NIOS Class 12 Environmental Science Chapter 30 Methods of Water Harvesting

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NIOS Class 12 Environmental Science Chapter 30 Methods of Water Harvesting

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Methods of Water Harvesting

Chapter: 30

Module 8 A: Water Resource Management

Textual Question Answer

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 scarcity of fresh water and increasing population, unequal distribution of rain in certain parts of our country, increasing industrialization and urbanization but excessive demand on this scarce resource. Therefore, harvesting rainwater and storing it for dry spells is a very wise step for ensuring availability.

4. List any three reasons for water shortage in the world.

Ans: Drought, expanding population, increasing irrigation demand, pollution which is reducing usability of water, abuse of available water.

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 system is found near Pune in the Western Ghats where large number of tanks were cut out in the rocks to provide drinking water to the tradesmen, forts like Raigad had tanks, ponds, rock cut cisterns to harvest and store water. These ponds and wells are still in use; well planned system of urban water supply and sewage in the ruins of Mohenjo Daro and Harappa of Indus Valley Civilization.

2. How do forests help in recharging ground water?

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 they could harvest rain water and this rain water 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 ground water.

Ans: Recharge wells shafts, trenches and pits.

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 provision for rain water harvesting. 

3. List any four benefits of rain water harvesting at any place of the states.

Ans: Increases water availability, checks declining water table, improves the quality of ground water through the dilution of salts, prevents soil erosion and flooding specially 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.

INTEXT QUESTIONS 30.4 

1. List the four main components required for harvesting water at household level.

Ans: Place/area to collect rain water, storage unit, distribution component, 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 minimize algal growth. 

3. How do we benefit by harvesting water at household level? (any three).

Ans: (a) Conserve groundwater and reduce the monthly water bill.

(b) Reduce local flooding and drainage problems. 

(c) Flushes salt build up from soils.

TERMINAL EXERCISE

1. Why we should go for rainwater harvesting?

Ans: The reason why we should go for rainwater harvesting is that it conserves water, recharges the groundwater, resolves water scarcity, and fulfils water needs.

2. Explain traditional methods of rainwater harvesting.

Ans: The traditional methods of rainwater harvesting are the Bamboo Drip Irrigation system, Kul, Johads, Talab, saza Kuva, etc. Most of the traditional rainwater harvesting is still in use in Rajasthan, some parts of Punjab also.

3. Which methods of rainwater harvesting prevailed in ancient India? 

Ans: The most common method of rainwater harvesting that prevailed in ancient India is rooftop water harvesting. This method was the practice in Rajasthan, people of Rajasthan used to build a rooftop harvesting system that was directly connected to the tanks, or other vessels that were used for storing water.

4. How rainwater harvesting helps in overcoming water scarcity? 

Ans: Rainwater harvesting helps in overcoming water scarcity in many ways such as rainwater harvesting recharges the groundwater table which later gives access to the underground water. Rainwater harvesting also recharges the local aquifers, reduces urban flooding, and ensure water availability,

5. Explain in brief roof-top rainwater harvesting. 

Ans: The roof-top rainwater harvesting method was mostly practiced in Rajasthan in ancient times, even it is also practiced in some regions of Rajasthan and Punjab. In this method, a catchment is built at the roof-top which is attached to the storage vessel and reservoir. In this way, the rainwater is collected for later household use such as cleaning, bathing, gardening and irrigation.

6. How ground water is artificially recharged?

Ans: Overuse or excess pumping out groundwater may lead to the depletion of groundwater. However, groundwater can be recharged either naturally or artificially. Groundwater can be recharged artificially by redirecting the water across the land surface through canals, ponds, infiltration basins, or by injecting water into the subsurface through injecting wells.

7. Narrate a success story of rainwater harvesting in India. 

Ans: Chennai is a coastal city in South India. This city was largely dependent on its groundwater source. Urbanization led to the depletion of groundwater by Over-exploitation. Rain water harvesting was promoted by creating awareness among various sections of the society. Citizens were aided to implement rainwater harvesting in their respective premises in an efficient and cost-effective manner. Various studies and research were also done prior to implementation. Akash Ganga Trust launched the Rain Centre in Chennai. This center is a one-stop information and assistance center for rainwater harvesting. The government enacted a law making RWH compulsory in all existing buildings of Tamil Nadu. The success can be seen from the results itself, the groundwater levels in the entire city have risen by 6 meters. The tanks which were waterless for 13 years got filled up to 3 feet from the bottom.

8. Explain in brief the important benefits of rainwater harvesting. 

Ans: Harvesting rainwater helps reduce the risk of floods and also decreases the community’s dependence on groundwater. Unlike groundwater, however, rainwater is remarkably pure with no dissolved salts or minerals. Due to this, rainwater is perfectly suited for landscape irrigation, use in evaporative coolers, washing, and many needs, hardness deposits do not accumulate, and there is no problem with soap scum.

9. Describe the steps involved in rainwater harvesting. 

Ans: The main stages involved in rainwater harvesting:

(a) Rainwater Collection: Collect rainwater from any rooftop area, driveway, or other catchment surfaces. The collected water is kept 3 feet away from the foundation of the house.

(b) Storage: An efficient system can be a 250-liter drum filled with rooftop gutters and downspouts. Buried cisterns, plumbing, and a timed watering system can also be included. Filtering can be done by placing screens over gutters or downspouts. Water kept in tanks should also be covered to reduce algal growth and eliminate the risk for mosquito breeding.

(c) Distribution: Gutters and downspouts or berms and swales can be made to collect rainwater and allocate it directly to landscape plants or into the soil. It can be stored and distributed later via a regular drip irrigation system.

(d) System Maintenance: Water harvesting systems need occasional maintenance, but this is easily done.

10. Provide in brief initiatives taken by the government on rainwater harvesting in India.

Ans: Several government buildings have taken the initiative for water harvesting in Delhi and other cities of India. Town planners and civic authorities are implementing bylaws making rainwater harvesting mandatory in all new structures. No connection would be granted if a new building did not have a system for rainwater harvesting. Board Central Ground Water, CAZRI, and NRAA are some authorities working on the initiative for rainwater harvesting. States like Tamil Nadu and Punjab give subsidies to farmers who practice rainwater harvesting.