qanat

· As early as 3000 BC, a system of irrigation began in Persia called the qanat. · Qanats are underground tunnels, with a canal in the floor of the tunnel, which carries water. · At regular intervals, well-like openings extend from the surface to the tunnel floor, and it is through these openings that the tunnels were built and through which they are maintained. · The underground nature of the canal reduces evaporation in the hot and windy desert, and allows 22,000 qanats to operate in Iran even today. · Qanats originate in highlands, with a mother shaft as deep as 400 metres, and the tunnel floor slopes at a moderate angle toward its destination, which can be up to 160 kilometres away. · The difference between the qanat and a surface canal is that the qanat can get water from an underground aquifer, so a surface river or stream is not needed. · Since it travels at a slope independent of the surface features, it can go in a straight line. The water carrying canal in qanats were usually lined with stone or tile to reduce water loss. · The control of water was a key issue to Persian agriculture, and documents demonstrated that Darius and Xerxes authorising the mass construction of qanats at Manâwir in Egypt in an effort to increase agricultural production.