Sustainable Yield

Sustainabilities: Eco-oriented | Market-oriented | Vernacular

Groundwater is a critical resource in many parts of the world, and how to balance its withdrawal and recharge to avoid declining levels and associated impacts has been central to groundwater management for the past century. Climate scientists predict that, due to global climate change, Northern California will lose at least a quarter of its annual Sierra snowpack by 2050. This anticipated decrease in California’s stored water supply, together with record drought, has catalyzed local water agencies to investigate groundwater storage opportunities, and this in turn has precipitated a renewed interest in defining “sustainable” groundwater management, including historic groundwater management legislation. Yet the term “sustainable yield” in groundwater management has been conceptualized, defined, and implemented differently by the state and by local water agencies in Northern California and throughout the state.

The term “sustainable yield,” defined by hydrologists as “the groundwater abstraction regime, measured over a specified time frame, that allows acceptable levels of stress and protects the higher value uses that have a dependency on the water,” has been the primary concept guiding groundwater management and policy.¹ But the term is inherently ambiguous, and presents difficulties in translating socioeconomic and political priorities into quantifiable system management.

For instance, hydrologists have primarily used a mass balance equation to attempt to quantify sustainable yield. If “sustainable” is regarded as the equilibrium of storage over time, then determining the average change in storage is a simple matter of subtracting the inflow from the outflow within a basin and ensuring that the amount of storage remains relatively constant. But the application and development of a quantifiable sustainable yield in such cases is difficult. Many basins are in states of deprivation that are not currently “sustainable” in the first place. In addition, basins that are at dynamic equilibrium over the long term (decades or centuries) may not operate at equilibrium for shorter time periods. Other basins may appear to be at equilibrium at present, but will not remain in equilibrium over the longer times because of large-scale hydrologic changes. And in all basins, calculating inflows and outflows is complex, often inaccurate, and can require expensive field monitoring and/or modeling studies. In addition, sustainability discourse is often fuzzy with respect to delineating relevant time frames and user prioritizations. The variety and ambiguity of the terms used to address the management of groundwater supplies raises the question: How do the state and local Northern California agencies utilize the subjective concept of “sustainable yield”?

The California Department of Water Resources (DWR) uses the term “sustainability” for a wide variety of planning activities, but the agency’s public documents acknowledge that “sustainable development” or “sustainable use of resources” may have different meanings depending on the perspective of the user, for example, those who use water for irrigation versus those who rely on a recreational fishing industry. In its 2009 California Water Plan, rather than utilize a strict definition, the department provides “general principles for sustainability planning,” defining a sustainable system (following the U.N.definition) as one that “meets today’s needs without compromising the ability of future generations to meet their own needs.” With this in mind, the agency encourages the establishment of any new water source to consider the needs of people and ecosystems up and down-stream and throughout the hydrologic cycle, and to avoid extreme situations that may deplete water in some regions to provide supplies elsewhere.

Yet, it is important to note that the DWR does not directly regulate nor permit groundwater withdrawals. Instead, it provides sustainability principles for water resources management, describing a renewable natural resource as sustainable only “if the rate of use does not exceed the rate of natural renewal.” To this end, interviews with five local water agencies, conducted for a recent study, provide more insight into the actual application of sustainability yield terminology on the ground.²

Overall, while the agencies frequently used the terms “sustainable” and “sustainable yield” in their management practices and public documents, personnel expressed dissatisfaction with the concept and its implications. All of the local agencies had recently moved or were in the process of moving away from using the term “sustainable yield” altogether in their groundwater management policies. This demonstrated a deliberate break from the vernacular utilized in the public documents reviewed above, and in decades of precedent. One manager called the term, which he said he had inherited from his predecessor, “the bane of my existence,” and another described it as “contentious and constantly debated.”

For one, agency managers were concerned that the word “sustainable” carries a normative and positive valence. They noted that the term implies that if a basin maintains its current groundwater levels this is a “good” thing. Yet for basins experiencing issues such as saltwater intrusion, sustaining current pumping levels would exacerbate the problem. In addition, agency managers and engineers expressed confusion around the timeframe inferred by “sustainable yield,” as well as worried that the term over-simplifies the complex and dynamic hydrology of a basin, the water supply of which varies over the course of seasons, years, and generations. Rather than stick with a quantified and constant number for sustainable yield, one manager suggested an alternative would be “a dynamic model that reflects changes in recharge, streamflow, pumping, water levels” so that “you can go forward and have various strategies for every year.”

The term “sustainable yield” overlooks additional variables that are central to equitable groundwater management practices. One agency manager pointed out that access to groundwater is predicated on the available infrastructure and technology used to shuttle water from underground to various users. Every groundwater user is reliant not only upon water, but upon water infrastructure, which is central to processes of distribution and is often rendered invisible in arguments about water “scarcity.”³ In addition, none of the agency managers accounted for non-human water users, such as local plants and animals, as important variables in assessing the “sustainable yield” of the basin, nor did issues related to water quality and human rights emerge in the interviews or discussions with water agency managers.

These examples underscore the inevitably political nature of the “sustainable yield” framework. As these “critical sustainabilities” projects demonstrate, the adoption of the term “sustainable” is a vernacular that has the tendency to exclude specific populations, such as non-humans and those who are disadvantaged economically and politically (eg. undocumented migrant workers, who are essential to California’s agricultural economy, and who often live in informal settlements lacking effective infrastructure and with extremely poor water quality). The term also naturalizes certain geographic and temporal contexts (such as the “water basin” and the timeframe necessary for recharge to occur), while rendering others invisible.

Kirsten Rudestam

Published June 1, 2015

1. Frans R. P. Kalf and Donald R. Woolley, “Applicability and methodology of
determining sustainable yield in groundwater systems,” Hydrogeology Journal 13:1 (2005): 295–312.
2. Kirsten Rudestam and Ruth Langridge, “Sustainability in Theory and Practice: Bridging
Scientific and Mainstream Vernacular” Groundwater (2014): 1–10.
3. See Eric Swyngedouw, Social Power and the Urbanization of Water—Flows of Power, (Oxford: Oxford University Press, 2004) and Matthew Gandy, Concrete and Clay: Reworking Nature in New York City, (Cambridge, MA: The MIT Press, 2002).