Groundwater is one of the most challenging resources to manage, in large part because it is hidden below ground and thus poorly understood. Many regions of the world have a high dependence on groundwater for agricultural, municipal, and domestic uses, as well as for aquatic habitats and other groundwater-dependent ecosystems. Yet aquifer depletion continues at an alarming rate, imposing costs on rural communities, farms, the environment, and society generally. This is particularly true in the western United States where consumptive use of water is expected to exceed available surface and groundwater by 2030. As surface water becomes fully allocated, groundwater withdrawals have increased, in part because western U.S. states have not done enough to regulate groundwater pumping. A recent detailed analysis of the problem by the New York Times found declining trends over the past 20 years in many areas – as indicated in red and orange in the map below.
The trend is particularly severe in Oregon where two-thirds of monitoring wells have declined since 1980. How and why has this happened? Like other states, Oregon has been slow to recognize that the accommodating approaches to managing an abundant resource of the past are insufficient in a world of scarcity, one where nearly all new uses of groundwater can be expected to cause interference with existing uses of both groundwater and surface water.
As in most parts of the western U.S., Oregon’s groundwater use is dominated by agriculture (about 90% of the total groundwater withdrawn), and the areas of concern across Oregon are widespread as indicated in the map below:
Efforts are underway, however, to fully recognize the realities of groundwater scarcity and, to some degree, groundwater’s unique management challenges. Over the past six months I’ve participated in this process as a member of the Oregon Water Resources Department’s Groundwater Allocation Rules Advisory Committee (RAC). The goals include clarifying and updating the rules for evaluating applications for new groundwater rights. Central to the approval process is determining whether “water is available” (in order to allow additional groundwater right). It is not an easy question. Groundwater resource rights are connected hydrologically to surface water. Pumping from a new well will potentially impact other existing wells, as well as surface water where it can interfere with surface water rights, springs, stream flow, and wetlands.
So how do we decide if “water is available” to allow development of a new right to withdraw groundwater? We need data on water levels and trends nearby and over a period of years. But reliable data is scant, and levels can fluctuate year to year. Most wells don’t collect or report the kind of data needed to develop a good understanding of the capacity of a given aquifer to sustain additional demands. Many well owners are reluctant to share information about their pumping rates and water levels. This unfortunate situation is counterproductive to gaining a good understanding of the state of the resource. Imagine trying to manage Oregon’s coastal fisheries if fishermen didn’t report their catch?
Central to Oregon’s water law is the “prior appropriations” seniority system that allocates water to senior water rights (established long ago) before more junior water rights (established more recently). Determining the “interference” of a junior water right on a senior water right is relatively easy with surface water (we observe stream diversions and know which way water flows). But knowing which junior groundwater right has interfered with a given senior groundwater right (or with a surface water right) is effectively impossible for purposes of regulation.
Interference among surface water irrigators occurs entirely within a given growing season. In the case of groundwater pumping, however, there is both within-season interference as well as longer-term aquifer depletion. But regulators don’t have sufficient information about the underground hydrological connections between specific wells to have a strong basis for knowing which junior water right should be shut off to protect more senior water right holders, so regulation is almost never used. This puts senior water right holders in overallocated basins at risk, where some water rights having seniority dating back more than 100 years are degraded from the interference of newly approved groundwater rights.
We can’t be sure if a new permit will impact existing groundwater rights and capacity, but given that Oregon’s surface waters are fully- or over-appropriated, there is a strong argument for erring on the side of caution. The current OWRD proposal seeks to establish a quantitative test to ensure that groundwater levels are “reasonable stable” and that a given aquifer is not “overdrawn.” Do water levels show declines of more than 0.5 feet per year? Do water levels show total declines greater than 25 feet or 8% of saturated thickness of the aquifer? A “yes” to either of these questions would trigger a finding of “water is not available.” And if there is insufficient data to evaluate these tests, then a precautionary finding of “water is not available” is also applied.
Oregon’s seniority water law system places emphasis on protecting existing rights above the approval of new, additional water rights. But the risks of unsustainability are high due to two factors: the lack of an effective or operational enforcement mechanism to adjust to within-season or long-term declines in groundwater supply, and the implied permanence of a new groundwater right — there is no way to fine-tune the amount of pumping allowed (no two-way adjustment mechanisms as in the case of a catch-share fishery where the total allowable catch can be revised up or down, year-to-year).
The revisions currently being considered by the groundwater RAC represent an important step, but more changes will be needed to better manage Oregon’s groundwater resources. There is an urgent need for more and better data, such as requiring groundwater right holders to measure and report water use and well levels. And we need to find policy mechanisms to adjust groundwater demand in response to changes in our understanding of groundwater supplies.