Class 9th Geography Drainage Notes

Introduction

• The term drainage describes the river system of an area.
• Rivers play a crucial role in shaping landforms, providing water, fertile soil, hydropower, and transport.
• India is home to some of the world’s largest river systems.
• Rivers are broadly divided into:
  1. Himalayan rivers – perennial (fed by glaciers + rain).
  2. Peninsular rivers – seasonal (mainly rain-fed).

The drainage system of India is controlled by:

• Relief (mountains, plateau, plains).
• Geological structure.
• Climatic conditions.

1. Drainage Patterns

Rivers form different patterns depending on slope, rock structure, and topography:

1. Dendritic Pattern
   • Tree-like structure.
   • Example: Ganga, Godavari.
2. Trellis Pattern
   • Tributaries join main river at right angles.
   • Example: Narmada, Tapti.
3. Rectangular Pattern
   • Rivers follow faults or fractures.
   • Example: Chambal basin.
4. Radial Pattern
   • Rivers flow outward in all directions from a central high point.
   • Example: Rivers from Amarkantak hills.

2. The Himalayan Rivers

2.1 Characteristics

• Perennial → fed by glaciers + rainfall.
• Long courses through mountains and plains.
• Large basins.

2.2 Major Himalayan River Systems

(A) The Indus River System

• Origin: Near Mansarovar lake (Tibet).
• Enters India in Ladakh, flows through J&K, then into Pakistan.
• Tributaries:
  • Zaskar, Nubra, Shyok, Hunza (in Ladakh region).
  • Jhelum, Chenab, Ravi, Beas, Sutlej (in Punjab).
• Indus Water Treaty (1960) → India can use waters of Ravi, Beas, Sutlej.

(B) The Ganga River System

• Origin: Gangotri glacier (Uttarakhand) → as Bhagirathi.
• Joined by Alaknanda at Devprayag → becomes Ganga.
• Major tributaries:
  • Yamuna (from Yamunotri glacier).
  • Ghaghara, Gandak, Kosi (from Nepal Himalayas).
  • Chambal, Betwa, Son (from Peninsular plateau).
• Divides into distributaries in West Bengal: Bhagirathi-Hooghly and Padma-Meghna (Bangladesh).
• Forms Sundarbans delta (world’s largest, UNESCO heritage site).

(C) The Brahmaputra River System

• Origin: Tibet (called Tsangpo).
• Flows eastwards, turns south near Namcha Barwa (Arunachal Pradesh).
• Enters Assam → known as Brahmaputra.
• Features: Wide river, frequent floods due to heavy rainfall + silt.
• Joins Ganga in Bangladesh → forms world’s largest delta.

3. The Peninsular Rivers

3.1 Characteristics

• Seasonal → depend on monsoon rainfall.
• Shorter courses compared to Himalayan rivers.
• Flow through hard, rocky terrain.
• More useful for hydropower.

3.2 West-Flowing Rivers

1. Narmada River
   • Origin: Amarkantak Hills (Madhya Pradesh).
   • Flows west → Arabian Sea.
   • Features: Marble Rocks (Jabalpur), Dhuandhar falls.
   • Forms estuaries.
2. Tapti River
   • Origin: Satpura ranges (Madhya Pradesh).
   • Flows west into Arabian Sea.
   • Shorter basin.

3.3 East-Flowing Rivers

1. Godavari River
   • Origin: Nasik (Maharashtra).
   • Length: 1,500 km (longest Peninsular river).
   • Tributaries: Purna, Wardha, Pranhita, Indravati, Manjra.
   • Forms fertile delta in Andhra Pradesh.
2. Krishna River
   • Origin: Mahabaleshwar (Maharashtra).
   • Tributaries: Koyna, Tungabhadra, Bhima.
   • Delta in Andhra Pradesh.
3. Kaveri River
   • Origin: Brahmagiri hills (Karnataka).
   • Tributaries: Amravati, Bhavani, Hemavati.
   • Forms delta in Tamil Nadu (known as Granary of South India).
4. Mahanadi River
   • Origin: Chhattisgarh.
   • Flows into Bay of Bengal (Odisha).
   • Known for Hirakud Dam.

4. Lakes in India

Lakes are formed due to glacial, tectonic, volcanic, or human activities.

4.1 Types of Lakes

• Freshwater lakes:
  • Formed by glaciers (Wular, Dal, Bhimtal, Nainital).
• Saltwater lakes:
  • Sambhar Lake (Rajasthan) → salt production.
• Man-made lakes:
  • Gobind Sagar (Bhakra Nangal Dam reservoir).

4.2 Importance of Lakes

• Moderate climate.
• Source of water for irrigation.
• Fishing, tourism.
• Hydropower generation.

5. Role of Rivers in Economy

• Agriculture: Irrigation, fertile alluvium.
• Industry: Water for processing, hydropower.
• Navigation & Transport: Cheap inland transport.
• Tourism: Scenic beauty, pilgrimage centres.

6. River Pollution and National River Conservation Plan

6.1 River Pollution

• Causes:
  • Industrial waste.
  • Sewage discharge.
  • Agricultural runoff (pesticides, fertilizers).
• Effects:
  • Kills aquatic life.
  • Spreads water-borne diseases.

6.2 Conservation Efforts

• Ganga Action Plan (1985): To clean Ganga, but limited success.
• National River Conservation Plan (NRCP): Covers many rivers (Ganga, Yamuna, Godavari, etc.).
• Aim: Reduce pollution, promote sustainable river management.

Quick Revision Points

• Drainage: River system of an area.
• Patterns: Dendritic, trellis, rectangular, radial.
• Himalayan Rivers: Indus, Ganga, Brahmaputra.
• Peninsular Rivers: Narmada, Tapti (west); Godavari, Krishna, Kaveri, Mahanadi (east).
• Lakes: Freshwater (Dal, Wular), saltwater (Sambhar), man-made (Gobind Sagar).
• Rivers in economy: Irrigation, hydropower, transport, tourism.
• Conservation: Ganga Action Plan, NRCP.