Saltwater Intrusion Management Research Articles

Management of Saltwater Intrusion in Coastal Aquifers: A Review and Case Studies from Egypt

Management of Saltwater Intrusion in Coastal Aquifers: A Review and Case Studies from Egypt

Integrating numerical modelling and scenario-based sensitivity analysis for saltwater intrusion management: case study of a complex heterogeneous island aquifer system

Population growth, industrialisation and increasing agricultural demands have significantly stressed groundwater resources in Pacific Island countries (PICs). Climate change and sea-level rise also affect the groundwater resources in PICs. These anthropogenic and natural factors give rise to saltwater intrusion (SWI), a major growing environmental problem in the PICs. SWI is a highly non-linear process which makes it more complex to manage. However, with the help of numerical modelling, SWI can be monitored, managed and controlled. In the present study, we used an illustrative study area where the hydrogeological parameters and other boundary conditions used are similar to the PICs aquifer systems in Vanuatu. The scenarios include changing the barrier wells, injection wells, recharge, hydraulic head, hydraulic conductivity and grid size. The numerical simulation model of the study area was developed, and different scenarios were tested using SEAWAT modules. Apart from salt, we also modelled leachate and engine oil present in the investigated study area to see how it affects the freshwater wells over time. The scenario-based sensitivity analysis tests indicate that injection wells, recharge and hydraulic conductivities are highly sensitive, and with the proper modification, SWI can be managed or regulated. The sensitivity of grid size showed that the simulated results varied within the 10% range of different gird sizes. Moreover, it was also found that the rise in sea level or coastal heads by 0.3–1 m does not significantly cause further SWI encroachment in aquifers. The results from this study are very crucial in this modern era when freshwater needs in coastal areas, especially PICs, are rapidly increasing, and fresh groundwater resources are declining. The novel outcome presented in this study opens pathways for further detailed modelling and numerical studies in the field of SWI management strategy development and is, therefore, beneficial for policymakers, groundwater modellers and general scientific communities.

Saltwater intrusion management at different coastal aquifers bed slopes considering sea level rise and reduction in fresh groundwater storage

Coastal fresh groundwater management is a challenging research topic due to the relevance of these resources and the huge suffered risks due to global change and overpopulation. The geometrical features of coastal aquifers play a control role in saltwater intrusion (SWI). Seawater level rise and the reduction in aquifer fresh groundwater storage are promoting SWI. All these key factors are considered with two different numerical approaches defining schematic management criteria bottom using the numerical code SEAWAT. The former approach adopts the well-known Henry’s problem; the latter is based on the real study case of the Gaza aquifer (Palestine). Different aquifer bed slopes (ABS), and hydraulic and physical methods for SWI management are considered together with SLR, recharge reduction, and over pumping. The results showed that the land side ABS cases show more SWI than sea side and horizontal ABS. Cut-off walls and check dams are effective to manage SWI in horizontal ABS more than in other slopes, also the subsurface dams, earth fill and recharge of freshwater are good methods in land side ABS while the abstraction of brackish water and combination of recharge with abstraction are better to mitigate of SWI in sea side ABS. Useful comparing tables and considerations are defined with the purpose to guide the preliminary selections of new management solutions for reducing the effect of the global change on groundwater resources for different slopes aquifers around the coastal world.Graphical abstract

Management of Saltwater Intrusion in Coastal Karstic Aquifers under Geological Uncertainties Associated with Shapes and Locations of Cave Networks

Management of Saltwater Intrusion in Coastal Karstic Aquifers under Geological Uncertainties Associated with Shapes and Locations of Cave Networks

Inclined Physical Subsurface Barriers for Saltwater Intrusion Management in Coastal Aquifers

Inclined Physical Subsurface Barriers for Saltwater Intrusion Management in Coastal Aquifers

Saltwater intrusion management in shallow and deep coastal aquifers for high aridity regions

Study regionThe current study was applied on two extensive and important regional aquifers: the first is the shallow aquifer of Gaza coastal aquifer (GCA), Palestine and the second is the deep aquifer of the Nile Delta (NDA), Egypt. The two sites are suffering from high stress water resource and contamination by saltwater intrusion (SWI). SWI is natural phenomena that damage the fresh groundwater in two sites and increase the aquifer. Shallow and deep aquifer plays a natural role for keeping the quality of freshwater from SWI in costal aquifers. This study aims to compare different methods for aquifer protection from SWI by analyzing their efficiency using numerical groundwater models in the two sites. Study focusThe finite difference for density dependent groundwater flow model SEAWAT was used on two sites to investigate the extension of SWI without management (base case) and the four methods to control SWI. The numerical models were calibrated for the base case using the other studies and field data to simulate the intrusion in GCA and NDA. The investigated four methods focused on (1) subsurface physical barriers of Cut-off walls), (2) subsurface physical barriers of subsurface dams, (3) the hydraulic method including Treatment and Recharge of collected wastewater, Abstraction and Desalination of low salinity by brackish water, and (4) the land reclamation using earth fill method. New hydrological insights for the regionThe simulated results indicated for the base cases that the intrusion salt mass (NaCl) reached 6068 × 103 kg for GCA and 8863 × 1010 kg for NDA. Moreover, the percentage of aquifer salt mass was decreased and reached 17.60%;, 23.30%; 7.85% and 6.20% in for shallow aquifer while it reached 2.05%; 0.90%; 5.30% and 0.80% in deep aquifer for the physical subsurface dam of cut-off wall, subsurface dam, hydraulic method and land reclamation technique respectively. On the other side the control methods in shallow aquifers is more effective than the deep one. The subsurface barriers and land fill method isn’t effective for deep aquifer while the hydraulic of TRAD method has a positive effect on SWI in shallow and deep aquifers. The current study could be carried out around the world in different coastal hydrological groundwater thickness using the effective method to increase the mitigation of SWI and increase the fresh groundwater resources in coastal aquifers.

Reliability in Multi-Objective Management of Saltwater Intrusion under Uncertainly of Hydraulic Conductivities. (Dept. C)

Reliability in Multi-Objective Management of Saltwater Intrusion under Uncertainly of Hydraulic Conductivities. (Dept. C)

Management of Saltwater Intrusion in Data-scarce Coastal Aquifers: Impacts of Seasonality, Water Deficit, and Land Use

Management of Saltwater Intrusion in Data-scarce Coastal Aquifers: Impacts of Seasonality, Water Deficit, and Land Use

Sustainable saltwater intrusion management in coastal aquifers under climatic changes for humid and hyper-arid regions

Saltwater Intrusion (SWI) in many coastal areas is accelerated by freshwater boundary changes due to over-pumping and decreasing aquifer recharge and sea-level rise. This study aims to control SWI due to the rise in sea levels in three climate regions: (i) humid and wet regions using storage dams at different heads and recharge ponds, (ii) hyper-arid and arid regions using physical barriers and wastewater treatment aquifer, brackish water abstraction, and desalination (TRAD) method, and (iii) semi-arid and semi-humid regions using a combination of flooding water recharge well-field and cut-off wall. The study was developed using the world benchmark problem of Henry's problem and Biscayne aquifer in the Cutler Ridge area near Deering Estate, Florida, USA. The finite-difference code SEAWAT was used in numerical simulations. The numerical results indicated that increasing the artificial recharge lake capacity minimizes the SWI in humid and wet regions with a high level of flooding. Moreover, the intrusion is mitigated using physical barriers and the TRAD method for hyper-arid and arid regions. Combining physical barriers during dry seasons and recharge wells for wet seasons resulted in suitable measures to managed the SWI in semi-arid and semi-humid regions. Finally, the best strategy to mitigate the SWI and minimize the desalination costs depends on the precipitation rates. Therefore, the methodology applied to this study represents a valuable tool in order to select the best method based on the climate conditions and particularly the precipitation intensity to increase the water budget in freshwater aquifers.

Management of saltwater intrusion in coastal aquifers using different wells systems: a case study of the Nile Delta aquifer in Egypt

Saltwater intrusion (SWI) is a type of pollution that adversely affects the quality of groundwater in coastal aquifers. The Nile Delta aquifer (NDA) in Egypt contains a large amount of freshwater. Increasing abstraction from the aquifer and sea level rise have led to an increase in SWI, which has reached up to 100 km inland. Therefore, practical measures are required to prevent further SWI. This study aims to identify an optimal well system to manage the intrusion of saline water in NDA using a number of management systems, including pumping of brackish water, aquifer recharge, and abstraction of the freshwater. SEAWAT code is used to simulate SWI in the aquifer considering different scenarios of pumping and sea level rise. Four scenarios are used to control SWI, including: decreasing pumping from the aquifer, increasing recharge using treated waste water, increasing abstraction of brackish water for desalination, and a combination of these systems. The results showed that increasing recharge could lead to greater retardation of SWI (19.5%) than decreasing pumping (6.2%) and abstraction of brackish water (5.9%). However, a combined well system of pumping, recharge and abstraction is shown to be a more effective tool to control SWI in coastal aquifers, with retardation percentage of 21.3%.

Modelling and management of saltwater intrusion in a coastal aquifer system: A regional-scale study

Increasing saltwater intrusion in the Barguna aquifer due to unplanned groundwater abstraction is a concern for the people of Barguna district, Bangladesh. A sustainable groundwater abstraction strategy capable of confining saltwater concentrations in the aquifer within acceptable limits is required for the Barguna aquifer system. In this study, a regional-scale integrated simulation-optimization (S–O) approach was used to prescribe an optimal groundwater abstraction strategy for the aquifer. The flow and transport processes were simulated by a calibrated and validated numerical simulation model using the available hydrogeological data. The simulation model was then used within the integrated S–O based management model to evolve ideal groundwater abstraction patterns to restraint saltwater intrusion in the study area. Computational efficiency of the management model was achieved by using a Multivariate Adaptive Regression Spline (MARS) based meta-model emulating the density dependent salinity transport processes of the study area. The developed MARS-based emulators were then externally linked with a Controlled Elitist Multiple Objective Genetic Algorithm (CEMOGA) as a replacement of the numerical model. The study area comprised of a set of production wells for abstracting groundwater for beneficial purposes. Barrier extraction wells placed along the coastline were also considered as a management option to control saltwater intrusion hydraulically. Grey Relational Analysis was utilized as a quick decision-making tool for selecting a relatively better solution from a large number of non-dominated solutions from the Pareto front. The proposed MARS-CEMOGA based saltwater intrusion management methodology was capable of obtaining accurate solutions for optimal groundwater abstractions from a combination of production and barrier extraction bores in a real-life coastal aquifer system. This study demonstrates the efficiency of the MARS meta-model, together with an integrated S–O approach, to solve real-life complex coastal aquifer management problems.

Managing saltwater intrusion using conjugate sharp interface and density dependent models linked with pumping optimization

Coastal areas are densely populated due to associated socioeconomic benefits, and therefore have higher demand for freshwater. This ever-increasing demand for freshwater can be met by coastal aquifers, which act as giant reservoirs of freshwater. Excessive and unmanaged pumping from coastal aquifer allows saltwater to flow inward encroaching the voids created by pumping of freshwater. This phenomenon is called saltwater intrusion. To stop saltwater intrusion, an optimal pumping strategy needs to be adopted. Simulation models are generally linked with an optimization algorithm to develop optimal pumping strategy for management of saltwater intrusion. Sharp interface based simulation models are often used which are computationally inexpensive but lacks in prediction accuracy, as it does not incorporate the effects of dispersion and diffusion. Density dependent simulation models include the effect of dispersion and diffusion, but have very high computational budget in evaluating an optimal pumping strategy. To overcome above mentioned limitations a new methodology is developed, where a density-dependent model is used in conjunction with a sharp interface model to derive an optimal density ratio, such that interface obtained using this density ratio implicitly accommodates the effect of dispersion and diffusion in a sharp interface model. The performance of the developed methodology is evaluated for three hypothetical scenarios of saltwater intrusion, and in densely populated coastal city of Puri in India. The performance evaluation results show the applicability of the developed methodology for management of saltwater intrusion while maximizing freshwater pumping from coastal aquifers.

Development of an efficient conjunctive meta-model-based decision-making framework for saltwater intrusion management in coastal aquifers

This paper presents an integrated framework for management of aquifers threatened by saltwater intrusion (SI). In this framework, SEAWAT model is used for simulating the density dependent groundwater flow. Three meta-models based on the artificial neural network (ANN), M5 tree and random subspaces model (RSM) are developed, as surrogate models for SEAWAT to accurately simulate the groundwater response to different pumping and recharge scenarios. Various patterns of recharge to and discharge from aquifer are used to generate a database for training the mentioned surrogate models. To decrease the number of training parameters, the aquifer area is divided into different zones using k-means clustering technique (KMC). Additionally, a conjunctive model (CM) using a combination of the three surrogate models is proposed to enhance the accuracy of the simulation. It is then integrated with the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) with the objectives of maximizing pumping rates and minimizing SI length. Next, the socially optimal scenarios are selected from the obtained Pareto-front using the Nash bargaining theory. The performance of the proposed model is evaluated by applying it to the Kahak aquifer, Iran, which is subjected to SI. The results show that the conjunctive model using KMC technique predicts SI length with a comparable accuracy and results in 95% reduction in runtime compared to a simulation-optimization (SO) model.

Optimal Groundwater-Use Strategy for Saltwater Intrusion Management in a Pacific Island Country

AbstractEscalating salinity levels in the Bonriki aquifer due to unplanned groundwater extraction is a major concern for the people of Kiribati. A multiobjective management model capable of providi...

Mapping saltwater intrusion with an airborne electromagnetic method in the offshore coastal environment, Monterey Bay, California

Study RegionThe northern coast of the Monterey Bay, California, USA, extending from the coastline to 3.5 km offshore. Study FocusThree-hundred and twenty line-kilometers of airborne electromagnetic (AEM) data were acquired offshore. These data spanned 20 km of coastline, extending up to 3.5 km offshore in water up to 18 m in depth. Inversion of these data resulted in resistivity models extending to depths between 50 and 200 m below sea level. The data were interpreted in conjunction with onshore monitoring well data, hydrologic and geologic reports, and electrical resistivity tomography (ERT) data to locate the freshwater/saltwater interfaces throughout the region. A resistivity-to-water-quality transform was established using well-based water quality and resistivity logging measurements. For resistivity values that could not be converted to water quality with this transform, local auxiliary information was used on a case-by-case basis to interpret the observed features. Some low resistivity anomalies were identified near the shore at depth, which were interpreted to be artifacts of the 1D assumption in the inversion scheme used for these AEM data. New Hydrogeological Insights for this RegionWe found that the acquisition of AEM data provided valuable information about water quality in the offshore extents of the aquifers, a region inaccessible to traditional monitoring methods, but one that plays an important role in the modeling, prediction, and management of saltwater intrusion.

Multi-objective groundwater management strategy under uncertainties for sustainable control of saltwater intrusion: Solution for an island country in the South Pacific

To date, simulation-optimization (S/O) based groundwater management models have delivered optimal saltwater intrusion management strategies for coastal aquifer systems. At times, however, uncertainties in the numerical simulation model due to uncertain aquifer parameters are not incorporated into the management model. The present study explicitly incorporated aquifer parameter uncertainty into a multi-objective management model for the optimal design of groundwater pumping strategies from the unconfined Bonriki aquifer situated in a small Pacific island country. The objective of the multi-objective management model was to maximise pumping from production wells and minimize pumping from the barrier wells (hydraulic barriers) to ensure that the water quality at different monitoring locations (MLs) were within pre-specified sustainable limits. To achieve the targeted management goal, a coupled flow and transport numerical simulation model of the Bonriki aquifer was developed using the FEMWATER numerical code. The developed three-dimensional numerical model was calibrated and validated using limited available hydrological data. To achieve computational efficiency and feasibility of the management model, the numerical simulation model in the S/O model was replaced with ensembles of Support Vector Machine Regression (SVMR) surrogate models. Each SVMR standalone surrogate model in the ensemble was constructed using datasets from different numerical simulation models with different hydraulic conductivity and porosity values. These ensemble SVMR models were coupled to the multi-objective genetic algorithm optimization model to solve the Bonriki aquifer management problem. The executed optimization model presented a Pareto-front with 600 non-dominated optimal trade-off pumping solutions. The reliability of the management model established after validation of the optimal solution results suggests that the implemented constraints of the optimization problem were satisfied, i.e., the salinity concentrations at respective MLs were within the pre-specified limits. Overall, the results from this study indicated that the developed management model has the potential to address groundwater salinity problems in small island countries.

An Ensemble Meta-Modelling Approach Using the Dempster-Shafer Theory of Evidence for Developing Saltwater Intrusion Management Strategies in Coastal Aquifers

The optimum abstraction policy of coastal groundwater resources is prescribed by solving a meta-model based saltwater intrusion management model. Groundwater parameter uncertainties are explicitly incorporated into the developed meta-models in order to address the uncertainties present in coastal aquifer processes. Nevertheless, the accuracy and consequent reliability of such a management model depends upon the right choice of meta-models or a combination of meta-models. The optimal combination of meta-models, also referred to as an ensemble meta-model, can be selected by applying the Dempster-Shafer (D-S) theory of evidence. D-S evidence theory provides a platform upon which to base the selection of the best meta-model or combination of meta-models to formulate the preferred ensemble. This study demonstrates the application of D-S theory to provide an ensemble of meta-models for developing saltwater intrusion management models in coastal aquifers. The prediction accuracy of the developed ensemble meta-model is compared with that of the best standalone meta-model in the ensemble. The results confirm that the ensemble meta-model performs equally well when compared with the best meta-model in the ensemble. The developed meta-models and their ensemble are then used to develop computationally feasible multiple objective saltwater intrusion management models by utilizing an integrated simulation-optimization approach. The solution results of the management models demonstrate the superiority of the ensemble meta-model approach over standalone meta-models in obtaining Pareto optimal groundwater abstraction patterns. The evaluation of the proposed methodology is demonstrated using an illustrative multilayer coastal aquifer system subjected to groundwater parameter uncertainties.

A Review of Surrogate Models and Their Ensembles to Develop Saltwater Intrusion Management Strategies in Coastal Aquifers

The complex physical processes in a typical coastal aquifer system with transient inputs to numerical simulation models (NSM) result in substantial computational burden in a coupled simulation–optimization (S/O) approach. In such situations, an approximate emulator of the complex physical processes provides a computationally efficient alternative to the NSM. The reliability of these surrogate models (SM) within the coupled S/O approach depends on how accurately they capture the trend of the underlying physical processes. Moreover, these SMs are often associated with prediction uncertainties, which hinder optimality of the solution of the coupled S/O methodology. In this review article, we summarize ensemble approach of combining data-driven SMs to address this prediction uncertainty. Different techniques of ensemble formation as well as their relative advantages and disadvantages are also discussed. Although a wide range of data-driven SMs have been used to approximate associated physical processes of coastal aquifers, the use of ensemble SMs is quite limited. Moreover, these ensemble-based modelling approaches are based on manipulating the training data set, i.e., using different realizations of training data set to train individual SMs within the ensemble. Although ensemble formation by combining multiple SMs based on different algorithms can be found in other application domains, the application of ensemble SMs in the prediction of saltwater intrusion processes has not been developed yet. In addition, more advanced ensemble surrogate-modelling approaches are yet to be established in the context of developing regional scale saltwater intrusion management models.

Trained meta-models and evolutionary algorithm based multi-objective management of coastal aquifers under parameter uncertainty

Abstract Meta-model based coupled simulation-optimization methodology is an effective tool in developing sustainable saltwater intrusion management strategies for coastal aquifers. Such management strategies largely depend on the accuracy, reliability, and computational feasibility of meta-models and the numerical simulation model. However, groundwater models are associated with a certain amount of uncertainties, e.g. parameter uncertainty and uncertainty in prediction. This study addresses uncertainties related to input parameters of the groundwater flow and transport system by using a set of randomized input parameters. Three meta-models are compared to characterize responses of water quality in coastal aquifers due to groundwater extraction patterns under parameter uncertainty. The ensemble of the best meta-model is then coupled with a multi-objective optimization algorithm to develop a saltwater intrusion management model. Uncertainties in hydraulic conductivity, compressibility, bulk density, and aquifer recharge are incorporated in the proposed approach. These uncertainties in the physical system are captured by the meta-models whereas the prediction uncertainties of meta-models are further addressed by the ensemble approach. An illustrative multi-layered coastal aquifer system is used to demonstrate the feasibility of the proposed approach. Evaluation results indicate the capability of the proposed approach to develop accurate and reliable management strategies for groundwater extraction to control saltwater intrusion.

Influence of Sea Level Rise on Multiobjective Management of Saltwater Intrusion in Coastal Aquifers

AbstractThis study demonstrates the influence of climate change-induced sea level rise on multiobjective saltwater intrusion management strategies in coastal aquifers. Three metamodels were develop...