Groundwater Vulnerability Modeling to Assess Seawater Intrusion: a Methodological Comparison with Geospatial Interpolation

Seawater intrusion has become a growing threat in coastal urban cities due to overexploitation of groundwater. This study examines the accuracy of the commonly used geospatial quality assessment models (GQA) and groundwater vulnerability assessment models (GVA) in determining the extent of seawater intrusion in urban coastal aquifers. For that purpose, interpolation methods (kriging, IDW and co-kriging) and vulnerability assessment models (DRASTIC, EPIK) were compared using groundwater salinity criteria (TDS, Cl^?) collected at three pilot areas along the eastern Mediterranean (Beirut, Tripoli, Jal el Dib). The results showed that while the GIS-based interpolation methods and the vulnerability assessment models captured elements of the groundwater quality deterioration, both had a limited ability to accurately delineate saltwater intrusion. This emphasizes that while interpolation methods and conventional vulnerability models may give general information about groundwater quality, they fail to capture the status of the aquifer at a finer spatial resolution.

     

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

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

     

Influences of coastal underground reservoir construction and utilization on saltwater and freshwater transport law in aquifersEI北大核心CSCD

In order to reveal the impact of underground reservoir construction and extraction methods on the saltwater and freshwater transport law in coastal aquifers, a 300m × 900m × 30m conceptual numerical model was established. The variable density current simulation method of unconfined aquifer was used to analyze the saltwater and freshwater transport law in coastal aquifer under different extraction scenarios before and after the construction of underground dam. The results show that the construction of underground dam can significantly reduce the scope and degree of seawater intrusion. Groundwater extraction can accelerate the intrusion and diffusion of residual saltwater in underground reservoirs within a certain time range. The coefficient of saltwater intrusion is exponentially related to extraction scale and the distance between extraction wells and underground dams. Reasonable layout of the location and scale of extraction wells can effectively reduce the negative impact of groundwater extraction on water salinity in the reservoir area. © 2023, Editorial Board of Water Resources Protection. All rights reserved.     

Monitoring and Predicting Saltwater Intrusion via Temporal Aquifer Vulnerability Maps and Surrogate Models

This article proposes a methodology to accurately monitor seawater intrusion (SWI) using time-varied GALDIT vulnerability maps. The properly produced samples are then used as input–output patterns for the approximate SWI simulation. As a novelty, the specific area of high susceptibility to SWI is proposed as the dynamic saltwater wedge position to suitably select the monitoring locations (MLs) from a narrowed area. It is observed that varied initial conditions over time periods have more influence than variable pumping rates on salinity at MLs far from the production wells. Support Vector Regression (SVR), Artificial Neural Network (ANN) and Gaussian Process Regression (GPR) models have been substituted for the numerical model of SWI. Input training patterns of the surrogate models are initial salinity concentrations at selected MLs plus transient pumping values via Latin hypercube sampling. The final salinity at MLs constitutes the output patterns. The paper applies this new methodology to a small study area subject to the SWI problem. The generalization ability of surrogate models for predicting new initial conditions-pumping datasets was evaluated using performance criteria considering the ML locations. All surrogates offered good results for predicting SWI at specified MLs. The SVR model had poor performance compared to ANN and GPR models in MLs near the pumping wells, due to their salinity fluctuations over time.

     

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

Coastal aquifers are vulnerable to saltwater intrusion (SWI) due to several drivers particularly increased water demand and groundwater overexploitation associated with population growth, reduced groundwater recharge, and lately climate change. This study examines the status of SWI in four data scarce coastal aquifers located along the Eastern Mediterranean by assessing how water cycle seasonality, water deficits, and changes in land use and land cover (LULC) have contributed to increased salinity. A framework that combines field monitoring with hydro-geochemical techniques, as well as multivariate and inferential statistical analysis was used to identify the main SWI drivers at play at each aquifer. The overall assessment showed that all four pilot areas exhibited signs of salinization with different severities. The current state of the aquifers ranged from slightly saline (TDS < 1500 ppm) to highly saline (15,000 < TDS < 31,000 ppm). While the level of the SWI was significantly correlated to the dominant land uses at each site, the extent of the water deficit played a dominant role in explaining the occurrence and intensity of observed SWI rates. The findings suggest a synergistic effect between increased water deficits and urbanization and SWI. Site specific measures are discussed for mitigating the impacts of land use, water demand and deficit towards the sustainable management of the groundwater aquifers.

     

Coupled Sharp-interface and Density-dependent Model for Simultaneous Optimization of Production Well Locations and Pumping in Coastal Aquifer

The main management challenge in coastal aquifers is to prevent saltwater intrusion, ensuring ample freshwater supply. Saltwater intrusion happens due to unregulated pumping from production wells. Therefore, it is essential to have an effective management policy, which ensures the requisite amount of freshwater to be withdrawn from coastal aquifers without causing saltwater intrusion. A methodology for optimizing production well locations and maximizing pumping from production wells is presented to achieve these conflicting objectives. The location of production wells directly affects the amount of freshwater pumped out of the coastal aquifer. Simultaneous optimization of production well locations and pumping from the same is achieved by linking mathematical simulation models with the optimization algorithm. A new methodology using coupled sharp-interface and density-dependent simulation models is developed to find optimal well locations and optimize the amount of freshwater pumped from the coastal aquifer. The performance of the developed methodology is evaluated for saltwater intrusion in the coastal city of Puri, India. The performance evaluation results show the developed methodology's applicability for managing saltwater intrusion while maximizing freshwater pumping in coastal aquifers under constraints of well location.

     

海水入侵模拟理论与方法研究进展

对海水入侵模拟研究涉及的海水入侵监测指标、数学模型及数值方法、临海边界处理和海水入侵防治对策研究等方面做了全面总结,并指出海水入侵数值模拟研究进一步发展的方向和研究中亟待解决的问题。认为变密度过渡带模型将是海水入侵研究的主流模型,而自适应欧拉拉格朗日方法是求解此类模型最有效的数值方法。另外,指出硼同位素特别适合于水文地质条件复杂的滨海含水层海水入侵的监测。     

Assessment of Water Resources Availability and Groundwater Salinization in Future Climate and Land use Change Scenarios: A Case Study from a Coastal Drainage Basin in Italy

The joint effect of changes in climate and land use on the future availability of water resources was assessed under the SRES A1B and A2 climate scenarios as well as five land use scenarios for the 2080–2100 time-frame in an Italian coastal watershed. The study area is a small coastal polder (100 km²) characterized by irrigated agriculture, urban expansion, drainage, quarrying and sensitivity to salt-water intrusion. The hydroclimatic budget and the GALDIT index have been computed for assessing water resources availability and groundwater vulnerability to salinization, respectively. The methodology developed is integrated into a tool based on Excel?, which supported the development of scenarios in participatory processes. The conclusions emerged from the analysis are the following: (1) climate change is more effective than land use change in controlling future freshwater availability and amplifies the imbalance between winter surplus and summer deficits, (2) freshwater availability in the summer will likely be affected by an increase in evaporation from open water surfaces due to increased temperature, whereas winter surplus would increase, (3) the vulnerability of the coastal aquifer to salinization will probably moderately increase but an inherent limitation of the GALDIT index to land use change parameters prevents a sound assessment. Strategies that may be proposed to administrators and stakeholders are based on increasing storage of seasonal water surplus.     

Mathematical models for saltwater intrusion in coastal aquifers

Flow of freshwater and saltwater intrusion in coastal aquifers has drawn the attention of many investigators. Several laboratory, as well as mathematical models have been developed to study the pattern of flow of groundwater in coastal aquifers. Mathematical models have wider range of application and are the concern of this paper. Due to the complex nature of the problem, each of these mathematical models are based on certain simplifying assumptions and approximations. This paper presents a critical review of various methods of solution which have been proposed. The validity of the results abtained and the limitations of these models are also discussed.     

Optimal Locations of Groundwater Extractions in Coastal Aquifers

A regional water supply management model for coastal aquifers was developed. One of its outcomes is the definition of the optimized locations for groundwater withdrawal. Such a tool permits the analysis of alternative plans for groundwater extraction and the sustainable use of water resources in a coastal aquifer subject to saltwater intrusion. The principal components are the evolutionary optimization and the analytical/numerical simulation models. The optimization technique looks for the best well locations taking into consideration the economic results and the satisfaction of the societal water demand. However these two concerns are conditioned by trying to control the saltwater intrusion, i.e., preserving the environmental equilibrium. The simulation model uses the governing mathematical equations for groundwater movement to find the interface between freshwater and saltwater. Because of the non-linearity in the system and the possibility of a jumping interface, a security distance was defined. This is a controlling variable which can be set by the decision makers. The model was applied to a typical case with interesting results. For example, diagrams showing the relationship between the location of the wells and the security distance(s) are of importance to the managers. It was also crucial to have an understanding of the tradeoffs between groundwater withdrawals, positions of the wells from the coast line, and the security distance. The model was also applied to a real case in order to relate the extractions, distances and artificial recharge (not presented in this paper).     

Global Assessment of Seawater Intrusion Problems (Status and Vulnerability)

In this research paper we propose a novel method to perform an integrated analysis of the status and vulnerability of coastal aquifers to seawater intrusion (SWI). The method is based on a conceptual approach of intrusion that allows to summarised results in a visual way at different spatial scales, moving from steady pictures (corresponding to instantaneous or mean values in a period) including maps and 2D conceptual cross-sections and temporal series of lumped indices. Our aim is to help in the identification of coastal groundwater bodies at risk of not achieving good chemical status according to the Water Framework Directive. The indices are obtained from available information about aquifer geometry and historical monitoring data (chloride concentration and hydraulic head data). This method may be applied even in cases where a reduced number of data are available. It does not require complex modelling and has been implemented in a GIS tool that encourages its use in other cases. Analysis of the evolution of historical time series of these indices can be used to assess resilience and trends with respect to SWI problems. This method can be also useful to compare intrusion problems in different aquifers and temporal periods.     

Impacts of Receding of the Lakes Located in the Arid and Semi-arid Areas on the Coastal Groundwater: Integrated Modeling and Experimental Study

The dropping of the water level of the lakes located in the arid lands leads to salt concentration increase. In this study, a combined experimental-computational method is developed to explore the effect of seawater concentration on the elevation of groundwater table and the rate of saltwater intrusion, while the lake water level is dropping. At the laboratory tank scale, we have collected experimental data by varying the saltwater concentration by 2.0 and 2.5 times its initial value while measuring the height of the groundwater table. Our simulation has shown an unexpected increase in height of groundwater by 5.0 and 13.0% relative to the head difference at the boundaries of the domain. Also, the intrusion rate of saltwater wedge increased by 2.0 and 3.0 times, respectively. We have used the verified model for a field state and found that if density variations are neglected in simulation, the calculated groundwater level is affected more than 2 times in response to fluctuation of lake water level (relative to simulations by including the effect of fluid density changes). Based on the results density variations can counteract; even reverse, the effect of water table changes. Remarkably, our simulations have shown that despite a severe decrease in the water level of a saline lake over time, the saltwater wedge has indeed intruded further because of the substantial increase in the density of the lake water due to the rising salinity. Based on the findings, to reach a reasonable result in the study of interaction between saline water of shrinking lakes with coastal groundwater, saltwater concentration as well as saline water density in the modeling must be considered.

     

陆源淡水流量对海岸水库海水入侵的影响

采用平板水槽系统开展了室内物理模型试验,探究了陆源地下水流量与入库地表水流量对海岸水库海水入侵的影响.结果表明:海岸水库的下盐水楔入侵长度与陆源淡水流量呈对数下降关系,随着陆源淡水流量的增大,下盐水楔入侵长度减小趋势减弱;与陆源地下水相比,入库地表水对海岸水库海水入侵的抑制作用更显著;随着陆源淡水流量增大,海岸水库库底...     

A Cost-Effective Method to Control Seawater Intrusion in Coastal Aquifers

Intrusion of seawater into coastal aquifers is considered one of the most important processes that degrade water-quality by raising the salinity to levels exceeding acceptable drinking standards. Therefore saltwater intrusion should be prevented or at least controlled to protect groundwater resources. This paper presents a cost-effective method to control seawater intrusion in coastal aquifers. This methodology ADR (Abstraction, Desalination and Recharge) includes; abstraction of saline water and recharge to the aquifer after desalination. A coupled transient density-dependent finite element model is developed for simulation of fluid flow and solute transport and used to simulate seawater intrusion. The simulation model has been integrated with an optimization model to examine three scenarios to control seawater intrusion including; abstraction, recharge and a combination system, ADR. The main objectives of the models are to determine the optimal depths, locations and abstraction/recharge rates for the wells to minimize the total costs for construction and operation as well as salt concentrations in the aquifer. A comparison between the combined system (ADR) and the individual abstraction or recharge system is made in terms of total cost and total salt concentration in the aquifer and the amount of repulsion of seawater achieved. The results show that the proposed ADR system performs significantly better than using abstraction or recharge wells alone as it gives the least cost and least salt concentration in the aquifer. ADR is considered an effective tool to control seawater intrusion and can be applied in areas where there is a risk of seawater intrusion.     

Synergy of climate change and local pressures on saltwater intrusion in coastal urban areas: effective adaptation for policy planning

ABSTRACT

This article examines the relative impacts of anthropogenic interventions and global climate change on the dynamics of saltwater intrusion in highly urbanized coastal aquifers. For this purpose, simulations of the impacts of sea-level rise and abstraction scenarios for the near future were undertaken for a pilot aquifer using a multi-objective 3D variable-density flow and solute transport model. We find that sea-level rise associated with climate change has less influence on the encroachment of salinity than anthropogenic abstraction, which has a more appreciable impact on saltwater intrusion through greater sensitivity to water consumption and seasonality.     

The Importance of Data Acquisition Techniques in Saltwater Intrusion Monitoring

A detailed vertical characterization of a coastal aquifer was performed along a flow path to monitor the seawater intrusion. Physico-chemical logs were obtained by both open-borehole logging (OBL) and multilevel sampling technique (MLS) via straddle packers in piezometers penetrating the coastal aquifer of the Po River Delta, Italy. The open borehole logs led to a satisfactory reconstruction of the extent of the fresh-saltwater interface but provided a misleading characterization of the distribution of redox environments within the aquifer. On the contrary, good fits between sedimentological, stratigraphycal and physico-chemical data were obtained using the straddle packers devices. This study demonstrates that, within coastal shallow aquifers evenly recharged by irrigation canals, the simple and economical OBL technique can lead to misleading results when used to characterize density dependent groundwater stratification but is deemed adequate for preliminary assessments of the saltwater wedge location.     

A Suitable Tool for Sustainable Groundwater Management

Artificial recharge is used to increase the availability of groundwater storage and reduce saltwater intrusion in coastal aquifers, where pumping and droughts have severely impaired groundwater quality. The implementation of optimal recharge methods requires knowledge of physical, chemical, and biological phenomena involving water and wastewater filtration in the subsoil, together with engineering aspects related to plant design and maintenance operations. This study uses a novel Decision Support System (DSS), which includes soil aquifer treatment (SAT) evaluation, to design an artificial recharge plant. The DSS helps users make strategic decisions on selecting the most appropriate recharge methods and water treatment technologies at specific sites. This will enable the recovery of safe water using managed aquifer recharge (MAR) practices, and result in reduced recharge costs. The DSS was built using an artificial intelligence technique and knowledge-based technology, related to both quantitative and qualitative aspects of water supply for artificial recharge. The DSS software was implemented using rules based on the cumulative experience of wastewater treatment plant engineers and groundwater modeling. Appropriate model flow simulations were performed in porous and fractured coastal aquifers to evaluate the suitability of this technique for enhancing the integrated water resources management approach. Results obtained from the AQUASTRESS integrated project and DRINKADRIA IPA CBC suggest the most effective strategies for wastewater treatments prior to recharge at specific sites.     

Evaluation of a GIS-Based Integrated Vulnerability Risk Assessment for the Mancha Oriental System (SE Spain)

It is widely recognized that groundwater-vulnerability maps are a useful tool for making decisions on designating pollution-vulnerable areas, in addition to being a requirement of European Directive 91/676/EEC. This study addressed the vulnerability of the Mancha Oriental System (MOS) to groundwater contamination with an integrated Generic and Agricultural DRASTIC model approach. In the MOS, groundwater is the sole water resource for a total population of about 275,000 inhabitants and for 1,000 km² of irrigated crops. DRASTIC vulnerability maps have been drawn up for two different years (1975 and 2002) in which the potentiometric surface has dropped dramatically (80 m in some areas) due to the considerable expansion of irrigated croplands. The quality of available resources has also deteriorated due to the agricultural practices and the discharge of wastewater effluents. Vulnerability maps are used to test the data on nitrate, sulphate, and chloride contents in groundwater in the Central and El Salobral-Los Llanos hydrogeologic domains of the MOS for 2002. Regardless of the method applied, the dramatic alteration in land use leads to a change in the DRASTIC index and vulnerability to groundwater contamination decreases for the study period. Vulnerability in the MOS increases in areas where the irrigation return flow is notable. The lack of a statistical correspondence between the DRASTIC index and the spatial distribution of nitrate, chloride, and sulphate contents and the distribution of the pollution load suggest that this method does not accurately assess the risk of the MOS to groundwater pollution.     

太行山前丘陵区基岩裂隙水赋存的非均一性和易疏干性特性

根据碧流河流域生态特征,分析了适合该流域的河道生态需水计算方法,应用于碧流河水库兴利调度,并以生态目标为基础,确定下游河道的生态需水量。结果表明:碧流河水库下游河道生态环境基本供水量及改善供水量分别需要2 765万m3和4 250万m3。为了保护和改善河流生态环境,促进流域水资源可持续利用,需要采取最严格的用水管理制度,加大非常规水源的开发利用力度,并结合调水工程以及河库连通工程等相关措施。     

滨海地下水库功能的价值评估

黄水河地下水库建成于1995年,是典型的滨海地下水库,由补源渗井、河道拦蓄工程、地下挡水坝、工业废水排放系统、供水工程、监测管理系统六部分组成,具有调蓄水资源、防止海水入侵、提高地下水位等多种功能。对水库功能的价值评估结果表明:黄水河地下水库功能的直接价值为1 925万元,间接价值为15 533.4万元;调蓄水资源和防止海水入侵的价值尤为突出,体现了黄水河地下水库巨大的生态环境效益。