NIOS Class 12 Environmental Science Chapter 30A
INTEXT QUESTIONS 30.1
1. India is the wettest country in the world, and yet certain parts of it suffer from severe water scarcity. What causes this water scarcity? (one reason)
Ans: Uneven distribution of rain in time and space.
2. What is the average number of rainy days in India?
Ans: 40 days
3. “Water harvesting is a wise step towards water conservation”. Justify giving reasons.
Ans: There is a scarcity of fresh water and an increasing population, unequal distribution of rain in certain parts of our country, increasing industrialisation and urbanisation, but excessive demand on this scarce resource. Therefore, harvesting rainwater and storing it for dry spells of times is a very important step.
4. List any three reasons for water shortage in the world.
Ans: Drought, expanding population, increasing irrigation demand, pollution, which is reducing the usability of water, and abuse of available water. (any three)
INTEXT QUESTIONS 30.2
1. Mention any two instances that prove that water harvesting existed in ancient India.
Ans: One of the oldest water harvesting systems is found near Pune in the Western Ghats, where a large number of tanks were cut out in the rocks to provide drinking water to the tradesmen. Forts like Raigad had tanks, ponds, and rock-cut cisterns to harvest and store water. These ponds and wells are still in use; a well-planned system of urban water supply and sewage in the ruins of Mohanjodaro and Harappa of the Indus Valley Civilisation. (Any two) or any other.
2. How do forests help in recharging groundwater?
Ans: In the forests, the vegetation helps in seepage of water into the ground and thus recharges the water table.
3. Mention how, in ancient times, houses in western Rajasthan conserved water.
Ans: Each house in this region was built in such a way that it could harvest rainwater, and this rainwater was stored in underground tanks. This system can be seen even today.
INTEXT QUESTIONS 30.3
1. List any three structures that can be constructed to recharge the groundwater.
Ans: Recharge wells, shafts, trenches, pits, check dams or bunds, lateral shafts with bore wells (any three)
2. Mention the new bylaws being introduced by the civic authorities in many cities to ensure water conservation.
Ans: No water or sewage connection would be given if a new building did not have a provision for rainwater harvesting.
3. List any four benefits of rainwater harvesting in any place of state.
Ans: Increases water availability, checks declining water table, improves the quality of groundwater through the dilution of salts, prevents soil erosion and flooding, especially in urban areas.
4. Name some of the structures that are used in Rajasthan, U.P. and Madhya Pradesh to collect rainwater for cultivating crops during dry seasons.
Ans: Khadin, Johad, Talai, Haveli (any three).
INTEXT QUESTIONS 30.4
1. List the four main components required for harvesting water at the household level.
Ans: Place/area to collect rainwater, storage unit, distribution component, and system maintenance.
2. List any two precautions to be taken while storing rain-harvested water in cisterns/tanks.
Ans: Storage structures should be covered to prevent mosquito breeding and minimise algal growth.
3. How do we benefit by harvesting water at the household level? (any three)
Ans:
- a) Conserve groundwater and reduce the monthly water bill
- b) Reduce local flooding and drainage problems.
- c) Flushes salt buildup from soils.
- d) Provide excellent quality water for gardening in water codes. (any three)
TERMINAL EXERCISE
1. Why should we go for rainwater harvesting?
Ans: During dry periods, our water demand is fulfilled through the water stored in lakes, reservoirs or underground water. With increasing demand for water, these sources are becoming increasingly inadequate. Hence, efforts are required to retain more and more rainwater for use during the dry period. Rainwater harvesting at the local level by either storing in ponds, tanks and lakes or by recharging groundwater is are simple method of augmenting the water supply.
2. Explain traditional methods of rainwater harvesting.
Ans:
- In ancient Rome, residences were built with individual cisterns and paved courtyards to capture rainwater to augment water from the city’s aqueducts.
- Farming communities in Baluchistan and Kutch impounded rainwater and used it for irrigation.
- Efforts have been made to collect water by building dams and reservoirs and digging wells.
- Some countries have also tried to recycle and desalinate (remove salt) water.
3. Which methods of rainwater harvesting prevailed in ancient India?
Ans:
- In ancient times, houses in parts of western Rajasthan were built so that each had a rooftop water harvesting system. Rainwater from these rooftops was directed into underground tanks; this system can be seen even today in all the forts, palaces and houses of the region.
- Underground baked earthen pipes and tunnels to maintain the flow of water and to transport it to distant places are still functional at Burhanpur in Madhya Pradesh, Golkunda and Bijapur in Karnataka, and Aurangabad in Maharashtra.
- They harvested the raindrops directly. From the rooftop, they collected water and stored it in tanks built in their courtyards. From open community lands, they collected the rain and stored it in artificial wells.
- They harvested monsoon runoff by capturing water from swollen streams and rivers during the monsoon season and stored it in various forms of water bodies.
4. How does rainwater harvesting help in overcoming water scarcity?
Ans: Not only does this recharge arrest groundwater depletion, but it also raises the declining water table and can help augment the water supply. Some of the benefits of rainwater harvesting are as follows:
- Increases water availability
- Check the declining water table
- It is environmentally friendly
- Improves the quality of groundwater through the dilution of fluoride, nitrate, and salinity
- Prevents soil erosion and flooding, especially in urban areas
5. Explain in brief the rooftop rainwater harvesting.
Ans: Typically, rain is collected on rooftops and other surfaces, and the water is carried down to where it can be used immediately or stored. It is into underground tanks or in tanks.
6. How is groundwater artificially recharged?
Ans:
- Pits: Recharge pits are constructed for recharging the shallow aquifer.
- Aquifer: The aquifer is a porous, water-saturated layer of sand, gravel or bedrock that can yield significant or usable amounts of water. These are constructed 1 to 2 m wide, 1 to 1.5 m deep, and are backfilled with boulders, gravel, and coarse sand.
- Trenches: These are constructed when the permeable rock is available at shallow depth. The trench may be 0.5 to 1 m wide, 1 to 1.5 m deep, and 10 to 20 m long, depending upon the availability of water. These are backfilled with filter materials.
- Dug wells: Existing dug wells may be utilised as recharge structures, and water should pass through filter media before being put into the dug wells.
- Hand pumps: The existing hand pumps may be used for recharging the shallow/deep aquifers, if the availability of water is limited. Water should pass through the filter media to avoid choking of recharge wells.
- Recharge wells: Recharge wells of 100 to 300 mm diameter are generally constructed for recharging the deeper aquifers, and water is passed through filter media to avoid choking of recharge wells.
- Recharge Shafts: For recharging the shallow aquifer, which is located below a clayey surface, recharge shafts of 0.5 to 3 m diameter and 10 to 25 m deep are constructed and backfilled with boulders, gravel and coarse sand.
- Lateral shafts with bore wells: For recharging the upper as well as deeper aquifers, lateral shafts of 1.5 to 2 m wide and 10 to 30 m long, depending upon availability of water, with one or two bore wells are constructed. The lateral shaft is backfilled with boulders, gravel and coarse sand.
7. Narrate a success story of rainwater harvesting in India.
Ans: Despite very little rainfall, the surrounding area of the River Ruparel in Rajasthan has ensured water availability throughout the year with proper management and conservation of water. Due to deforestation and agricultural activities along the banks, the area suffered a drought-like situation in the 1980s. The locals were encouraged to build johads (round ponds) and dams to hold rainwater. Gradually, water began coming back as proper methods of conserving and harvesting rainwater were followed. The revival of the river has transformed the ecology of the place and the lives of the people living along its banks. Their relationship with their natural environment has been strengthened. It has been proven that mankind is not the master of the environment, but a part of it. If human beings put in an effort, the damage caused by us can be undone.
8. Explain in brief the important benefits of rainwater harvesting.
Ans: Some of the benefits of rainwater harvesting are as follows:
- Increases water availability
- Check the declining water table
- It is environmentally friendly
- Improves the quality of groundwater through the dilution of fluoride, nitrate, and salinity
- Prevents soil erosion and flooding, especially in urban areas
- Conserves valuable groundwater and reduces your monthly water bill
- Reduces local flooding and drainage problems
- Flush salt build-up from soils- your plants, and notice the difference
- Decreases landscaping and property maintenance needs
- Provides excellent quality water for various uses
9. Describe the steps involved in rainwater harvesting.
Ans: The main steps involved in rainwater harvesting are rainwater collection, storage, distribution, and system maintenance.
- (a) Rainwater collection: Capture rainwater from the rooftop area, patio, driveway, or other impermeable surface and keep it at least three feet away from the foundation. The amount of water you will be able to harvest depends on the size of the catchment area.
- (b) Storage: An effective storage system can involve a 250 litre drum fed by rooftop gutters and downspouts. A more involved system might include buried cisterns, plumbing, and a timed watering system. Debris and leaves should be filtered by placing screens over gutters or downspouts. Water kept in tanks or cisterns should also be covered to minimise algal growth and eliminate the potential for mosquito breeding using floating lids.
- (c) Distribution: Gutters (a narrow channel which collects rainwater from the roof of a building and diverts it away from the structure, typically into a drain) and downspout (is a vertical pipe for carrying rainwater from a rain gutter to ground level)or berms ( is a level space, shelf or raised barrier separating two areas) and swales(is a low tract of land, especially one that is moist or marshy) can be designed to catch rainwater and distribute it directly to landscape plants or into the soil. Many people store harvested rainwater and then distribute it later through their regular drip irrigation system.
- (d) System maintenance: Water harvesting systems require occasional maintenance, but this is easily accomplished. Debris screens over gutters should be cleaned periodically, and storage tanks should be drained and cleaned when it is convenient to do so.
10. Provide in brief initiatives taken by the government on rainwater harvesting in India.Ans: Several government buildings have been asked to take up water harvesting in Delhi and in some other cities of India. Town planners and civic authorities are introducing bylaws making rainwater harvesting compulsory in all new structures. No water or sewage connection would be given if a new building did not have provisions for rainwater harvesting. Such rules should also be implemented in all the other cities to ensure a rise in the groundwater level.
Additional Study Materials
- Chapter 27A Global Circulation of Water
- Chapter 28A Groundwater Resources
- Chapter 29A Freshwater Resources
