Appraisal seawater intrusion vulnerability for the Moghra coastal aquifer, Egypt– application of the GALDIT index, sensitivity analysis, and hydro-chemical indicators

• Published in: Groundwater for sustainable development 2024-05, Vol.25, p.101166, Article 101166
• Main Authors: Emara, Sobhy R., Armanuos, Asaad M., Shalby, Ahmed
• Format: Article
• Language: English
• Subjects: Coastal aquifers; GALDIT; Groundwater management; Groundwater quality index; HFE diagram
• ISSN: 2352-801X; 2352-801X
• DOI: 10.1016/j.gsd.2024.101166

The Moghra aquifer is being intensively exploited within a mega desert reclamation project in Egypt. Due to the ongoing unprecedented overdraft, a drastic drawdown was observed in such a nonrenewable aquifer. Ration pumping was advocated to maintain a drawdown threshold and avoid paleowater depletion. The aquifer potential in terms of water storage may satisfy the water duty of the proposed development. However, seawater intrusion (SWI) would exacerbate the imposed stress on the aquifer to supply agricultural-suitable groundwater. Herein, a comprehensive approach integrating a GIS-based model with hydro-chemical indicators was adopted to assess the aquifer's intrinsic vulnerability to SWI. GALDIT is a representative mapping index for evaluating SWI vulnerability using six hydrogeological parameters. Sensitivity analysis was implemented to determine the relative influence of each criterion. The resulting significance of each parameter was used to develop an actual-weighted vulnerability map. Moreover, the hydrogeochemical analysis, including the hydro-chemical facies Evolution (HFE) diagram and groundwater quality index (GQISWI), was integrated to accomplish the SWI investigation. GALDIT rated two-thirds of the development area as moderately vulnerable, while one-fifth was highly vulnerable. The correlation strength between the GALDIT-based vulnerability maps and the TDS measurements confirmed its reliability. However, the modified GALDIT model outperformed in zoning the highly susceptible plots. It has expanded the high and medium vulnerability classes by 13.38% and 5.17% of the wells' field area. Piper diagram distinguished 94 out of 101 samples as (Na+ - K+ - Cl− - SO42−) ion association, indicating the presence of SWI. HFE diagram classified most (91%) samples as Na–Cl chemical water type. However, the GQISWI was more consistent with the GALDIT index, rating 77 wells as mixed water and the others as saline. The findings urged implementing management measures for remediation and mitigation of the aquifer salinization. [Display omitted] •Different techniques revealed the lack of resilience of the Moghra system to SWI.•GALDIT rated the aquifer's one-fifth as highly vulnerable and two-thirds as moderate.•Sensitivity analysis adjusted parameters' significance to refine the index skill.•Piper and HFE diagrams demonstrated abundance of Na–Cl chemical water type.•GQISWI was more consistent with GALDIT, classifying most samples as mixed water.