نوع مقاله : مقاله پژوهشی
نویسندگان
1 1. دانشجوی دکترا علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه بیرجند، بیرجند، ایران.
2 استاد، گروه مهندسی عمران، دانشکده مهندسی، دانشگاه بیرجند، بیرجند، ایران.
3 3. دانشیار، گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه بیرجند، بیرجند، ایران
4 استاد، گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان، ایران
5 دانشیار، گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه بیرجند، بیرجند،ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Coastal fresh groundwater management is a challenging research topic due to the importance of this resource and the significant risks arising from global changes and population growth. Rising sea levels and declining groundwater tables alter the hydraulic gradient and cause the expansion of the saltwater front in coastal aquifers. Moreover, the geometric configuration and morphology of coastal aquifers play a controlling role in saltwater intrusion. In this study, the management of saltwater intrusion in a sloping coastal aquifer using an impermeable cutoff wall was investigated numerically through the Meshless Local Petrov–Galerkin (MLPG) method. Three aquifer bed slope models—including seaward slope (coastal slope, SS), horizontal bed (H), and landward slope (landside slope, LS)—were simulated for different scenarios (no cutoff wall, and cutoff walls with depths of 0.15, 0.30, 0.45, and 0.60 m). The results were compared with previous studies. The findings showed that the geometric shape of the aquifer can affect the extent of saltwater intrusion. Specifically, the advancement of the saltwater front in the seaward and landward sloping aquifers, compared to the horizontal case without a cutoff wall, decreased by 5% and increased by 10%, respectively. In all models, the saltwater intrusion for the 0.60 m wall scenario was 0.50 m, representing the least penetration. Therefore, this scenario can be considered the optimal and most effective wall depth for all cases. To evaluate the accuracy of the MLPG numerical model, the simulation results were compared with the Henry problem and the study by Abd-Elaty & Polemio (2023), and assessed using the RMSE, R², and NSE indices. The results showed that RMSE values in all scenarios were less than 0.06, and R² values exceeded 0.95, indicating excellent agreement between the model and reference data. Model performance, based on the Nash–Sutcliffe Efficiency (NSE) index, was above 0.9 in all cases, confirming the high accuracy and stability of the model in predicting the distribution of the saltwater front.
کلیدواژهها [English]
Coastal aquifers are vital sources of freshwater for densely populated coastal regions. Under natural conditions, groundwater flows from inland areas toward the sea. However, excessive groundwater extraction can reverse the hydraulic gradient, allowing seawater to intrude into aquifers and degrade water quality. Climate change, sea-level rise, and reduced aquifer recharge further intensify this process, increasing the risk of groundwater salinization. Given that nearly 70% of the world’s population lives in coastal zones, managing seawater intrusion has become a major environmental and economic challenge. Among various management solutions, subsurface cutoff walls have been recognized as one of the most effective techniques to control the advancement of the saline front. The present study investigates the influence of aquifer bed slope geometry and cutoff wall depth on the extent of saltwater intrusion using the Meshless Local Petrov–Galerkin (MLPG) numerical method.
In this research, the MLPG numerical model was developed to simulate seawater intrusion in a coastal aquifer. This mesh-free approach eliminates the need for complex grid generation and provides higher accuracy in solving partial differential equations compared to finite element and finite difference methods. Modeling was performed in MATLAB using a computational grid of 231 nodes with a uniform spacing of 0.1 m in both directions. Three aquifer slope geometries were considered: seaward slope (SS), horizontal bed (H), and landward slope (LS). Each geometry was simulated under four cutoff wall depths (0.15, 0.30, 0.45, and 0.60 m) and one scenario without a wall. Model parameters were based on the Henry problem, and the model’s accuracy was validated against the study by Abd-Elaty & Polemio (2023). The statistical indicators RMSE, R², and NSE were used to evaluate the model’s precision and performance.
The findings revealed that increasing the cutoff wall depth significantly reduces seawater intrusion. In the horizontal (H) model, increasing wall depth from 0.15 m to 0.60 m reduced intrusion from 0.93 m to 0.50 m—a 50% reduction. In the landward slope (LS) model, the intrusion decreased from 1.05 m to 0.50 m (52.4%), and in the seaward slope (SS) model, it decreased from 0.90 m to 0.50 m (45%).The LS condition showed the highest saltwater advancement, while the SS condition showed the least. In all models, the 0.60 m cutoff wall depth consistently produced the minimum intrusion (0.50 m) and can therefore be identified as the optimal depth. Statistical validation confirmed the high accuracy of the MLPG model: RMSE < 0.06, R² > 0.95, and NSE > 0.9 in all scenarios, indicating excellent agreement with benchmark data. Sensitivity analysis showed that a ±20% change in hydraulic conductivity (K) caused a 6–9% variation in the position of the saline front, highlighting the importance of accurately defining hydraulic properties in simulation models.
This study demonstrates that aquifer bed geometry and cutoff wall depth have a significant impact on seawater intrusion in coastal aquifers. A landward slope increases intrusion by about 10%, while a seaward slope reduces it by about 5%, compared to the horizontal case. The 0.60 m cutoff wall depth was found to be the most effective and optimal configuration across all scenarios. The high accuracy and numerical stability of the MLPG method confirm its potential as a reliable and efficient tool for modeling and managing coastal groundwater systems.
Conceptualization A. Akbarpour and Z. Baazm; methodology, , A. Akbarpour; software, Z. Baazm and A. Akbarpour; validation S. S. Islamian and H. Khozaimenejad; formal analysis, A. Akbarpour and Z. Baazm; investigation, M. Yaqubzadeh and H. Khozaimenejad. ; resources, Z. Baazm; data curation Z. Baazm, A. Akbarpour and M. Yaqubzadeh,; writing-original draft preparation, Z. Baazm; writing-review and editing, Z. Baazm, A. Akbarpour, M. Yaqubzadeh and H. Khozaimenejad.; visualization, Z. Baazm and M. Yaqubzadeh; supervision, Z. Baazm and A. Akbarpour,; project management A. Akbarpour and M. Yaqubzadeh; funding acquisition, Z. Baazm and A. Akbarpour. All authors have read and agreed to the published version of the manuscript.
Data available on request from the authors.
The author declares no conflict of interest.
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