Conjunctive Surface Water and Groundwater Management: A New Framework for Strategic Decision-Making
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Conjunctive use of water, or the optimized use and storage of surface water and groundwater, has become increasingly recognized over the past decades as an approach that facilitates efficient management of water resources. Recent research on conjunctive management primarily relies on economic evaluations or numeric modeling for specific regions; however, less research has focused on variables such as water laws and government institutions that affect water management policy options. There is a lack of consensus on its appropriate implementation, and no single document provides key parameters and standards for successful policies and programs of conjunctive use. Accordingly, the goal of this research was to identify and evaluate essential factors in conjunctive management. Objectives to accomplish this goal first involved evaluation of quantitative and qualitative components and their relationships in conjunctive management. Based on the evaluation results, a new decision framework for strategically understanding and designing a conjunctive program was created to support consideration and decisions concerning conjunctive management options. Finally, the research goal of determining key factors that support viable conjunctive management was demonstrated through application of the framework in the Rio Grande basin. Previous research on conjunctive use management strategies provided an extensive body of literature regarding the efficacy of conjunctive studies and programs. Many programs recognized the predominance of balancing and optimizing surface water and groundwater supplies as well as the economic efficiencies possible through conjunctive use and the limitations imposed by the interactions between surface and subsurface water systems. In addition, some studies recognized the role of legal and social systems. Thus, this work initiated with research in understanding how these four systems – physical water, economics, water laws, and social – support conjunctive use concepts. The research utilized previous conjunctive studies to better understand key elements. The studies were evaluated both within each study and across all reviewed programs, an analytical approach not previously applied. Models of water balance and economic studies, located around the world, were assessed for model goals, techniques, assumptions, and associated parameters and data ranges. Overall results demonstrated that conjunctive use programs are supported by common parameters that are applicable regardless of site-specific factors, geographic location, or model design. The results also illustrate the flexibility inherent in conjunctive use concepts. Factors qualitative or subjective in nature were also evaluated for their relative effects on viable conjunctive management. To address possible issues of legal support for conjunctive programs, water doctrines and laws in five western U.S. states were assessed for their potential impacts on conjunctive programs. The assessment indicated that, despite varying development in each state’s water law framework and differences in statutory and case law, conjunctive use programs progressed over time in each state and furthermore, created unique program activities in response to legal concerns. In addition, societal and stakeholder perspectives on conjunctive use programs were studied using a survey of and interviews with water management researchers and professionals. Analysis of the survey and interview results suggested gaps in agreement, even within the water industry, of what conjunctive use is and how the approach can be implemented. Based on the research results concerning quantitative and qualitative factors, a conjunctive strategy decision framework was created to support improvements in understanding, designing, and implementing conjunctive strategies. A new conceptual model, minimum criteria, and a decision matrix of conjunctive components and external factors comprised the framework. The conceptual model incorporated seven major components of regional, surface water, and groundwater systems, ecosystems, economic/financial issues, legal/institutional frameworks, and social/stakeholder input. These components established the foundation of the framework. Key criteria necessary to design a conjunctive strategy were developed from analysis of the major components. The criteria were compiled for each component and used as a basis for evaluation of conjunctive goals. The matrix detailed the relationships between major components and external factors, including parameters identified through evaluation of previous conjunctive models, studies, and programs. The conjunctive decision framework was prepared to support decisions concerning conjunctive strategies. Development of the framework was formed with the knowledge that water user groups and water professionals do not necessarily share an understanding of conjunctive use and its benefits and limitations. To test its efficacy, the framework’s criteria base was applied to the Rio Grande basin of the southwestern United States. The basin was selected based on its unique geographical, social, and ecological features and the water-stressed conditions varying from floods to droughts that the basin has periodically experienced. Within the basin, the region selected for application of the framework was the lower Rio Grande valley. Existing technical reports and water management planning documents were utilized. The majority of criteria were addressed and integrated with existing information, thus theoretically minimizing program design costs. However, review of the reports and documents showed that planning teams in the region have yet to fully realize conjunctive goals, strategies, standards, and an efficient approach to achieve an operational and successful conjunctive program. The framework can provide a path for achieving the overall goal of improved water management in the region. Currently, conjunctive management is undergoing a revival of interest in how a conjunctive strategy can aid or improve future water management. Previous programs, particularly those initiated several decades ago, focused on large-scale projects. This research, including review of multiple models, programs, and the closeness of fit between targets and achieved efficiencies, indicates that local- to regional-scale programs, rather than state-wide programs, may be likely. The conjunctive strategy framework aids in evaluation of conjunctive management goals and a wide range of site conditions. For example, at the local or municipal scale, an aquifer storage and recovery program may provide a cost- and time-effective approach to managing low water flow or drought conditions. To streamline costs, conjunctive strategies that incorporate groundwater storage capabilities appear to best support rather than replace existing water management programs. In addition, conjunctive optimization can occur through multiple technical approaches that fit site-specific needs. The information, data, and decision framework presented in this research address gaps in understanding and implementing viable, long-term conjunctive programs.