Tag: irrigation and power

• 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. 

The geological structure of South India consists largely of hard crystalline rocks (peninsular shield), which makes digging wells difficult and expensive compared to the soft alluvial soil of the North.

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.