Rainwater harvesting
How can we collect and use water efficient and sustainable?
Proper water collection and use require the differentiation between the different water categories blue water, green water and grey water.
The distinction between the three water categories allows us to more efficient water utilisation for different purposes.
A Khadin, also called a Dhora, is an ingenious construction designed to harvest surface runoff water for agriculture. Its main feature is a very long (100-300 m) earthen embankment built across the lower hill slopes lying below gravelly uplands. Sluices and spillways allow excess water to drain off.
During monsoon rain significant run off is generated in the gravelly uplands of the catchment. The catchment area is generally 15 times the area of the Khadin. This water is held back by the bund and saturates the soil in the Khadin area. Excess water is released from by a sluice or spillway and then crops are grown in the moist soil. Salinity is often a problem in dry land irrigation however this system avoids it due to the intermittent flushing of salts from the Khadin area. Below the bund shallow groundwater levels are raised and shallow wells are installed for drinking water. First designed by the Paliwal Brahmins of Jaisalmer, western Rajasthan in the 15th century, this system has great similarity with the irrigation methods of the people of Ur (present Iraq) around 4500 BC and later of the Nabateans in the Middle East. A similar system is also reported to have been practiced 4,000 years ago in the Negev desert, and in southwestern Colorado 500 years ago.
The schematic sketch of a Khadin rainwater harvesting system highlights the simple, but effective construction. This construction combines three important effects:
- automatic rainwater harvesting
- groundwater availability for cropping area
- perched aquifer is protected against intensive evaporation
In the 1600’s villagers of the Thar Desert evolved an ingenious system of rainwater harvesting known as kunds or kundis. They are simply an impermeable catchment area of about 2,000 square meters that drains into a covered underground tank. The tank is about 2m wide and 6m deep. Originally the impermeable catchment area was created from clay, however concrete is now commonly used. To reduce costs, a soil binding polymer is now been investigated.
