Irrigation and drainage play a critical role in meeting the food requirements of the world's population on a sustainable basis. More than one third of the total global food harvest comes from an estimated 260 million ha of irrigated lands which is about one sixth of the total cultivated land. The World Food Summit convened by FAO in Rome in 1996, the United Nations Conference on the Environment and Development (UNCED) held in Rio de Janeiro in 1992, and the International Conference on Water and Environment, Dublin 1992, have all emphasized the importance of protecting the world's land and water resources in order to produce the necessary food and preserve the environment.
In humid regions, agricultural drainage is required to remove excess soil water in the plant root zone. In irrigated agriculture, drainage is of critical importance in controlling salinity and waterlogging. In seeking these benefits, drainage systems have sometimes led to adverse environmental impacts. Specifically, the disposal of low quality drainage effluent to water bodies has damaged some aquatic ecosystems, and inhibited the beneficial uses of the receiving water. Public pressure is growing for drainage systems to be planned in ways that ensure that important ecological habitats are preserved, and that agricultural practices do not impair water quality.
This technical document was prepared in response to public statements and societal concerns for environmental protection, and to provide for a safe, secure and sustainable food production system. The need for this publication was identified by the Working Group on Drainage of the International Commission on Irrigation and Drainage (ICID) and was fully supported by FAO.
The publication is intended for use by planners, irrigation and drainage engineers and environmental specialists. It would be useful in project identification and to assess potential adverse water quality impacts of drainage disposal practices and identify alternative mitigation technologies. In addition, monitoring programmes to collect desired information are suggested. The individual papers, prepared by specialists, were edited into a volume by Professor Chandra Madramootoo, McGill University, Quebec, Canada; Mr. William R. Johnston, California, USA, and Professor Lyman S. Willardson, Utah State University, Utah, USA.
The publication is a welcome addition to FAO's Water Reports series. It is hoped that the document will serve to improve the design, installation and operation of drainage systems. This in turn will improve the productivity of poorly drained cropland, and ensure that the twin objectives of food production and preservation of water quality are harmoniously achieved.
FAO welcomes comments, if any, from the readers and the practitioners who use the publication in their work. Comments should be addressed to: Chief, Water Resources, Development and Management Service, Land and Water Development Division, Food and Agriculture Organization, Viale delle Terme di Caracalla, 00100 Rome, Italy.