role of qanats in reclamation of kavirs(playas)

in dry parts of asia and africa where the rain was sparse and the surface water inadequate, man has had to search for-other sources of water namely ground water. through this need he learned to tap ground water and extract it to the surface. thus qanats were developed in persia.techniques of qanat construction were later introduced by persians to parts of asia and dry lands of africa.construction of qanats which can be considered one of the world's few wonders(miraculous works of ancient man)and certainly has been the most beneficial of all to mankind was continued up to recent decades by simple, however geneous, methods and measuring devices and with the use of hand tools. some qanats have served generation after generation, days and nights. techniques of qanat construction reveal that persians had a good knowledge of the occurrence and movement of ground water millenniums earlier. through qanats they could bring ,by gravity, groundwater from hillside aquifers to playa skirts and establish cities and centers of an ancient civilization. in recent decades, due to the growth in population,expanded uses of water and changes in cropping(which resulted from improvement of living standards due to higher incomes)qanat waters alone could not satisfy demands. thus,farmers and small landowners had to turn to the use of deep wells. extended pumping from these wells,lowered water table and decreased flow of many qanats and carelessness in their up-keep left many dry. difficulties of qanat construction and disputes in qanat ownership have been amongst the major problems resulting in abondoning qanats. unless these problems are overcome, the qanats will continue to dry.