ABSTRACT
Management of ground water in the Southwest often is governed by the principle of “Safe Yield,” which, in the most basic form, states that annual withdrawals from an aquifer should not exceed the average annual recharge to the aquifer. Other definitions of safe yield have been developed to limit pumping to levels that will not produce various undesirable effects; however, the traditional focus of safe yield has been on the economic and legal aspect of ground-water development. The evolving concept of “sustainability” states that development of resources will not leave future generations worse off than the present generation. Sustainability, like safe yield, has different meanings to different groups of people and is tied to societal values. Regardless, the goal of sustainability promotes a long-term view of the consequences of use of ground-water resources. Ground-water reservoirs commonly are immense and ultimate effects of a development may not be realized for decades or centuries. In the past, hydrologists have seldom studied long-term effects of pumping; however, with an increasing focus on sustainability, work by hydrologists will be key in societal decisions on ground-water development.