Limitations of the Groundwater-Management Model


The groundwater-management model described in this report is a simplification of the complex and multi-faceted issues associated with groundwater management in the upper Klamath Basin. The groundwater-management model identifies groundwater-pumping plans that, to the extent possible, meet the Project supplemental groundwater demand while avoiding adverse effects to groundwater and surface-water resources. The groundwater-management model was formulated in consultation with groundwater users and resource-management agencies in the study area, and the objective and constraints were defined to capture the essential goals and policy elements associated with supplemental groundwater use by the Project. As with all optimization models, opportunities for error occur in the formulation of the groundwater-management problem (equations 1–11). Errors may occur because the management objective is misidentified, constraints are misidentified or omitted, or constraint limits are unknown. The logical next step would be to refine the groundwater-management model to include management goals, regulatory limits, and (or) operational considerations not identified in this study. 


The groundwater-management model defined by equations 1–11 is a deterministic analysis that does not consider uncertainties associated with the groundwater-simulation model, which is a simplified mathematical representation of the complex regional groundwater-flow system in the upper Klamath Basin. Uncertainty is an element of every groundwater-simulation model and can arise with respect to the processes that control groundwater flow, or with respect to the parameters that define those processes, or both. A discussion of the sources of uncertainty in the upper Klamath Basin groundwater-simulation model is available in Gannett and others (2012). As a result of model uncertainty, the simulated responses to groundwater pumping that are embedded in the groundwater-management model also are uncertain. The method of stochastic optimization addresses groundwater-simulation-model uncertainty by using the concept of reliability and identifying groundwater-management strategies that have a desired probability of success (Freeze and Gorelick, 1999). Although stochastic optimization techniques are available to solve the groundwater management problem, that analysis is beyond the scope of this project.


Because climate can influence supplemental groundwater needs in the upper Klamath Basin, the analysis of groundwater-management alternatives involves making assumptions about plausible climate conditions. The results provided in this report are based on the historical climate conditions observed during 1970–2004. Global climate models, however, project that changing precipitation patterns in the Pacific Northwest likely will result in changes to the amount, timing, and spatial distribution of groundwater recharge (Stewart and others, 2004; Intergovernmental Panel on Climate Change, 2007; Waibel and others, 2013). Any change to the general patterns of groundwater recharge could affect the availability of groundwater as a supplemental irrigation supply. The groundwater-management analysis described in this report could be enhanced by considering an array of plausible future climate conditions and assessing groundwater-management alternatives for a range of climate and water-use scenarios. A general discussion of water-resources management in the presence of climate change is available in Brekke and others (2009).


Groundwater-management decisions in the upper Klamath Basin may need to be modified to account for uncertainties associated with the groundwater-flow model and future climate conditions. Adaptive management is an approach used to make decisions sequentially over time and adjustments can be made as new information becomes available (Williams and others, 2007; Brekke and others, 2009). The adaptive management approach is useful for any dynamic system where there is uncertainty about the system response to management actions, such as the predicted effects of pumping on groundwater levels and discharge. In the context of groundwater management in the upper Klamath Basin, the adaptive management approach would follow an iterative process: (1) design and implement a plan for supplemental groundwater pumping by the Project,
(2) monitor the effects of on-Project groundwater pumping,
(3) evaluate the effects of on-Project pumping in relation to model simulations, and (4) adjust the groundwater-management plan as model-simulation errors are observed. Because adaptive management requires flexibility to change management decisions when presented with new information, it is best suited to guide operational decisions, such as the amount to be pumped at existing wells, rather than changes in infrastructure, such as the construction of new wells.


If an adaptive-management approach is to be applied in the upper Klamath Basin, a central element will be a groundwater-monitoring plan that provides data to reduce uncertainty and inform decision making. The focus of the monitoring plan should follow the focus of the groundwater-management program it supports. In the upper Klamath Basin, groundwater management focuses on avoiding adverse effects caused by excessive drawdown and reductions in groundwater discharge to surface water, and estimates of water levels and discharge are directly included in the management-model constraints that limit these effects. A groundwater-monitoring plan should include elements to track these critical variables. Although the design of a groundwater-monitoring plan is beyond the scope of this report, it is possible to identify some key elements of a sound monitoring program: (1) targeted monitoring at sites where water levels or discharge are expected to reach limiting values because of supplemental on-Project groundwater pumping, (2) a monitoring schedule that tracks changes in water levels and discharge during periods of supplemental groundwater use as well as between irrigation seasons and during extended periods with no on-Project groundwater pumping, and (3) a monitoring component designed to assess the effects of climate variability on water levels and discharge.


First posted April 23, 2014