Water In Coastal Aquifers Research Articles

Groundwater Quality Monitoring in Response to Marine Intrusion: A Case Study in Northern Morocco

Water stress, resulting from a demand for water exceeding the available quantity, is a major global challenge. Groundwater usage is a commonly adopted strategy to address this situation, but it often leads to marine intrusion, threatening the quality of water in coastal aquifers. This phenomenon typically stems from overexploitation of aquifers, declining water table levels, and rising sea levels due to climate change. Our study aims to monitor the quality of groundwater intended for human consumption and provide a detailed assessment of its current state. We identified several physicochemical parameters, such as temperature, pH, and bicarbonates, with maximum electrical conductivity values reaching 2810 µs/cm, a total hardness of 21 meq/L, sulfate levels of 689 mg/L, and chloride levels of 628 mg/L, from six boreholes and one well located along the coastal area of the Al Hoceima region. These samples were also subjected to Principal component analysis (PCA) of the chemical parameters, revealing two factors that represent approximately 62.15% of the total variance in the groundwater quality dataset. Simulation results indicate signs of seawater intrusion in several areas, particularly near the coast, emphasizing the urgency of protecting groundwater resources and developing sustainable management strategies to ensure a safe and reliable supply of drinking water in the region.

Coastal aquifer water quality for domestic supply of small communities in the semiarid Potiguar - Brazilian Northeast

This study analyzed groundwater quality used to supply small communities in the coastal zone of the Brazilian Northeast, identifying the risks from domestic use of water, and potential contaminants from domestic effluents. We realized analyses of 24 chemical and physical parameters in 15 samples of water from shallow wells. The data was processed through quality modeling, descriptive statistics, principal component analysis, and geoespacialization through kriging. The groundwater used by communities showed some limitations to domestic use. Parameters of Br, hardness, Na+, NO3−, Cl−, SO4−, and turbidity exceed the allowed for Brazilian Health Minister (Ministerial Order n. 888/2021). Furthermore, TDS values present low water quality, predominantly brackish and saltwater, most salinity waters are related to depth and sea proximity. Depth of saturated zone probably is a determinant in nitrate concentrations, comparing the study areas. Water self-supply is considered a risk by health because inferior natural quality of water used and contaminations from domestic sewage determine concentrations of some parameters above of legislation.

Groundwater Potential Zone Delineation Using Multi-criteria Decision-making Approach: A Case Study

Over-exploitation of groundwater from coastal aquifers causes seawater intrusion and depletion of freshwater resources. As 40 percent of the world’s population live within 100 km of the coast. This will increase the demand for potable water in coastal aquifers. Hence, it is essential to evaluate the sources of fresh-groundwater potential and productivity in coastal aquifers. Nowadays, integrated studies based on geographic-information systems play a major role in groundwater-exploration studies. Thus, the current study was carried out with the objective to delineate groundwater potential in the Nambiyar river basin in Tamil Nadu's southeast coastal area, where groundwater is in a critical condition. In order to improve groundwater recharge, it is very important to identify possible recharge areas. A novel work of the integration of remote sensing, geographic information system (GIS) and multi-criteria decision-making approaches of analytical hierarchical-process methodologies (AHP) was used in the present study. A total of 11 thematic layers, such as slope, curvature, soil, roughness, topographic-wetness index, drainage density, land use/land cover, geology, geomorphology, lineament density and rainfall, were generated for delineating groundwater potential zones. All the thematic maps are weighted using AHP based on the attributes of the classes and the potential capacity of their water supply. The demarked region of groundwater potential was validated by comparing pre-monsoon and post-monsoon groundwater levels. The groundwater potential zone map was classified into five categories: very high, high, moderate, low and very low. Areas with very high and very low potentials are delineated only in very limited areas. 64% of the regions are covered under the moderate-potential zones. The low-and high-groundwater potential zones are delineated at 22% and 14%, respectively. KEYWORDS: GIS, Recharge areas, Groundwater potential, Nambiyar river basin, AHP

Preliminary study on saltwater distribution of lowland area at West Coast, Johor Malaysia

Saltwater intrusion is a severe concern in coastal locations that pose a threat to the groundwater environment. Climate change, tidal effects, and groundwater exploitation all have the potential to disrupt the balance of salt water and fresh water in coastal aquifers which is the result of seawater intrusion that included the studies area. The sea-level rise is regarded as a cause that can enhance saltwater interface inland migration. Therefore, the purpose of this study is to assess saltwater intrusion in a zone mapping through the open channel distribution. This is qualified for monitoring a saltwater intrusion around West Johor which is approximately 10 km especially Batu Pahat, Johor such as Parit Botak, Parit Hailam Laut, Kampung Bahru Laut, Kampung Sri Pantai, and Sungai Senggarang. The salinity parameter was measured by the refractometer salinity instruments in percentage units (ppt) to PSU units. The high and low tides data collection on-site was monitored and analyzed saltwater intrusion distributed data into the interface mapping by using ArcGis 10.8 software. As the result, Kampung Sri Pantai was the highest data in the saline test 3 PSU for high tides and 4 PSU for low tides. However, the saltwater intrusion mapping was distributed through saline data obtained from the display maps to monitor the value of saline water in the study area. The contribution of this study to the community can be maintaining the ecosystem and monitoring existing structures such as tidal water gates and bunds of clean water resources for communities and irrigation purposes.

Spatial Characterization of Seawater Intrusion in a Coastal Aquifer of Northeast Liaodong Bay, China

The safety of groundwater resources in coastal areas is related to the sustainable development of the national economy and society. Seawater intrusion is a serious problem threatening the groundwater environment in coastal areas. Climate change, tidal effects and groundwater exploitation may destroy the balance between salt water and fresh water in coastal aquifers, leading to seawater intrusion. The threat of seawater intrusion has attracted close attention, especially in the coastal areas of northern China, and the accuracy and efficiency of seawater intrusion monitoring need to be improved. The aim of this study was to fill the blanks in seawater intrusion research in the coastal aquifer of the Daqing River Catchment, northeastern Liaodong Bay, China, and determine the extent and evolutionary characteristics of seawater intrusion in this area. In this study, historical chloride concentration data were used to trace the evolution of the salinization, and electrical resistivity tomography (ERT) was used to supplement the data in areas with limited hydrochemical data and to detect the saltwater/freshwater interface, especially in the area near the Xihai Sluice. The results show that seawater intrusion in the Daqing River Catchment is mainly caused by overexploitation of groundwater. Since 2012, strict controls have been placed on the groundwater exploitation rate, and the chloride concentration of 250 mg/L has receded year by year, with saltwater being significantly reduced by 2018. The Daqing River plays an important role in the saltwater distribution. The Xihai Sluice, located in the lower reaches of the Daqing River, intercepts and controls the seawater intrusion in a certain range by raising the level of fresh groundwater to intercept and control saltwater intrusion within a certain range. The research results also confirmed that a combination of geophysical and geochemical methods is of great value in studying seawater intrusion, especially in areas with limited available hydrochemical data. A monitoring network with ERT instruments and wells should be established to collect regular measurements of the electrical resistivity distribution, as well as the groundwater level and chemical composition.

Sea surficial waves as a driving force that enhances the fresh shallow coastal groundwater flux into the oceans

Submarine groundwater discharge (SGD) is a process through which groundwater and solutes are transferred from coastal aquifers into the oceans. Generally, the SGD is composed of two basic components: (1) fresh groundwater, FSGD; and (2) recirculated seawater, RSGD. Radon, a naturally occurring geochemical tracer, is a useful tool to evaluate the SGD in coastal areas. This study aims to evaluate the impact of wind waves on each components of submarine groundwater discharge. We monitored temporal fluctuations of seawater 222Rn concentration at Shiranui and Minamata bays, where elevated seawater 222Rn concentration spatial distribution observed during our previous studies. The measurements were conducted in coastal seawater where the connected coastal aquifer water table is very shallow. Additionally, a seawater model was applied to evaluate the seawater 222Rn concentration that originates from rivers in the study area. The 222Rn inventory in the study area implies that the groundwater advection is one of the major sources of 222Rn in the seawater. The obtained dataset suggests that the seawater 222Rn concentration increases, but the salinity decreases during windy periods. This means that more fresh groundwater contributes to dilute the recirculated seawater (RSGD) during windy conditions. Therefore, when the sea is windy and seawater waves propagate onshore, the fresh groundwater flux may increase where shallow coastal aquifers exist.

Stochastic and Robust Multi-Objective Optimal Management of Pumping from Coastal Aquifers Under Parameter Uncertainty

Combined simulation-optimization approaches have been used as tools to derive optimal groundwater management strategies to maintain or improve water quality in contaminated or other aquifers. Surrogate models based on neural networks, regression models, support vector machies etc., are used as substitutes for the numerical simulation model in order to reduce the computational burden on the simulation-optimization approach. However, the groundwater flow and transport system itself being characterized by uncertain parameters, using a deterministic surrogate model to substitute it is a gross and unrealistic approximation of the system. Till date, few studies have considered stochastic surrogate modeling to develop groundwater management methodologies. In this study, we utilize genetic programming (GP) based ensemble surrogate models to characterize coastal aquifer water quality responses to pumping, under parameter uncertainty. These surrogates are then coupled with multiple realization optimization for the stochastic and robust optimization of groundwater management in coastal aquifers. The key novelty in the proposed approach is the capability to capture the uncertainty in the physical system, to a certain extent, in the ensemble of surrogate models and using it to constrain the optimization search to derive robust optimal solutions. Uncertainties in hydraulic conductivity and the annual aquifer recharge are incorporated in this study. The results obtained indicate that the methodology is capable of developing reliable and robust strategies for groundwater management.

Reactive dispersive contaminant transport in coastal aquifers: Numerical simulation of a reactive Henry problem

The reactive mixing between seawater and terrestrial water in coastal aquifers influences the water quality of submarine groundwater discharge. While these waters come into contact at the seawater groundwater interface by density driven flow, their chemical components dilute and react through dispersion. A larger interface and wider mixing zone may provide favorable conditions for the natural attenuation of contaminant plumes. It has been claimed that the extent of this mixing is controlled by both, porous media properties and flow conditions. In this study, the interplay between dispersion and reactive processes in coastal aquifers is investigated by means of numerical experiments. Particularly, the impact of dispersion coefficients, the velocity field induced by density driven flow and chemical component reactivities on reactive transport in such aquifers is studied. To do this, a hybrid finite-element finite-volume method and a reactive simulator are coupled, and model accuracy and applicability are assessed. A simple redox reaction is considered to describe the degradation of a contaminant which requires mixing of the contaminated groundwater and the seawater containing the terminal electron acceptor. The resulting degradation is observed for different scenarios considering different magnitudes of dispersion and chemical reactivity. Three reactive transport regimes are found: reaction controlled, reaction-dispersion controlled and dispersion controlled. Computational results suggest that the chemical components' reactivity as well as dispersion coefficients play a significant role on controlling reactive mixing zones and extent of contaminant removal in coastal aquifers. Further, our results confirm that the dilution index is a better alternative to the second central spatial moment of a plume to describe the mixing of reactive solutes in coastal aquifers.

On the interpretation of coastal aquifer water level trends and water balances: A precautionary note

The changes in seawater volumes caused by seawater intrusion are often neglected in coastal aquifer management studies. The conditions under which this can result in significant water balance errors are not well understood. Interface movements also influence temporal trends in coastal aquifer water levels, but there is little guidance on this effect. In this study, we use steady-state, sharp-interface, analytic modelling to generate idealised relationships between seawater volume, freshwater volume and water levels. The approach assumes quasi-equilibrium conditions, which are evaluated using a selection of transient, dispersive simulations. The results demonstrate that seawater volume changes can influence significantly coastal aquifer water level trends, relative to the corresponding non-coastal aquifer situation, particularly within deep aquifers with high hydraulic conductivity and low net recharge. It is also shown that seawater volume changes can be a significant component of coastal aquifer water balances, e.g., relative to freshwater discharge to the sea, especially within deep aquifers characterised by low hydraulic conductivity and low freshwater discharge. Transient simulations show that steady-state conditions are a reasonable approximation for a range of transient seawater intrusion situations, including two of the three cases considered in this analysis. We conclude that changes in seawater volumes should be included routinely in coastal aquifer water balances. Also, temporal trends in coastal aquifer water levels may not provide an adequate measure of freshwater storage trends. It follows that the assessment of coastal aquifer condition should consider groundwater levels relative to the hydraulic head imposed by the ocean, accounting for density effects.

Finite element modelling of seawater intrusion in Wadi Ham aquifer, UAE

PurposeSeawater intrusion represents a major problem in many coastal aquifers all over the world. It degrades the water‐quality and hence the groundwater may become unsuitable for domestic and agriculture purposes. Due to the direct hydraulic contact between the freshwater and saline water in coastal aquifers and the density difference between the two water bodies, the seawater migrates inland. The problem is exacerbated when the groundwater abstraction rates exceed the natural recharge from rainfall events. The key to controlling this problem is to maintain the proper balance between water being pumped from the aquifer and the amount of water recharging it. The purpose of this paper is to present a coupled transient finite element model for simulation of fluid flow and solute transport in soils with application to study seawater intrusion in coastal aquifers.Design/methodology/approachThe model includes coupling of fluid flow and solute transport. Transient density‐dependent flow and the dependency of dispersion on velocity are considered. After validation, the model is applied to predict the seawater intrusion in the Wadi Ham aquifer, UAE in vertical sections and the results are compared with those from a commercial code (SEWAT) which was used to simulate seawater intrusion in the aquifer in a horizontal section.FindingsA good agreement is observed between the results of the current model in the vertical cross‐section and those of SEWAT in the horizontal cross‐section for the case of Wadi Ham. The results show that the model can predict the extent of seawater intrusion (and the transition zone) and distribution of salt concentration in the aquifer with a good accuracy.Originality/valueThe developed model includes coupling of fluid flow and solute transport in saturated and unsaturated porous media. Transient density‐dependent flow and the dependency of dispersion on velocity are considered. The model has been applied to a real world case study. A combination of the results in vertical and horizontal sections has been used to build a 3D picture of seawater intrusion in the aquifer.

An integrated approach to assess the quality of groundwater in a coastal aquifer of Andhra Pradesh, India

The Narava basin in Visakhapatnam district situated on the east coast is a productive agricultural area, and is also one of the fastest growing urban areas in India. The agricultural and urban-industrialization activities have a lot of impact on this coastal aquifer water quality. The hydrochemistry of the groundwater was analyzed in the basin area with reference to drinking and agricultural purposes. The area is underlain by Precambrian rocks like khondalites, charnockites and migmatites. The water samples were collected from shallow wells for the year 2008. Physical and chemical parameters of groundwater such as pH, total alkalinity (TA), electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, NO3−, F− were determined. The analytical results revealed that the most of the groundwater found to be in polluted category. Geographical information system (GIS) was utilized to generate different spatial distribution maps of various chemical constituents in the study area. The analytical data were used to compute certain parameters such as salinity hazard, percent sodium (Na%), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), permeability index (PI), Kelley’s ratio (KR) and corrosivity ratio (CR) to determine the quality of water for agricultural purposes. The abundance of the major ions in the basin area was found to be in the following sequence: Na+ > Ca2+ > Mg2+ > K+:Cl− > HCO3− > SO42− > NO3− > F−. According to Gibbs’ diagram most of the samples fall under rock dominance. As per Wilcox and USSL classification most of the groundwater samples are suitable for irrigation except few samples which are unsuitable due to the presence of high salinity and high sodium hazard. From the obtained data, it can be concluded that the water quality profile was good and useful for normal irrigation agriculture.

A Simple Method for Locating the Fresh Water–Salt Water Interface Using Pressure Data

Salt water intrusion is a key issue in dealing with exploitation, restoration, and management of fresh ground water in coastal aquifers. Constant monitoring of the fresh water-salt water interface is necessary for proper management of ground water resources. This study presents a simple method to estimate the depth of the fresh water-salt water interface in coastal aquifers using two sets of pressure data obtained from the fresh and saline zones within a single borehole. This method uses the density difference between fresh water and saline water and can practically be used at coastal aquifers that have a relatively sharp fresh water-salt water interface with a thin transition zone. The proposed method was applied to data collected from a coastal aquifer on Jeju Island, Korea, to estimate the variations in the depth of the interface. The interface varied with daily tidal fluctuations and heavy rainfall in the rainy season. The estimated depth of the interface showed a good agreement with the measured electrical conductivity profile.

Stack unit mapping of coastal aquifer to predict and control sea water intrusion using remote sensing and a geographical information system

AbstractAquifers are inherently susceptible to contamination and coastal aquifers in specific are highly vulnerable to sea water intrusion. For efficient planning and management of coastal aquifers in Kayalpattu and Tiruchopuram villages, which extend over 4·05 km2, it is essential to delineate and predict the extent of intrusion into the shallow aquifer. Management of ground water in coastal aquifers is composed of major elements that should be properly evaluated, and special attention is given to the sea water intrusion problem. Different data, like hydro‐geomorphological and depth‐wise iso‐apparent resistivity, are integrated spatially using a geographical information system. The stack‐unit mapping approach is used to delineate the zones with iso‐apparent resistivity of less than 10 Ω m have been found to be increasing in areal extent with reference to depth. Copyright © 2003 John Wiley & Sons, Ltd.

Numerical modelling and hydrochemical characterisation of a fresh-water lens in the Belgian coastal plain

The distribution of fresh and salt water in coastal aquifers is influenced by many processes. The influence of aquifer heterogeneity and human interference such as land reclamation is illustrated in the Belgian coastal plain where, around A.D. 1200, the reclamation of a tidally influenced environment was completed. The aquifer, which was filled with salt water, was thereafter freshened. The areal distribution of peat, clay, silt and sand influences the general flow and distribution of fresh and salt water along with the drainage pattern and results in the development of fresh-water lenses. The water quality in and around the fresh-water lenses below an inverted tidal channel ridge is surveyed. The hydrochemical evolution of the fresh water lens is reconstructed, pointing to cation exchange, solution of calcite and the oxidation of organic material as the major chemical reactions. The formation and evolution of the fresh water lens is modelled using a two-dimensional density-dependent solute transport model and the sensitivity of drainage and conductivities are studied. Drainage level mainly influences the depth of the fresh-water lens, whereas the time of formation is mainly influenced by conductivity.

Maintaining Fresh-Water Aquifers Over Saline Water in Coastal Aquifers

Seepage analysis is used to investigate the location dependence of fresh-water inputs and outputs in maintaining the depth of the fresh water over the saline water intruding from the sea in coastal aquifers in steady state conditions. Examples are given that show that maximum depths occur when the inputs are in the vicinity of the watershed and the outputs are near the coast.

Mitigation of Seawater Intrusion by Pumping Brackish Water

This paper presents a technique to restore the balance between freshwater and saline water in coastal aquifers in order to mitigate seawater intrusion problems. Brackish water can be pumped from the dispersion zone and then used to develop green lands in the coastal areas or to irrigate certain types of crops. A two-dimensional finite element model (2D-FED), has been employed to verify this technique. The model is based on the dispersion zone approach with a variable density flow. Simulations were preformed in the vertical view and equiconcentration and equipotential lines were plotted for different locations of brackish water pumping. In all of the tested runs the width of dispersion zone has reduced significantly due to brackish water pumping. The quality of the pumped water differs according to the location of pumping. A study case on the Madras aquifer in India is presented.

AN OVERVIEW OF CONTROL OF SALT WATER INTRUSION IN COASTAL AQUIFERS

ABSTRACT The increasing demand for fresh water is being met presently by groundwater resources on a larger scale. Unplanned exploitation of fresh water in coastal aquifers has aggravated the already existed problem of sea water intrusion in several parts of the world. Further deterioration of the situation has to be prevented at this stage by adopting a suitable management scheme dealing with the control of saline water intrusion. Although considerable development has been made in understanding the behaviour of salt water—fresh water relationships in groundwater systems since the time of Badon Ghyben and Herzberg, salt water intrusion control methods are yet to be explored to the full extent. This paper presents an overview of major theoretical and field investigations regarding the techniques for control of salt water intrusion.

An analytic element model for transient axi-symmetric interface flow

The problem of axi-symmetric flow of two immiscible fluids is solved by use of the analytic element method. A sharp interface divides the flow into two domains with different but homogeneous fluids. The sharp interface is realistic for truly immiscible fluids, and is an approximation for miscible fluids such as fresh and salt water in coastal aquifers. A specific discharge potential is introduced which is discontinuous across the interface. The jump in the specific discharge potential depends both on the difference in fluid viscosity and fluid density. The discontinuous specific discharge potential is realized by use of a singularity distribution along the interface. For the case of axi-symmetric flow, the singularity distribution may be approximated by a set of either sink rings or vortex rings. The approach is implemented in a computer program, which is validated by simulating the movement of a spherical inclusion of one fluid in an infinite domain of another fluid, and comparing the results with an exact solution. Finally, the practical use of the program is demonstrated by simulating a saltwater upconing problem underneath a partially penetrating well. The critical pumping rate for which the interface remains stable is determined and compared with both a laboratory experiment and numerical calculations reported in the literature.

GEOCHEMICAL INTERPRETATIONS OF GROUNDWATER FLOW SYSTEMS1

ABSTRACT. Interest in the geochemistry of groundwater is increasing owing to the great number of current projects involving underground liquid waste storage, artificial recharge of potable water, accidental contamination of groundwater bodies, sanitary landfills, and pollution monitoring. Geochemical techniques used to facilitate the understanding of a groundwater system range from extremely simple to those requiring sophisticated theories, equipment, and procedures. An interpretation of the simple trilinear diagram for samples collected from the Yucatan Peninsula of Mexico provided evidence that the fresh‐water body was only a few tens of meters thick and was underlain everywhere by an extensive body of salt water. A geochemical technique that has been used effectively to identify the source of salt water in coastal aquifers is measurement of the carbon‐14 concentrations. Carbon‐14 has been used in a regional carbonate aquifer to determine the velocity of groundwater movement, rates of chemical reactions, and distribution of hydraulic conductivity. The application of principles of irreversible thermodynamics to groundwater systems provides a basis for constructing models which permit prediction, over both time and space, of changes in head distribution and chemical character of the water resulting from imposed stresses on the system. In essence, proper application of irreversible thermodynamics combines the potential theory of Hubbert with principles of reversible chemical thermodynamics, such as solution of carbonate minerals, to describe and explain controlling chemical reactions and processes of groundwater systems.

On the Management of Ground Water in Coastal Aquifers

ABSTRACTManagement of ground water in coastal aquifers is composed of major elements which should be properly evaluated. Emphasis should be made on evaluating these elements by means of basic research; otherwise, the management approaches and research would have no sound foundation. The major elements needed for a proper management are critically discussed and some current misconceptions are pointed out. Special attention is given to leakage and salt‐water encroachment problems. The current means of alleviating salt‐water effects are discussed and a new approach is presented.