Saltwater Intrusion In Coastal Aquifers 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

Groundwater salinization risk in coastal regions triggered by earthquake-induced saltwater intrusion

AbstractAnthropogenic factors such as over-pumping and natural events such as earthquakes impact coastal aquifers by reducing freshwater recharge, aquifer water budgets, and increasing saltwater intrusion (SWI). This study investigates the impact of hydrodynamic forces induced by earthquakes on SWI in one hypothetical case, namely, the Henry problem, and a real case of the Biscayne aquifer located in Florida, USA. The analysis was carried out using the analytical solution of estimating the earthquake’s induced hydrodynamic pressure and applying the SEAWAT code to investigate the SWI for the base case and three scenarios, namely for the horizontal acceleration (αh) by 0.10 g, 0.20 g, and 0.30 g. The results show that earthquakes might considerably increase the SWI in coastal aquifers. Moreover, the rise in salinity across expansive land areas significantly threatens agricultural productivity and jeopardizes food security. Namely, in the case of Biscayne aquifer, salinity was increased by 12.10%, 21.90%, and 45.70% for the horizontal seismic acceleration of 0.1 g, 0.20 g, and 0.30 g, respectively. Hence, the conclusions drawn from this study underscore the need for carefull consideration of earthquake impacts in future planning and water management strategies for coastal regions. This proactive approach is crucial to preemptively address and mitigate the groundwater salinization hazard associated with SWI fluctuations due to earthquakes.

Developing Functional Recharge Systems to Control Saltwater Intrusion via Integrating Physical, Numerical, and Decision-Making Models for Coastal Aquifer Sustainability

Controlling the hydraulic heads along a coastal aquifer may help to effectively manage saltwater intrusion, improve the conventional barrier’s countermeasure, and ensure the coastal aquifer’s long-term viability. This study proposed a framework that utilizes a decision-making model (DMM) by incorporating the results of two other models (physical and numerical) to determine proper countermeasure components. The physical model is developed to analyze the behavior of saltwater intrusion in unconfined coastal aquifers by conducting two experiments: one for the base case, and one for the traditional vertical barrier. MODFLOW is used to create a numerical model for the same aquifer, and experimental data are used to calibrate and validate it. Three countermeasure combinations, including vertical barrier, surface, and subsurface recharges, are numerically investigated using three model case categories. Category (a) model cases investigate the hydraulic head’s variation along the aquifer to determine the best recharge location. Under categories (b) and (c), the effects of surface and subsurface recharges are studied separately or in conjunction with a vertical barrier. As a pre-set of the DMM, evaluation and classification ratios are created from the physical and numerical models, respectively. The evaluation ratios are used to characterize the model case results, while the classification ratios are used to classify each model case as best or worst. An analytical hierarchy process (AHP) as a DMM is built using the hydraulic head, salt line, repulsion, wedge area, and recharge as selection criteria to select the overall best model case. According to the results, the optimum recharging location is in the length ratio (LR) from 0.45 to 0.55. Furthermore, the DMM supports case3b (vertical barrier + surface recharge) as the best model case to use, with a support percentage of 48%, implying that this case has a good numerical model classification with a maximum repulsion ratio (Rr) of 29.4%, and an acceptable wedge area ratio (WAR) of 1.25. The proposed framework could be used in various case studies under different conditions to assist decision-makers in evaluating and controlling saltwater intrusion in coastal aquifers.

Verification of experimental saltwater intrusion interface in unconfined coastal aquifers using numerical and analytical solutions

Saltwater intrusion (SWI) is a widespread environmental problem that poses a threat to coastal aquifers. To address this issue, this research employs both numerical and experimental methods to study saltwater intrusion under the impact of sea level rise and varying freshwater boundary conditions in two homogeneous aquifers. The study compares transient numerical groundwater heads and salt concentrations to experimental results under receding-front and advancing front conditions. In the low permeability aquifer, the root mean square error is 0.33 cm and the R2 is greater than 0.9817. Similarly, in the high permeability aquifer, the root mean square error is 0.92 cm and the R2 is greater than 0.9335. The study also compares the results of ten experimental tests for steady-state saltwater intrusion wedge and toe length with seven different analytical solutions. The experimental results are then compared to these analytical solutions to find the most suitable equation. The Rumer and Harleman equation shows good agreement with experimental saltwater intrusion wedge, while the Anderson equation is a good fit for saltwater intrusion toe length. Overall, this research provides valuable insights into saltwater intrusion in coastal aquifers, and the findings can be used to inform policies and management strategies to mitigate the negative impacts of saltwater intrusion. The investigation shed light on how inland water head and Sea Level Rise (SLR) affect SWI behavior.

Seasonal fluctuations in the groundwater level accelerate the removal of residual saltwater upstream of subsurface dams

Subsurface dams have been applied as an effective countermeasure against saltwater intrusion in coastal aquifers. However, part of the saltwater wedge (“residual saltwater”) may be trapped upstream of the dam and take years to decades to remove, hindering groundwater exploitation. This study examines the mechanism of residual saltwater removal under seasonal groundwater level fluctuations induced by intermittent precipitation or pumping. The residual saltwater removal timescale for constant-head (CH) and fluctuating head (FH) scenarios are quantified and compared using field-scale numerical simulations. The results show that seasonal fluctuations in the groundwater table enhanced the dilution of residual saltwater, thereby accelerating the removal of residual seawater compared to the CH scenario. However, the critical dam height (i.e., the minimum height for complete removal of residual saltwater) is higher in the FH scenario than in the CH scenario. The sensitivity analysis indicates that the fastest residual saltwater removal in the FH scenario is generally obtained by a dam height slightly higher than the critical dam height. The impact of seasonal groundwater level fluctuations on residual saltwater removal timescale is more pronounced with a higher amplitude of inland hydraulic head variations, a lower average inland hydraulic head over the seasonal cycle, a larger dispersivity, a greater aquifer hydraulic conductivity, or a smaller porosity. These results provide valuable insights into the design of engineered subsurface dams and the management of existing subsurface barriers in coastal aquifers.

A benchmark for variably saturated variable-density variable-viscosity flow and solute transport in porous media

In natural environments, fluid density and viscosity can be affected by spatial and temporal variations of solute concentration, for example, due to saltwater intrusion in coastal aquifers, leachate infiltration from waste disposal sites, and upconing of saline water from deep aquifers. Potentially unstable situations may arise in which a dense fluid overlies a less dense fluid. This situation can produce instabilities manifested by dense plume fingers moving vertically downwards counterbalanced by vertical upward flow of the less dense fluid. The resulting free convection increases solute transport rates over large distances and times relative to constant-density flow. Unstable brine flow is further complicated if the porous medium is variably saturated. The results from a laboratory experiment of variably saturated variable-density flow and solute transport from Simmons et al. (2002) are used as the physical basis to define a new mathematical benchmark. This benchmark aims at realistically reproducing the experimental fingering patterns. Random hydraulic conductivity fields were used in the simulations as a numerical perturbation method to realistically mimic the observed dense plume fingering. The HydroGeoSphere code coupled with PEST are used to calibrate the parameter set that defines the benchmark. A grid convergence analysis is performed to obtain the adequate spatial and temporal discretizations. The new mathematical benchmark is useful for model comparison and testing of variably saturated variable-density flow in porous media. Simmons CT, Pierini ML, Hutson JL (2002) Laboratory investigation of variable-density flow and solute transport in unsaturated–saturated porous media. Transp Porous Media. 47(2): 215–244, 10.1023/A:1015568724369.

Characteristics of hydrochemical and d2H, d18O stable isotopic composition to study saltwater intrusion in coastal aquifers in Danang city

The situation of saltwater intrusion in coastal aquifers in Da Nang city is greatly affected by urban planning, exploitation and water resources use. This article presents research data on hydrogeochemical characteristics and stable isotope composition, thereby determining the origin of groundwater in aquifers then study on saltwater intrusion. The relationship between δ2H and δ18O during rainy season shows that the water in the Holocene aquifer in Da Nang coastal area has isotopic composition similar to regional meteorological water and does not mix with seawater, the main source recharges to the aquifer is rainwater. During dry season, d18O in groundwater is low but d2H is enriched by recharged rainwater from higher attitude area and also affected by exchange with leakage water from landfills. The saline water in this aquifer tends to be washed by rainwater leading to the phenomenon of paleness and the area of salt water in the aquifer is gradually shrinking. These research results are very important in propose a solution for ground water extraction plan and control saltwater intrusion for groundwater

Laboratory study of the simultaneous effect of discharge well and cut of wall on reducing saltwater intrusion in coastal aquifers

Laboratory study of the simultaneous effect of discharge well and cut of wall on reducing saltwater intrusion in coastal aquifers

Vertical Saltwater Intrusion in Coastal Aquifers Driven by Episodic Flooding: A Review

AbstractLow‐elevation coastal areas are increasingly vulnerable to seawater flooding as sea levels rise and the frequency and intensity of large storms increase with climate change. Seawater flooding can lead to the salinization of fresh coastal aquifers by vertical saltwater intrusion (SWI). Vertical SWI is often overlooked in coastal zone threat assessments despite the risk it poses to critical freshwater resources and salt‐intolerant ecosystems that sustain coastal populations. This review synthesizes field and modeling approaches for investigating vertical SWI and the practical and theoretical understanding of salinization and flushing processes obtained from prior studies. The synthesis explores complex vertical SWI dynamics that are influenced by density‐dependent flow and oceanic, hydrologic, geologic, climatic, and anthropogenic forcings acting on coastal aquifers across spatial and temporal scales. Key knowledge gaps, management challenges, and research opportunities are identified to help advance our understanding of the vulnerability of fresh coastal groundwater. Past modeling studies often focus on idealized aquifer systems, and thus future work could consider more diverse geologic, climatic, and topographic environments. Concurrent field and modeling programs should be sustained over time to capture interactions between physical processes, repeated salinization and flushing events, and delayed aquifer responses. Finally, this review highlights the need for improved coordination and knowledge translation across disciplines (e.g., coastal engineering, hydrogeology, oceanography, social science) to gain a more holistic understanding of vertical SWI. There also needs to be more education of communities, policy makers, and managers to motivate societal action to address coastal groundwater vulnerability in a changing climate.

Assessing the Impact of Groundwater Extraction on the Performance of Fractured Concrete Subsurface Dam in Controlling Seawater Intrusion in Coastal Aquifers

Among the well-known approaches for controlling seawater intrusion during extensive freshwater abstraction from coastal aquifers is the construction of subsurface dams. In the current research, the SEAWAT code is being implemented to examine the impact of groundwater extraction on the effectiveness of a damaged subsurface dam for controlling saltwater intrusion. Simulations were performed numerically to check impact of the subsurface dam height, dam location, well height, well location, abstraction rate, fracture aperture, fracture location, seawater density and fracture dimension on the effectiveness of subsurface dam as a countermeasure to prevent saltwater intrusion in coastal aquifers. Increasing the abstraction rate from 1 × 10−6 to 5 × 10−6 m3/s caused the seawater to advance more into the freshwater, and the loss of effectiveness increased. The minimum and maximum value of loss of subsurface dam effectiveness was recorded to be 34.6% to 93%, respectively, for the abstraction rates from the well equal 1 × 10−6 and 5 × 10−6 m3/s, consequentially. When the dimensionless value of well height location Lw/Ld is increased from 1.0 to 2.0, the effectiveness of the subsurface dam is reduced by around 20%. The findings demonstrate that the well location, well depth, abstraction rate, location of the dam, fracture aperture, and density of saltwater all affect the effectiveness impairment of the fractured subsurface dam for controlling saltwater intrusion. Decision makers could use findings of this research to better manage groundwater resources in coastal aquifers.

Saltwater Intrusion into Coastal Aquifers and Associated Risk Management: Critical Review and Research Directives

Basack, S.; Loganathan, M.K.; Goswami, G., and Khabbaz, H., 2022. Saltwater intrusion into coastal aquifers and associated risk management: Critical review and research directives. Journal of Coastal Research, 38(3), 654–672. Coconut Creek (Florida), ISSN 0749-0208. Coastal regions mainly rely on sources of local fresh groundwater for domestic, irrigational, and industrial usages, which are vulnerable to high-risk of getting intruded by saltwater. Excessive pumping of fresh groundwater initiates advances of saltwater-freshwater interface inward due to hydraulic equilibrium and continuity. This introduces saline water intrusion into coastal aquifers. This is also caused by natural hazards like sea-level rise and storm-surge. The saltwater intrusion in coastal aquifers contaminates the freshwater storage, thereby emerging as a major environmental issue. To incorporate adequate coastal groundwater control and management techniques that are effective and conveniently implementable, understanding the phenomenon of saline water intrusion and the risk assessment is of utmost importance. Several scientific contributions including theoretical (analytical and numerical) solutions, experimental (laboratory and field) results, design recommendations, and risk analysis are available, indicating remarkable advances in the research area. The authors have attempted to summarize the significant contributions over the last few decades in each of these study aspects through extensive literature survey and critical analysis of the existing knowledge. It is observed that risk prevention and control methodologies such as qanat-well structure, shallow and deep wells might not be effective in many coastal areas as the complex intrusion process is yet to be understood clearly. Moreover, the high intensity coastal hazards that often occur due to climate change continue to make aquifers more vulnerable, adversely affecting the coastal groundwater management. The paper presents a critical overview of existing studies on saline water intrusion into coastal aquifers and associated risks and management techniques. Furthermore, adequate research directives with recommendations for future development are also provided.

Comparative study of saltwater intrusion in coastal aquifers: application to the aquifer of Oued Laou (Morocco)

Groundwater is a fundamental and strategic resource for water supply of coastal areas, especially in the Mediterranean basin where the irregularity of precipitation, both seasonally and year-on-year, put at risk the availability of surface water in the rivers, which go from being dry for long periods to causing torrential discharges. In particular, if the exploitation of coastal aquifers is not properly managed and the quality of groundwater is not monitored regularly, important sectors of the aquifer may be affected by saltwater intrusion, and cause the abandonment of the wells. Geophysical methods are a very effective complement to provide indirect information on groundwater salinity in areas of the aquifer where wells or piezometers are not available for sampling. This study presents the results obtained from the application of different geophysical methods in the coastal aquifer of Oued Laou (Morocco) as a complement to hydrochemical data. Four geophysical methods, two electrical: vertical electrical sounding and electrical resistivity tomography, and two electromagnetic: frequency domain EM and time domain EM sounding. The comparative analysis of the results obtained by each method has made it possible to assess the coherence and complementarity of each method, as well as their corresponding advantages and limitations in terms of resolution and cost-effectiveness.

Experimental and Numerical Study to Investigate the Impact of Changing the Boundary Water Levels on Saltwater Intrusion in Coastal Aquifers

Experimental and numerical models can be used to investigate saltwater intrusion (SWI) in coastal aquifers. Sea level rise (SLR) and decline of freshwater heads due to climate change are the two key variables that may affect saltwater intrusion. This study aims to give a better understanding of the impact of increasing seawater levels and decreasing freshwater heads due to climate change and increasing abstraction rates due to overpopulation using experimental and numerical models on SWI. The experimental model was conducted using a flow tank and the SEAWAT code was used for the numerical simulation. Different scenarios were examined to assess the effect of seawater rise and landside groundwater level decline. The experimental and numerical studies were conducted on three scenarios: increasing seawater head by 25%, 50% and 75% from the difference between seawater and freshwater heads, decreasing freshwater head by 75%, 50% and 25% from the difference between seawater and freshwater heads, and a combination of these two scenarios. Good agreement was attained between experimental and numerical results. The results showed that increasing the seawater level and decreasing freshwater head increased saltwater intrusion, but the combination of these two scenarios had a severe effect on saltwater intrusion. The numerical model was then applied to a real case study, the Biscayne aquifer, Florida, USA. The results indicated that the Biscayne aquifer is highly vulnerable to SWI under the possible consequences of climate change. A 25 cm seawater rise and 28% reduction in the freshwater flux would cause a loss of 0.833 million m3 of freshwater storage per each kilometer width of the Biscayne aquifer. This study provides a better understanding and a quantitative assessment for the impacts of changing water levels’ boundaries on intrusion of seawater in coastal 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%.

Groundwater Circulation Well for Controlling Saltwater Intrusion in Coastal aquifers: Numerical study with Experimental Validation

Saltwater intrusion into coastal aquifers has become a prominent environmental concern worldwide. As such, there is a need to prepare and implement proper remediation techniques with careful planning of freshwater withdrawal systems for controlling saltwater intrusion in coastal marine and estuarine environments. This paper investigates the performance of groundwater circulation well (GCW) in controlling saltwater intrusion problems in unconfined coastal aquifers. The GCWs have been established as a promising in-situ remedial technique of contaminated groundwater. The GCW system creates vertical circulation flow by extracting groundwater from an aquifer through a screen in a single well and injecting back into the aquifer through another screen. The circulation flow induced by GCW force water in a circular pattern between abstraction and recharge screens and can be as a hydraulic barrier for controlling saltwater intrusion problem in coastal aquifers. In this study, an effort has been made to investigate the behavior of saltwater intrusion dynamics under a GCW. An experiment has been conducted in a laboratory-scale flow tank model under constant water head boundary conditions, and the variable-density flow and transport model FEMWATER is used to simulate the flow and transport processes for the experimental setup. The evaluation of the results indicates that there is no further movement of saltwater intrusion wedge towards the inland side upon implementation of GCW, and the GCW acts as a hydraulic barrier in controlling saltwater intrusion in coastal aquifers. The present study reveals the GCWs system can effectively mitigate the saltwater intrusion problem in coastal regions and could be considered as one of the most efficient management strategies for controlling the problem.

Saltwater intrusion prediction in coastal aquifers utilizing a weighted-average heterogeneous ensemble of prediction models based on Dempster-Shafer theory of evidence

ABSTRACT Accurate and meaningful prediction of saltwater intrusion in coastal aquifers requires appropriate prediction tools. Artificial intelligence-based prediction models and their ensembles have been a better choice for mimicking the complex and nonlinear seawater intrusion progressions in coastal aquifers. This study utilizes a weighted-average ensemble of ‘heterogeneous’ prediction models to predict the saltwater intrusion progression in a coastal aquifer study area. The Dempster-Shafer theory of evidence is employed to calculate the weights of five different prediction model algorithms. Corresponding weights for individual prediction models are utilized in developing the ensemble prediction. Ensemble prediction performance for salinity intrusion in coastal aquifers in this effort is evaluated using several descriptive metrics. The values of the descriptive metrics suggest that the ensemble model performs in the same way as the best model in the ensemble. The methodology is evaluated for an illustrative coastal aquifer study area exposed to pumping-induced saltwater intrusion.

Mitigation of seawater intrusion in coastal aquifers using coastal earth fill considering future sea level rise

Saltwater intrusion (SWI) is a physical problem that threatens many coastal aquifers all over the world. Saltwater intrusion is increasing with abstraction and rise in sea level. Coastal aquifer protection is essential to protect groundwater resources in these areas. A number of methods have been developed to protect coastal aquifers from SWI. This paper presents the impact of sea level rise on SWI in coastal aquifers and application of coastal earth fill as a new technique to control SWI. Different future sea level rise scenarios were studied and different coastal earth fill with an appropriate soil to extend the coastline towards the sea in order to control SWI was studied using SEAWAT model. The proposed control measure is numerically assessed by Henry's problem and then applied to a real case study of Biscayne aquifer, Florida, USA. For each aquifer, the corresponding relation was developed between the intrusion length of saltwater wedge and the width of fill. The results showed that increasing the fill width resulted in decreasing the intrusion length. In the case of Biscayne aquifer, increasing the fill width by 10, 20, 30, and 40% of the aquifer length resulted in retarding the intrusion to 329, 192, 42, and - 48m respectively. Using 150- and 300-m fill widths retards the intrusion length by 32.3% and 60.5%. In addition, increasing the fill width to 465m can retard SWI by 91.3%. This approach is capable to control the future risks of SWI and sea level rise.

Effects of Aquifer Bed Slope and Sea Level on Saltwater Intrusion in Coastal Aquifers

The quality of groundwater resources in coastal aquifers is affected by saltwater intrusion. Over-abstraction of groundwater and seawater level rise due to climate change accelerate the intrusion process. This paper investigates the effects of aquifer bed slope and seaside slope on saltwater intrusion. The possible impacts of increasing seawater head due to sea level rise and decreasing groundwater level due to over-pumping and reduction in recharge are also investigated. A numerical model (SEAWAT) is applied to well-known Henry problem to assess the movement of the dispersion zone under different settings of bed and seaside slopes. The results showed that increasing seaside slope increased the intrusion of saltwater by 53.2% and 117% for slopes of 1:1 and 2:1, respectively. Increasing the bed slope toward the land decreased the intrusion length by 2% and 4.8%, respectively. On the other hand, increasing the bed slope toward the seaside increased the intrusion length by 3.6% and 6.4% for bed slopes of 20:1 and 10:1, respectively. The impacts of reducing the groundwater level at the land side and increasing the seawater level at the shoreline by 5% and 10% considering different slopes are studied. The intrusion length increased under both conditions. Unlike Henry problem, the current investigation considers inclined beds and sea boundaries and, hence, provides a better representation of the field conditions.

Numerical analysis of physical barriers systems efficiency in controlling saltwater intrusion in coastal aquifers.

Saltwater intrusion (SWI) increases salinity of aquifers and depletion of groundwater resources in coastal aquifers. Different methods have been used to control SWI in the coastal aquifers in order to protect groundwater. In this paper, applicability of physical subsurface barriers (PSB) methods to control SWI in the Biscayne aquifer in Florida, USA, is studied. Numerical models have been developed to study and compare performance of two types of the PSB namely cutoff wall and subsurface dam for SWI control. The developed numerical models have been verified through simulation of benchmark examples and then have been used to simulate a semi-hypothetical case study relying on hydrogeological data measured in the Biscayne aquifer. Different scenarios of barriers depths, locations, and permeability have been analyzed. The results indicated that the PSB can effectively control the intrusion of saline into coastal aquifers. However, cutoff wall gave higher retardation than sub-surface dams.

ADAPTED SUBSURFACE WATER SOLUTIONS ACROSS CONTINENTS

Temporary water scarcity and saltwater intrusion in coastal aquifers are problems which are common in various parts of the world and can be addressed by subsurface water solutions (SWS). SWS comprise of various intelligent well and sensor configurations for different hydrogeological aquifer conditions. They can be combined for aquifer storage, (treatment), and recovery (AS(T)R), managed aquifer recharge (MAR), and various water reuse options including rainwater harvesting or treated waste water usage. To date, pilot SWS are implemented in the Netherlands, where they demonstrate highly beneficial applications for the above-mentioned purposes. This report presents the technology transfer to other coastal regions by utilising a participatory co-design approach with key stakeholders and institutions. The methodology developed mainly consists of two missions, which were applied to four target regions: Brazil, Mexico, Vietnam, and Cyprus. In these regions stakeholders were identified, framework conditions were assessed, and public events and project development workshops were conducted aiming to adapt the technology and implementation approach to the specific local requirements. General drivers and barriers were identified for institutional, political, legal, and socio-economic aspects. The report provides an outline of general implementation concepts, region-specific prerequisites, and ideas for follow-up projects.