Presented at Contemporary challenges for irrigation and drainage: proceedings from the USCID 14th technical conference on irrigation, drainage and flood control held on June 3-6, 1998 in Phoenix, Arizona.Includes bibliographical references.The required level of management of the fresh water supply practiced within a given watershed is defined by all of the physical, chemical, economic, environmental, and sociological factors involved. Efficiency of water use, consumptive versus non-consumptive utilization of water, diversion requirements, and environmental requirements all need to be understood and balanced to optimize use of the available water. Where watersheds span states and sovereign nations, treaties and agreements are required for orderly use of the fresh water resource. Understanding of the nature of water use and the hydrology of the water resource system is a key element in rational utilization of the resource. Elevation, water quality, and temporal availability are some of the parameters that must be considered. Ground water and surface water need to be treated as a single resource for effective management
