Groundwater Vulnerability Mapping Research Articles

Modified DRASTIC index model for groundwater vulnerability mapping using geostatistic methods and GIS in the Mitidja plain area (Algeria)

The Mitidja plain area, located in north Algeria, is one of the main agricultural plains in the Mediterranean basin where water supplies are mainly provided by groundwater resource. Due to the effects of a rapid population increase, followed by an intensification of agricultural activities, a proper groundwater vulnerability assessment became urgent. In this study, the DRASTIC model has been utilized to produce a map of groundwater vulnerability for nitrate pollution. To improve the standard DRASTIC vulnerability map, and to offer an innovative and easy tools for water resource protection and water forensics, the rating classes of the DRASTIC model was modified using the real nitrate concentrations analyzed in 44 groundwater sample while sensitivity analysis was used to change the parameter’s weights. The validation of the standard DRASTIC model shows a coincidence rate of 67% while the validation of the modified DRASTIC model shows a coincidence rate of 82% (improvement of 15%) with nitrates. The results highlighted two main findings: i) the reliability of modified DRASTIC model, and ii) the dependence of nitrate vulnerability on net recharge, aquifer type, soil texture and topography. The proposed approach demonstrated to be more appropriate in assessing the groundwater vulnerability compared to standard DRASTIC proving to be easy applicable and suitable in any arid and semi-arid region around the world.

A multi-methodological approach to create improved indicators for the adequate karst water source protection

Karst water sources already meet about a quarter of the world's drinking water needs, and their importance is growing. Due to the complexity of water flow in carbonate aquifers, karst water sources require particularly appropriate protection. The scientific literature lacks analytical evidence of the effects of the current legislative frameworks and improved methodological approaches for ecological indications to design alternative strategies. This gap is addressed in the present study, which draws on a combination of investigation methods considering specifics of water flow in karst and on a comprehensive database of general knowledge to gain relevant understanding of the hydrological system functioning. An advanced, multi-methodological approach, which was developed in this study and includes geological and hydrogeological mapping, spring monitoring, tracer tests, water balance and groundwater vulnerability assessment, enabled achievement of optimized indicators for the adequate karst water source protection measures. It demonstrates, that protection zoning based solely on fundamental hydrogeological knowledge, general prediction of groundwater residence times or distance criteria may lead to a high degree of imprecision. Currently valid protection measures may therefore generally be associated with great uncertainties and the high vulnerability of karst areas may be underestimated. In addition to the existing legal requirements for karst water source protection zoning, environmental indicators such as natural and artificial tracers should be considered, which most reliably confirm the directions and characteristics of groundwater flow in karst. Similarly, mapping of groundwater vulnerability to contamination can be of particular importance for the implementation of freshwater protection and spatial planning at least in karst-rich countries. The approach enables scientists to gain relevant insights into the functioning of the hydrological system and environmental managers to protect karst water sources.

Groundwater vulnerability assessment using GIS-based DRASTIC model in Nangasai River Basin, India with special emphasis on agricultural contamination

Nangasai basin is a semi-arid watershed where agriculture is the main source of economy. In present day, increasing population demands increase in food productivity which leads to increase use of fertilizers and chemical pesticides in agriculture. These fertilizers on the other hand mix up with the groundwater and increase the pollution, which affects human health adversely. So, for controlling the groundwater contamination risk proper water resource management and assessment of groundwater vulnerability is extremely important. Total 7 hydrogeological parameters have been considered for this study, and the final groundwater vulnerability map has been prepared by overlay weighted method with the help of DRASTIC index, which is classified into 5 vulnerable classes (very high, high, moderate, low, and very low). In the south and south-eastern regions of the basin namely Deghi, Bankada, Baram, Macha, Katin, Tilabani high groundwater contamination is been observed. For validating the model, the water quality parameters-nitrate and TDS have been used with the accuracy of 89% and 86% respectively. Using effective as well as scientifically approved methods, the anthropogenic and agricultural contamination can be controlled and managed which will lower the risk of contamination. This map can be further utilized as a base map for management of groundwater pollution and its planning.

Groundwater vulnerability to pollution in karst aquifers, considering key challenges and considerations: application to the Ubrique springs in southern Spain

Groundwater vulnerability mapping is one of the tools most often applied to analyse the sensitivity of karst aquifers to pollution. These maps aim to support stakeholders in decision-making and to promote land-use management compatible with water protection; however, the validation of these maps is still a challenge in many cases, triggering high uncertainty. For karst media, due to the strong heterogeneity in recharge mechanisms and hydraulic characteristics, validation is a significant stage and it must be inherent within the groundwater vulnerability assessment process. This work aims to assess the implementation of tools used for protecting the quality of water discharging or extracted from the Ubrique karst system in southern Spain, which supplies drinking water that is threatened by periodical pollution/turbidity episodes. A groundwater vulnerability map, attained by application of the COP method and validated by multiple in-situ observations, shows an extremely vulnerable system due to the absence of protective overlayers and the significant development of exokarst landforms, including shallow holes. This map could constitute the basis for defining protection zones for the Ubrique springs; however, their comprehensive protection requires the implementation of monitoring tools and an effective management strategy, through an early warning system that assures stable environmental and hydrogeological conditions and improves operational procedures associated with the drinking water service. This research establishes the strong relationship of the different methods applied to protect the source from contamination events, ranging from classical hydrodynamic and hydrochemical approaches to the implementation of protection zones and early warning groundwater quality monitoring networks.

Groundwater vulnerability mapping using the modified DRASTIC model: the metaheuristic algorithm approach.

Vulnerability assessment and mapping is a significant tool for sustainable management of the precious natural groundwater resources. DRASTIC is an extensively used index model to map groundwater vulnerable zones. However, the original DRASTIC model rates and weights used in most of the research depict the poor correlation between nitrate concentration and groundwater vulnerability index. Wilcoxon test and five population-based metaheuristic (MH) algorithms, namely, firefly algorithm (FA), invasive weed optimization (IWO), teaching learning-based optimization (TLBO), shuffled frog leaping algorithm (SFLA), and particle swarm optimization (PSO), were used to optimize the rates and weights of the DRASTIC model to improve its accuracy. The performance of all the employed metaheuristic algorithms converges to a global optimal solution at different iterations, and to choose the best algorithm for DRASTIC weights optimization, a ranking methodology was proposed. The algorithms were ranked by calculating the relative closeness of alternatives with computational speed and the number of iterations as attributes in the TOPSIS method.This study identifies FA as the outperforming algorithm among the employed for this specified weight optimization problem based on ranking. The result of the optimization model proposed depicts significant improvement in the correlation coefficient between the groundwater vulnerability index and nitrate concentration from 0.0545 for the original DRASTIC model to 0.7247 for the Wilcoxon-MH- DRASTIC. Hence, this ranking approach can be adopted when global optimal solution is found by all employed algorithms in DRASTIC weight optimization.

Assessment of groundwater vulnerability using modified DRASTIC-Analytical Hierarchy Process model in Bucak Basin, Turkey

This study includes hydrogeological studies covering the Bucak Basin located in the feeding area of Kirkgoz Springs, which is the drinking water source of Antalya. Hydrogeological data has been evaluated based on Geographic Information Systems with modified DRASTIC-Analytic Hierarchy Process methods. The aim of the study is to present groundwater vulnerability in order to evaluate the pollution potential of groundwater in the Bucak Basin. For this purpose, the DRASTIC method, which includes 7 different parameters, was used to determine the vulnerability of groundwater. The method has been modified via Analytic Hierarchy Process during the weighting of the DRASTIC parameters. In the preparation of thematic maps of weighted parameters, Geographic Information Systems was utilized. Two different basin-based groundwater vulnerability maps were obtained with the calculation of the DRASTIC index and modified DRASTIC-Analytic Hierarchy Process index values. While on the DRASTIC index vulnerability map, 29.7% of the study area has high, 53.4% has medium, and 16.9% has low groundwater vulnerability; on the modified DRASTIC-Analytic Hierarchy Process index vulnerability map, 10% of the study area has very high, 26.3% has high, 60% has a medium, and 3.7% has a low vulnerability. On both groundwater vulnerability maps, the environment with the highest pollution vulnerability has been found to be the alluvium aquifer in which agricultural activities are carried out. As a result of the study, it has been concluded that the pollution sources of agricultural origin are the important pollution factors in terms of groundwater vulnerability in the Bucak Basin. It has been established that the DRASTIC method alone cannot represent the features of the application area, therefore by adding the lineament and land use parameters and weighting the parameters again with Analytic Hierarchy Process, more sensitive and accurate results have been obtained. Geographic Information Systems-based modified DRASTIC-Analytic Hierarchy Process integration has been demonstrated to be an effective tool for the assessment of groundwater pollution vulnerability and water resources management in the Bucak Basin. The results of the study are thought to become an important source in the decisions of local authorities on water resources management.

Groundwater vulnerability mapping using the Susceptibility Index (SI) method: Case study of Takelsa aquifer, Northeastern Tunisia

The Takelsa phreatic aquifer currently shows stress signs and the contamination risk of groundwater by different chemical elements and pesticides is a likely concern. Here we assessed the aquifer vulnerability using the Susceptibility Index (SI) method, considered as a specific vulnerability method that takes into consideration the impact of land uses chemical fertilizers, anthropogenic activities and natural factors as a source of contaminants in groundwater. WetSpass and MODFLOW models were applied to quantify groundwater recharge and water table depth, the two of the most important parameters in groundwater vulnerability mapping.The obtained recharge map for 2015 showed values ranging between 0 and 342 mm/year with an average value of 111 mm/yr, corresponding to about 16% of the annual average rainfall. Regarding the groundwater flow model and for a steady and transient state, a reasonable correlation between the observed and simulated values was obtained confirming that results can be used to establish the vulnerability map.The Susceptibility Index (SI) results showed that the groundwater vulnerability of the studied aquifer ranges from low to very high. Most of the area (90%) has moderate to very high pollution susceptibility mainly due to low slope, agricultural land, high recharge rate, sandy soil dominance and low water table depth. The validation of the obtained map was undertaken through a comparison of areas of high salinity hazard with their relative vulnerability index. For most wells, the different salinity hazard parameters matched with areas of moderate to high vulnerability.The integration between the SI method and WetSpass and MODFLOW models for the study area is a valuable and applicable approach for the assessment of the groundwater vulnerability.

Evaluation of Groundwater Vulnerability to Pollution using GIS Based DRASTIC Method in Koradi, India - A Case Study

Abstract Groundwater (GW) contamination due to urbanization, industrialization and agriculture is a major environmental problem in India. The present case study aims to estimate the vulnerability of the aquifer with the help of GIS based DRASTIC method. A micro watershed, characterized by Granites and Gondwana Formation in the vicinity of Koradi, 15 km from Nagpur in Central India has been considered. The DRASTIC method accounts for hydrogeological parameters like depth to water, net recharge, aquifer media, soil media, impact of vadose zone and hydraulic conductivity. The DRASTIC index (DI) for GW vulnerability to pollution is calculated as the sum of the product of ratings and weights assigned to each of the parameter on the scale of 1 to 10 and 1 to 5 respectively. A Groundwater vulnerability map has been prepared using the Arc GIS software (Version 10.1) and it delineates the total study area into two vulnerable zones with vulnerability score ranging from 107 to 142 and indicates that 33% and 67% of the area lies in low and moderate vulnerability zones respectively. The vulnerability score as obtained is also verified with field data.

A new approach for vulnerability assessment of coastal aquifers using combined index

A new approach, developed for coastal aquifers, consists of determination of saltwater-freshwater interface as well as obtaining map of groundwater vulnerability, for which a number of methods have been provided, including index method and numerical modelling. In the previous studies, the common vulnerability methods such as DRASTIC have not took the coastal regions into account, or that method of GALDIT, proposed for coastal regions, assumed the saltwater intrusion fixed. The vulnerability of coastal aquifer is determined in two distinct regions (coastal and non-coastal areas) using two distinct methods (Index and Numerical modelling) and finally they are combined together. The results of this study in coastal aquifer in north of Iran suggest that due to overexploitation, the intrusion of saltwater from coastline into centre of aquifer is as deep as 720 m, inducing very high vulnerability in coastal regions. The correlation of DRASTICSea method with qualitative parameter is obtained 68%.

GROUNDWATER VULNERABILITY ASSESSMENT OF SYLHET SADAR USING GIS

Groundwater has been treated as a vital water supply because of its comparatively low vulnerability to pollution compared to surface water. Due to the health and economic impacts of groundwater contamination, steps to measure groundwater vulnerability are necessary for sustainable groundwater protection and management planning. In this study, an attempt has been made to assess groundwater vulnerability using the overlay index method and to prepare a groundwater vulnerability map using Geographic Information System (GIS) of Sylhet Sadar, a northeastern region of Bangladesh. Also, for the water depth-wise vulnerability assessment, the Water index was generated to observe the effect on chemical concentration for the depth of water. By assigning weight to each pollutant map in the overlay index approach, a combined hazard map was successfully created. The combined hazard map shows a total of 16.04%, 41.36%, and 42.59% of the studied area located in a less, moderate, and severely vulnerable zone, respectively. The combined effect of the chemical concentrations of water gradually decreases with the increase in water depth. Therefore, the developed map can be used as a tool for the management to take initiatives for sustainable use of groundwater.

GROUNDWATER VULNERABILITY ASSESSMENT OF SYLHET SADAR USING GIS

Groundwater has been treated as a vital water supply because of its comparatively low vulnerability to pollution compared to surface water. Due to the health and economic impacts of groundwater contamination, steps to measure groundwater vulnerability are necessary for sustainable groundwater protection and management planning. In this study, an attempt has been made to assess groundwater vulnerability using the overlay index method and to prepare a groundwater vulnerability map using Geographic Information System (GIS) of Sylhet Sadar, a northeastern region of Bangladesh. Also, for the water depth-wise vulnerability assessment, the Water index was generated to observe the effect on chemical concentration for the depth of water. By assigning weight to each pollutant map in the overlay index approach, a combined hazard map was successfully created. The combined hazard map shows a total of 16.04%, 41.36%, and 42.59% of the studied area located in a less, moderate, and severely vulnerable zone, respectively. The combined effect of the chemical concentrations of water gradually decreases with the increase in water depth. Therefore, the developed map can be used as a tool for the management to take initiatives for sustainable use of groundwater.

Groundwater Vulnerability in the Piedmont Region under Climate Change

Groundwater vulnerability has increased in recent decades due to several factors, but mainly due to climate change. In this study, we applied a complex approach to determine groundwater vulnerability at a regional scale in the Piedmont region including high-resolution climate models. Aquifers, terrain model, climate data, land cover, and groundwater monitoring stations data of nitrate (NO3) concentration were the main layers used for the vulnerability and risk mapping. Validation of the groundwater vulnerability map consisted of pixel pair comparison (PPC) using the quality status of a monitored groundwater station, dating from 2005 to 2012. The groundwater vulnerability maps that related to the 1990s and 2020s periods indicated very high and high vulnerability of groundwater in the central and eastern parts of the region, especially in the porous aquifers of Po Plain. The areas with very low and low vulnerability extend into the north and west, mainly in the non-aquiferous media and fissured aquifers. The future scenarios of groundwater vulnerability indicate a consistent increase of the very high vulnerability class, from the 1990s to the 2050s periods, in all scenarios, and mainly in the Po Plain.

Risk Assessment of Groundwater Abstraction Vulnerability Using Spatial Analysis: Case Study at Salatiga Groundwater Basin, Indonesia

DOI:10.17014/ijog.7.2.215-224Salatiga Groundwater Basin (SGB) is located in Java Island, Indonesia. Administratively, it covers Semarang Regency, Salatiga City, and Boyolali Regency. Industry and community use groundwater to fulfil their daily need. Increasing number of deep wells that extract groundwater will cause some environmental problems, such as lowering groundwater level and subsidence at SGB. Thus, there is a need to assess the adverse impacts of groundwater abstraction. Risk assessment of groundwater vulnerability due to abstraction is the goal of this study. The research method was taking account of weighting of geological parameters, such as response characteristics of the aquifers, characteristics of aquifer storage, aquifer thickness, piezometric depth, and distance from the shoreline to conduct the groundwater vulnerability mapping. It was then overlaid on a map of regional spatial plan to develop the map of vulnerability risk due to abstraction. The groundwater vulnerability due to abstraction is categorized in the medium level. After being overlaid by the land use map, the risk of groundwater vulnerability due to abstraction is classified into three kinds, which are low, medium, and high. Regions with a low class can be neglected. Areas with moderate risk require an exhaustive review of technical requirements of the use of borewell. Areas with high-risk need a comprehensive consideration to use artesian wells by monitoring wells with drill licenses, tightening the permit to add new production wells, and conducting periodic review of groundwater monitoring.

Groundwater Vulnerability and Nitrate Contamination Assessment and Mapping Using DRASTIC and Geostatistical Analysis

The Gaza Strip is in a chronic state of water shortage and the coastal aquifer as the only freshwater source is increasingly depleted and polluted, especially by nitrate. Assessment of groundwater vulnerability to pollution is essential for adequate protection and management. In this study, the assessment of the aquifer vulnerability to contamination is derived by applying the DRASTIC procedure, firstly with original default weights and ratings and, secondly, improved by estimating rating values by multiple linear regression of observed log-transformed nitrate concentration in groundwater, with DRASTIC factors extended to land-use. The results are very different because high and low vulnerability areas shift considerably. Subsequently, a geostatistical analysis of the spatial distribution of the nitrate concentration is performed, firstly by ordinary kriging interpolation of the observed nitrate concentration and secondly by regression kriging using DRASTIC factors and land-use as indicators of the spatial variation in nitrate occurrence. These maps differ because the map obtained by regression kriging interpolation shows much more details of environmental factors such as dunes, ridges, soil types and built-up areas that affect the presence of nitrate in groundwater. The results of this study can be used by the Palestinian authorities concerned with sustainable groundwater management in the Gaza Strip.

Determining the lake protected zones using GIS-based DRASTIC model to groundwater vulnerability in Salda Lake basin (Burdur/Turkey)

Groundwater quality is a crucial parameter for sustainable wetland management. The evaluation of the aquifer vulnerability is important for the protection of groundwater resources. The DRASTIC model is the most significant technique for the assessment of aquifer vulnerability. This study aimed to build a vulnerability map for groundwater of the Salda Lake wetland basin by DRASTIC method in a GIS environment. Seven environmental parameters (depth to water table, net recharge, aquifer media, soil media, topography, impact of the vadose zone media, and hydraulic conductivity of the aquifer) were used in the DRASTIC method and GIS was used to constitute a groundwater vulnerability map. This study showed that 13.71% of the area had high pollution potential, 10.13% had moderate pollution potential, and 76.15% had low pollution potential in respect to groundwater pollution. Intensive agricultural activities are carried out in the study area. The DRASTIC vulnerability index value of the study area was well correlated with the nitrate map of the study area. In addition, Salda Lake protection areas were determined. All of the defining protection areas of the Salda Lake are within the most sensitive areas in DRASTIC map.

Spatial analysis of groundwater vulnerability to contamination and human activity impact using a modified DRASTIC model in Elalla-Aynalem Catchment, Northern Ethiopia

Once if groundwater has been contaminated, it is difficult to treat it since natural dilution is slow and artificial flushing is impractical. Hence, this study was aimed to analyse the spatial vulnerability to contamination and human activities impact on the groundwater of Elalla-Aynalem Catchment, using depth to water table, net recharge, aquifer type, soil media, topography, impact of vadose zone, hydraulic conductivity and land use/cover. DRASTIC index gives three different groundwater vulnerability zones, namely: high (6.7%), moderate (32%) and low (61.3%), and the modified DRASTIC (Human activity impact) index map gives four vulnerability zones as low, medium, high and very high with area coverage of 18.5%, 29.1%, 32.6% and 19.8% of the study area, respectively. The depth to water table and vadose media are the most significant hydrogeological factors determining the DRASTIC vulnerability resulted from sensitivity analyses. The groundwater vulnerability map with measured NO3 data shows 70.69% and 84.48% agreement for DRASTIC model and modified DRASTIC model, respectively, indicated that the role of LuLc is important. Solid waste disposal, sewerage, gases from industries, municipal wastes, garages, fuel station, health centers and agricultural activities are some of the possible pollutants that could continuously deteriorate the quality of groundwater in the catchment. This study provides integrated plat form and compressive data set of hydrogeological factors for spatial analysis to fill spatial data gaps, and it can be effectively utilized in the planning and management of the groundwater resources in vulnerable zones of Elalla-Aynalem Catchment.

Nitrate-leaching and groundwater vulnerability mapping in North Bihar, India

Aquifer vulnerability assessment is crucial for studying the impact of increasing pollution load scenarios on the quantification of contaminant concentration with movement of plume for protecting groundwater resources. Only a few recent studies have focused on the performance evaluation of vulnerability assessment methods using process-based modeling approach. However, the moisture flow and pollutant transport through partially saturated zone plays a crucial role under varying hydrogeological conditions, which are generally ignored in index-based methods. Thus, the objective of this research is to evaluate the vulnerability of groundwater resources to nitrate in Samastipur, Darbhanga and Madhubani districts of Bihar State, India, using soil moisture flow and solute transport modeling. Richard’s equation integrated with the classical advection dispersion equation is simulated using HYDRUS 1D by incorporating a constant head and atmospheric boundary conditions. The time taken to reach the nitrate peak concentration at groundwater table is considered to estimate vulnerability index (VI). Results have shown that high risk in terms of nitrate-leaching vulnerability in southern part of study area is dominated by Gangetic kankar in subsurface. Further, high pollution risk was reported in eastern north part of study area having alluvial deposition in subsurface. The main causes of high risk were due to the short depth of water table, little discharge and more hydraulic conductivity presence in the subsurface media. Moreover, comparatively low vulnerability was observed in area having clay capping of 2–4 m from surface. This research may help in better implementation of agricultural, soil–water conservation practices and urban/industrial infrastructure development in and around the study area.

Mapping specific groundwater vulnerability to nitrate using random forest: case of Sais basin, Morocco

The objective of this study was to assess the groundwater vulnerability to nitrate (NO3−) pollution in the Sais basin, based on the drinking threshold (50 mg/L), using the random forest (RF) model. A spatial dataset consists of the nitrate concentrations observed in 154 water samples and 14 explanatory variables was considered in this research. These variables are rainfall, texture (sand, silt, and clay), lithology, organic matter, piezometric level, altitude, land use, calcium carbonate (CaCO3), carbon/nitrogen ratio (C/N), slope, hydraulic gradient, and soil classification. 80% of the dataset was randomly selected for training and validation, and the remaining 20% for testing the RF model. The RF model was validated and tested using out-of-bag (OOB) error and receiver operating characteristic (ROC) curve. The error computed and the area under the curve for success rate were 0.11 and 82.2%, respectively. In addition, the RF result revealed that rainfall, sand content, clay content, piezometric level, organic matter, and lithology are the key factors determining groundwater vulnerability to NO3− in the Sais basin. However, using only these most important factors as RF inputs, the prediction accuracy was found to be slightly similar to that obtained using all variables. The groundwater vulnerability maps were created using the groundwater vulnerability indexes predicted. The most reliable groundwater vulnerability maps to NO3− showed that about 48 and 63% of the surface area of the basin are under high to very high vulnerability level, using all and most important explanatory variables, respectively. This study serves to determine the most vulnerable areas and to identify the factors affecting NO3− pollution in the Sais basin, to properly control and protect groundwater.

Regional Aquifer Vulnerability and Pollution Sensitivity Analysis of Drastic Application to Dahomey Basin of Nigeria.

Shallow groundwater vulnerability mapping of the southwestern Nigeria sedimentary basin was assessed in this study with the aim of developing a regional-based vulnerability map for the area based on assessing the intrinsic ability of the aquifer overlying beds to filter and degrade migrating pollutant. The mapping includes using the established seven parameter-based DRASTIC vulnerability methodology. Furthermore, the developed vulnerability map was subjected to sensitivity analysis as a validation approach. This approach includes single-parameter sensitivity, map removal sensitivity, and DRASTIC parameter correlation analysis. Of the Dahomey Basin, 21% was classified as high-vulnerability and at risk of pollution, 61% as moderate vulnerability, and 18% as low vulnerability. Low vulnerability areas of the basin are characterised by thick vadose zones, low precipitation, compacted soils, high slopes, and high depth to groundwater. High-vulnerability areas which are prone to pollution are regions closer to the coast with flat slopes and frequent precipitation. Sensitivity of the vulnerability map show the greatest impact with the removal of topography, soil media, and depth to groundwater and least impact with the removal of the vadose zone. Due to the subjectivity of the DRASTIC method, the most important single parameter affecting the rating system of the Dahomey Basin DRASTIC map is the impact of the vadose zone, followed by the net recharge and hydraulic conductivity. The DRASTIC vulnerability map can be useful in planning and siting activities that generate pollutants (e.g., landfill, soak away, automobile workshops, and petrochemical industries) which pollute the environment, groundwater, and eventually impact the environmental health of the Dahomey Basin’s inhabitants.

Meta-heuristic algorithms in optimizing GALDIT framework: A comparative study for coastal aquifer vulnerability assessment

Creating a reliable groundwater vulnerability map is a key solution for protecting the groundwater resources and further planning in coastal aquifers. The GALDIT framework, which is an abbreviation for six parameters of Groundwater occurrence, Aquifer hydraulic conductivity, Level of groundwater above sea level, Distance from the shoreline, Impact of the existing status of seawater intrusion, and Thickness of the aquifer, is a well-known framework for evaluating the groundwater vulnerability in coastal zones. In this study, two meta-heuristic algorithms of Grey Wolf Optimizer (GWO) and Genetic Algorithm (GA) were proposed to optimize the weights of GALDIT framework. This framework was tested in the Gharesoo-Gorgan Rood coastal aquifer located in the north of Iran. The GALDIT index illustrated poor evaluation of vulnerability to seawater intrusion. Contrariwise, GALDIT-GWO and GALDIT-GA frameworks provided results that are more reasonable. Both vulnerability maps showed a close similarity in terms of vulnerability to seawater intrusion. The vulnerability maps demonstrated that the west and northwest parts of the study area suffer from seawater intrusion. Additionally, the values of Spearman’s rank correlation coefficient between the indices of GALDIT, GALDIT-GWO and GALDIT-GA and the parameter of Cl/HCO3 were obtained as 0.31, 0.53, and 0.49 and the corresponding values for the parameter of TDS were obtained 0.45, 0.64 and 0.60, respectively. Therefore, it can be concluded that the proposed optimization models are able to provide accurate results. Furthermore, these models reduce the subjectivity and increase the capability of the GALDIT index.