Extent Of Seawater Intrusion Research Articles

Quality and health impact of groundwater in a coastal region: a case study from west coast of southern India.

Seawater intrusion seriously threatens the quality of coastal groundwater, affecting nearly 40% of the world's population in coastal areas. A study was conducted in the Kamini watershed situated in the Udupi district of Karnataka to assess the groundwater quality and extent of seawater intrusion. During the pre-monsoon period, 57 groundwater and 3 surface water samples were analyzed to understand the impact of seawater on the groundwater and surface water. The analysis revealed that the groundwater in the study area is slightly alkaline. The weighted overlay analysis map indicated that 11% of the study area is unsuitable for drinking water due to the influence of seawater. The Piper plot analysis revealed that the groundwater is predominantly CaMgCl facies. The hydrogeochemical facies evolution diagram (HFED) showed that 62% of the groundwater is affected by seawater. The HFED and Piper plots also indicate that the surface water is also affected by seawater. These results are also supported by various molar ratios such as Cl- vs. Cl⁻/HCO3⁻, Cl⁻ vs. Na⁺/Cl⁻, Cl- vs. SO42-/Cl-, and Cl⁻/HCO3- vs. Mg2+/Ca2+, suggesting that the majority of the water sample has been affected by seawater. The saturation indices indicated that mineral dissolution has significantly contributed to groundwater salinization. The correlation between sulfate concentration and calcite and dolomite dissolution suggested the influence of seawater intrusion in the coastal aquifer. The process of reverse ion exchange mainly influences the groundwater chemistry according to chloroalkali indices. The total hazard index (THI) values of nitrate and fluoride exceeded limits, posing health risks to adults and children. Studies suggest that with time and space, seawater intrusion is increasing in some pockets of the study area, especially along the west coast.

Water Resource Management of Salalah Plain Aquifer Using a Sustainable Approach

A sustainable approach is proposed for managing the effects of salinity ingression in Salalah coastal aquifer, Oman. This paper aims to analyze and compare the groundwater levels and salinity of the aquifer from 1993 to 2027, considering both predictive and actual transient scenarios. Two novel scenarios were proposed, established, and examined in this study to bring back the aquifer to steady-state condition. The first scenario entails ceasing groundwater pumping from both Salalah and Saada wellfields, while compensating for the groundwater supply from these sources with surplus desalinated water. This scenario is projected to occur during the predictive period spanning from 2023 to 2027, denoted Scenario A. The second scenario is business as usual and involves continuing pumping from both wellfields during the same predictive period, denoted Scenario B. A numerical model for 3D flow simulation and advective transport modeling showed that on the eastern side of the Salalah coastal aquifer, the extent of seawater intrusion (SWI) was identified stretching from the shoreline to a distance of 1800 m, 1200 m, 0 m, and 600 m, in years 2011, 2014, 2018, and 2022 under the transient period, whereas SWI was delineated in land up to 0 m and 700 m in the predictive year 2027 under Scenarios A and B, respectively. In the western side of Salalah coastal aquifer, SWI was delineated in land up to 2000 m, 1700 m, 0 m, and 800 m, in years 2011, 2014, 2018, and 2022 under the transient period, whereas SWI was delineated in land up to 0 m and 750 m in the predictive year 2027 under Scenarios A and B, respectively. This study claims that Scenario A effectively pushed the seawater interface back to the coastline, projecting its reach to the shoreline (0 m) by 2027. In contrast, in baseline Scenario B, the wedge of saline intrusion in the Salalah coastal aquifer was delineated from the shoreline, up to 800 m inland, which accounted for continuation of pumping from both wellfields during the predictive period. The study concludes that Scenario A has the capability to efficiently reduce the impact of saline inflows from the coast, while Scenario B results in a more pronounced impact of salinity intrusion.

The Spatio-Temporal Dynamic Patterns of Shallow Groundwater Level and Salinity: The Yellow River Delta, China

Shallow groundwater in coastal aquifers is a highly dynamic and complex system with a high risk of seawater intrusion. Analyzing the spatio-temporal dynamic patterns of groundwater can help to manage the groundwater resource and prevent it from degradation. Based on the groundwater level (GWL) and electrical conductivity (EC) monitoring data of 18 observation wells in the Yellow River Delta (YRD) from 2004 to 2010, this research analyses the groundwater dynamics using a robust seasonal trend decomposition technique (STL) and spatial interpolation method to detect the groundwater spatio-temporal dynamic patterns of groundwater level and salinity. Combined with hydro-climatic data, the Pearson correlation method and the Mann-Kendall (MK) trend analysis were used to further reveal the impacts that induce their trends and seasonal variations. Our analyses show that the risk of seawater intrusion into local shallow aquifers in this region is high, with the mean groundwater level over 42% of the region lower than the local sea level, and the mean groundwater EC over 96% of the region met the standards for seawater intrusion. In addition, the trends of groundwater level generally declined by 0.01~0.45 m/a and salinity increased by 1.153~25.608 μs/cm.a, which are consistent with the trend of precipitation decline. The seasonal dynamics of groundwater level and salinity are highly correlated with the seasonal components of rainfall and evaporation. It can be concluded that the extent of seawater intrusion will increase in the future with sea level rise. The approaches used in this study proved to be effective and can certainly serve as an example for the analysis of the spatio-temporal dynamics of groundwater in other coastal regions.

Microbial Diversity in Groundwater and Its Response to Seawater Intrusion in Beihai City, Southern China.

Seawater intrusion is a major concern commonly found in coastal aquifers worldwide. Because of the intense aquifer exploitation and land-based marine aquaculture in the coastal area of Beihai City, Guangxi Zhuang Autonomous Region, China, numerous underground aquifers in this area have been affected by seawater intrusion. However, the microbial communities in freshwater aquifers and their response to seawater intrusion are still unclear. In this study, groundwater from three aquifers was collected from three monitoring sites at different distances from the coastline in the coastal area of Beihai City, and the hydrochemical characteristics of these groundwater samples and the structure of the associated microbial communities were analyzed. The Cl− concentration of the samples indicated that seawater intrusion had occurred in the research area up to 1.5 km away from the coastline, but the monitoring site 2 km away from the coastline had yet to be affected. Statistical analysis showed that the bacterial communities in different groundwater aquifers were significantly correlated with the Cl− concentration, thereby suggesting that the extent of seawater intrusion might be one of the primary factors shaping bacterial composition in groundwater of this area, but the composition and distribution of archaea did not show a significant response to seawater intrusion and presented no apparent correlation with the Cl− concentration. α-, γ-Proteobacteria and Bacteroidota were the dominant bacterial lineages, accounting for about 58–95% of the bacterial communities. Meanwhile, the predominant archaeal taxa were mainly composed of Crenarchaeota, Nanoarchaeota, and Thermoplasmatota, as accounting for 83–100%. Moreover, there was significant spatial heterogeneity of microbial communities in the aquifers affected by varying degrees of seawater intrusion. The microbial communities inhabiting the unconfined aquifer were influenced by the geochemical fluctuation caused by seawater infiltration from land-based marine aquaculture ponds and the diffusion of eutrophic surface water. In contrast, changes in microbial community structure in the confined aquifers were closely related to the environmental gradient caused by different degrees of seawater intrusion. In addition, we also found that the tidal cycle did not significantly affect the structure of microbial communities inhabiting confined aquifers that had been long affected by seawater intrusion.

Seawater intrusion into an underground water-sealed oil storage cavern: Effects of water curtain system, hydraulic conductivity and dispersivity

The construction of underground facilities in coastal area usually results in seawater intrusion, which affects the service life of underground facilities. Considering the effects of different water curtain systems, hydraulic conductivity, and dispersivity, the dynamic seawater intrusion characteristics of an underground water-sealed oil storage cavern in coastal area have been obtained by numerical simulation based on multi-physical field coupling theory. The results show that in terms of the extent and scope of seawater intrusion, compared with only setting horizontal water curtain, adding vertical water curtain is more effective in controlling seawater intrusion; as the depth of the vertical water curtain increases, the effect of preventing seawater intrusion is better. When the equivalent hydraulic conductivity is the same and the anisotropy ratio of hydraulic conductivity increases, the extent of seawater intrusion is weaker; when the anisotropy ratio of hydraulic conductivity is the same and the equivalent hydraulic conductivity increases, the extent of seawater intrusion is weaker. As the longitudinal dispersivity becomes larger, the extent of seawater intrusion is weaker. The water-sealed safety and water inflow of the underground water-sealed oil storage cavern have been analyzed. The research results could provide a theoretical basis for the seawater intrusion problem faced by the construction of underground water-sealed oil storage caverns in coastal area, and have a certain guiding effect on the excavation of underground facilities in coastal area.

Influence of Dynamically Stable‐Unstable Flow on Seawater Intrusion and Submarine Groundwater Discharge Over Tidal and Seasonal Cycles

AbstractTemporal changes in the external forcing conditions of coastal aquifer systems, such as seasonal inland freshwater input, may disturb the balance between the ocean forces and freshwater hydraulic gradient. An increase or decrease in this imbalance may affect the stability of tide‐induced upper saline plume (USP). In this study, we performed laboratory experiments and numerical simulations to investigate the influence of seasonal inland freshwater input on USP stability and the associated behavior of seawater intrusion (SWI) and submarine groundwater discharge (SGD). In contrast to previous studies, we found that USP was not always stable or unstable in the intertidal zone, but experienced a dynamically stable‐unstable process as the seasonal inland freshwater input varied. The extent of SWI and SGD showed a dual response to the seasonal inland freshwater input. On one hand, seasonal fluctuation in inland freshwater input directly induced responsive changes in SWI and SGD; on the other hand, dynamic stability of the USP caused by the seasonal fluctuation resulted in an additional high‐frequency fluctuation in the extent of SWI and SGD during the unstable flow. Moreover, the response of saline SGD and total SGD to the seasonal fluctuation in the inland freshwater input was nonlinear. This overall increased the SGD compared to the scenarios with a temporally constant inland freshwater input. Therefore, ignoring seasonal changes in the inland freshwater input may underestimate the amount of water exchanges across the aquifer‐sea interface.

Development of Multi-Criteria Decision Making Methods for Reduction of Seawater Intrusion in Coastal Aquifers Using SEAWAT Code

Unplanned pumping of groundwater in the past two decades has caused many regional problems and tensions, leading to seawater intrusion into coastal aquifers. The main objective of this paper is the use of a Multi-Criteria Decision-Making (MCDM) approach combining with numerical simulation for reducing seawater intrusion in the Tajan coastal aquifer located on the southern seashores of the Caspian Sea, Iran, taking into account economic, social, and environmental issues. The MODFLOW code was used to simulate the groundwater flow. MT3DMS and SEAWAT codes were used to simulate the solute transport and seawater intrusion. A 10-year period from 2010 to 2020 was simulated for evaluating the current conditions and forecasting the future conditions of the aquifer. The results indicated an increase in the extent of seawater intrusion. To assess the proposed eleven curative solutions, the economic, social, and environmental criteria such as efficiency of applying of curative solutions in improvement of the aquifer's water level and efficiency of applying of curative solutions on reduction in the extent of the seawater intrusion were weighted using the Analytic Hierarchy Process (AHP) method. The results of the AHP method showed that the criterion of efficiency of applying of curative solutions in improvement of the aquifer's water level with the weight of 0.311 was the most important one. Three multi-criteria decision making methods namely, Simple Additive Weighting (SAW), Technique for Order Performance by Similarity (TOPSIS), and VIse Kriterijumska Optimizacija kompromisno Resenje (VIKOR) were utilized to select the best curative solution. The solution of 10% reduction of pumping rate and the construction of Gelvard dam in the SAW and TOPSIS methods and the solution of 3% reduction of pumping rate and the construction of Gelvard dam in the VIKOR method ranked first. Combined techniques namely, the Rank Average Method, Borda's Method, and Copeland's Method were used to develop a consensus on prioritizing curative solutions for the Tajan Aquifer. The results of these techniques showed that the solution of 10% reduction in pumping rate along with the construction of the Gelvard dam was the best. The results of simulating this solution demonstrated a 1.91 m improvement in the groundwater level of the aquifer in the MODFLOW code and a 361.5-m recede in seawater intrusion length along the coast in the SEAWAT code.

Influence of Tide‐Induced Unstable Flow on Seawater Intrusion and Submarine Groundwater Discharge

AbstractRecent studies have confirmed the instability of tide‐induced upper saline plume (USP) in tidal beach aquifers. A systematic understanding of how the unstable USP contributes to groundwater flow and salinity distribution is still lacking. Here we used laboratory experiments and numerical simulations to examine the responses of the salinity distribution and submarine groundwater discharge (SGD) to tide‐induced unstable flow. The results revealed that changes in physical forcing conditions (tides and inland freshwater input) drove the transition of the USP from stable to unstable states. Meanwhile, the phase‐averaged SGD and its components fluctuated over time, and their oscillation amplitudes depended on the physical forcing conditions. There was a correlation between USP instability and the fluctuation of water exchange across the aquifer‐sea interface. The fluxes across the aquifer‐sea interface under unstable conditions usually varied considerably over time with a lower frequency in comparison to stable conditions. The extent of seawater intrusion (SWI) measured by the total salt mass stored in the aquifer also varied over time, especially under unstable conditions. The vibration tendency of the total salt mass was opposite to that of the sum of inland freshwater discharge and tide‐induced circulation efflux. For coastal aquifers affected by tides, SWI was dominated by the sum of inland freshwater discharge and tide‐induced circulation efflux, followed by the sum of inland freshwater input and tide‐induced circulation influx. These findings lay the foundation for gaining a better understanding of tide‐induced unstable flow and its potential implications.

Study of seawater intrusion in coastal aquifer using total dissolved solid, conductivity and salinity measurement in Labuhan Kertasari Village, West Sumbawa

Indonesia is an archipelagic country that has a larger ocean area than land, many people live in coastal areas and still experience difficulties in obtaining springs that can be used for their daily needs. This study was conducted to see the extent of seawater intrusion into a coastal aquifer in Labuhan Kertasari Village. The method of measuring Total Dissolved Solids, Conductivity, and Salinity is used in studying seawater intrusion into a coastal aquifer. Coastal aquifer samples were taken from open wells and boreholes belonging to residents which are actively used on a daily basis. Analysis of the relationship between TDS, conductivity and, salinity used simple linearity analysis, and distribution mapping using surfer 8. The highest TDS concentration, conductivity, and salinity were 5770 ppm; 8700 MS/cm; and 4600 ppm on the S8. While the TDS concentration, conductivity, and salinity were the lowest consecutively were 836 ppm; 1258 MS/cm; 700 ppm on S26. In general, the coastal aquifer in residents’ wells has experienced various intrusions and has decreased at a distance from the shoreline.

A conjunctive management framework for the optimal design of pumping and injection strategies to mitigate seawater intrusion

Coastal aquifer management (CAM) considering conjunctive optimization of pumping and injection system for seawater intrusion (SI) mitigation poses significant decision-making challenges. CAM needs to pose multiple objectives and massive decision variables to explore tradeoff strategies between the conflicting resources, economic, and environmental requirements. Here, we investigate a joint artificial injection scheme for ameliorating SI by establishing an evolutionary multi-objective decision-making framework that combines simulation-optimization (S–O) modelling with a cost-benefit analysis, and demonstrate the framework on a large-scale CAM case in Baldwin County, Alabama. First, a SI numerical model, using SEAWAT, was configured to predict the vulnerable region as an SI encroachment area with the scenarios of minimum and maximum pumping capacity. As a result, a smaller number of candidate sites were selected in the SI encroachment area for implementing groundwater injection to avoid the computationally infeasible SI optimization with an inordinate number of injection related decision variables. Second, the effective S–O methodology of niched Pareto tabu search combined with a genetic algorithm (NPTSGA), which considers the moving-well option, was applied to discover optimal pumping/injection (P/I) strategies (including P/I rates and injection well locations) between three conflicting management objectives under complicated SI constraints. Third, for practical operation of the P/I schemes, a cost-benefit analysis provides judgment criteria to allow decision-makers to implement more sustainable P/I strategies to capture the different realistic preferences. The implementation of three extreme optimization solutions for the case study indicates that, compared to the initial unoptimized scheme, a maximum increase of a factor of 3 in groundwater extraction rates, a maximum reduction of 17% in extent of SI, and a maximum 82.3 million US dollars in comprehensive benefits are specifically achieved by conjunctive P/I optimization. The robustness in the decision alternatives attributed to the uncertainty in physical parameters of hydraulic conductivity was discovered through global sensitivity analysis. The proposed framework provides a decision support system for multi-objective CAM with combined pumping control and engineering measures for SI mitigation.

Groundwater Flow Assessment Using Modflow 6 and Model Muse: Application to Pointe-Noire Coastal Aquifers, Congo-Brazzaville

As numerical modeling is an effective tool for managing groundwater resources and predicting future responses, in this study, the author has intended to assess groundwater flow through Modflow 6 and Model Muse into Pointe-Noire coastal aquifers. The results showed that the fourth scenario has the biggest effect on the drawdown and seawater intrusion extent. Different parameters including evapotranspiration, recharge, model boundary, etc. were adjusted to run the model. The fourth scenario with the highest pumping rate value caused a slight increase of head values over the values simulated.

Assessing the origin and processes controlling groundwater salinization in coastal aquifers through integrated hydrochemical, isotopic and hydrogeochemical modelling techniques

ABSTRACT The origin of groundwater and the processes controlling its chemical composition in complex coastal aquifers are of interest, as about 44% of the world’s population lives in coastal areas. Groundwater over-exploitation in the highly urbanized coastal regions has exerted pressure on these aquifers, leading to seawater intrusion. This study aimed to identify (1) the complex relationship between natural and anthropogenic factors, and (2) the hydrogeochemical processes controlling the groundwater chemistry in an over-stressed coastal aquifer of southern India. The results indicate an increase in the extent of seawater intrusion from 4 km in 1969 to 17 km in 2014. Major hydrogeochemical processes controlling the aquifers are evaporation, ion exchange and dissolution of aluminosilicates, gypsum, halites and calcites. The integrated use of field investigation with hydrochemical, isotopic and hydrogeochemical modelling techniques allowed a conceptual model of the groundwater salinization process over 46 years to be developed as a basis for designing sustainable management measures.

An integrated electrical resistivity and geochemical approach to delineate groundwater contamination due to seawater intrusion in the southern part of Mangalore, Karnataka, India

In this paper, integration of electrical resistivity survey and chemical analyses of groundwater has been executed in Mangalore’s southern part, Karnataka to delineate seawater intrusion phenomena. About 11 locations representing different hydrogeological and geomorphological setups were selected for the vertical electrical sounding (VES) to identify the subsurface formations and the extent of seawater intrusion. With the VES, the contaminated groundwater zones and the depth to fresh and saline water interface have been demarcated. Overall, 59 groundwater samples were subjected to various geochemical analysis viz; pH, electrical conductivity (EC), total dissolved solids (TDS), salinity, total hardness, alkalinity, calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), sodium (Na2+), potassium (K+)and sulfate (SO4 2-) to understand the nature of salinity in the aquifer. The geochemical analyses show that good groundwater conditions characterize the study area except for the southern part. The southern part is under the moderate to high salinity hazard risk, possibly due to its proximity to the sea and hydraulic connection with the seawater through the tidal creek. Two among the VES locations situated in this region show a saline water trend towards the bottom, and in the rest of the VES locations, a freshwater trend is encountered towards the depth.

Stochastic Simulation of the Spatial Heterogeneity of Deltaic Hydrofacies Accounting for the Uncertainty of Facies Proportions

The spatial geological heterogeneity of an aquifer significantly affects groundwater storage, flow and the transport of solutes. In the particular case of coastal aquifers, spatial geological heterogeneity is also a major determining factor of the spatio-temporal patterns of water quality (salinity) due to seawater intrusion. Whist the hydraulics of coastal hydrogeology can be modelled effectively by various density flow equations, the aquifer geology is highly uncertain. A stochastic solution to the problem is to generate numerical realisations of the geology using sequential stratigraphy, geophysical models or geostatistical approaches. The geostatistical methods (two-point geostatistics, Markov chain models and multiple-point geostatistics) have the advantage of minimal data requirements, e.g., when the only data available are from cores from a few sparsely located boreholes. We provide an extension of sequential indicator simulation by including the uncertainty of the hydrofacies proportions in the simulation approach. We also deal with the problem of variogram estimation from sparse boreholes and we discuss the implicit transition probabilities and the connectivity of simulated realisations of a number of categorical variables. The variogram model used in the simulation of hydrofacies significantly influences the degree of connectivity of the hydrofacies in the simulated model. The choice of model is critical as connectivity determines the amount and extent of seawater intrusion and hence the environmental risk. The methodology is illustrated with a case study of the Andarax river delta, a coastal aquifer in south-eastern Spain. This is a semi-arid Mediterranean region in which the increasing use of, and demand for, groundwater is exacerbated by a transient tourist population that reaches its peak in the summer when the demand for the permanent population is at its highest. The work reported here provides a sound basis for designing flow simulation models for the optimal management of groundwater resources. This paper is an extended version of a presentation given at the 2012 GeoENV Conference held in Valencia, Spain.

Degradation of groundwater quality in the coastal aquifers of the USA

The objective of this study is to analyze groundwater types and the extent of seawater intrusion in terms of ion concentrations in groundwater sample using USGS monitoring wells. Groundwater quality indices [fsea, GQI (dom), GQI (mix), GQI (swi)] were used to estimate the spatial distributions of groundwater types in the US coastal aquifers. Results showed that the dominating groundwater chemistry in the study area was Na+ and Cl−. Results also indicated that seawater intrusion of groundwater occurred in the US coastal aquifers. Based on the results of GQI (mix) and GQI (dom), most of the wells fell under domain II in the Piper diagram, indicating that they were of the Na–Cl water type. Na–Cl and mixed Ca–Mg–Cl were determined to be the two dominant groundwater types in the coastal aquifers of the US seawater intrusion evident in the Palm Beach and Miami-Dade counties of Florida, the San Diego and Santa Barbara areas of California, and within Virginia and New Jersey on the east coast. As the sea level continues to rise further inland, Na–Cl concentration in groundwater will increase, particularly in aquifers along low-lying coasts.

Seawater intrusion in the coastal aquifers of East and Horn of Africa: A review from a regional perspective

As coastal areas continue to experience population and economic growth, there is a need for more holistic understanding of the attendant environmental challenges towards ensuring sustainability. The over 8300km continental coastline stretch of East and Horn of Africa from Sudan to Tanzania is not an exception. A typical challenge associated with coastal areas is seawater intrusion (SWI) into coastal aquifers. Several efforts have been made in understanding this phenomenon and developing management strategies in different parts of the world. This has led to an evolution of different techniques for assessing the extent of seawater intrusion. This paper explores the status and extent of SWI studies in the region, focusing on the trend of techniques and methodologies used in the past 5 years. The findings show that at a regional level, there is more empirical knowledge on SWI in Kenya, Djibouti, and Tanzania while that of Sudan, Eritrea, and Somalia is largely vague for obvious reasons – more studies have been conducted in the former countries. Hydrogeochemical techniques coupled with statistical and analytical tools are the most prevalent approaches. Furthermore, the extents of SWI vary significantly from location to location but rarely extend beyond a few km inland in the region. SWI extent and severity were also shown to vary with seasons in studies covering temporal dimensions. The review shows that more research capacity building is needed especially in countries like Sudan, Somalia, Djibouti and Eritrea. Finally, recommendations on SWI research and management frontiers to explore in the region are suggested.

Effects of Temperature on Tidally Influenced Coastal Unconfined Aquifers

AbstractAquifer‐ocean temperature contrasts are common worldwide. Their effects on flow and salinity distributions in unconfined coastal aquifers are, however, poorly understood. Based on laboratory experiments and numerical simulations, we examined the responses of flow processes in tidally influenced aquifers to aquifer‐ocean temperature differences. The extent of seawater intrusion and seawater circulation were found to vary with the aquifer‐ocean temperature contrast. Compared with the isothermal case, an increase of up to 40% of the tide‐induced seawater circulation rate in the intertidal zone was observed when seawater is warmer than groundwater. In contrast, saltwater circulation in the lower saltwater wedge declines notably no matter whether the seawater is warmer or colder than groundwater. As the seawater temperature rises, the contribution of tide‐induced circulation to the overall increase of submarine groundwater discharge becomes more important compared with that of density‐driven seawater circulation. Both the upper saline plume and the freshwater discharge zone expand significantly with warmer seawater whereas the lower saltwater wedge contracts.

Numerical investigation on seawater intrusion and water leakage in different types of stratified coastal aquifers

Prediction of seawater intrusion (SWI) will increase the proper planning for withdrawal of groundwater, and it will help the freshwater management in the future. Since heterogeneous aquifers are more widespread than homogeneous one, this study aims to use the density-dependent SEAWAT code to investigate the influence of different combinations of hydraulic conductivity (K) on SWI. The effects of numbers and arrangement of layers with different K are examined on (a) toe position, (b) freshwater–seawater mixing zone thickness (Wt) and (c) leakage from adjacent layers in a steady-state condition. For this purpose, numerous scenarios with different K were simulated and analyzed. The results of horizontally layered aquifers showed that the streamlines are broken on boundary of layers. It was observed that when K is decreased, especially at the middle layer, the refraction angle is increased and consequently Wt is increased. The Wt in vertically layered cases was less than horizontally layered aquifers because of less streamline breakage. Also, random arrangement of K directs the saline flow to higher permeability zones. Thus, the SWI extent in this type of aquifer was more tangible than other types. Because of the difference in hydraulic head at layer borders, the seepage rate significantly increases nearby toe position and the dominant direction is upward. However, in the steady-state condition, the type of flow did not differ significantly for boundary cells of layers at the vicinity of toe position.

Gaussian Process Regression Tuned by Bayesian Optimization for Seawater Intrusion Prediction.

Accurate prediction of the seawater intrusion extent is necessary for many applications, such as groundwater management or protection of coastal aquifers from water quality deterioration. However, most applications require a large number of simulations usually at the expense of prediction accuracy. In this study, the Gaussian process regression method is investigated as a potential surrogate model for the computationally expensive variable density model. Gaussian process regression is a nonparametric kernel-based probabilistic model able to handle complex relations between input and output. In this study, the extent of seawater intrusion is represented by the location of the 0.5 kg/m3 iso-chlore at the bottom of the aquifer (seawater intrusion toe). The initial position of the toe, expressed as the distance of the specific line from a number of observation points across the coastline, along with the pumping rates are the surrogate model inputs, whereas the final position of the toe constitutes the output variable set. The training sample of the surrogate model consists of 4000 variable density simulations, which differ not only in the pumping rate pattern but also in the initial concentration distribution. The Latin hypercube sampling method is used to obtain the pumping rate patterns. For comparison purposes, a number of widely used regression methods are employed, specifically regression trees and Support Vector Machine regression (linear and nonlinear). A Bayesian optimization method is applied to all the regressors, to maximize their efficiency in the prediction of seawater intrusion. The final results indicate that the Gaussian process regression method, albeit more time consuming, proved to be more efficient in terms of the mean absolute error (MAE), the root mean square error (RMSE), and the coefficient of determination (R2).

An Efficient Simulation–Optimization Approach for Controlling Seawater Intrusion

ABSTRACT Yang, Y.; Wu, J.; Lin, J.; Wang, J.; Zhou, Z., and Wu, J., 2018. An efficient simulation–optimization approach for controlling seawater intrusion. In: Wang, D. and Guido-Aldana, P.A. (eds.), Select Proceedings from the 3rd International Conference on Water Resource and Environment (WRE2017). Journal of Coastal Research, Special Issue No. 84, pp. 10–18. Coconut Creek (Florida), ISSN 0749-0208. The management of freshwater stored in coastal aquifers involves decisions regarding not only the sustainable utilization and exploration of optimal coastal groundwater resources but also the designing of optimal strategies for controlling seawater intrusion (SI). Simultaneously optimizing pumping operation, the extent of SI, and design of mitigation measures is a challenging task because mitigating SI has become imperative for groundwater management of coastal aquifers. This study proposed a simulation-optimization framework (SWT-NPTSGA) to search Pareto-optimal solutions for estimating the optimal pumping ...