It sounds incredible but it’s true that the world’s wettest town - Cherrapunji - is now suffering from a shortage of drinking water. The problem is that Cherrapunji lies atop a high limestone plateau. Rain falling on the town drains away immediately. Very little rain collection takes place, because the locals don’t like the taste of water running off rusty tin roofs. With a growth in the town population, water has to be carried up from the plains during the drier winter months.

Irrigation in India includes both major and minor canals from Indian rivers, tanks, and other rainwater harvesting projects for agricultural activities. The Economic Survey of $2018$ states that agriculture in India even today relies heavily on weather because the percentage of irrigated land in India is $34.5\%$ as per the survey.

Based on the availability of surface (river) and groundwater, relief, soils, and climatic conditions, different means of irrigation are utilised in India. The conventional means of irrigation include wells, tanks and inundation canals. 

It is the most advanced and efficient method of irrigation. It is usually used to irrigate fruits and vegetables. It helps in water conservation.

Irrigation is the method by which water is collected, stored and supplied controllably when required by artificial means.

Dams are one of the sources of irrigation. This is achieved by construction of reservoirs where water is stored and utilised when required in the absence of rain.

B.  Reduction of Water table

One of the main threats to tubewell irrigation is that of over-abstraction leading to a lowering of the water table. If the rate of withdrawal is greater than the rate at which an aquifer is re-charged from surface water intrusion, there is a risk of eventual exhaustion.

Groundwater use and over use can raise important equity issues, particularly in rural areas when, following increased consumption, the level of water tables has been lowered. Only the richer farmers or land owners can afford to sink deep wells and boreholes and to purchase the more powerful pumps necessary to abstract groundwater.

Excessive use of water for cultivation of rice and other crops leads to environmental degradation, fall of groundwater level and threatening to the sustainability of agricultural development.

Based on the availability, resources are classified as renewable and non-renewable.

• Renewable resources: These are the sources which can be replenished over a period of time. An example is forest wood because wood can be grown by reforestation.
  
• Non-renewable: These are the sources that cannot be renewed and available in limited quantities. Examples include coal, nuclear, oil, and natural gas.
  

As ground water can continuously supply water resources it falls under the category of renewable resource. 

• A dam is a man-made structure built across a river.
•  Most dams are built to control river flow, improve navigation, and regulate flooding.
  
• Dams are made from earth, rocks or concrete and are usually constructed on rivers to store the water in a reservoir.
  
• All rivers contain sediments: a river, in fact,can be considered a body of flowing sediments .
•  When a river is stilled behind a dam, the sediments it contains sink to the bottom of the reservoir. 
  
• The amount of sediment carried into a reservoir is at its highest during floods .
  
• The construction of a dam blocks the flow of sediment downstream,  and increased sediment build-up in the reservoir.
  
• This triggers floods,

Freshwater sources include:

• Groundwater - Water found in shallow aquifers beneath the earth's surface. This water is generally found at depths up to 2,000 feet deep.
  
• Precipitation: It is nothing but the rain water which is an important source of fresh water. In fact it is the purest natural source of freshwater.
  
• Surface water - Water found in streams, rivers, lakes, and reservoirs.
  

 Dams are built not just for irrigation but for electricity generation, water supply for domestic and industrial uses, flood control, recreation, inland navigation and fish breeding. Hence, dams are now referred to as multi-purpose projects.

Water scarcity may be an outcome of a large and growing population and consequent greater demands for water and unequal access to it. A large population means more water not only for domestic use but also to produce more food. Hence, to facilitate higher food-grain production, water resources are being over-exploited to expand irrigated areas and dry-season agriculture. 

In India monsoon usually lasts from July to September. It is very irregular and unpredictable. India usually have no rains when needed and hence India requires highly sophisticated irrigation facilities and construction of reservoirs by which rain water can be stored and used all along the year. This is the major problem with Indian water potential though it has abundant rainfall. 

Tungabhadra project is the joint project of Andhra Pradesh and Karnataka governments located in Bellari district. The dam is built across the Tungabhadra river which is a tributary of Krishna. It is one of the biggest multipurpose projects in India.

Ans. 25%-Canals are useful sources of irrigation where there are perennial sources of water. Since the water availability has declined, canal as a source of irrigation has also declined. However Punjab, Haryana and certain regions in UP still use canals as their preferred source. Wells and tubewells are the most important source of irrigation today. 

• Karez is also called turpan water system. It is usually followed in China. Turpan's karez water system is made up of a horizontal series of vertically dug wells that are then linked by underground water canals to collect water.
  
• These are not followed in India.
  

• Tank irrigation includes storage of water by constructing a bund across the stream. Peninsular plateau is leading in tank irrigation out of which Andhra Pradesh stands first.
  
• It is also suitable in Tamil Nadu region.
  
• Tank irrigation becomes continuous source of water and helps in preventing wastage of rain water especially in Deccan region where temperature is very high.
  
• But the demerit of tank irrigation is that water can be lost through evaporation.
  

• Sprinklers are used as irrigation tools that supply water to agricultural crops.
  
• It is very much useful as water is let out and sprinkled through small knobs. This checks wastage of water by seepage and evaporation.
  
• Apart from irrigation sprinklers are also used in industrial purposes.
  

• Tank irrigation includes storage of water by constructing a bund across the stream. Peninsular plateau is leading in tank irrigation out of which Andhra Pradesh stands first.
  
• Tank irrigation becomes continuous source of water and helps in preventing wastage of rain water especially in Deccan region where temperature is very high
  
• But the demerit of tank irrigation is that water can be lost through evaporation.
  

In India monsoon usually lasts from July to September. It is very irregular and un predictable and hence India requires highly sophisticated irrigation facilities by which rain water can be stored and used all along the year. 

• India's rank in the world with respect to the amount of water available per person per year is 133.
  
• India is the second largest consumer of water in the world. Its consumption contributes 20.1% of world’s consumption of water.
  
• The per capita water available in India is 297.7 cubic meter. 
  

• India is currently, under no such stress; however, it is expected to become a moderate water scarce country by 2050.India is a developing country which needs water for its increasing population and economy. It is being projected that water demand in India is going to be as high as 24% by 2025.

• Irrigation is the method by which water is collected, stored and supplied controllably when required by artificial means.
  
• All the given options like increase in salinization, groundwater depletion, etc., are not the outcome of irrigation projects. But sometimes reservoirs may result in floods due to loss of capacity in the reservoirs caused by sedimentation.
  

• Rajasthan canal which is renamed as Indira Gandhi canal starts at Harike barrage, Punjab and terminates in Thar Desert of Rajasthan. It takes its waters from Sutlej River one of the tributaries of Indus River.
  
• The canal has transformed the barren deserts of this district into rich and lush fields.
  

• Chilika is the name of a lake present in the aster coast of India.
  
• It is a brackish water lagoon present in the state of Odisha. It flows into Bay of Bengal.
  
• The lake is an ecosystem with large fishery resources.
  

Canal irrigation occupies the second place after well irrigation and accounts for about 27% of the total irrigated area. India has one of the world’s largest canal systems. Canal irrigation is extensive in Uttar Pradesh, Punjab, Bihar.

In India, the irrigation of agricultural land is carried out maximum by Canals (29%). The longest canal in India is Indira Gandhi Canal about (650 km) this canal is also called Rajasthan feeder.

Sources of irrigation in India includes a network of major and minor canals from Indian rivers, groundwater well based systems, tanks, and other rainwater harvesting projects for agricultural activities. Irrigation in India helps improve food security, reduce dependence on monsoons, improve agricultural productivity and create rural job opportunities. India’s total area under irrigation is 64.7 million hectares. Of this maximum 45% is shared by tube wells followed by Canals and wells. So, in India wells and tubewells has the maximum area.

In Eastern and Southern states, pond irrigation is a major source is a wrong statement. Wells and tube wells are the most important sources of irrigation followed by canal irrigation. Pond irrigation or rainwater harvesting form only a small portion of the irrigation system.

Irrigation in India includes a network of major and minor canals from Indian rivers, groundwater well based systems, tanks,etc. About 2/3rd cultivated land in India is dependent monsoons. Uttar Pradesh is the highest irrigated state (17.6 million hectares) in India.

Himachal Pradesh, Assam, Maharashtra, and Karnataka having the lowest net sown area under irrigation Whereas Punjab and Haryana have the highest net sown area.

The maximum part of the total irrigated area of the country by canals is in Uttar Pradesh. Other major states where irrigation is done by canals are Madhya Pradesh, Andhra Pradesh, Haryana, Punjab and Bihar.

India's irrigation is mostly groundwater well based. At 39 million hectares (67% of its total irrigation), India has the world's largest groundwater well equipped irrigation system (China with 19 mha is second, USA with 17 mha is third).

The blowing away of loose soil in large quantity is known as soil erosion. Soil erosion occurs when soil is removed through the action of wind and water at a greater rate than it is formed.

Sprinkler irrigation system helps in limiting water use. It helps in conserving water as it can also be easily adjusted during droughts.

Excessive irrigation increases the amount of salt on the surface of soil due to evaporation. The accumulation of salts damages the soil fertility, except rice; almost all crops receive as ever set back in their growth when excess water stagnates.