Transcript Water Harvesting

Water Harvesting
Sangati CPR work group
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 hectaremeters (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
But….
• 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 selfsufficiency
Importance of Water Harvesting
(contd.)
• 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?
Importance of Water Harvesting (contd.)
• 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
Water Harvesting Structures in the
Thar Desert and Central Highlands
• Urban/rural water harvesting structures:
– Tankas, Nadis, Talabs, Bavdis, Tanks, Rapats,
Kuis, Virdas
• Rural water harvesting structures:
– Kunds, khadins
Tanka
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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.
Bavdi
• 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
• Nadis
– 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
Jhalara
• Human-made tanks, found in Rajasthan and Gujarat
• Essentially meant for community use and for religious rites.
• Often rectangular in design, jhalaras have steps on three or
four sides. The steps are built on a series of levels .
• The jhalaras collect subterranean seepage of a talab or a lake
located upstream .
Kunds
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Covered underground tank,
developed primarily for tackling
drinking water problems.
Usually constructed with local
materials or cement, kunds were
more prevalent in regions where
groundwater is saline.
Before the onset of rains every
year, meticulous care was taken to
clean up the catchment of the
kunds.
Cattle grazing and entry with
shoes into the catchment area of
the kunds was strictly prohibited.
The proximity of a kund to the
house or village saved time and
effort in searching for drinking
water.
Kunds
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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.
Kui
• 10-12 m deep pits dug near tanks to collect
the seepage. Kuis can also be used to
harvest rainwater in areas with meagre
rainfall.
• The mouth of the pit is usually made very
narrow. This prevents the collected water
from evaporating.
• The pit gets wider as it burrows under the
ground, so that water can seep in into a
large surface area.
• The openings of these entirely kuchcha
(earthen) structures are generally covered
with planks of wood, or put under lock and
key.
• The water is used sparingly, as a last
resource in crisis situations.
Khadin (or Dhora)
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Practiced in Jaisalmer area
– Not enough rain to fulfill crop
requirements
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Designed to harvest surface runoff
water for agriculture.
Its main feature is a very long
(100-300 m) earthen embankment
(khadin bund) built across the
lower hill slopes lying below
gravelly uplands.
Sluices and spillways allow
excess water to drain off.
The khadin system is based on
the principle of harvesting
rainwater on farmland and
subsequent use of this watersaturated land for crop production.
Khadin
• Requirements:
– Catchment area: shallow, gravelly and rocky uplands with high
runoff potential
– Flood plain or gently sloping plain area (khadin area) where soils
are suitable for crop production
• Before rainfall: kharif crop
– If good rain, half grown kharif crop (e.g. bajra) used for fodder,
and rabi crop grown instead
• Khadin area – few salts
• But area just outside khadin bund has salt accumulation;
hence khadin farmers better off than non-khadin farmers
• Maintenance:
– Grass on catchment, plus restricted cattle grazing
– Periodic cleaning of khadin area, including leveling the land plus
possible removal of deposited gravel and sand
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Virdas
Shallow wells dug in low depressions called jheels
(tanks).
They are found all over the Banni grasslands, a part
of the Great Rann of Kutch in Gujarat.
They are systems built by the nomadic Maldharis,
who used to roam these grasslands. Now settled,
they persist in using virdas.
These structures harvest rainwater. The topography
of the area is undulating, with depressions on the
ground. By studying the flow of water during the
monsoon, the Maldharis identify these depressions
and make their virdas there.
They separate potable freshwater from unpotable salt
water. After rainwater infiltrates the soil, it gets stored
at a level above the salty groundwater because of the
difference in their density.
A structure is built to reach down (about 1 m) to this
upper layer of accumulated rainwater.
Between these two layers of sweet and saline water,
there exists a zone of brackish water.
As freshwater is removed, the brackish water moves
upwards, and accumulates towards the bottom of the
virda.
There are also tank structures where the rainwater is
collected and multiple virdas (wells-in-a-tank) are
built
Rapats
• 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.
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Johads
Began in Rajasthan’s Alwar district, which
was a desert.
To solve the water scarcity, the village
collective started rainwater harvesting.
They started by repairing the old checkdams
or Johads. Johads are the traditional way of
harvesting rainwater.
A johad is a crescent-shaped bund which is
built across a sloping catchment to capture
the surface water before it runs off.
Water accumulating in the johad percolates
in the soil to augment the groundwater. The
groundwater then can be used when there is
no rainfall.
Over the next few years, the water table in
the ground have been increased through the
Johads. The village needs water for
drinking, sanitation, cooking, cattle and
irrigation.
Water is distributed based on the needs by
the collective. The collective has the
following rules:
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All villagers must benefit from the efforts of
the collective
All decisions will be arrived after informal
discussions
All decisions will be strongly enforced
Each person in the collective will be
responsible to carry out the task
Collective will use external help only for
guidance and they will do all the work
Before RWH &
reforestation
Johad
After RWH &
reforestation
Check dam
Johads
• Johad collects water during monsoons
• Later used for cultivation
• Johads became the basis for community
participation with general developmental
impact – fewer migrations, higher
participation by women, micro-credit, etc.
• Decisions on johads taken in local gram
sabhas
Health Hazards
• Water quality of traditional water systems often
does not satisfy drinking water quality standards
– Faecal contamination of tankas
– Floating organic debris, weeds, etc. in tankas
– Excessive presence of chemicals such as fluorides
and nitrates
– Breeding ground for mosquitoes
• WHO estimates that 80% of all sickness and
disease in the world is due to inadequate water
and sanitation (from both piped and traditional
systems)
Strategies for Improvement
• Specifically:
– Construction of water sources that cannot be contaminated by
infected persons
– Filtration of water
– Disinfection through chemicals (such as chlorine)
• Broadly
– Community involvement, coupled with health education
– Protect the catchment area; fencing it off to keep out cattle and
human beings from polluting the area
– Improvements in the design and construction of the catchment
area, storage and withdrawal so as to reduce pollution
– Awareness regarding traditional water systems and their health
impact
Points
• Importance of reforestation
• Keeping cattle away from catchment
• Uthnau – “holes” dug up in the stone quarries
act as water tanks
– Soil isn’t very deep, mostly rocky land
– No trees
– Volunteers from outside very hard to find (remote
area)
• Volunteers need to not feel superior to the local tribals
– Too Goria centric
Motivations for water harvesting
• India too diverse for dams
• Working examples
• Modern technology potentially lead to
regression
• Water crucial in India (50% people will
suffer from lack of drinking water)