GALDIT Method Research Articles

Cross Comparison of GALDIT Method Application in Three Costal Aquifers in Greece

Seawater intrusion into Greece’s coastal aquifers is a prevalent issue. The Greek coastline extends for 15,147 km. Once groundwater sources become contaminated, remediation methods are often challenging, costly, and protracted. This study focuses on three coastal aquifer systems in the Peloponnese region. Initially, the main ions and cations were determined for these aquifers. Hydrochemical analyses revealed elevated concentrations of Na+, Mg2+, Ca2+, SO42−, and Cl−, indicating a significant impact from seawater intrusion. The study evaluates the vulnerability of groundwater to this intrusion. Utilizing Geographical Information Systems (GIS) software (ArcGISPro), maps were created to illustrate each parameter of the GALDIT method. The acronym GALDIT encapsulates the main elements influencing seawater intrusion. Each parameter is analyzed as follows: Groundwater occurrence (including the following aquifer types: unconfined, confined, and leaky confined), Aquifer hydraulic conductivity, depth to groundwater Level above the sea, Distance from the shore (inland distance perpendicular from shoreline), Impact of existing status of sea water intrusion in the area, and Thickness of the aquifer. The final map that emerged from this study shows their vulnerability to seawater intrusion in Peloponnese. Notably, Larissos exhibits lower vulnerability in contrast to the seawater incursion in the other two groundwater systems.

Advancing aquifer vulnerability mapping through integrated deep learning approaches

Groundwater vulnerability maps are crucial for safeguarding groundwater quality. A research gap exists in using advanced data fusion techniques to identify areas subject to seawater intrusion. To address this gap, this research enhances the GALDIT method and applies diverse deep learning models, combined with machine learning techniques, to improve the precision of aquifer vulnerability mapping. The new GALDITMW model incorporates the seawater mixing index and the parameters related to the production well density and aquifer porous medium. For the first time, supervised and unsupervised deep learning models, such as deep neural networks, deep belief networks, deep stacked autoencoders, and convolutional neural networks, are used for vulnerability mapping. In the second stage, the results of various machine learning models are fused to improve performance. The models' effectiveness is evaluated using a vulnerability index based on total dissolved solids (TDS) in an aquifer hydraulically connected with Salt Lake in central Iran, which faces groundwater depletion and salinization. The evaluation of the models based on performance metrics and the confusion matrix demonstrates that initial deep-learning models perform well. Significant improvements were observed in the second stage involving machine learning models, confirming their strong correlation (R2 > 0.985) with observed chloride values. The GPR model achieved an F1 score of 86.92%, an NSE of 0.911, and an RMSE reduction of 0.026 mg/L compared to the first-stage models. The proposed method offers a novel and accurate method for identifying vulnerable areas and provides helpful information for groundwater resource management.

A robust decision-making approach for designing coastal groundwater quality monitoring networks.

This paper presents a new approach to the spatiotemporal design of groundwater quality monitoring networks for coastal aquifers. A fusion model combines the outputs of several developed simulation models to make estimates more accurate. A modified GALDIT method is used to incorporate the aquifer vulnerability to saltwater intrusion. The value of information (VOI) theory is applied to determine sufficient monitoring wells. The groundwater quality monitoring network is designed by employing a robust decision-making (RDM) approach under different management strategies and economic considerations. This approach incorporates the deep uncertainties of some critical variables, including water level and total dissolved solids (TDS) concentration at the coastline and pumping flow rates of agricultural wells. The new methodology is implemented in the coastal Qom-Kahak aquifer, Iran. The results illustrate that the combination model has significantly improved evaluation criteria compared to individual prediction models. The fusion model results indicate that thirty monitoring wells would be ideal. The RDM-based analyses in the Qom-Kahak aquifer showed that an optimal network with 30 monitoring wells outperforms the current network regarding various criteria, such as VOI and variance of estimation error. The new well configuration also demonstrates a suitable spatial distribution. Given that the current sampling frequencies are unsuitable for areas with varying vulnerabilities, we recommend sampling every 3months in areas with moderate vulnerabilities and once every three seasons in areas with low vulnerabilities, based on the information transfer index. Finally, a management strategy in which the pumping rate should be less than 60% of the current rate is suggested to prevent saltwater intrusion into the aquifer.

GIS based – GALDIT method for aquifer vulnerability assessment to seawater intrusion: Case of a qp2-3 aquifer of Mekong Delta

Recently, seawater intrusion (SWI) in coastal aquifers is a global issue that is exacerbated by sea-level rise, climate change, and an increasing dependency on coastal fresh groundwater resources for water supply. Vietnam's Mekong Delta has a flat topography, a dense river network, and a 700 kilometer coastline covering the region's west and east. The Mekong Delta is facing increasingly serious saline intrusion. This paper describes the results of the examination using the GALDIT method as a model to evaluate the vulnerability of seawater intrusion. The method is used to determine the trend of groundwater contamination by seawater intrusion in the qp2-3 aquifer of the Mekong Delta, this Upper-middle Pleistocene aquifer (qp2-3) is one of the main productive aquifers in the Mekong Delta. The analysis result in 2015 shows a moderate and high level of vulnerability in which the highly vulnerable area is along the Tien River and at the depression cone area in Ca Mau. The analysis is reconducted for the time of 2030 with the predicted values for the groundwater level through the forecasting tool. By comparing the model of two times of 2015 and 2030, the results indicated that the impact of the continuous decline of groundwater level is greater than the impact of sea level rise. If the rate of drawdown is kept the same, by 2030 the highly vulnerability area will have expanded to two-thirds of the Mekong Delta. The GALDIT method is a good approach for saltwater intrusion research and moreover water management, and environmental management, such as evaluating the most sensitive areas for monitoring or imposing restrictions where necessary.

Identifying intrusion of seawater in coastal aquifers by modified GALDIT (M-GALDIT) index

Contamination of coastal aquifers by seawater intrusion (SWI) is a major environmental problem. A modified GALDIT method (M-GALDIT), and multi-criteria decision model AHP has been used to identify regions vulnerable to seawater intrusion. We have used the groundwater suitability index for seawater intrusion (GQISWI) in estimating the M-GALDIT index. While the GALDIT analysis indicates that ∼28% of the area is moderately vulnerable, and 8% of the area is relatively highly vulnerable, our estimates using AHP and M-GALDIT method indicate ∼19% of the area as moderately vulnerable, ∼22% of the area as relatively highly vulnerable zones. The GQISWI values in the region vary between 0 and 96.96, indicating that most of the groundwater samples belong to mixed water types. Faults and fractures, population distribution, water-rock interaction, ionic exchange reactions, and evaporation appear to be the dominant mechanisms, besides seawater intrusion that control the overall groundwater geochemistry in the region. Ca2+-HCO3-, Ca2+-Na+-HCO3−, and Ca2+-Mg2+-Cl− are the most dominant water types in the study area. The seawater mixing index (SMI) reveals that ∼34.5% of samples are of relatively freshwater types, whereas ∼61% of samples appear contaminated to some extent, presumably due to the mixing of seawater, or anthropogenic activities such as mining, agricultural activities, etc. Furthermore, analysis of the HFE-D diagram indicates that ∼23% of samples are directly affected by seawater intrusion.

Integrated SEAWAT model and GALDIT method for dynamic vulnerability assessment of coastal aquifer to seawater intrusion

Seawater intrusion (SI) has become a global issue exacerbated by intense anthropogenic activities and climate change. It is imperative to seek a synergistic strategy to reconcile environmental and economic benefits in the coastal regions. However, the intricate SI process and data scarcity present formidable challenges in dynamically assessing the coastal groundwater vulnerability. To address the challenge, this study proposed a novel framework that integrates the existing vulnerability assessment method (GALDIT) and variable-density groundwater model (SEAWAT). The future scenarios from 2019 to 2050 were investigated monthly under climate change (SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5) and human activities (80 % and 50 % of current groundwater abstraction) in Longkou city, China, a typical coastal region subject to extensive SI, compared with the status quo in 2018. Results indicated that by 2050, the high vulnerability area, is in a narrow buffer within 1.2 km from the shoreline and exhibits minor changes while the salt concentration here increased by about 2700 mg/L compared with the current situation. The moderate vulnerability zone expands by about 30 km2, and the low vulnerable area decreases proportionally. The groundwater over-abstraction is identified as a more critical factor compared to the regional precipitation under climate change. When groundwater abstraction is reduced to 80 % of the current scale, the expansion rate of the moderate-vulnerable area slows down significantly, with an expansion area of only 18 km2 by 2050. Further reducing groundwater abstraction to 50 % of the current scale shifts the evolution trend of the medium-vulnerable area from expansion to contraction, with the area shrinking by about 11 km2 by 2050. The integrated vulnerability assessment framework can be applied not only in the similar coastal regions but also provides insights into other natural hazards.

Z-number based assessment of groundwater vulnerability to seawater intrusion

Groundwater (GW) quality assessment is an essential issue, especially in arid and semi-arid regions, due to its critical role in obtaining requirements for freshwater. The GALDIT method is widely recognized as a practical approach for assessing GW susceptibility, which considers six key factors, including the occurrence of groundwater (G), hydraulic conductivity of the aquifer (A), elevation of groundwater above sea level (L), distance from the shoreline (D), impact of existing seawater intrusion (I), and thickness of the aquifer (T). The GALDIT method, being an unsupervised model, has a drawback in that it depends on expert opinion for parameter ranking, leading to an increase in uncertainty. To address this uncertainty and evaluate the susceptibility of the aquifers of Urmia lake basin to saltwater intrusion, this study employed the Z-number which is a novel adaptation of Fuzzy Logic (FL). In contrast to classic FL that does not account for data reliability, the Z-number approach considers both constraints and data reliability, making it a more effective method to manage data uncertainty compared to classic fuzzy models. To illustrate this methodology, the GALDIT parameters (inputs) and Electrical Conductivity (EC) values (outputs) were employed to determine the vulnerability of aquifers. Additionally, the GALDIT method was utilized as a benchmark model to evaluate the inherent vulnerability of aquifers, and its outcomes were compared with those of the proposed model. Upon analyzing the results, it was found that the Z-number Based Modeling (ZBM) not only outperformed the GALDIT method but also enhanced the quality of outcomes by 85% and 35% based on Heidke Skill Score (HSS) and Total Accuracy (TA) criteria compared to the classic FL.

A Modified GALDIT Method to Assess Groundwater Vulnerability to Salinization—Application to Rhodope Coastal Aquifer (North Greece)

Aquifer overexploitation in coastal aquifers has led to seawater intrusion that causes severe salinization effects on the groundwater system. The most widespread method for assessing groundwater vulnerability to seawater intrusion, the dominant cause of salinization in coastal aquifers, is the GALDIT method, with numerous applications globally. The present study proposes a modified version of the GALDIT method (GALDIT-Ι) to evaluate the vulnerability of salinization, including its potential additional sources. Both methods have been applied to Rhodope coastal aquifer, an intensively cultivated agricultural area subject to multiple salinization sources. The basic modifications of the proposed GALDIT-I method include different weighting factors and modification of classes for critical parameters, the use of a different indicator (TDS) for the estimation of the Impact factor and, overall, the address of the concept of groundwater salinization instead of seawater intrusion only. The differences in the results of the two methods were significant, as the modified version exhibited a more finite and realistic vulnerability capture, according to the area’s existing hydrogeological and hydrogeochemical knowledge. The original GALDIT method showed an area of nearly 80% as medium vulnerable with very limited spatial deviations. On the other hand, the proposed modified GALDIT method depicted high vulnerability hotspots away from the shoreline, indicating various salinity sources. The validation of the modified method showed that nearly 80% of the sampling points present very good to perfect match between the salinity assessment and the concentration of Cl−, indicating the successful validation of the method. Overall, the GALDIT-I method facilitated groundwater vulnerability assessment to salinization more accurately and exhibited a more discrete spatial assessment, thus, it could be regarded as a promising proactive tool for groundwater management and decision-making.

Aplikasi Metode GALDIT Untuk Analisis Kerentanan Airtanah Terhadap Intrusi Air Laut di Kabupaten Rembang, Jawa Tengah

Groundwater is water that is found below the ground surface or in rock layers. Seawater intrusion is a problem caused by excessive groundwater extraction which often occurs in coastal areas. Rembang is an area located in the coastal area. Rembang Regency has the potential for seawater intrusion. The impact of seawater intrusion can affect economic, social and cultural development in coastal areas as well as the quantity and quality of groundwater. The purpose of this study is to determine areas that have potential for seawater intrusion in the study area. The methods were geological mapping, groundwater quality analysis, GALDIT approach and its validation using TDS, DHL and Chloride. The interpretation of the area that has the potential for seawater intrusion is carried out with validation in the research area. The results conducted that in the research area consists of limestone, sandstone, claystone, the presence of porphyry andesite and alluvium. Based on the analysis of the vulnerability of seawater intrusion using the GALDIT method, it was found that there are 3 levels of vulnerability, namely middle to very high vulnerability. High vulnerability has GALDIT index > 7.5, located on the north coast of Rembang and Kaliori sub-districts.. The high vulnerable is 5-7.5, located mostly in Kaliori and Rembang sub-districts, and a little in Sulang, Sumber, Bulu, and Gunem sub-districts. The middle vulnerable is in the range of 2.5-5 mostly in Bulu, Gunem, Sumber, Sulang sub-districts, and a little in Rembang and Kaliori sub-districts. The validation carried out has a high match in the north of the study area. The very high level of vulnerability is in accordance with the distribution of the population and the land use map where the Kaliori and Rembang sub-districts have a large population and the land use is filled with buildings and settlements.

Hybridization of GALDIT method to assess actual and future coastal vulnerability to seawater intrusion.

In the recent years, the coastal aquifer of Jijel plain (North Algeria) located on the south of the Mediterranean Sea was utilized for cities growth and agricultural development of the region. Consequently, overexploitation and seawater intrusion were identified as major risks to the groundwater resource. In this work, a new approach integrating groundwater vulnerability method and numerical model for predicting the actual and future seawater is proposed. The groundwater vulnerability assessment has been performed by applying the GALDIT method using GIS and the MODFLOW model was used to simulate the actual and future groundwater level of the aquifer over the period 2020-2050. Three scenarios were simulated under water demand and climate conditions (drought, recharge) to obtain the changes in the groundwater level variation. The results of the GALDIT model application to the actual conditions (year 2020) showed that the high class of groundwater vulnerability is located in the coastal fringe and the terminal stretches of wadis where the seawater intrusion limit is located at a distance range between 840 and 1420m from the shoreline. However, the results for predicting future groundwater vulnerability showed that the scenario which proposed the artificial recharge basins, although predicting a worrying situation compared to the actual condition, has the best figure of the groundwater vulnerability assessment and seawater intrusion despite the other two scenarios. In this case the limit in the year 2050 is located between distances of 850-1640m from the shoreline with a forward speed of seawater intrusion of 1-8m/year, compared to the reference year 2020. This showed that groundwater level variation and recharge were the key factors in controlling groundwater vulnerability to seawater intrusion. The presented new approach can be used to mapping the actual and future groundwater vulnerability assessment to seawater intrusion and groundwater resources management in any coastal areas worldwide.

Hybridization of Galdit Method to Assess Actual and Future Coastal Vulnerability to Seawater Intrusion

Hybridization of Galdit Method to Assess Actual and Future Coastal Vulnerability to Seawater Intrusion

Application of Aquifer Surface Recharge in the Modification of GALDIT Method to Assess the Risk of Seawater Intrusion in Qom Aquifer

درک واقع‌بینانه آسیب‌پذیری آبخوان نسبت به پیشروی آب شور یکی از پیش‌نیازهای مهم مدیریت آبخوان‌های ساحلی است. روش GALDIT ابزار مناسبی است که علی‌رغم درنظر گرفتن خصوصیات کیفی، هیدروژئولوژیکی و زمین‌شناسی آبخوان، نقش تغذیه سطحی آبخوان را درنظر نگرفته است. محدوده مطالعاتی قم-کهک بخشی از حوضه آبریز دریاچه نمک است که در بخش خشک و بیابانی ایران مرکزی قرار گرفته است. به‌علت کمبود منابع آب‌های سطحی و زیرزمینی منطقه، بخشی از نیازهای شرب و صنعت شهر قم از آب‌های خارج از این محدوده مطالعاتی تأمین می‌شود. در این پژوهش با افزودن پارامتر تغذیه سطحی آبخوان، روش GALDITR معرفی شد و آسیب‌پذیری آبخوان ساحلی قم به پیشروی آب شور دریاچه نمک ارزیابی شد. سپس با توجه به ویژگی‌های آبخوان مورد بررسی از روش تحلیل سلسله مراتبی برای بازبینی وزن پارامترهای مدل GALDITR استفاده شد. بر اساس نتایج به‌دست آمده، رتبه زیاد پارامتر تغذیه سطحی آبخوان در بخش وسیعی از آبخوان، منجر به افزایش وسعت ناحیه با آسیب‌پذیری متوسط مدل GALDITR نسبت به روش GALDIT شد. در مدل GALDITR-AHP، پارامترهای فاصله از خط ساحلی، تراز سطح آب زیرزمینی نسبت به سطح دریاچه و تأثیر آب شور پیشروی کرده به‌ترتیب وزن بیشتری از سایر پارامترها گرفتند. با افزایش وسعت ناحیه با آسیب‌پذیری کم در مدل GALDITR-AHP، آسیب‌پذیری آبخوان در حوالی شهر قم به پیشروی آب شور کاهش یافت. شاخص آسیب‌پذیری مدل‌هایGALDITR-AHP، GALDITR و GALDIT به‌ترتیب بیشترین هم‌بستگی را با مقدار کلر در نقاط مشاهده‌ای نشان دادند. نتایج پژوهش نشان داد که نواحی با آسیب‌پذیری زیاد و متوسط در بخش شرقی آبخوان قم با وسعت حدود 14 درصد از کل مساحت آبخوان مستعد پیشروی آب شور بوده و می‌توانند به‌عنوان محدوده گسترش آب شور برای پایش و مدیریت بهینه آبخوان ساحلی درنظر گرفته شوند.

Development of Seawater Intrusion Vulnerability Assessment for Averaged Seasonality of Using Modified GALDIT Method

Climate change and anthropogenic activities are necessitating accurate diagnoses of seawater intrusion (SWI) to ensure the sustainable utilization of groundwater resources in coastal areas. Here, vulnerability to SWI was assessed by classifying the existing GALDIT into static parameters (groundwater occurrence (G), aquifer hydraulic conductivity (A), and distance from shore (D)) and dynamic parameters (height to groundwater-level above sea-level (L), impact of existing status of seawater intrusion (I), and aquifer thickness (T)). When assessing the vulnerability of SWI based on observational data (2010–2019), 10-year-averaged data of each month is used for GALDIT dynamic parameter for representing the seasonal characteristics of local water cycles. In addition, the parameter L is indicated by the data observed at the sea-level station adjacent to the groundwater level station. The existing GALDIT method has a range of scores that can be divided into quartiles to express the observed values. To sensitively reflect monthly changes in values, the range of scores is divided into deciles. The calculated GALDIT index showed that the most vulnerable month is September, due to relatively low groundwater level. The proposed method can be used to apply countermeasures to vulnerable coastal areas and build water resources management plan considering vulnerable seasons.

Modeling and Mapping of coastal aquifer vulnerability to seawater intrusion using SEAWAT code and GALDIT index technique: the case of the Rmel aquifer – Larache, Morocco

The study area of Rmel-O. Ogbane aquifer, located in the north of Morocco, currently faces major water challenges related to the sustainable management of water resources. Climate change and Sea-Level-Rise can increase the risks and costs of water resources management and impact water resources' quantity and quality. Hence, for planning and management, an integrated approach is developed for linking climate models and groundwater models to investigate future impacts of climate change on groundwater resources. Climate projections show an increase in temperature of about 0.45 °C and a reduction in precipitation of 16.7% for 2016-2050. Simulations of seawater intrusion corresponding to various combinations of groundwater extraction predicted climate change and sea-level-rise show that the area will be contaminated on the NW sector of the coastal part. The toe would reach about 5.2 km inland and intrude on high salinity (15–25g/l). Beyond these zones, the contamination of the aquifer will be limited. Moreover, these results were confirmed by the application of the GALDIT method. They reveal that the fringe littoral areas of the aquifer are the most affected by seawater intrusion, with a high risk in the north-western part of the study area.

Mapping of the vulnerability to marine intrusion “in coastal Cherchell aquifer, Central Algeria” using the GALDIT method

Located in the south of the western Mediterranean, in the central Algerian region, the Cherchell coastal aquifer has participated over time in the economic development of the region (agriculture and seaside tourism). The construction of the Boukerdene dam in the watershed of the region, thus the exploitation of the aquifer in response to the excessive demand of agriculture and the potable water supply, has caused the piezometric level of the aquifer to decline and threatens its sustainability and makes it more vulnerable to marine intrusion, noting that no work has been realized in this study area despite the inestimable value of this aquifer in the region, it's the only aquifer in Cherchell town. The aim of this paper is to map the vulnerability of this aquifer to marine intrusion, based on the proven methodology of the GALDIT model for coastal aquifers combined with Geographic Information Systems (GIS). The GALDIT methodology requires six input parameters: groundwater occurrence (G), aquifer hydraulic conductivity (A), groundwater head above sea level (L), distance from the shore (D), impact of the existing status of seawater intrusion l'impact (I), and thickness of the aquifer (T).The results indicate low to moderate vulnerability upstream and high vulnerability downstream. This high vulnerability can be as much as 700 m from shoreline inland. This vulnerability is mainly due to the hydrological disruption linked to the construction of the Boukerdene dam, which reduces surface water inflows. These results provide a basic tool for local managers and decision-makers, for future management and protection strategies for the Cherchell area aquifer in the face of marine intrusion.

Application of GIS-Base GALDIT for vulnerability assessment to saltwater intrusion of Holocene coastal aquifer: a case of Quang Nam - Da Nang city, Vietnam

Groundwater is an essential resource which is influenced by salt water due to the groundwater exploitation in Holocene aquifer of Quang Nam - Da Nang. Hence, the measures for preventing saltwater intrusion and better groundwater management are required. In this study, GALDIT method was utilized to identify the salt water intrusion (SWI) vulnerability zones using monitoring data in Holocene aquifer of Quang Nam - Da Nang. The results of GALDIT method indicated that Da Nang and Hoi An cities were in the high SWI vulnerability zones. The moderate SWI zones were dominant and low vulnerability zones were at the southern part of the study area. The analysis of the monitoring data showed the occurrence of SWI far inland, up to the distance of 12.5 km from the sea shore and suggested the impact of human activities on SWI. The analysis of monitoring data together with GALDIT index indicated that the important of the groundwater abstraction depth or the occurrence of fresh-salt groundwater interface should be considered to improve the result of GALDIT method for the prevention of SWI. In short, the GALDIT used in this study is an important approach for the prevention of SWI in the study area.

Vulnerability Indexing to Saltwater Intrusion from Models at Two Levels using Artificial Intelligence Multiple Model (AIMM)

Unplanned groundwater exploitation in coastal aquifers results in water decline and consequently triggers saltwater intrusion (SWI). This study formulates a novel modeling strategy based on GALDIT method using Artificial Intelligence (AI) models for mapping the vulnerability to SWI. This AI-based modeling strategy is a two-level learning process, where vulnerability to SWI at Level 1 can be predicted by such models as Artificial Neural Network (ANN), Sugeno Fuzzy Logic (SFL), and Neuro-Fuzzy (NF); and their outputs serve as the input to the model at Level 2, such as Support Vector Machine (SVM). This model is applied to Urmia aquifer, west coast of Lake Urmia, where both are currently declining. The construction of the above four models both at Levels 1 and 2 provide tools for mapping the SWI vulnerability of the study area. Model performances in the paper are studied using RMSE and R2 metrics, where the models at Level 1 are found to be fit-for-purpose and the SVM at Level 2 is improved particularly with respect to the reduced scale of scatters in the results. Evaluating the result and groundwater samples by Piper diagram confirms the correspondence of SWI status with vulnerability index.

Assessment of Groundwater Vulnerability in the North Aquifer Area of Rhodes Island Using the GALDIT Method and GIS

Salinization of coastal aquifer systems constitutes a major threat for groundwater. Especially areas with high population density due to increasing tourist activity may face severe problems. In this study, the GALDIT method was applied in the north side of Rhodes Island, Greece, in order to assess groundwater vulnerability to seawater intrusion. Hydrogeological data were elaborated in geographical information systems (GIS), and appropriate thematic maps were produced. The final vulnerability map was obtained from the combination of the thematic maps using overlying techniques. Based on the application of the GALDIT method, a zone up to 1000 m from the shore is characterized by medium to high vulnerability, while medium vulnerability characterizes the eastern part of the study area. Overexploitation of the aquifer, due to the intense touristic activity in Ialysos area, constitutes the main reason for groundwater salinization due to seawater intrusion in the study area. Consequently, planning of proper groundwater management and systematic monitoring of the groundwater reserves are of the utmost importance in order to solve existing problems and prevent future issues of salinization.

GALDIT-SUSI a modified method to account for surface water bodies in the assessment of aquifer vulnerability to seawater intrusion

The salinization of coastal aquifers is one of the major environmental issue worldwide. Overexploitation is the most common reason of salinization, since it generates a piezometric inversion, which in turn leads to groundwater flow from the coast towards inland. This also occurs in water bodies connected to the sea like lagoons, rivers, torrents and wetlands. In this study, a modification of the GALDIT method including “SUperficial Seawater Intrusion (SUSI)” is proposed. Six new parameters were added to the classical ones. The analytical hierarchy process and the sensitivity analysis were performed for weights definition and validation of the proposed GALDIT-SUSI method. Two study areas, with different characteristics were chosen for the application of both methods: the coastal area of Epanomi (Greece) and the Po River lowland (Italy). The application of the standard GALDIT in both sites showed a poor discrimination of the vulnerability to seawater intrusion, confining it only in proximity to the coastline. Conversely, GALDIT-SUSI divided the two sites in five classes of vulnerability ranging from very low to very high, stressing the higher vulnerability of lagoons and wetland for Epanomi and lagoons and rivers for the Po River lowland. GALDIT-SUSI is easy to apply and versatile, since it can be adapted to the specific hydrogeological setting of the area of interest. Moreover, GALDIT-SUSI can be further improved to deal with other salinization mechanisms.

Application of the GALDIT method combined with geostatistics at the Bouteldja aquifer (Algeria)

This paper aims to spatially characterize the marine intrusion in the case of the Bouteldja main aquifer using the GALDIT method coupled with a geostatistical approach. The latter was used to compensate the weakness of GALDIT method for not considering the spatial variability of the studied variables. Using a field data set of the Bouteldja aquifer, the semi-variograms of four continuous important variables (hydraulic conductivity A, groundwater level L, thickness T and sea water intrusion I) were studied and modeled. The obtained structures were mainly composed of spherical models with a small nugget effect, except the I variable which has shown a perfectly continuous Gaussian model with zero nugget effect, arguing that the marine intrusion is seriously present and continuous. These individual results were also mapped by kriging and the intrusion easily shown on the field. However, the GALDIT computation and mapping did not confirm the found intrusion. It has merely shown a medium to low vulnerability in narrow and parallel bands close to the shore area. This work has shown that the GALDIT method used solely, without a geostatistical approach, would lead to a misinterpretation of the vulnerability of a main aquifer to saline intrusion.