Geography - 2. Plains and Rivers -

Main Definition

A plain is :
A naturally occurring feature on the earth’s surface – occupies over one-third of the planet’s landmass.
Plains are located not more than 200 metres above mean sea level.
It is described as :
A large area of relatively flat land with gentle changes in elevation, typically with fewer trees.

General Description of Plains

Landscape Features

Plains have different types of landscapes.
They are mostly flat land with gentle slopes.
Sometimes, they are lowlands in valleys, near mountains (foothills), on uplands, or along the sea coast (coastal plains).

Formation

Plains are usually formed by river systems and their tributaries.

Fertility and Use

Plains are often fertile, which makes them important for farming.
Because of this, they also support rural development such as roads, canals, and transport networks.

Population and Settlements

Plains have flat surfaces that make them easy to live on.
They are usually densely populated because they are:
Good for cities and towns (urban development).
Useful for farming and agriculture.

Types of plains

Plains are classified according to the characteristic vegetation within the ecosystem, which is a response to the availability of light and heat.

Tropical savanna

Savannas are a combination of woodland and grassland with scattered trees and drought-resistant grasses. The dry season generally lasts for more than five months and causes drought out of vegetation that can only grow.

Temperate grasslands

Grasslands are extensive areas dominated by grasses where only a few more metre high. They are not affected by factors. Pampas (South America), prairies (Central and North America), steppes (Eurasia), downs (UK and America), and veld (South Africa). An example of grassland is the Great Plains region of North America.

Deserts

Deserts are the driest places on earth. The extreme aridity and very low rainfall in the region result in landscapes. They usually have few plants and harsh climatic conditions, with surfaces covered with rocks and sand dunes that experience wide variations of temperatures between broad, with very high daytime temperatures and cold night temperatures. Sand dunes cover about 25 per cent of the world’s deserts. The remaining areas are either exposed rock or stone-covered plains.

Tundra

Tundra refers to the vast, treeless plains found in cold Antarctic regions. They have frozen ground, low temperatures, and minimal rainfall. These harsh environments only support sparse vegetation such as mosses and shrubs.

Coastal Plains

Coastal plains are low-lying, flat expanses of land along coastlines formed by sediment deposited by rivers and ocean. They are typically fertile and best suited for agriculture, shaped by interactions between land and sea processes.

Case Study: The Indus River Plain

Introduction

Plains in Pakistan

Pakistan has many plains that are very important for the country’s geography, farming, and economy.

Uses and Importance

Plains are not only used for agriculture, but also serve as important transportation routes.
They also hold historical and cultural importance.

Human Settlement and Civilizations

These plains have been inhabited for centuries.
They were the centers of many civilizations throughout history.

The Indus River Plains

General Overview

Course of the River

The Indus River and its tributaries flow through China, India, and Pakistan.
Each year, they carry about 300 million tons of sediments into the sea.

Size and Length

The Indus is one of the longest rivers in the world.
Its total length is about 3,200 km.

Importance for People

The river is very important for the livelihood of people.
It supports:
Agriculture
Water supply
Transportation
It also sustains a rich cultural heritage.

Variety of Landscapes

The Indus River Plain covers many different kinds of land.
It stretches from coastal plains to glacier-covered mountain regions.
The plain includes deserts, forests, hills, and plateaus.

River Journey and Formation

Origin of the Indus

The Indus River begins in the Tibetan Plateau.
It starts from meltwater of snow and ice from glaciers.

Course through Mountains

The river plunges nearly 3000 metres.
It emerges through the mountains and reaches the plains of Pakistan at Attock.

Southward Flow

From Attock, the Indus flows southwards.
It continues to descend towards sea level in all seasons.
On its way, it meanders across a flood plain that is more than 200 km wide.

Tributaries and Drainage

The river floods and its main tributaries — Jhelum, Chenab, Ravi, Sutlej, and Beas — flow through Punjab (land of the 5 rivers).
These rivers merge with the Indus.
Together, they drain into the Arabian Sea near Karachi, passing through a maze of channels.
This creates one of the world’s significant deltas.

Catchment Area

The Indus catchment covers about 1.1 million square kilometres.

Geographic Context

In Punjab, the rivers Jhelum, Chenab, Ravi, and Sutlej flow into the Indus one by one.
Most of Punjab up to Mithankot has been formed by the deposits of these rivers.
This makes the land very fertile and excellent for farming.
Main crops include: wheat, rice, cotton, and sugarcane.
Farming here is supported by extensive canal irrigation systems.

Indus Plain Sub-Regions

The plains of the Indus River cover most of Punjab and the central part of Sindh.
They consist of three sub-regions:

1. Upper Indus Plain

Extends from the foothills of the Himalayas to Attock, roughly near Mithankot.

2. Lower Indus Plain

Lies just below the Upper Indus Plain.
Starts where the Upper Indus Plain ends and continues as a giant river until the Arabian Sea.
Characteristics:
A flat alluvial plain.
Faces problems of waterlogging and salinity in the northwest.
Extensive deserts in the southeast, including the Cholistan (Rohi) Desert in Bahawalpur, Punjab.
A notable feature: the Rohri Ridge, made of limestone.
The Great Thar Desert (southern Sindh):
A coastal desert.
Has rolling plains, sand dunes, and ridges.
Agriculture:
Crops: rice, cotton, and fruits grown in fertile alluvial soil.
Scarce rainfall limits farming activities.

3. Indus Deltaic Plain

The Indus River Delta (Deltaic Plain) is a low-lying coastal area where the Indus meets the Arabian Sea.
It makes up a major part of Pakistan’s geographical area.
The delta is marked by old and new river channels.
The river has shifted its delta position many times.
The Indus Deltaic Plain is well known for its mangrove forests, which are important for marine ecology.
It also extends into the Rann of Kutch, a seasonal salt marsh to the west.
This marsh forms part of the India–Pakistan border (India at Gujarat, Pakistan at Sindh).

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River Erosion

I. River Erosion Processes

1. Basic Erosion Mechanism

As rivers flow across the land, they wear it down and carve out valleys.
This natural wearing away of the land by moving water is called river erosion.

2. Sediment Transport and Deposition

The eroded soil and rocks (sediment) are carried by the river.
This sediment scrapes and grinds against the sides and banks of the river channel, making erosion stronger.
Rocks and other fragments also collide with the riverbed, breaking into smaller pieces.
The current pushes this material downstream, where each fragment becomes smaller and smaller, until it turns into fine particles and even soil.

3. Chemical and Physical Erosion Actions

Water does not only erode by force; it also has a chemical effect.
Its solvent action dissolves soluble minerals from rocks and carries them away in solution.
Physically, water wears down rocks along the river channel, especially where the rocks have cracks or weak points.

II. Transporting Sediment

1. What Sediment Transport Means

The broken-down material (sediment) is moved by the river in two main ways:
- Bed load: Larger rock fragments that roll, slide, or bounce along the bottom.
- Suspended load: Smaller, lighter fragments that float and travel within the moving water.
This process of transport is shown in Figure 2.9.
Eventually, all transported material is deposited further downstream.

III. Transforming the Land

1. How River Flow Changes the Land

From its source in the mountains to its mouth at the sea or a lake, a river constantly shapes and reshapes the land it crosses.

2. Valley Formation and Development

a. Upper Reaches (Young Stage)

In the upper parts of the river (see Figure 2.9, A), the flow is steep and fast, tumbling through hills or mountains.
Here, the river mainly cuts downwards, forming a narrow V-shaped valley.
Over time, a small flood plain appears, and the earliest signs of river bends (meanders) can be seen (Figure 2.9, B).

b. Middle Reaches (Mature Stage)

As the river enters its middle course, the flood plain becomes wider.
More and more meanders (curves or bends) develop.
These bends form as the river flows through sediments deposited on the valley floor (Figure 2.9, C).

c. Lower Reaches (Old Stage)

In the lower course (Figure 2.9, D), the flood plain is very broad.
The river channel meanders widely across the flat valley floor.
The valley has a wide, flat bottom, with gently sloping sides marking the path of the river over long periods of time.

2. Geographic Terms and Features

Valley floor: The flat area at the bottom of the valley.
Flood plain: The wide, flat land alongside the river that floods when the river overflows.
Meandering stream: A river that bends and curves across its flood plain.
Cut bank: The outer edge of a meander where the river erodes the bank.
Point bar: The inner edge of a meander where the river deposits sediment.

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