Drainage under increasing and changing requirements

This year the Working Group on Drainage of the International Commission on Irrigation and Drainage (ICID) celebrates its 25th anniversary. This paper reviews the development of drainage for three different agro-climatic zones, i.e. the temperate (humid), the arid/semi-arid and the humid/semi-humid zones. Drainage is referred to as crop-season drainage, off-season drainage, intermediate drainage and salt drainage. Its specific properties, requirements, socio-economic functions and environmental implications are considered. Global statistics on the areas with and without irrigation and drainage are presented as well as the outlook of anticipated drainage developments in the future. The role of drainage in global food production is illustrated. Drainage design criteria over these last 25 years have evolved from the dual objectives of draining waterlogged agricultural lands and controlling soil salinity, to multi-criteria objectives that include the original criteria, satisfying more stringent environmental and water quality criteria, involve multi-stakeholder participation and social benefits, and satisfy economic criteria. Interaction with urban drainage and flood protection has also become an essential part in design considerations. Most importantly the designs need to be sustainable. This article briefly describes the evolution of these various aspects over the last 25 year