This book contains papers presented at the ASCE Irrigation and Drainage Division specialty conference, ""Irrigation Systems for the 21st Century,"" held in Portland, Oregon, July, 1987. Environmental and water management aspects of irrigation include agricultural drainage, quantification of components for crop water budget, water resources data collection, wastewater reuse, groundwater quality, and land disposal of food processing wastes. A special section on selenium is included. Sections on management and operation of irrigation systems include sizing and operation of irrigation projects, water production functions applied to irrigation projects, surge flow irrigation, automation of on-farm irrigation projects, and computer applications in irrigation and drainage. Other areas of discussion include evaluation of hydraulic structures under extreme events, operation and safety of dams, weather modification, and institutional and economic aspects of project formation.