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Water Management (Conservation of Water) - Fresh Water Management

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notes

ADVANTAGES:
1. Once a dam is constructed, electricity can be produced at a constant rate.

2. If electricity is not needed, the sluice gates can be shut, stopping electricity generation. The water can be saved for use another time when electricity demand is high.

3. Dams are designed to last many decades and so can contribute to the generation of electricity for many years / decades.

4. The lake that forms behind the dam can be used for water sports and leisure / pleasure activities. Often large dams become tourist attractions in their own right.

5. The lake's water can be used for irrigation purposes.

6. The build up of water in the lake means that energy can be stored until needed, when the water is released to produce electricity.

7. When in use, electricity produced by dam systems do not produce green house gases. They do not pollute the atmosphere.

DISADVANATGES:
1. Dams are extremely expensive to build and must be built to a very high standard.

2. The high cost of dam construction means that they must operate for many decades to become profitable.

3. The flooding of large areas of land means that the natural environment is destroyed.

4. People living in villages and towns that are in the valley to be flooded, must move out. This means that they lose their farms and businesses. In some countries, people are forcibly removed so that hydro-power schemes can go ahead.

5. The building of large dams can cause serious geological damage. For example, the building of the Hoover Dam in the USA triggered a number of earth quakes and has depressed the earths surface at its location.

6. Although modern planning and design of dams is good, in the past old dams have been known to be breached (the dam gives under the weight of water in the lake). This has led to deaths and flooding.

7. Dams built blocking the progress of a river in one country usually means that the water supply from the same river in the following country is out of their control. This can lead to serious problems between neighbouring countries.

8. Building a large dam alters the natural water table level. For example, the building of the Aswan Dam in Egypt has altered the level of the water table. This is slowly leading to damage of many of its ancient monuments as salts and destructive minerals are deposited in the stone work from rising damp caused by the changing water table level.

Alternatives:

  • biomass gasifiers, which burn waste products from agricultural production (such as rice or corn husks) to produce electricity
  • small-scale micro- (<100kw) and pico-hydro (<5 kw), which require no dam and run on the river’s natural flow
  • solar and wind generation
  • co-generation, a combination of electricity, heating and cooling from waste heat, usually sited to consumer needs. Surplus can be shared/sold to nearby customers using low voltage systems

notes

Water Harvesting

Water harvesting is another way in which we can manage our water needs properly. Since ancient times, many communities have used hundreds of indigenous water saving methods to capture every trickle of water that had fallen on their land; dug small pits and lakes, put in place simple watershed systems, built small earthen dams, constructed dykes, sand and limestone reservoirs, set up rooftop water-collecting units. This has recharged groundwater levels and even brought rivers back to life.

In largely level terrain, the water harvesting structures are mainly straight concrete-and rubble “check dams” built across seasonally flooded gullies. Monsoon rains fill ponds behind the structures.  These structures then recharge the ground-water beneath.

Water harvesting is an age-old concept in India. Khadins, tanks and nadis in Rajasthan, bandharas and tals in Maharashtra, bundhis in Madhya Pradesh and Uttar Pradesh, ahars and pynes in Bihar, kulhs in Himachal Pradesh, ponds in the Kandi belt of Jammu region, and eris (tanks) in Tamil Nadu, surangams in Kerala, and kattas in Karnataka are some of the ancient water harvesting, including water conveyance, structures still in use today (see Fig. 16.4 for an example). Water harvesting techniques are highly locale specific and the benefits are also localised. Giving people control over their local water resources ensures that mismanagement and over-exploitation of these resources is reduced/removed.

In largely level terrain, the water harvesting structures are mainly crescent shaped earthen embankments or low, straight concrete-andrubble “check dams” built across seasonally flooded gullies. Monsoon rains fill ponds behind the structures. Only the largest structures hold water year round; most dry up six months or less after the monsoons. Their main purpose, however, is not to hold surface water but to recharge the ground water beneath.

Advantages of storing water in ground

The advantages of water stored in the ground are:

-It does not evaporate, but spreads out to recharge wells and provides moisture for vegetation over a wide area.

-It does not provide breeding grounds for mosquitoes like stagnant water collected in ponds or artificial lakes.

-The ground-water is also protected from contamination by human and animal waste.

 

notes

Rain water harvesting is a technique of collection and storage of rainwater into natural reservoirs or tanks, or the infiltration of surface water into subsurface aquifers (before it is lost as surface runoff). One method of rainwater harvesting is rooftop harvesting. With rooftop harvesting, most any surface  tiles, metal sheets, plastics, but not grass or palm leaf can be used to intercept the flow of rainwater and provide a household with high-quality drinking water and year-round storage. Other uses include water for gardens, livestock, and irrigation, etc.

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