| Rain Harvesting Development
Since ancient times, a number of techniques have
been developed in many parts of the
world to collect rainwater for various purposes. India,
in particular, has developed rain
harvesting technologies since thousands of years. In the
Tar Desert, in Rajasthan, rain
harvesting technologies have been adopted in various
forms and for various purposes since
centuries. A recent book entitled “Dying Wisdom -
Rise, Fall and Potential of India’s
Traditional Water Harvesting System”, edited by Anil
Agarwal and Sunita Narain, ref. n.
3, illustrates in detail all the many aspects of the
traditional water harvesting systems in the
various states of India.
For the hilltop villages, specially those included in the
list of tanker villages, the water
harvesting system could be the best solution for
alleviating the water demand during the
dry months by impounding water in reservoirs. For hilltop
villages, where other
alternatives, such as drilling or digging wells,
impounding water by nala dams, excavating
tanks in depressions, are not appropriate, the
construction of artificial catchments,
connected with underground tanks, may be the only
solution.
The most popular rain harvesting systems adopted in the
hilly areas of northern Thana
District, are the nala dams and the bandaras.
Other rain harvesting technologies such as roof
catchments, rock catchments and paved
catchment could be appropriate in water scarcity
villages. The catchments are connected with a storage
tank as illustrated in the picture below.
These technologies, however, may be applied only if
climatic, geological and local
conditions are appropriate; roof catchments, for
instance, are not suitable in small adivasi
villages as their huts have roofs not suitable for
collecting water. For these villages, the
most appropriate solution, is to construct paved ground
catchments connected with
underground storage tanks. This technology is very
popular in certain arid and semi-arid
African countries where rainfall is even less than
200-300 mm per year. Most of the water
scarcity villages in Maharashtra have quite a high yearly
rainfall; therefore rain harvesting
could be very successful. In constructing ground
catchments, it will be necessary to take
into consideration a number of factors, such as the
rainfall regime, the number of days in a
year that rain harvested water is required, number of
users, appropriate catchment and
reservoir design, operation and maintenance.
Roof catchments have the advantage that they can be
constructed directly near the users, if
the roof is suitable for this purpose. The amount of
harvested water depends on roof area
and its nature, and rainfall regime.
Ground catchments are costly to install and require a
careful maintenance. They provide a
fairly good quality water and satisfy the water needs of
the entire community. To
construct a ground catchment requires, relatively, large
plots of land that may not always
be available in hilltop villages. The size of the area to
be cleared depends from the factors
mentioned for the roof catchment. The cleared area should
be graded to reduce losses due
to evaporation and infiltration, to avoid soil erosion
and to prevent silt content in the
water. The type of paving and its cost depends from the
type of material used (concrete,
tiles, plastered flat stones, etc.) and its local
availability . In the USA chemicals are used
for this purpose, such paraffin wax shredded and spread
on the ground surface. Wax is melted by sun light and
seals soil pores, making a water repellent surface.
Reinforced
asphalt membranes are also used where this material is
cheap. In Arizona, USA, the
ground catchment is made impervious by lying polyethylene
sheets covered with gravel for
protection against damage and sunlight. Catchments are
generally fenced.
A drain placed at the downward end of catchment collects
and delivers water into a silt
settling basin before reaching the underground storage
tank.. Fig. 11 and fig. 12 show the
roof catchment and paved ground catchment systems,
respectively; ref. 11.
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Fig.
11 - Roof catchment
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Fig.
12 - Paved ground catchment
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