3. Drainage

Competency Based Questions:

 

  1. Why do the Himalayan rivers carry a large amount of alluvium compared to Peninsular rivers?
    Ans:     Himalayan rivers originate in snow-covered mountains and flow through soft alluvial soils, causing greater erosion. Their large volume and long courses allow them to transport huge quantities of silt, unlike Peninsular rivers which flow over hard rocks and have limited erosion.

 

  1. A village near the Ganga floodplain faces annual flooding. Suggest two realistic measures to reduce the impact.
    Ans:     Two realistic measures to reduce the impact.
  2. Construction of raised embankments and flood shelters for safety.
  3. Promoting afforestation along riverbanks and desilting to maintain flow capacity.

 

  1. A map shows that the Narmada and Tapi flow westward while most Indian rivers flow eastward.
    Q: Give one geological reason for this difference.
    Ans:     The Narmada and Tapi flow through rift valleys created by faulting, directing their flow westward into the Arabian Sea. Most other rivers follow the natural eastward slope of the Peninsular plateau towards the Bay of Bengal.

 

  1. A state government wants to use river water more efficiently. Suggest two measures.
    Ans:     Two measures that the state government can use river water more efficiently may be:

a) Construction of interlinking canals to transfer water from surplus to deficit basins.

b) Improving irrigation efficiency using drip, sprinkler systems, and lining of canals.

 

  1. Explain how river pollution affects the drainage system of India.
    Ans:     Pollution reduces water quality, harms aquatic ecosystems, accelerates eutrophication, and disrupts natural drainage functions. It also affects downstream users, agriculture, and potable water supply.

 

  1. Evaluate the significance of rivers in shaping India’s economy.
    Ans:     Rivers provide water for irrigation, hydropower, fisheries, drinking water, and transportation. They deposit fertile alluvium supporting agriculture and create opportunities for settlement and trade, making them crucial for economic development.

 

  1. How do human activities increase river flooding?
    Ans:     Encroachment on floodplains, deforestation in catchment areas, urbanization without proper drainage, and dumping of waste reduce river capacity and increase flood frequency and intensity.

 

  1. Why is river rejuvenation more common in Peninsular rivers than Himalayan rivers?
    Ans:     Peninsular rivers have reached maturity, but tectonic uplift or sea-level changes can increase their erosive power again—causing rejuvenation. Himalayan rivers are already youthful and actively eroding, so rejuvenation is less evident.

 

  1. How do river disputes between states affect development?
    Ans:     They delay irrigation projects, limit hydropower production, affect agriculture, cause political tension, and slow economic growth in water-dependent sectors.

 

  1. A map shows the Ganga-Brahmaputra-Meghna basin as the world’s largest delta.
    Q: What two physical factors help form this delta?
    Ans:     The Ganga-Brahmaputra-Meghna basin are the world’s largest delta as:

a) Huge sediment load carried by the rivers.

b) A gentle slope and slow river velocity near the mouth that encourages deposition.

 

CASE STUDY – 1: Himalayan and Peninsular Rivers

Read the passage and answer the questions:

India has two major river systems—Himalayan and Peninsular. The Himalayan rivers such as the Ganga, Indus and Brahmaputra are perennial and carry huge amounts of alluvium from the young fold mountains. They have long courses, meandering paths, and form large floodplains.
Peninsular rivers such as the Godavari, Krishna and Narmada are older, flow over hard rocks, and have shorter courses. Most Peninsular rivers flow eastward into the Bay of Bengal, except the Narmada and Tapi, which flow westward through rift valleys.

Questions

  1. Himalayan rivers carry more alluvium because:
    a) They originate from plateaus
    b) They flow over hard rocks
    c) They flow through soft alluvial soil
    d) They have no tributaries

Ans: c) They flow through soft alluvial soil

 

  1. Which of the following is a feature of Peninsular rivers flowing westward?
    a) Large meanders
    b) Perennial flow
    c) Flow through rift valleys
    d) Strong erosion in upper course

Ans: c) Flow through rift valleys
(Only Narmada and Tapi specifically, but it fits the case study context.)

 

  1. Why do most Peninsular rivers flow eastward?
    Ans: Peninsular rivers flow eastward because the Peninsular plateau slopes eastward, causing rivers to naturally flow towards the Bay of Bengal.

 

  1. Give one reason why Himalayan rivers form large floodplains.
    Ans: Their large water volume and high sediment load cause frequent deposition in the plains, forming extensive floodplains.

 

CASE STUDY – 2: Ganga-Brahmaputra Delta

Read the passage and answer the questions:

The Ganga-Brahmaputra-Meghna River system forms the world’s largest delta, spanning India and Bangladesh. The deltaic region receives high rainfall and floods frequently, which contribute to soil fertility. However, the region is also prone to damage from cyclones, river erosion, and sediment deposition. Despite these challenges, the delta supports dense population and intensive agriculture, especially rice, jute, and fishery activities.

Questions:

  1. The Ganga-Brahmaputra Delta is the world’s largest delta mainly because:
    a) It flows through rift valleys
    b) It carries enormous sediment load
    c) It has no tributaries
    d) It is located near the Himalayas

Ans: b) It carries enormous sediment load

 

  1. Which factor makes the delta region suitable for agriculture?
    a) Dry climate
    b) High temperature
    c) Frequent soil deposition
    d) Rocky terrain

Ans: c) Frequent soil deposition

 

  1. What major natural hazard affects the delta region?
    Ans: Cyclones and flooding are major hazards that frequently endanger lives and property.

 

  1. Explain how flooding can be both beneficial and harmful in the delta.
    Ans: Flooding deposits fresh alluvium that increases fertility (beneficial), but it also causes destruction of crops, homes, and infrastructure (harmful).

 

 

CASE STUDY – 3: River Pollution and Management

Read the passage:

Many Indian rivers, especially those flowing near industrial and urban centres, are experiencing increasing pollution levels. Wastewater, sewage, and industrial effluents reduce oxygen content and harm aquatic life. The government has taken several initiatives such as the Ganga Action Plan, National River Conservation Plan, and laws against untreated waste discharge. However, rapid urbanisation and ineffective waste management remain major challenges.

Questions

  1. The major cause of river pollution in urban areas is:
    a) Snowmelt
    b) Untreated sewage discharge
    c) Excessive rainfall
    d) Canal irrigation

Ans: b) Untreated sewage discharge

 

  1. Which program me aims at cleaning Indian rivers?
    a) Green India Mission
    b) Ganga Action Plan
    c) Blue Revolution
    d) National Waterway Project

Ans: b) Ganga Action Plan

 

  1. Why does untreated sewage reduce oxygen levels in rivers?
    Ans: Untreated sewage reduces oxygen levels in rivers because sewage promotes bacterial activity, which consumes dissolved oxygen, leaving less oxygen for aquatic life.

 

  1. Suggest one sustainable practice to reduce river pollution.
    Ans: The most sustainable practice to reduce river pollution may be installing sewage treatment plants (STPs) to ensure only treated water enters rivers.

 

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