Extent Of Seawater Intrusion Research Articles

Groundwater resources evaluation in calcareous limestone using geoelectrical and VLF-EM surveys (El Salloum Basin, Egypt)

Understanding and developing groundwater resources in arid regions such as El Salloum basin, along the northwestern coast of Egypt, remains a challenging issue. One-dimensional (1D) electrical sounding (ES), two-dimensional (2D) electrical resistivity imaging (ERI), and very low frequency electromagnetic (VLF-EM) measurements were used to investigate the hydrogeological framework of El Salloum basin with the aim of determining the potential for extraction of potable water. 1D resistivity sounding models were used to delineate geoelectric sections and water-bearing layers. 2D ERI highlighted decreases in resistivity with depth, attributed to clay-rich limestone combined with seawater intrusion towards the coast. A depth of investigation (DOI) index was used to constrain the information content of the images at depths up to 100 m. The VLF-EM survey identified likely faults/fractured zones across the study area. A combined analysis of the datasets of the 1D ES, 2D ERI, and VLF-EM methods identified potential zones of groundwater, the extent of seawater intrusion, and major hydrogeological structures (fracture zones) in El Salloum basin. The equivalent geologic layers suggest that the main aquifer in the basin is the fractured chalky limestone middle Miocene) south of the coastal plain of the study area. Sites likely to provide significant volumes of potable water were identified based on relatively high resistivity and thickness of laterally extensive layers. The most promising locations for drilling productive wells are in the south and southeastern parts of the region, where the potential for potable groundwater increases substantially.

Assessment of sea water inundation along Daboo creek area in Indus Delta Region, Pakistan

Indus Deltaic Region (IDR) in Pakistan is an erosion vulnerable coast due to the high deep water wave energy. Livelihood of millions of people depends on the fisheries and mangrove forests in IDR. IDR consists of many creeks where Daboo is a major creek located at southeast of the largest city of Pakistan, Karachi. Unfortunately, there has been no detailed study to analyze the damages of sea water intrusion at a large temporal and spatial scale. Therefore, this study is designed to estimate the effects of sea water inundation based on changing sea water surface salinity and sea surface temperature (SST). Sea surface salinity and SST data from two different surveys in Daboo creek during 1986 and 2010 are analyzed to estimate the damages and extent of sea water intrusion. Mean salinity has increased 33.33% whereas mean SST decreased 13.79% from 1987 to 2010. Spatio-temporal analysis of creek area using LANDSAT 5 Thematic mapper (TM) data for the years 1987 and 2010 shows significant amount of erosion at macro scale. Creek area has increased approximately 9.93% (260.86 m2 per year) which is roughly equal to 60 extensive sized shrimp farms. Further Land Use Land Cover (LULC) analyses for years 2001 and 2014 using LANDSAT 7 Enhanced Thematic Mapper Plus (ETM+) has indicated 42.3% decrease in cultivated land. Wet mud flats have spread out at the inner mouth of creek with enormous increase of 123.3%. Significant sea water intrusion has increased the area of barren land by 37.9%. This also resulted in overall decrease of 6.7% in area covered by mangroves. Therefore, this study recorded a significant evidence of sea water intrusion in IDR that has caused serious damages to community living in the area, economical losses. Additionally, it has also changed the environment by reducing creek biological productivity as reported by earlier studies over other regions of the world.

Modeling of seawater intrusion in a coastal aquifer of Karaburun Peninsula, western Turkey

Seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could be easily influenced by seawater. This study presents the development of a conceptual and numerical model for the coastal aquifer of Karareis region (Karaburun Peninsula) in the western part of Turkey. The study also presents the interpretation and the analysis of the time series data of groundwater levels recorded by data loggers. The SEAWAT model is used in this study to solve the density-dependent flow field and seawater intrusion in the coastal aquifer that is under excessive pumping particularly during summer months. The model was calibrated using the average values of a 1-year dataset and further verified by the average values of another year. Five potential scenarios were analyzed to understand the effects of pumping and climate change on groundwater levels and the extent of seawater intrusion in the next 10 years. The result of the analysis demonstrated high levels of electrical conductivity and chloride along the coastal part of the study area. As a result of the numerical model, seawater intrusion is simulated to move about 420 m toward the land in the next 10 years under “increased pumping” scenario, while a slight change in water level and TDS concentrations was observed in “climate change” scenario. Results also revealed that a reduction in the pumping rate from Karareis wells will be necessary to protect fresh groundwater from contamination by seawater.

Assessment of drought impacts on semi-arid coastal aquifers of the Mediterranean

Long-term impacts of drought, such as groundwater decline, can emerge during a persisting drought. Though not easily visible, they are severe and harder to cope with. Groundwater is considered a resilient source during drought in semi-arid areas. In this paper the response of a coastal aquifer to meteorological drought severity is investigated. The relation between drought severity and natural undisturbed coastal aquifer flow conditions is determined, based on the seawater intrusion extent, at a temporal scale. The Reconnaissance Drought Index (RDI) is used to assess the meteorological drought severity, since it incorporates precipitation and potential evapotranspiration, which both affect the recharge processes. Recharge volumes for different timeseries, estimated through a hydrological model, are used as input to a transient variable-density and salt transport numerical model. An indicator based on the freshwater volume and RDI index, are used to assess the aquifer response to drought. The multi-year drought effect is also investigated. The results show that the RDI index can be utilised successfully to associate the meteorological drought with aquifer flow conditions. Specifically, a reliable early prediction of the freshwater availability at the end of the hydrological year can be achieved by the RDI of the first semester.

Numerical modeling of seawater intrusion in Zhoushuizi district of Dalian City in northern China

Since 1980s, seawater intrusion in coastal aquifers caused by groundwater over-abstraction has led to extensive deterioration in groundwater quality and quantity and has been fazing local residents in Zhoushuizi district of the metropolitan Dalian City in northern China. In this study, a three-dimensional (3D) density-dependent numerical model was constructed to simulate the seawater intrusion process in heterogeneous coastal aquifers in Zhoushuizi district of the metropolitan Dalian City. Considering that the groundwater flow in karst aquifers in northern China is relatively uniform, approximately following Darcy’s law, the fracture-karst aquifer in Zhoushuizi district of Dalian City was simplified as an equivalent porous medium. To further identify the hydrogeological parameters of the aquifers in the study area, the model was calibrated and validated using the observation heads and concentrations. Based on the current groundwater abstraction conditions of the study area, the calibrated and validated model was then applied to predict the dynamics and trend of seawater intrusion for the following 30 years from 2010 to 2040 under different rainfall scenarios. The overall extent of seawater intrusion in the future would be even more severe under different prediction scenarios. This 3D seawater intrusion model provides the theoretical basis for implementing a reasonable allocation of groundwater resource, which may significantly affect the sustainability of water resources.

Study of Seawater Intrusion in Tajoura Area

The aim of this study is to know the extent of seawater intrusion into groundwater. The geo-electrical method was used to measure the resistivity of subsurface layers. Field measurements were conducted using a resistivity device with a Schlumberger array. Variable electrodes were spread with a maximum distance of 400 m. Readings of 18 Vertical Electrical Soundings were taken in the area of study which has several wells that were formerly studied using chemical analysis method of well samples. Electrical data were analyzed and interpreted and horizontal and vertical sections of apparent resistivity were drawn, also contour maps of iso-resistivity lines were constructed. It has been clearly shown that seawater intruded into groundwater in the study area.

Assessment of seawater intrusion into underground oil storage cavern and prediction of its sustainability

Operation of underground oil (gas) storage cavern in coastal area can induce seawater intrusion because excavation of underground storage cavern causes the groundwater level decrease of coastal aquifer. Seawater intrusion has the potential to cause the corrosion of underground cavern facility and leakage of gas and oil from the storage caverns, therefore, seawater intrusion into the underground storage caverns should be evaluated carefully to avoid unexpected operation problems. In this study, the extent of seawater intrusion into underground oil storage cavern in Yeosu, Korea, was assessed through field monitoring and numerical modeling to evaluate the storage cavern sustainability against seawater intrusion. The mean values of seawater mixing ratios of seepage water in each cavern, estimated through modeling, range from 0.01 to 8.70 %, which are less than the measured mixing ratio (2.3–12.8 %) based on the Cl− concentrations. This result indicates that other source of Cl− may have contributed to the observed salinity in the cavern seepage water. Spatial and temporal variations in monitoring data and numerical modeling demonstrate that the location of storage, seepage water flow rate, and the fracture zones are important factors controlling seawater mixing ratio. Seawater intrusion barrier wells located along the coastline were shown to be important to prevent seawater intrusion into the storage caverns significantly. The predicted seawater mixing ratio after 100 years of cavern operation is 0.06–12.7 % varying depending on the caverns’ location.

Soil microbial community response to seawater intrusion into coastal aquifer of Donghai Island, South China

Due to the sea level rise and the excessive exploitation of freshwater, seawater intrusion is becoming a critical issue. To clarify the degree of seawater intrusion in Donghai Island and the microbial community structure and functional response to seawater intrusion, groundwater samples and sediment samples were collected at profiles A, B; the profiles were along the direction of groundwater flow, perpendicular to the coastline, a hydrogeochemical survey and soil microbial community analysis were also performed. The hydrogeochemistry analysis showed that the chemical type of groundwater was Na–Cl, brackish water was dominant in the area, and coastal groundwater was strongly affected by seawater intrusion. The effect of seawater intrusion on structural and functional diversity of soil microbes was analyzed from soil samples of the study area, by polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). The results of DGGE patterns and phylogenetic tree show that the extent of seawater intrusion has directly influenced soil microbial community structure. The changes of microbial community structure might be related to the major elements’ concentrations in groundwater. Phylogenetic affiliation indicated that γ-proteobacteria were dominated in the profile A, while β-proteobacteria were mainly appeared in the profile B. The Flavobacteriaceae was only appeared at the shrimp ponds nearby.

A Modelling Study of Seawater Intrusion in the Liao Dong Bay Coastal Plain, China

To investigate the extent of seawater intrusion in the Liao Dong Bay coastal plain, China, a numerical model for variable-density groundwater flow and miscible salt transport was developed. The SEAWAT code was used to solve the density-dependent groundwater flow and solute transport governing equations. The simulation was conducted for 55 months from October, 2004 to April, 2009. The numerical model was calibrated by the hydraulic heads measured in April, 2009. Using the calibrated model and the same hydrogeological conditions in 2004, the extent of seawater intrusion prediction was conducted for the next 40 years. The results show that the extent of seawater intrusion area will increase in all geologic layers with nearly 6.2 km in the upper Quaternary aquifer and 4.3 km in lower Quaternary aquifer for 40 years. In the Minhuazhen group aquifer, the maximum speed of seawater intrusion is 62.2 m/yr. Therefore, some protection of the freshwater aquifer from seawater intrusion in the Liao Dong Bay coastal plain is imperative.

A note on “Origin of components in Chilean thermal waters” by

Risacher et al. (2011) have presented voluminous data on thermal waters of Chile that is quite appreciable; however, their work still falls short on several counts. The most notable shortcoming of the work is the presentation and treatment of data. The interpretations are based on questionable premises (viz., extent of seawater intrusion) and considerations (viz., using average chemical composition of rock types for geochemical modeling, considering volcanic rocks as the only rock type in contact with the geothermal fluids) and assumptions not always substantiated by facts (with proper references) could have been corroborated. Use of Cl/Br ratio for discrimination purpose is unconvincing, considering the uncertainty in the measurement of low (<1 mg/L) Br concentration.

Assessment of seawater intrusion in Langat basin, Malaysia

Seawater intrusion is threatening freshwater resources in coastal regions worldwide. Modelling this phenomenon can help in the management and control of such problems. This study presents a numerical model of seawater intrusion in a semi-confined aquifer in the lowland area of the Langat basin, Selangor, Malaysia, where groundwater is the only source of water supply for mega industrial projects. To provide useful measures for protecting groundwater from pollution by seawater intrusion, a three-dimensional numerical model, Seawat-2000, was applied. The numerical model incorporates regional geological, geographical, and hydrogeological features. The input parameters to the model were determined from well logs, well drillers' reports, and pumping tests. After the model was calibrated using data for the year 2010, the model was used to predict the extent of seawater intrusion for the future (2011–2045) assuming that the current condition of the Langat basin remains unchanged. The results show that the aquifer in the study area will be significantly influenced by seawater intrusion for the next 35 years.

A Combined Radio- and Stable-Isotopic Study of a California Coastal Aquifer System

Stable and radioactive tracers were utilized in concert to characterize geochemical processes in a complex coastal groundwater system and to provide constraints on the kinetics of rock/water interactions. Groundwater samples from wells within the Dominguez Gap region of Los Angeles County, California were analyzed for a suite of major cations (Na+, K+, Mg2+, Ca2+) and anions (Cl−, SO42−), silica, alkalinity, select trace elements (Ba, B, Sr), dissolved oxygen, stable isotopes of hydrogen (δD), oxygen (δ18O), dissolved inorganic carbon (δ13CDIC), and radioactive isotopes (3H, 222Rn and 223,224,226,228Ra). In the study area, groundwater may consist of a complex mixture of native groundwater, intruded seawater, non-native injected water, and oil-field brine water. In some wells, Cl− concentrations attained seawater-like values and in conjunction with isotopically heavier δ18O values, these tracers provide information on the extent of seawater intrusion and/or mixing with oil-field brines. Groundwater 3H above 1 tritium unit (TU) was observed only in a few select wells close to the Dominguez Gap area and most other well groundwater was aged pre-1952. Based on an initial 14C value for the study site of 90 percent modern carbon (pmc), groundwater age estimates likely extend beyond 20 kyr before present and confirm deep circulation of some native groundwater through multiple aquifers. Enriched values of groundwater δ13CDIC in the absence of SO42− imply enhanced anaerobic microbial methanogenesis. While secular equilibrium was observed for 234U/238U (activity ratios ~1) in host matrices, strong isotopic fractionation in these groundwater samples can be used to obtain information of adsorption/desorption kinetics. Calculated Ra residence times are short, and the associated desorption rate constant is about three orders of magnitude slower than that of the adsorption rate constant. Combined stable- and radio-isotopic results provide unique insights into aquifer characteristics, such as geochemical cycling, rock/water interactions, and subsurface transport and mixing.

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.

Tidal influence on seawater intrusion in unconfined coastal aquifers

Studies of seawater intrusion in unconfined coastal aquifers typically neglect oceanic oscillations such as tides and assume a static seaward boundary condition defined by the mean sea level. Laboratory experiments and numerical simulations were conducted to investigate the influence of tidal oscillations on the behavior of the saltwater wedge. For the conditions examined, the experiments showed that an upper saline plume formed in the intertidal zone due to tide‐induced seawater circulation. The presence of the upper saline plume shifted the fresh groundwater discharge zone seaward to the low‐tide mark and restricted the intrusion of the saltwater wedge. The overall seawater intrusion extent, as indicated by the wedge toe location, was reduced significantly compared with the nontidal (static) case. Results from the numerical model matched these experimental observations and further demonstrated the similar type of tidal influence on the saltwater wedge in a field‐scale aquifer system. The Glover (1959) solution for predicting the saltwater wedge was modified to account for the tidal effect by including the tide‐induced circulation as a “recharge” to the aquifer. The findings highlight the significant impact of the tide in modulating the groundwater behavior and salt‐freshwater dynamics, not only within but also landward of the intertidal zone.

Application of groundwater model in coastal aquifer: A case study of Veraval area of Gujarat

The development and management of fresh ground water resources in coastal aquifers are seriously constrained by the presence of seawater intrusion. Seawater intrusion is a process that occurs in virtually all coastal aquifers, where they are in hydraulic continuity with seawater. This process is caused by the higher density of sea water than freshwater. Over the years, many models have been developed to represent and study the problems related to seawater intrusion. Numerical models provide effective tool to handle ground water problems. This paper presents simulation of seawater intrusion in a section of the Veraval coast of Gujarat through Saturated and Unsaturated Transport model and examines the impact of increased pumping scenarios on extent of seawater intrusion. The density driven salt-water intrusion process was simulated with the use of commercially available finite element based software, SUTRA (Saturated–Unsaturated TRAnsport). Initial and boundary conditions determined from the aerial calibration were used to evaluate steady-state, hydraulic heads. Pumping and inflow of coastal area was estimated for three different time periods using the model.

The Influence of Seawater on a Coastal Aquifer in an International Protected Area, G&amp;#246;ksu Delta Turkey

Goksu Delta is an important wetland where the Goksu River reaches the sea in the eastern part of the town of Tasucu-Ice1. The delta is classified as a Wetland of International Importance according to the Ramsar Convention. In the Goksu Delta area, urban and agricultural expansions have caused an ever-growing need for fresh water. High groundwater pumping rates and overexploitation of the aquifers, leading to seawater mixing in the Goksu coastal aquifers. The chemical types of groundwater from alluvial aquifer are Ca-Mg-HCO3, but in the region where sea water mixing is occurred it changes and the Na and Cl ions are added to groundwater. The similar occurrence can be observed in the groundwater from the limestone aquifer. The chemical types of groundwater are Ca-HCO3 or Ca-Mg-HCO3 and they change to Ca-Na-Mg-HCO3-Cl in the vicinity of seawater mixing regions. A statistical comparative analysis also shows that some of the samples are affected by sea water mixing. The extent of seawater intrusion is reflected by the distribution of salinity and electrical conductivity as an equiconcentration map.

Analytical models of contaminant transport in coastal aquifers

The Henry formulation, which couples subsurface flow and salt transport via a variable-density flow formulation, can be used to evaluate the extent of sea water intrusion into coastal aquifers. The coupling gives rise to nontrivial flow patterns that are very different from those observed in inland aquifers. We investigate the influence of these flow patterns on the transport of conservative contaminants in a coastal aquifer. The flow is characterized by two dimensionless parameters: the Péclet number, which compares the relative effects of advective and dispersive transport mechanisms, and a coupling parameter, which describes the importance of the salt water boundary on the flow. We focus our attention on two regimes – low and intermediate Péclet number flows. Two transport scenarios are solved analytically by means of a perturbation analysis. The first, a natural attenuation scenario, describes the flushing of a contaminant from a coastal aquifer by clean fresh water, while the second, a contaminant spill scenario, considers an isolated point source.

Spatial Analysis of Small-Loop Electromagnetic Survey Data in a Seawater Intrusion Region

The main purpose of this study is to apply spatial analysis using semivariograms to small-loop electromagnetic survey data to assess the extent of seawater intrusion in an experimental watershed. To indicate the extent of seawater intrusion over the study area, vertical electrical soundings at 33 points and electrical conductivity logging in two wells were conducted. From the correlation between resistivities obtained by inversion and the depth of the aquifer at the two wells, the region of seawater intrusion was identified and demonstrated by electrical conductivity logging results obtained over two years. To measure the variation of apparent conductivity with depth, an electromagnetic survey in six frequency bands was adopted. Apparent conductivity mapping with spatial analysis using semivariograms is an effective technique for identifying the region of seawater intrusion at shallow depth.

Simulation of coastal groundwater remediation: the case of Nardò fractured aquifer in Southern Italy

A new theoretical approach for evaluating the sharp interface position in a fractured aquifer was applied to the Nardò aquifer (Southern Italy). The results, based on Dupuit and Ghyben–Herzberg approximations, clearly show both the extent of seawater intrusion and how the latter can be reduced by means of artificial recharge. The new methodology describes a simplified mathematical formulation based on the sharp freshwater–saline interface in a fractured aquifer, rather than solving complicated density dependent partial differential equations of flow and solute transport in porous media. Application of the method requires, in a preliminary stage a knowledge of the freshwater flow rates in the fractured media. This can be derived by means of specific computational codes, under steady conditions. In the second stage, the extent of seawater intrusion can be evaluated in vertical planes of a three-dimensional domain. The methodology was applied to the Nardò fractured rock aquifer in order to estimate the extent to which seawater had intruded into it. The procedure was easily implemented in a job file of EXCEL Microsoft Office and performed well. Results indicated a good correlation between the coastal spring zones of the model with Landsat Thematic Mapper sensor photos and field investigation.

Assessment of seawater intrusion using geophysical well logging and electrical soundings in a coastal aquifer, Youngkwang-gun, Korea

A combination of drilling, geophysical well logging, and electrical soundings was performed to evaluate seawater intrusion in Baeksu-eup, Youngkwang-gun, Korea. The survey area extends for over 24 km2. To delineate the extent of seawater intrusion, 60 vertical electrical soundings (VES) have been carried out. Twelve wells were also drilled for the collection of hydrogeological, geochemical, and geophysical well logging data, to delineate the degree and vertical extent of seawater intrusion. To map the spatial distribution of seawater in this coastal aquifer, geophysical data and hydrogeochemical results were used, and the relation between the resistivity of groundwater and equivalent NaCI concentration was found. Layer parameters derived from VES data, various in-situ physical properties from geophysical well logging, and the estimated equivalent NaCI concentration were very useful for quantitative evaluation of seawater intrusion. Our approach for evaluating seawater intrusion can be considered a valuable attempt at enhancing the use of geophysical data.