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Water Harvesting ppt

Water Harvesting

.ppt   Water Harvesting.ppt (Size: 1.37 MB / Downloads: 236)

Why is Water Harvesting especially important for India?

In India, most water reaches the ground through rain.
In contrast, in Western countries (mid-latitude regions), 50% of water coming down (precipitation) is in the form of snow
Snow melts slowly and percolates into the ground and recharges ground water
What about rain water?

Rain Water Pattern in India

Total annual rainfall in India: 400 million hectare-meters (area x height)
India’s area: 329 million hectares
If evenly spread, average height: 1.28m
Actual distribution:
Highly skewed area-wise
Thar desert receives less than 200mm annually, while Cherrapunji receives 11,400mm
But almost every part of India receives at least 100mm annually
Key: even 100mm annual rainfall sufficient if harvested properly and where it falls
Temporal distribution of rain in India also skewed
Rainfall in India seasonal (unlike Western countries)
Most of the country receives rainfall only for about 100 hours each year
Rough rule of thumb: #cm of rain = #hours rain received
E.g.: Jodhpur receives 40cm of rain in about 40 hours
Half of this rainfall is precipitated in just 1/5 th of the total hours
E.g.: Jodhpur receives more than half its annual rain in about 8 hours
Natural implication of such skew:
Most of the rain water lost due to runoffs
Unlike the west, very little water percolates into the ground
Hence, the importance of harvesting structures for local self-sufficiency

Importance of Water Harvesting

Ground water exploitation in India is very high
Area irrigated by ground water has increased 5 times since independence
Tubewells and borewells constructed primarily by larger farmers, encouraged by cheap electricity drain ground water
Big dam projects have hardly had any positive impact
Very few surface irrigation initiatives completed since independence
Too expensive to complete (estimate: Rs. 60000 crore to complete all ongoing major irrigation projects)
More importantly, displace communities,
Also reduce soil quality, lead to deforestation, all of which is detrimental to ground water levels
To find out: what is the proportion of land irrigated by ground water versus dams?
Traditional water harvesting systems have withstood the test of time
Hence, worth taking seriously, of course in the current context and fully understanding their limitations
Example of the stellar success of traditional water harvesting systems:
The city of Jodhpur, even though several hundred years old and right in the middle of a desert, has never been evacuated for lack of water.
The traditional water harvesting systems worked even in droughts when piped water supply failed
Om Thanvi, a Rajasthan journalist found over a 45-day survey that
In villages where traditional water systems were maintained and used, there was no scarcity of drinking water even during times of drought
In villages which relied purely on piped supply, the drying up of the Rajasthan canal meant an acute water crisis


Tankas (small tank) are underground tanks, found traditionally in most Bikaner houses.
Built in the main house or in the courtyard.
Circular holes made in the ground, lined with fine polished lime, in which raiwater was collected.
Tankas were often beautifully decorated with tiles, which helped to keep the water cool. The water was used only for drinking.
If in any year there was less than normal rainfall and the tankas did not get filled, water from nearby wells and tanks would be obtained to fill the household tankas.
The tanka system is also to be found in the pilgrim town of Dwarka where it has been in existence for centuries. It continues to be used in residential areas, temples, dharamshalas and hotels.


Traditional stepwells are called vav or vavadi in Gujarat, or baoris or bavadis in Rajasthan and northern India.
They were secular structures from which everyone could draw water.
Most of them are defunct today.
Stepwell locations often suggested the way in which they would be used.
Within or at the edge of a village - utilitarian purposes and as a cool place for social gatherings.
Outside the village, on trade routes - resting places.
When stepwells were used exclusively for irrigation, a sluice was constructed at the rim to receive the lifted water and lead it to a trough or pond, from where it ran through a drainage system and was channeled into the fields.

Nadis, Talabs, Lakes

Natural surface depression which receives rain water from different directions
They receive their water supply from erratic, torrential rainfall.
Can lead to heavy sedimentation and siltation
Trees can prevent some of this
Dredging out the sediment before monsoon can also help
Can lose water by evaporation
Talabs, lakes are similar
Toba is similar as well – natural depression with a natural catchment area


Saucer-shaped catchment area with a gentle slope towards the centre where a tank is situated.
Openings or inlets for water to go into the tank are usually guarded by a wire mesh to prevent the entry of floating debris, birds and reptiles.
The top is usually covered with a lid from where water can be drawn out with a bucket.
Kunds are by and large circular in shape, with little variation between the depth and diameter which ranges from 3-4.5 m.
Lime plaster or cement is typically used for the construction of the tank
The success of a kund depends on the selection of the site, particularly its catchment characteristics. An adequately large catchment area has to be selected or artificially prepared to produce adequate runoff to meet the storage requirements of the kund.
The catchment size of kunds varies from about 20 sq m to 2 ha depending on the runoff needed and the availability of spare land.
The catchment areas of kunds were made using locally available sealing materials such as pond silt, murrum, charcoal ash, and gravel. After clearing the soil surface of vegetation, the land was given a smooth gradient of 3-4 per cent towards the kund and the cleared surface was lined with pond silt obtained from nearby talabs or nadi beds.
Rainfall data collected showed that areas with 100 mm of rainfall can use the kund system effectively.


A rapat is a percolation tank
There is a bund to impound rainwater flowing through a watershed and a waste weir to dispose of the surplus flow.
If the height of the structure is small, the bund may be built of masonary, otherwise earth is used.
Rajasthan rapats, being small, are all masonry structures.
Rapats and percolation tanks do not directly irrigate land, but recharges well within a distance of 3-5 km downstream.
Silting is a serious problem with small rapats and the estimated life of a rapat varies from 5 to 20 years.
the collection of water is the activity of direct collection of rainwater. Collected rainwater can be stored for direct use or can be recharged into groundwater. Rain is the first form of water we know in the hydrological cycle, therefore it is a primary source of water for us. Rivers, lakes and groundwater are secondary sources of water. In current times, we depend entirely on these secondary sources of water. In the process, it is forgotten that rain is the ultimate source that feeds all these secondary sources and continues to ignore its value. Collecting water means understanding the value of rainfall and making optimal use of rainwater where it falls.

Collecting rainwater from the roofs of buildings can easily take place within our cities and towns, not just in rural Australia. All that is needed to capture this water is to direct the flow of rainwater from the roof gutters to a rainwater storage tank. By doing this, water can be collected and used for different uses.

If it depends on the rainwater collected and is not connected to a water supply of cities, then the water collected will be especially important to you. If you are from the city, then it is possible to replace all or at least a substantial part of your freshwater needs by capturing and storing rainwater from your roof. Being largely self-sufficient in water supply is possible for a large majority of Australian homes and buildings.

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