as water fall. Shiva Sundram (91 mtrs) and Jog (260 mtrs) on river Kaveri, while Dhuandhar (9 mtrs) on river Narmada are famous water falls in India. At time water from the fall lands on soft rock creating a deep on the spot.

(iv) Rapids:

These are the reactions of a river where the bed has a relatively steep gradient, causing an increase in water velocity and turbulence. When a river flows through an area of alternating bonds of resistant and less resistant rocks, the less resistant rocks are eroded more quickly.

Therefore, the soft rocks are at lower level compared to hard rocks which results in river falling in series of step along the bonds of hard rocks to form ‘rapids’. Rapids which are in a series of very short and fast falls are known as cascades. River Nile is a good example of rapid formation.

(v) Pot Hole:

When river flows it creates holes of various sizes. Some rocks are soft and they get eroded easily, resulting in deepening of holes. When water fills in the holes new landforms called ‘Pot holes’ are formed. They have ‘cylindrical’ shape and sometimes they look like ‘discs’.

Their diameter may vary from centimeters to meters and they may be upto a few meters deep. These are considered very dangerous because it is very hard to come out of these deeps. Because of this, these are also known as ‘Devil Punch Bowls’.

2. The Middle Course of the River:

As river enters in plains from mountains, it starts deposition along with erosion because the volume of water is high but velocity decreases.

This process results in formation of various landforms:

(i) Alluvial Cones:

As the velocity of river decreases, its transportation capacity also decreases. Due to this decline deposition starts in Foot Hills. This deposition forms Alluvial Cones. This is the first landform/pasture which a river makes with deposition. Mostly the Alluvial Cones have stones, rocks and sand (coarse debris).

(ii) Alluvial Fans:

While passing through alluvial cones, river is divided into various channels and alluvial cones convert into alluvial fans. Their size varies from some meters to various kilometers and they have semicircular shape.

Cedar creek alluvial fan of U.S.A. and Kosi Megafan are its best examples. Alluvial fan of river Kosi is situated in foot hills of Himalayas and it is 151 kilometer long and 143 kilometer wide. Kosi river has recorded a continuous westward shifting of around 113 KM in last 228 years.

(iii) Alluvial Plains:

These plains are formed by deposition of soil by rivers. Rivers bring soil particles of various rocks. With the continuous deposition of these soil particles layers are formed which further forms the fertile alluvial plains.

(iv) Natural Levees:

With the continuous deposition of soil on the banks by the river, the level of banks rises and they look like natural dams. These dams might rise upto 2 meters. Sometimes artificial Levees are also formed for the protection from floods.

(v) Flood Plains:

“A flood plain is a feature of low relief build adjacent to stream channel by the unconsolidated material derived from the related river”. In simple words, it is because of floods that layer of soil is deposited on the low lying areas near to the river. With the repetition of this process flood plains are formed. This process of flood plains formation is repeated annually, bi-annually or tri-annually.

3. Lower Course of the River:

At this stage river flows very slowly and almost there is no erosion and friction procedure. At this stage river starts deposition on its bed because of this the level of these parts rises.

At this stage river meets its mouth forming following land forms:

(i) Ox-Bow Lakes and Meanders:

Word ‘Meander’ is basically related to Turkish language which means ‘small winding river’. A river never flows completely straight, it flows in ‘S’ shaped (meanders). At low gradients, the deposition process is very common and width of river also increases. Due to obstacle in its way, river take turns with which meanders are formed.

Mississippi river of U.S.A., Ganga of India and Po of Italy are famous for ‘meanders’ and ‘ox-bow’ lakes.

An Ox-bow lake is a U-shaped body of water which is formed when a river creates a meander, due to the erosion of bank through abrasion. After a long period of time, meanders become very curved and eventually the neck of the meander becomes narrower and the river cuts through the neck during a flood, cutting of the meander and forming an ‘ox-bow lake’.

(ii) Braided Stream:

According to Miller, A braided stream is one which does not flow in a single definite channel but rather a network of ever changing, branching and reuniting channels. At lower course, river starts depositing soil on its bed. Continuous deposition forms soil layers. Because of this river is divided into small channels. With further deposition small ‘Bars’ or ‘Islands’ are formed which results in formation of ‘Braided Stream’.

(ii) Delta:

Greek historian ‘Herodotus’ (485 to 425 B.C.) used word ‘Delta’ for the delta of river Nile (Egypt) for the first type. This delta resembles the fourth word of Greek language i.e. ‘A’. When river flow reaches at its ‘mouth’, it is divided into various small channels.

Ganga and Brahmaputra Delta:

Deltas are formed with deposition of sediments carried by a river as the flow leaves its mouth. Its shape look like triangle ‘ A’, that’s why it is called ‘delta’.

Formation of Delta:

The total area of Ganga-Brahmaputra delta is 1,25,000 sq. km. and is biggest delta on the Earth.

All the rivers of world do not form deltas because for such formation, certain necessities are there:

(i) Volume of water should be high at the first stage of river so that erosion and friction process also be high.

(ii) Some other rivers or streams i.e. tributaries should conjugate with the main river so that amount of debris increases.

(iii) There should not be any obstacle at first stage of river like lake etc. so that river has a long bed.

(iv) Gradient should be low at last stage.

(v) Sea waves or Estuaries should not act as obstacle in the natural flow and deposition process of river.

The rivers which do not form delta, they form ‘estuaries’. These types of deltas are formed in those rivers which have volcanic soil at its mouth. The mouths of such rivers get submerged into the sea. No river flowing to western coast of India forms delta.

Types of Delta:

(a) Estuary- Examples are Rhine, and Amazon rivers.

(b) Accurate (Fan shaped)- Examples are Nile & Niger rivers.

(c) Cuspate (Pointed like tooth)- Examples are Ebro & Tiber rivers.

(d) Bird’s Foot (with fingering branches)- Examples is Mississippi river.