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