WBBSE Class 7 Geography Chapter 5 River Introduction
Usually, mountains and plateaus or other highlands from where a river originates is called the source of the river.
- The place where a river joins a sea, lake or any other water body or the place where the course of the river ends is known as its mouth.
- The extensive area over which several small streams or channels and the main river flow is called the catchment area of the river. These numerous small streams originate from the highlands and join to form a river at the foothills.
- The highland which separates the basin of one river system from another is called the watershed or water divide.
- The peak of the highland divides and distributes the rainwater and makes parts of it flow in different directions.
Tributaries are called small streams or rivers that flow from different source regions and join the main river.
- Small streams that branch off the main river channel, flow independently, and have their mouths somewhere else are called distributaries.
- A river valley is a valley confined by lateral banks through which a river drains from its source to its mouth.
- The total surface area covered by a river, its tributaries and distributaries, from the source to its mouth is known as the river basin.
- A river originating in a highland or a lake and emptying itself into a lake or any water body or swamp within the same country is called an inland river.
- A perennial river is a stream or river that has a continuous flow of water in its channel throughout the year.
- The streams have their sources high up in the mountains and are generally fed by ice-melt water.
- A non-perennial river is a river that does not have a continuous flow of water throughout the year, except in the rainy season. These rivers have their sources in a lower land like a plateau and are rain-fed.
Read And Learn Also WBBSE Class 7 Geography Notes
In humid regions, a steep and narrow ‘V-shaped river valley is known as a gorge.
- In arid and semi-arid regions, a very steep and narrow ‘T’ shaped valley is known as a canyon.
- When landforms formed of resistant and soft rocks lie in the course of a river, arranged in alternate layers, the soft rocks are eroded more and faster due to river action than the resistant rocks.
This results in the creation of a step-like structure, from over which the river water seems to plunge down a certain height. This is known as a waterfall.
- In the middle course of a river, due to a sudden decrease of the slope of the land and higher discharge of water, the river moves in a sinuous track. This zigzag course is known as a meander.
- the River deposits the transported sand, silt, etc. on its bed in this middle course because of the reduction in the carrying capacity due to the gentle slope of the land. This load accumulates on the river bed to form a riverine island.
- In the middle course of a river, there is continuous erosion on one side and deposition on the other side of the sinuous river bends. At times, the river meanders to such an extent, or if the water flow increases, a loop of the meander gets separated from the main channel.
This abandoned channel of the river is known as an oxbow lake or a horse-shoe lake, as it resembles the foot of a horse in shape.
- In the lower course of the river during floods, the river overflows its banks and deposits fine silt particles of the river bed on the low-lying areas along the channel and further away. As a result, a fertile plain is formed and it is known as a floodplain.
- When the sand, silt and clay get deposited at the mouth of a river, a triangular-shaped landform is formed. As it looks like the Greek letter delta, it is known as delta. The river bifurcates at the delta and flows along its sides.