Groundwater “Durability” Not “Sustainability”?

Abstract

Water, perhaps more than any natural resource, is the universal nexus between development and human existence thus, society is apprehensive about future availability. Potable groundwater is an important component of the total water resource and unlike most other extractable resources can be renewable. As a consequence, it is possible to develop a groundwater source that will last indefinitely—a highly desirable societal outcome. Groundwater, however, is a shared resource in which usage by one party may be highly beneficial to that party but harmful to others and/or to the long-term viability of the resource. Thus, to prevent the “Tragedy of the Commons,” societal management is necessary with the term “sustainability” having been proposed for this role. Sustainability was first used in the 1970s in defining an economic steady state lasting over hundreds of years. In 1987, however, the Brundtland Commission (United Nations 1987) popularized the term in the larger environmental sense. They defined sustainability as, “the ability to meet the needs of the present generation without compromising the ability of future generations to meet their needs.” Or more generally, circumvention of the depletion of a natural resource in order to continue an ecological balance. Groundwater sustainability has been proposed for groundwater management of this concept, yet as shown below that this concept does not capture the reality of most groundwater development! Sustainability in groundwater development is frequently interpreted as withdrawal from a basin not exceeding natural recharge. This is the “safe yield” concept that has been challenged by Bredehoeft et al. (1982); who referred to this concept as a “myth” as it significantly underestimates the potential steady-state yield from a developed aquifer system! In the expansion of the seminal 1940 publication by C. V. Theis, it was quantitively demonstrated that developed groundwater originates from expansion of the cone of depression that has the potential to capture additional water from rejected recharge, induced infiltration from adjacent surface water, as well as capturing water that would have been naturally discharged. If extraction is balanced by these sources, a new dynamic steady-state equilibrium is achieved referred to as “sustained yield” and the volume extracted is greater than that for “safe yield” of the same system. Sustained yield, however, neglects the impact on other interconnected water resources of the larger hydrologic cycle in which change in one part impacts the others and thus, may have cultural or legal implications. Implicitly imbedded in the word groundwater is the perception of quality. That is, “groundwater” suggests potable or agriculturally useful quality, and if not, it is usually specified with a modifier such as saline, brackish, brine, contaminated, toxic, and so on. Hence the concept of quality is inextricably incorporated in the expression of sustainability and the societal value of groundwater includes both quantity and quality aspects. It is obvious that a system could be in dynamic equilibrium (sustained yield) in terms of water balance but owing to change in quality with time (geogenic or anthropogenic) might make the water unusable for the intended purpose. Similarly, it is possible to envision a system in which the water quality remains unchanged while the withdrawals are increased beyond “sustained yield.” Thus, it is clear that most groundwater developments are unlikely to attain sustainability and the term should be discontinued for use as a goal in groundwater management. What is necessary is a word or concept that incorporates both quantity and quality; the philosophical problem, however, is that quantity is a thing (mass, volume, time, etc.), whereas quality is functional utility of an object or its usefulness. Perhaps “groundwater robustness” or “groundwater durability” is a more suitable term. Maybe a word from the Klingon language would be better, who knows. I will let the reader decide, but let us lose the word “sustainability”!