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The conjunctive use of surface water and groundwater is practiced worldwide as a measure to address water supply uncertainty. This paper focuses on a scenario in which an aquifer is open to multiple users and examines the impact of such an open-access environment on the stabilization function of conjunctive management. We construct a non-cooperative stochastic dynamic game model where multiple users utilize groundwater intake from a common aquifer as a complement to fluctuating surface water. We also propose a simpler baseline applicable to dynamic environments to compute the benefits of the stabilization function when users are unable to adjust groundwater intake to surface water uncertainties. We then apply the model to the real-world case of the water supply environment of the Cao'e River in China. Simulation results show that open access leads to diminishing stabilization values as higher pumping costs due to declining stocks lead to a weakening of users' incentive to utilize groundwater flexibly. Furthermore, the stabilization function itself is destabilized as the number of users increases. This is because greater groundwater intake and a decline in stocks amplify variations in pumping costs caused by different patterns of surface-water fluctuation. [ABSTRACT FROM AUTHOR]

Regulating groundwater in the Eastern United States (U.S.), particularly transboundary aquifers between states, is a challenge given the patchwork quilt of common law, statutory frameworks, and agency rules. Such regulation is made more challenging by the need for better quantification of pumping and use. These dynamics are exemplified through several case studies, including the first ever U.S. Supreme Court case related to groundwater withdrawals (set in the Eastern U.S.). As dynamics such as expanded irrigation, population increases, and ecological considerations influence groundwater use across the Eastern U.S., water use will continue to be an important driver for economic activity and interaction within and between states. To effectively regulate transboundary aquifers, governance solutions must incorporate current science into decision making and be implemented at local, state, regional, and federal scales. Research Impact Statement: Advanced planning and incorporation of best science for adaptable policy frameworks are vital tools to ensure effective regulation of transboundary aquifers in the Eastern United States. [ABSTRACT FROM AUTHOR]

Recent severe droughts in U.S. western and Great Plains states have highlighted the challenges that socio-ecological disturbances can pose for governing groundwater resources, as well as the interconnections between groundwater and surface water and the need to manage the 2 in an integrated way. Conjunctive management recognizes these interconnections and can be used to mitigate disturbances and achieve a variety of water management goals. However, comparative studies of how and to what extent various states have implemented conjunctive management strategies are few. Here we compare and assess the use of conjunctive management practices in 4 western states—Arizona, California, Nebraska, and Texas—with a particular focus on groundwater. Special attention is paid to factors of geography and infrastructure, degree of administrative (de)centralization, and monitoring and modeling in relation to conjunctive management. Despite the commonality of bifurcated regimes for groundwater and surface water, all 4 states have responded to disturbances with conjunctive management strategies in various ways. Although it has groundwater management challenges similar to those in the other 3 states, Texas has overall been slower to adopt conjunctive management strategies. Citation: Sugg ZP, Ziaga S, Schlager EC. 2016. Conjunctive groundwater management as a response to socio-ecological disturbances: a comparison of 4 western U.S. states. Texas Water Journal. 7(1):1-24. Available from: https://doi.org/10.21423/twj.v7i1.7019.

Climate variability and insufficient irrigation are primary constraints to stable and higher agricultural productivity and food security in Nepal. Agriculture is the largest global freshwater user, and integration of surface- and ground-water use is frequently presented as an strategy for increasing efficiency as well as climate change adaptation. However, conjunctive management (CM) planning often ignores demand-side requirements and a broader set of sustainable development considerations, including ecosystem health and economics of different development strategies. While there is generic understanding of conjunctive use, detailed technical knowhow to realize the CM is lacking in Nepal. This article presents a holistic framework through literature reviews, stakeholders consultations and expert interviews for assessing CM and implementation prospects from a systems-level perspective. We demonstrate the framework through a case study in Western Nepal, where climatic variability and a lack of irrigation are key impediments to increased agricultural productivity and sustainable development. Results show that knowledge of water resources availability is good and that of water demand low in the Western Terai. Additional and coordinated investments are required to improve knowledge gaps as well as access to irrigation. There is therefore a need to assess water resources availability, water access, use and productivity, to fill the knowledge gaps in order to pave pathways for CM. This paper also discusses some strategies to translate prospects of conjunctive management into implementation., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

Management of surface and ground water resources in drought-stricken regions with increasing water consumption poses a major challenge to water resource managers and decision makers. The situation is even graver in areas naturally classified as semiarid regions. Conjunctive management of ground and surface water is an appropriate strategy in such regions and in areas involving many stakeholders with various views and different water demands. It is, indeed, an effective approach that can enhance the reliability of water supplies. In the present study, the artificial neural networks (ANNs) and genetic algorithm (GA) are exploited to develop a simulation multiobjective optimization model. Conflict resolution models are also used to solve the problems and to seek a reliably stable solution for the study area, one of the subbasins of the Zayandehrood River Basin in central Iran, where recent water shortages and increased demands have led to conflicts between the Regional Water Company and the Agriculture Organization. To address the issue, the Pareto frontier or trade-off curve is generated and a unique solution is obtained by applying two conflict resolution methods. The conjunctive management model is then applied to establish stable and satisfactory conditions governing the relations between stakeholders that aim at supplying at least 65% of their demands and limiting groundwater level drawdown to 3 m per year. [ABSTRACT FROM AUTHOR]

Recent severe droughts in U.S. western and Great Plains states have highlighted the challenges that socio-ecological disturbances can pose for governing groundwater resources, as well as the interconnections between groundwater and surface water and the need to manage the 2 in an integrated way. Conjunctive management recognizes these interconnections and can be used to mitigate disturbances and achieve a variety of water management goals. However, comparative studies of how and to what extent various states have implemented conjunctive management strategies are few. Here we compare and assess the use of conjunctive management practices in 4 western states--Arizona, California, Nebraska, and Texas--with a particular focus on groundwater. Special attention is paid to factors of geography and infrastructure, degree of administrative (de)centralization, and monitoring and modeling in relation to conjunctive management. Despite the commonality of bifurcated regimes for groundwater and surface water, all 4 states have responded to disturbances with conjunctive management strategies in various ways. Although it has groundwater management challenges similar to those in the other 3 states, Texas has overall been slower to adopt conjunctive management strategies. [ABSTRACT FROM AUTHOR]

When surface water and groundwater resources are hydraulically connected, groundwater pumping may reduce surface water flows. In recognition of hydraulic connectivity between surface and groundwater resources, many states in the western United States have begun to develop systems of conjunctive administration in which property rights for surface water and groundwater are jointly managed. Implementing conjunctive administration requires an understanding of when and where surface and groundwater resources are connected. This article analyzes how decisions about water use and changes in irrigation technology influence connectivity across space and time, generating a challenge for policy instrument design. I develop and estimate an econometric model that reflects the simultaneity in surface and groundwater levels that arises due to the two-way flow of water in a hydraulically connected system. The model also traces the effect of changes in irrigation technology on consumptive water use and return flows, and the consequences for changes in water availability. Estimation results using a panel dataset for the Eastern Snake River Plain of Idaho from 1960 to 2011 indicate that connectivity between surface and groundwater resources has decreased over time due to declining groundwater levels. Declining groundwater levels are attributable not only to groundwater pumping, but also to a widespread shift from flood to sprinkler irrigation. This transition in irrigation technology has conserved surface water but depleted groundwater by reducing aquifer recharge. As connectivity declines, reducing groundwater pumping to augment surface water flows, a common approach to conjunctive administration, yields diminishing marginal benefits. [ABSTRACT FROM AUTHOR]

Despite recognition of the potential economic benefits and increasing interest in developing marketing instruments, water markets have remained thin and slow to evolve due to high transactions costs, third party effects, and the persistence of historical institutions for water allocation. Water banks are a marketing instrument that can address these obstacles to trade, allowing irrigators within a region to exchange water in order to mitigate the short-term effects of drought. Water banks coexist with the institutions governing water allocation, which implies that rule changes, such as adoption of a system of conjunctive surface water-groundwater administration, carry implications for the economic impacts of banking. This paper assesses and compares the welfare and distributional outcomes for irrigators in the Eastern Snake River Plain of Idaho under a suite of water management and drought scenarios. We find that water banking can offset irrigators' profit losses during drought, but that its ability to do so depends on whether it facilitates trade across groundwater and surface water users. With conjunctive administration, a bank allowing trade by source realizes 22.23% of the maximum potential efficiency gains from trade during a severe drought, while a bank that allows trade across sources realizes 93.47% of the maximum potential gains. During drought, conjunctive administration redistributes welfare from groundwater to surface water producers, but banking across sources allows groundwater irrigators to recover 88.4% of the profits lost from drought at a cost of 2.2% of the profit earned by surface water irrigators. [ABSTRACT FROM AUTHOR]

The present study develops and evaluates a decision support system for the conjunctive management of the current surface and proposed aquifer storage and recovery (ASR) facility of the city of Corpus Christi, TX using a simulation-optimization approach. The objective of the model is to maximize water storage in the surface and subsurface storage units while meeting (1) the freshwater inflow requirements to the Corpus Christi estuary and (2) the water demands of the city and its service area. The model is parameterized using streamflow data from the U. S. Geological Survey gauging stations on the Nueces River and its tributaries as well as long-term climatic data and regional hydrogeologic information. Results indicate that a single-well field ASR facility is capable of storing approximately 925 ha-m (7,500 ac-ft) of water over a 5-year period in the Evangeline Aquifer with a total potential storage of about 2,715 ha-m (22,000 ac-ft) of water over the jurisdictional area of the Corpus Christi Aquifer Storage and Recovery Conservation District. Surplus surface water sources are seen to contribute approximately 49-96 % of the water stored in the ASR during the simulation period. The remaining storage came from either Choke Canyon Reservoir or Lake Corpus Christi, which also resulted in a slight reduction in evapotranspiration in both reservoirs. The analysis indicates that the proposed ASR system is not limited on the supply side but multiple well fields may be required to increase the storage capacity within the aquifer. [ABSTRACT FROM AUTHOR]

The Pacific Northwest is expected to witness changes in temperature and precipitation due to climate change. In this study, we enhance the Snake River Planning Model ( SRPM) by modeling the feedback loop between incidental recharge and surface water supply resulting from surface water and groundwater extraction for irrigation and provide a case study involving climate change impacts and management scenarios. The new System Dynamics-Snake River Planning Model ( SD- SRPM) is calibrated to flow at Box Canyon Springs located along a major outlet of the East Snake Plain Aquifer. A calibration of the model to flow at Box Canyon Springs, based on historic diversions (1950-1995) resulted in an r2 value of 0.74 and a validation (1996-2005) r2 value of 0.60. After adding irrigation entities to the model an r2 value of 0.91, 0.88, and 0.87 were maintained for modeled vs. observed (1991-2005) end-of-month reservoir content in Jackson Lake, Palisades, and American Falls, the three largest irrigation reservoirs in the system. The scenarios that compared the impacts of climate change were based on ensemble mean precipitation change scenarios and estimated changes to crop evapotranspiration ( ET). Increased ET, despite increased precipitation, generally increased surface water shortages and discharge of springs. This study highlights the need to develop and implement models that integrate the human-natural system to understand the impacts of climate change. [ABSTRACT FROM AUTHOR]

Abstract: Groundwater discharge constitutes a significant proportion of the total flow volume in most rivers. The exchange flux between surface and groundwater greatly impacts the surface as well as the groundwater balance with serious implications on ecosystem health especially during low flow conditions. There is a move towards conjunctive river–aquifer management with the integration of surface–groundwater exchange fluxes into surface and groundwater models to manage water as a single resource. Groundwater–Surface water (GW–SW) exchange fluxes are seldom integrated into river operation and planning models. The time lags associated with the impacts of groundwater processes on nearby rivers can greatly compromise the forecasting capacity of river models especially during low flow conditions. This paper presents a conceptual framework for integrating GW–SW exchange fluxes into the new generation river operation–planning model ‘Source Integrated Modelling System’. The proposed GW–SW Link Module adopts a simple pragmatic approach for estimating the exchange fluxes between a river reach and the underlying aquifer using explicit analytical solutions. This flux becomes an inflow/outflow to that river reach and forms part of the routing and calibration processes. The exchange flux comprises four components: (1) natural exchange flux resulting from river stage fluctuations during low flow conditions, within bank and overbank fluctuations; (2) flux due to groundwater extraction; (3) flux due to changes in aquifer recharge; and (4) flux due to changes in evapotranspiration. The sum of those components during every time step dictates whether the river loses water to or gains water from the aquifer. The proposed analytical solutions were found to provide flux predictions that agree favourably with those derived from a numerical groundwater model. Recognising that the simplifying assumptions that underpin the explicit analytical solution are likely to be violated in the natural world, a suite of criteria was recommended for their use under many violating conditions related to boundary conditions, head gradients, and aquifer heterogeneity. Low flow indices were adopted to demonstrate the critical role of GW–SW exchange flux when predicting river low flows. Explicit accounting of GW–SW interactions into river operation and planning models greatly enhances their forecasting capacity during low flow conditions. [Copyright &y& Elsevier]

This article examines what is generally considered to be an unattainable goal in the western United States: integrated water resources management (IWRM). Specifically, we examine an organization that is quite unique in the West, Montana's Clark Fork River Basin Task Force (Task Force), and we analyze its activities since its formation in 2001 to answer the question: are the activities and contributions of the Task Force working to promote a more strongly integrated approach to water resources management in Montana? After reviewing the concepts underlying IWRM, some of the issues that have been identified for achieving IWRM in the West, and the Montana system of water right allocation and issues it faces, we adapt Mitchell's IWRM framework and apply it to the analysis of the Task Force's activities in the context of IWRM. In evaluating the physical, interaction, and protocol/planning/policy components of IWRM, we find that the Task Force has been contributing to the evolution of Montana's water resources management towards this framework, though several factors will likely continue to prevent its complete realization. The Task Force has been successful in this regard because of its unique nature and charge, and because of the authority and power given it by successive Montana legislatures. Also critical to the success of the organization is its ability to help translate into policy the outcomes of legal and quasi-judicial decisions that have impacted the state's water resources management agency. [ABSTRACT FROM AUTHOR]

This study develops a production well management model for the conjunctive management of water resources in semi-arid areas. The management model integrates a large-scale pressurized water distribution system and a three-dimensional groundwater model under an optimization framework. The well pump operations optimization problem is formulated as a Boolean integer nonlinear programming (BINLP) problem to optimize the periodic 24-h pump on/off operations over a 1-week operation horizon. The management model considers multiple objectives and is solved by a parallel genetic algorithm (PGA) to overcome the difficulty of solving the BINLP problem. The PGA significantly reduces computation time for a case study in Chandler, Arizona. The Chandler water distribution model is built based on EPANET, and the Chandler three-dimension groundwater model is developed using MODFLOW. The high performance computing (HPC) of the genetic algorithm makes it possible to obtain 24-h real-time operations in the 7-day forecast model. The tank reliability, resilience, and vulnerability (R-R-V) are evaluated to infer the system reliability. The Pareto curve provides compromise solutions between the two competing objectives of energy reduction and pressure violation reduction. [ABSTRACT FROM AUTHOR]

The Salt River Project (SRP) was created in the early 1900s to assure an adequate water supply for its shareholders in the Salt River Valley, Arizona, USA. The straight forward job of storing inflows and meeting demand from a single reservoir system soon became more complex. As the population of the Salt River Valley swelled, additional reservoirs were added to the system, alternative supplies of water were developed, and hydro-power generation became a financial consideration in reservoir operations. Nevertheless, the primary operational objective continues to be the conjunctive management of multiple sources of water to ensure an adequate carry-over supply of water for SRP’s shareholders in the Salt River Valley. This objective has traditionally been accomplished by managing the reservoir system as if each time the reservoirs fill to capacity is the beginning of an extended drought comparable to the worst historical drought in recorded history. Over the past 20 years, several subtle yet significant events have taken place which raise concerns regarding SRP’s traditional method of water planning and management. Changes in demand patterns as land is converted from mainly agricultural use to urban use, an ongoing drought rivaling the historical drought of record, tree-ring studies suggesting even more severe droughts having occurred in pre-historic times and, the specter of a changing climate due to global warming all suggest that a business as usual approach to water management and planning may no longer be appropriate. [ABSTRACT FROM AUTHOR]

The article provides information on the progress in water-balance planning and the supply of environmental flows to ground water-dependent ecosystems. Most rivers, lakes and wetlands are fed to varying degrees by groundwater. Through percolation, soil moisture is fed by ground water. According to the Australian water agencies in September 2007, there are two core ground water policy commitments for water management plans which include the use of a conjunctive water balance and providing environmental water allocations to ground water-dependent ecosystems. However, relevant ecological values should be identified and scientific evidence associating to necessary water regimes be referenced and concisely discussed within water allocation plans or related planning documents.

Groundwater resources (GW) account for nearly 30% of the world's sustainable water supplies. Yet, this resource, which is fraught with externalities, has largely been left unregulated. The economic literature on GW is predominantly of a partial equilibrium type. We analyze GW regulation in a general equilibrium setting, focusing on the stabilization value of GW under natural (drought) and economic (rural–urban water transfer) shocks. A general equilibrium approach allows evaluating direct and indirect effects of GW regulation on agriculture and nonagriculture sectors and extends the scope for water policy. The analysis is applied to Morocco by extending an existing computable general equilibrium (CGE) model to include ground and surface water (SW) resources. We study effects of (i) an increase in GW extraction cost (e.g., as a result of prolonged extraction beyond natural recharge that lowers the aquifer's water table), (ii) a transfer of SW from rural (irrigation) to urban (domestic) use, and (iii) a reduction of water availability due to severe drought. We estimate the value of GW and assess the direct (partial equilibrium) and indirect (general equilibrium) impacts. We find that GW plays a critical role in mitigating the negative effects of these types of shocks. [ABSTRACT FROM AUTHOR]

Changes in irrigation and land use may impact discharge of the Snake River Plain aquifer, which is a major contributor to flow of the Snake River in southern Idaho. The Snake River Basin planning and management model (SRBM) has been expanded to include the spatial distribution and temporal attenuation that occurs as aquifer stresses propagate through the aquifer to the river. The SRBM is a network flow model in which aquifer characteristics have been introduced through a matrix of response functions. The response functions were determined by independently simulating the effect of a unit stress in each cell of a finite difference groundwater flow model on six reaches of the Snake River. Cells were aggregated into 20 aquifer zones and average response functions for each river reach were included in the SRBM. This approach links many of the capabilities of surface and ground water flow models. Evaluation of an artificial recharge scenario approximately reproduced estimates made by direct simulation in a ground water flow model. The example demonstrated that the method can produce reasonable results but interpretation of the results can be biased if the simulation period is not of adequate duration. [ABSTRACT FROM AUTHOR]

The conjunctive management of surface water and groundwater resources is essential to sustainably manage water resources. The target study is the Osan watershed, in which approximately 60–70% of rainfall occurs during the summer monsoon in Central South Korea. Surface water resources are overexploited six times as much as groundwater resources in this region, leading to increasing pressure to satisfy the region's growing agricultural water demand. Therefore, a simulation-optimization (S-O) model at the sub-basin scale is required to optimize water resource allocation in the Osan watershed. An S-O model based on an artificial neural network (ANN) model coupled with Jaya algorithm optimization (JA) was used to determine the yearly conjunctive supply of agricultural water. The objective was to minimize the water deficit in the watershed subject to constraints on the cumulative drawdown in each subarea. The ANN model could predict the behaviour of the groundwater level and facilitate decision making. The S-O model could minimize the water deficit by approximately 80% in response to the gross water demand, thereby proving to be suitable for a conjunctive management model for water resource management and planning. [ABSTRACT FROM AUTHOR]