Coastal Aquifer Management Research Articles

Saltwater intrusion simulations in coastal karstic aquifers related to climate change scenarios

Coastal zones are crucial ecosystems supporting significant biodiversity and pertinent socio-economic activities. However, anthropogenic development contributes to socio-environmental complexities, particularly public water supply threats caused by climate change. This research presents a case study on the north-western coast of Yucatan, Mexico, which models potential saltwater intrusion in groundwater for multiple projections of sea level rise and recharge change due to climate change and its implications for the public water supply of the regional population and ecosystem. For this purpose, a previously calibrated and validated numerical model is employed, adapting its boundary conditions, keeping its calibrated hydrogeologic parameters, and considering the 2040 and 2100 climate change projections. Simulation results show that under these projections, significant saltwater intrusion may occur, reducing freshwater thickness due to increased salinity in groundwater and a loss of freshwater sources resulting from brackish-saline wedge intrusion. These scenarios are of particular concern as freshwater in this coastal region is the main source for public water supply and for freshwater input in coastal ecosystems. Moreover, this study underscores the susceptibility of karstic aquifers to salinization, especially in the face of rising sea levels, given their unique hydrogeological characteristics and substantial responsiveness to marine forcings. In spite of the uncertainties in global climate change predictions, this study enhances our understanding of the dynamics of these unique aquifers, and presents future saltwater intrusion projections that offer valuable technical insights to design and implement pertinent and resilient coastal aquifer management strategies.

Groundwater Flow Model Calibration Using Variable Density Modeling for Coastal Aquifer Management

The paper investigates the mechanism of seawater intrusion and the performance of free and open-source codes for the simulation of variable density flow problems in coastal aquifers. For this purpose, the research focused on the Marathon Watershed, located in the northeastern tip of Attica, Greece. For the simulation of the groundwater system, MODFLOW, MT3DMS and SEAWAT codes were implemented, while sensitivity analysis and calibration processes were carried out with UCODE. Hydraulic head calibration was performed on the MODFLOW model, and TDS concentration was validated in the SEAWAT model. The calibrated parameters of the MODFLOW model were obtained for the variable density flow simulation with SEAWAT. The MODFLOW and SEAWAT hydraulic head outputs were analyzed and compared to one another. The outcome of this analysis is that SEAWAT produced slightly better results in terms of the hydraulic heads, concluding that parameter transferability can take place between the two models. For the purpose of the seawater intrusion assessment, the use of the SEAWAT code revealed that the aquifer is subjected to passive and passive–active seawater intrusion during wet and dry seasons, respectively. Finally, an irregular shape of a saltwater wedge is developed at a specific area associated with the hydraulic parameters of the aquifer.

Estimation of Ground Water Recharge in the Command Area of Krishna Central Delta

Groundwater recharge is the most important component in all the water balance studies and in ground water development projects as a part of sustainable groundwater management. Norms set by the Groundwater Resource Estimation Committee, GEC-2015 was used for the estimation of recharge. The study was conducted for the Bandar canal command area constituting the Krishna Central Delta in Andhra Pradesh. Following the norms of GEC-2015, the recharge was estimated for the past decade from 2012-13 to 2021-22 and it was found that recharge rate ranged from 438135.8 ha-m in the year 2015-16 to 1677730 ha-m in the year 2013-14. While computing the gross recharge, recharge attributed by rainfall, canal seepage, irrigation return flow and from the ponds/tanks are considered. Recharge estimated sheds information on replenishment and improved management of coastal aquifers where seawater intrusion is a major problem.

Coastal Aquifer Management: Hydrological, Environmental, Economic and Social Challenges in the Context of Global Change

Groundwater is limited and its sustainable use is peremptory if we are to preserve dependent ecosystems and human supplies [...]

An adaptive multi-fidelity optimization framework based on co-Kriging surrogate models and stochastic sampling with application to coastal aquifer management

Surrogate modelling has been used successfully to alleviate the computational burden that results from high-fidelity numerical models of seawater intrusion in simulation-optimization routines. Nevertheless, little attention has been given to multi-fidelity modelling methods to address cases where only limited runs with computationally expensive seawater intrusion models are considered affordable imposing a limiting factor for single-fidelity surrogate-based optimization as well. In this work, a new adaptive multi-fidelity optimization framework is proposed based on co-Kriging surrogate models considering two model fidelities of seawater intrusion. The methodology is tailored to the needs of solving pumping optimization problems with computationally expensive constraint functions and utilizes only small high-fidelity training datasets. Results from both hypothetical and real-world optimization problems demonstrate the efficiency and practicality of the proposed framework to provide a steep improvement of the objective function while it outperforms a comprehensive single-fidelity surrogate-based optimization method. The method can also be used to locate optimal solutions in the region of the global optimum when larger high-fidelity training datasets are available.

Performance comparison of physics-based and machine learning assisted multi-fidelity methods for the management of coastal aquifer systems

In this work we investigate the performance of various lower-fidelity models of seawater intrusion in coastal aquifer management problems. The variable density model is considered as the high-fidelity model and a pumping optimization framework is applied on a hypothetical coastal aquifer system in order to calculate the optimal pumping rates which are used as a benchmark for the lower-fidelity approaches. The examined lower-fidelity models could be classified in two categories: (1) physics-based models, which include several widely used variations of the sharp-interface approximation and (2) machine learning assisted models, which aim to improve the efficiency of the SI approach. The Random Forest method was utilized to create a spatially adaptive correction factor for the original sharp-interface model, which improves its accuracy without compromising its efficiency as a lower-fidelity model. Both the original sharp-interface and Machine Learning assisted model are then tested in a single-fidelity optimization method. The optimal pumping rated which were calculated using the Machine Learning based SI model sufficiently approximate the solution from the variable density model. The Machine Learning assisted approximation seems to be a promising surrogate for the high-fidelity, variable density model and could be utilized in multi-fidelity groundwater management frameworks.

Optimal management of the groundwater coastal aquifer based on the hydraulic characteristics in Wadi Al Marwani basin: KSA

Optimal management of the groundwater coastal aquifer based on the hydraulic characteristics in Wadi Al Marwani basin: KSA

Ant-Inspired Metaheuristic Algorithms for Combinatorial Optimization Problems in Water Resources Management

Ant-inspired metaheuristic algorithms known as ant colony optimization (ACO) offer an approach that has the ability to solve complex problems in both discrete and continuous domains. ACOs have gained significant attention in the field of water resources management, since many problems in this domain are non-linear, complex, challenging and also demand reliable solutions. The aim of this study is to critically review the applications of ACO algorithms specifically in the field of hydrology and hydrogeology, which include areas such as reservoir operations, water distribution systems, coastal aquifer management, long-term groundwater monitoring, hydraulic parameter estimation, and urban drainage and storm network design. Research articles, peer-reviewed journal papers and conference papers on ACO were critically analyzed to identify the arguments and research findings to delineate the scope for future research and to identify the drawbacks of ACO. Implementation of ACO variants is also discussed, as hybrid and modified ACO techniques prove to be more efficient over traditional ACO algorithms. These algorithms facilitate formulation of near-optimal solutions, and they also help improve cost efficiency. Although many studies are attempting to overcome the difficulties faced in the application of ACO, some parts of the mathematical analysis remain unsolved. It is also observed that despite its popularity, studies have not been successful in incorporating the uncertainty in ACOs and the problems of dimensionality, convergence and stability are yet to be resolved. Nevertheless, ACO is a potential area for further research as the studies on the applications of these techniques are few.

Simulation-based multi-objective optimization framework for sustainable management of coastal aquifers in semi-arid regions

Groundwater is a strategic source of water supply, especially in arid and semi-arid coastal regions. Growing demand, along with scarce water sources, may impose intense pressure on this precious resource. This pressure will degrade water quality for future use and cause social inequality, despite supplying current needs. A novel sustainable management model for water allocation is developed to address these interconnected concerns in coastal aquifers. Three aspects of sustainable development are considered: groundwater quality with total dissolved solids (TDS) indicator for the environmental part, gross value added from water for the economic efficiency, and the Gini coefficient for social inclusion and equity. The problem is solved with a simulation-based multi-objective optimization framework using a numerical variable-density simulation code and three approved evolutionary algorithms, NSGA-II, NRGA, and MOPSO. The obtained solutions are integrated to enhance the solutions' quality by using each algorithm's strengths and dominated members' elimination. In addition, the optimization algorithms are compared. The results showed that NSGA-II is the best in terms of solutions quality, with the least number of total dominated members (20.43%) and a 95% success rate of obtained Pareto front. NRGA was supreme in finding extreme solutions, the least computational time, and diversity, with an 11.6% higher diversity value than the second competitive NSGA-II. MOPSO was the best in spacing quality indicator, followed by NSGA-II, showing their great arrangement and evenness in obtained solution space. MOPSO has the propensity for premature convergence and needs more stringent stopping criteria. The method is applied to a hypothetical aquifer. Still, the obtained Pareto fronts are determined to assist decision-makers in real-world coastal sustainable management problems by illustrating existing patterns among different objectives.

Coastal urban reliance on groundwater during drought cycles: Opportunities, threats and state of knowledge

Abstract Urbanisation and population growth are concentrated on the coast with approximately 40% of the human population living within 100 km of the ocean. The freshwater systems on which coastal urban areas rely are vulnerable to bidirectional pressures including coastal processes such as sea-level rise and coastal erosion coupled with land use changes and pollution occurring in inland catchment areas. These threats are likely to be amplified in the future under climate change conditions and more frequent and severe drought periods are expected to jeopardise already constrained water supply systems. Groundwater is used as a freshwater resource globally and is especially important as a conjunctive supply during drought periods due to perceived buffer capabilities. However, several threats impact coastal aquifers due to over-abstraction, such as salinisation, land subsidence and groundwater flooding and often these subterranean resources are “out of sight and out of mind” when it comes to management strategies. Here, we present an assessment of current issues and management options relevant to coastal aquifers using recent literature. These insights provide knowledge on global issues relevant to groundwater resources, especially regarding water use during droughts. This is exemplified using a South African case study of two metropolitan municipalities that have experienced or are experiencing severe multi-year droughts. Both municipalities have grappled with the depletion of surface water resources, which constitutes the bulk of the local water supply systems. Consequently, groundwater resources have been explored as an augmentation strategy. Although groundwater resources may be useful in alleviating drought effects, it is crucial that a local understanding of the aquifers is developed through baseline hydrological studies and long-term monitoring. Furthermore, unregistered groundwater use needs to be quantified. Finally, a holistic groundwater management view, and the communication thereof, is required to ensure the sustainable management of coastal aquifers.

Analyzing spatial and temporal evolution of groundwater salinization through Multivariate Statistical Analysis and Hydrogeochemical Facies Evolution-Diagram

The growing groundwater withdrawal rates in coastal aquifers in arid/semi-arid regions exacerbate seawater intrusion and saltwater upconing by causing groundwater salinization and potential adverse and cascading effects to related groundwater-depending systems. This study aims to highlight the dynamics of groundwater salinization in time and space by comparing the efficacy of statistical (hierarchical cluster and factor analyses) and hydrogeochemical (hydrogeochemical facies evolution) methods. Multi-temporal groundwater samples collected from the monitoring well network in the study area (Salento Aquifer, Puglia region, Southern Italy) have been considered to recognize such dynamics. By comparing the spatial and temporal evolution of water clusters, factor scores, and hydrogeochemical facies, the proposed methodological approach enables the identification of zones characterized by low dynamics of freshening and intrusion processes (with invariant features during the investigated period), which correspond to groundwater recharge areas and zones subject to groundwater salinization respectively. On the contrary, a high spatial and temporal variability of salinization dynamics typifies the zones subject to alternation of groundwater characteristics. These results allow outlining a preliminary hazard map related to groundwater salinization processes, which might be a useful tool for policymakers and stakeholders involved in groundwater management of coastal aquifers. Results suggest that generally, a thoughtful understanding of limitations concerning the aquifer heterogeneity and anisotropy, distribution and density of control points, and depth of sampling is crucial for handling the study outcomes, especially for the aims of management.

Challenges and approaches for management of seawater intrusion in coastal aquifers

Coastal aquifers provide water for over one billion people worldwide; however, they face seawater intrusion due to overpumping. The current and future challenges of coastal aquifer management involve issues such as climate change and the control of abstraction and recharge. Different management approaches are being used globally to prevent aquifer salinization. This essay presents the challenges and possible solutions while also discussing the different approaches and their needs for improvement.

Analytical solutions for seawater intrusion and the maximum pumping rate of a well in unconfined coastal aquifers bounded by L-shaped coastlines

Determining the maximum pumping rate (i.e., the maximum allowable pumping rate that does not cause seawater intrusion into the well under the steady-state condition) of a well is the key for sustainable management of coastal aquifers, as overexploitation of coastal aquifers could lead to the widespread occurrence of aquifer salinization (i.e., seawater intrusion). In this study, we develop steady-state analytical solutions to describe seawater intrusion and the maximum pumping rate of a well located in unconfined coastal aquifers bounded by L-shaped coastlines. Rectangular coastal aquifers bounded by two orthogonal constant-head boundaries (i.e., two coastlines) and two orthogonal no-flow inland boundaries are assumed in conceptual models, where replenishment of aquifers is via surface recharge. Analytical solutions are derived by the potential theory and the conformal mapping method, and validated by variable-density flow numerical simulations. It is found that analytical solutions based on the sharp-interface approximation overestimate seawater intrusion and underestimate the maximum pumping rate. An acceptable, conservative maximum pumping rate is obtained by using the correction factor proposed by Lu and Werner (2013). Moreover, the sensitivity of the well location on the maximum pumping rate is investigated, showing that an optimal well location exists. Analytical solutions developed in the current study provide a convenient tool for assessing pumping effects in coastal aquifers bounded by L-shaped coastlines, servicing to various management objectives.

Investigation of the impact of the implementation of the coastal aquifer management plan on nitrate pollution in Gaza Strip Aquifer using modeling techniques

Groundwater is the principal source of public water supply and for satisfying the daily water needs. The Gaza strip coastal aquifer is suffering from salinity and contamination due to human activities especially agriculture activities. Although, the nitrate is necessary for agriculture activities it can affect the groundwater quality if leached nitrate from the soil into freshwaters after some time. The main objective of this research is to evaluate the current situation of the Gaza strip coastal aquifer and to predict the nitrate concentrations resulting from agriculture activities over the next twenty years using modelling approach. 3D Numerical groundwater flow modeling was developed to simulate the impacts of transport of nitrate loading from agricultural land on groundwater system using finite difference method GMS 10.4 software (MODFLOW 2005 code and MT3DMS package). Five management scenarios were considered to study the effect of pumping and recharge parameters on the groundwater flow system and the impacts of transport of nitrate loading from agricultural areas on the aquifer. Ten different wells were selected to investigate the impact of management scenarios on the nitrate concentration. All management scenarios indicated that there is a relationship between the water level and nitrate concentration in aquifer therefore the rates of nitrate concentration in the southern regions of Gaza strip is more than the northern regions.

Optimal management of mixed hydraulic barriers in coastal aquifers using multi-objective Bayesian optimization

• Optimum mixed hydraulic barriers location and rate obtained by Bayesian optimization. • Constrained multi-objective Bayesian optimization solved coastal management problem. • BO with few evaluations outperforms NSGA-II with a large number of evaluations. • Injection barriers have higher control over the remediation system. • Abstraction barriers useful as an alternative source of water. Mixed hydraulic barriers is an effective method to control seawater intrusion (SWI), particularly in regions that suffer from water shortages. However, determining the optimal well locations and rates for injection and abstraction is challenging due to the computational burden resulting from the huge number of calls for the high-fidelity hydrogeological simulation model. To alleviate this issue, we utilized a constrained multi-objective Bayesian optimization (BO) approach to optimize rates and locations of the hydraulic barriers to minimize total cost, aquifer salinity, and salt-wedge intrusion length, while satisfying regional abstractions with acceptable salinity levels. BO is useful for optimizing computationally expensive problems in few iterations by using a surrogate model and an acquisition function. Despite being an efficient optimization tool, the use of BO in the field of coastal aquifer management has not been explored. The proposed framework was evaluated on an unconfined aquifer subjected to three management scenarios considering different physical and technical constraints and was benchmarked against the widely used robust NSGA-II (Non-dominated Sorting Genetic Algorithm II) method. The results proved the effectiveness of BO in achieving an optimum mixed hydraulic barriers design in much fewer runs of the variable density aquifer model. BO with 350 evaluations yielded comparable results to 4150 evaluations using NSGA-II. BO solutions were spatially well-distributed along the approximated Pareto front. For the same number of evaluations, the hypervolume obtained by BO was larger by 30%. Based on different scenarios, the average amount of water required for abstraction ranged from 1.5% to 25% of that for injection. The injection has a significant impact on SWI management, but the abstracted water provides an alternative source of water. A sensitivity analysis was conducted on the optimization problem to illustrate its efficiency by omitting the barriers one at a time and assessing impacts on objective and constraint functions.

Cost-effective management measures for coastal aquifers affected by saltwater intrusion and climate change.

Sustainable management of natural water resources and food security in the face of changing climate conditions is critical to the livelihood of coastal communities. Increasing inundation and saltwater intrusion (SWI) will likely adversely affect agricultural production and the associated beach access for tourism. This study uses an integrated surface-ground water model to introduce a new approach for retardation of SWI that consists of placing aquifer fill materials along the existing shoreline using Coastal Land Reclamation (CLR). The modeling results suggest that the artificial aquifer materials could be designed to decrease SWI by increasing the infiltration area of coastal precipitation, collecting runoffs from the catchment area, and applying treated wastewater or desalinated brackish water-using coastal wave energy to reduce water treatment costs. The SEAWAT model was applied to verify that it correctly addressed Henry's problem and then applied to the Biscayne aquifer, Florida, USA. In this study, to better inform Coastal Aquifer Management (CAM), we developed four modeling scenarios, namely, Physical Surface Barriers (PSB), including the artificial aquifer widths, permeability, and side slopes and recharge. In the base case scenario without artificial aquifer placement, results show that seawater levels would increase aquifer salinity and displace large amounts of presently available fresh groundwater. More specifically, for the Biscayne aquifer, approximately 0.50% of available fresh groundwater will be lost (that is, 41,192 m3) per km of the width of the aquifer considering the increasing seawater level. Furthermore, the results suggest that placing the PSB aquifer with a smaller permeability of <100 m per day at a width of approximately 615 m increases the available fresh groundwater by approximately 45.20 and 43.90% per km of shoreline, respectively. Similarly, decreasing the slope on the aquifer-ocean side and increasing the aquifer recharge will increase freshwater availability by about 43.90 and 44.50% per km of the aquifer. Finally, placing an aquifer fill along the shallow shoreline increases net revenues to the coastal community through increased agricultural production and possibly tourism that offset fill placement and water treatment costs. This study is useful for integrated management of coastal zones by delaying aquifer salinity, protecting fresh groundwater bodies, increasing agricultural lands, supporting surface water supplies by harvesting rainfall and flash flooding, and desalinating saline water using wave energy. Also, the feasibility of freshwater storage and costs for CAM is achieved in this study.

Evaluation of strategies for pumping optimization of coastal aquifers using numerical simulation and game theory

In this study, after simulating 5 years of saltwater intrusion with SEAWAT package in Astaneh–Kouchesfahan coastal aquifer, Iran, 19 strategies, including managerial, structural, and combined strategies, were investigated to reduce the saltwater intrusion. Since managerial solutions cause users’ dissatisfaction and structural solutions increase the costs, two-player game theory was used to identify the most appropriate solution. According to the results obtained from game theory, the two strategies of implementing artificial recharge and the construction of an underground dam had the greatest impact on preventing the saltwater intrusion with the highest satisfaction of stakeholders, and these strategies decreased the extent of saltwater intrusion into the aquifer from 740 m by 150 and 300 m, respectively, after 5 years. Therefore, the combined simulator–optimizer method presented in this study can be used to evaluate various solutions, and the most appropriate solution can be proposed with the lowest cost and maximum satisfaction for the sustainable management of coastal aquifers.

Simulating the effects of model parameters on stagnation points position during seawater intrusion.

Several works have been performed in order to understand seawater intrusion by simulating the Henry problem. Investigations were implemented by simulating the effect of many parameters (fractured aquifer, dispersion and diffusion, geochemical reactions, heterogeneity, anisotropy, boundary conditions) on the flow and transport. This paper focus on the concept of the "stagnation point," and this concept plays an important role in modeling, management and characterization of coastal aquifer. A total of forty-eight simulations, including the base case, were made to explore the effect of molecular diffusion coefficient, dispersivity, and seawater density on the position of the stagnation point. It was found that the increase of the molecular diffusion coefficient or the dispersivity leads to a downward displacement of the stagnation to the aquifer bottom and the lowest point position is reached for a Pe value of 0.35. For the seawater density effect, numerical results predict a nonlinear behavior of the stagnation point position, where the downward displacement is detected only for a ρs ranging from 1025 to 1045kg/m3.

Complex or Simple—Does a Model Have to be One or the Other?

The primary tasks of decision-support modelling are to quantify and reduce the uncertainties of decision-critical model predictions. Reduction of predictive uncertainty requires assimilation of information. Generally, this information resides in two places: 1) expert knowledge emerging from site characterization and 2) field measurements of present and historical system behavior. The former is uncertain and should therefore be expressed stochastically in a model. The range of parameter and predictive possibilities can then be constrained through history-matching. Implementation of these Bayesian principles places conflicting demands on the level of model structural complexity. A high level of structural complexity can facilitate expression of expert knowledge by establishing model details that are recognizable by site experts, and through supporting model parameters that bear a close relationship to real-world hydraulic properties. However, such models often run slowly and are numerically delicate; history-matching therefore becomes difficult or impossible. In contrast, if endowed with enough parameters, structurally simple models facilitate the achievement of a good fit between model outputs and field measurements. However, the values with which parameters are endowed may bear a looser relationship with real-world properties and are therefore less receptive to information born of expert knowledge. The model design process is therefore one of compromise. In this paper we describe a methodology that reduces the cost of compromise by allowing expert knowledge of system properties to inform the parameters of a structurally simple model. The methodology requires the use of a complementary model of strategic, but not excessive, structural complexity that is stochastic, fast-running and requires no history-matching. We demonstrate the approach using a real-world case in which modelling is used to support management of a stressed coastal aquifer. We empirically validate the approach using a synthetic model.

Optimal management of coastal aquifers using artificial jellyfish search algorithm

In the current study, a simulation-optimization model is presented using a new metaheuristic optimization algorithm called artificial Jellyfish Search (JS) to develop sustainable saltwater intrusion optimal management strategies for coastal aquifers. The simulation model is based on the finite element method (FEM). The effectiveness of the proposed model is tested by application to the real aquifer system of Miami Beach aquifer, Spain with management decisions of maximizing the total economic benefit and the total pumping rate. The model is also applied to the case study of El-Arish Rafah aquifer, Egypt to maximize the total pumping rate. The results of both cases are compared to that obtained by using genetic algorithm (GA), probabilistic global search Lausanne (PGSL), shuffled frog leaping (SFL) and particle swarm optimization (PSO). The efficiency rate metric and statistical indices are used to assess the performance of the proposed model. For Miami Beach aquifer, an optimal benefit of 24.93 ($/d) was obtained and which is equivalent to that by PSO and SFLA but higher than that of GA and PGSL and with the highest pumping rate of 5544.62 (m3/s). The model also had the highest efficiency rates compared to PSO, PGSL and SFLA. For El-Arish Rafah aquifer, a maximum optimal pumping rate of 55,619.43 (m3/s) is determined. The results show that the model can be considered as an effective and efficient management tool.