3 worked answers · short steps first, explanations when you need them
Exercises
Textbook pages 29
Question 1
Classify each situation as suffering or not suffering from water scarcity: (a) high annual rainfall (b) high rainfall and a large population (c) high rainfall but highly polluted water (d) low rainfall and a low population. Also choose the statement that is not an argument in favour of multi-purpose river projects, then correct the three false statements about urban water use, river regulation and rooftop rainwater harvesting in Rajasthan.
Steps only
(a) Usually not scarce by rainfall alone; (b) may suffer because population raises demand; (c) suffers because polluted water is unsafe to use; (d) may not be scarce if demand is low, though local access still matters.
Answer
(a) Usually not scarce by rainfall alone; (b) may suffer because population raises demand; (c) suffers because polluted water is unsafe to use; (d) may not be scarce if demand is low, though local access still matters. The statement that is not an argument in favour is (c): displacement and livelihood loss are disadvantages. Corrections: (1) dense urban growth and lifestyles can put pressure on water resources rather than ensure proper use; (2) dams change a river’s natural flow and sediment movement; (3) rooftop rainwater harvesting remains useful and is practised in Rajasthan even with the Indira Gandhi Canal.
Question 2
In about 30 words each: (i) Explain how water becomes a renewable resource. (ii) What is water scarcity and what are its main causes? (iii) Compare advantages and disadvantages of multi-purpose river projects.
Steps only
(i) The water cycle continually moves water through evaporation, condensation and precipitation, replenishing rivers and groundwater.
Answer
(i) The water cycle continually moves water through evaporation, condensation and precipitation, replenishing rivers and groundwater.
(ii) Water scarcity is insufficient safe water for people’s needs. Causes include low rainfall, overuse, unequal access, growing demand and pollution.
(iii) Dams can provide irrigation, drinking water, flood control and electricity, but may displace people, disrupt ecosystems and block natural sediment flow.
Question 3
In about 120 words: (i) Discuss how rainwater harvesting is carried out in semi-arid Rajasthan. (ii) Describe modern adaptations of traditional rainwater-harvesting methods.
Steps only
(i) In semi-arid Rajasthan, people traditionally collect rainwater from rooftops and courtyards and direct it through pipes or channels into underground tanks called tankas.
Answer
(i) In semi-arid Rajasthan, people traditionally collect rainwater from rooftops and courtyards and direct it through pipes or channels into underground tanks called tankas. The first rain is often allowed to wash the roof; later rain is stored for drinking through dry periods. Johads and other local structures also collect runoff and help recharge groundwater.
(ii) Modern adaptations include rooftop systems that carry water through filters into storage tanks or recharge pits. Schools and homes can add gutters, first-flush devices and covered tanks. These methods reduce runoff and improve local supplies, but tanks must be kept clean and harvesting should complement careful water use and watershed management.