Assessment of seawater intrusion under different pumping scenarios in Moghra aquifer, Egypt

https://doi.org/10.1016/j.scitotenv.2021.146710Get rights and content

Highlights

  • In this research, a 3-D numerical model for flow and solute transport has been built using the SEAWAT module.

  • The model shows the quantitative and qualitative changes in the aquifer under different pumping conditions considering SWI.

  • The procedure followed for SWI simulation and calibration process depends on two different approaches.

  • Mass balance calculations were shown to describe how the conceptual model works.

  • Sensitivity analysis has been set up for the model parameters to describe the uncertainty degree.

Abstract

The Moghra aquifer has shown promise in land reclamation projects conducted in the Western Desert of Egypt. Although this aquifer has hundreds of pumping wells in new urban communities built to meet the needs of the increased population, the system is threatened by the phenomenon of seawater intrusion (SWI). The present study evaluates the degree to which these pumping wells will attract seawater to the aquifer system in the Western Desert region under different pumping conditions. Using the SEAWAT module of Groundwater Modeling System (GMS) software, a three-dimensional (3D) finite-difference model is built to simulate the flow and salinity distribution in the Moghra aquifer considering the geological and hydrogeological characteristics of the aquifer system. The procedure used to solve the mathematical model relied on merging two different approaches. The first approach described the dividing lines of the transition zone due to the SWI. The second approach was applied to conduct the perfect calibration process for the aquifer system. The results show that the flow and quality of the groundwater aquifer are affected by pumping. The water level and salinity are predicted under different pumping rates, a fivefold increase in the pumping rate results that the salinity increased between 4% and 26.8% according to the well location. Moreover, the drawdown values reached 162 m, which is about 46.3% of the saturated thickness.

Introduction

Groundwater has become the savior resource for freshwater in many countries globally, particularly in arid and semi-arid regions such as Egypt (Negm, 2019). Substantial increases in population and surface water limitations have motivated the government to search for alternate water resources, such as groundwater and water from seawater desalinization. The Egyptian government has announced plans to expand development in the Western Desert to reduce the pressure on surface water resources, especially after the Grand Ethiopian Renaissance Dam construction, which reduced Egypt's quota from the Nile River (Abdelhaleem and Helal, 2015). The residents of Moghra, a newly developed area, depend on the Moghra aquifer to cater to their water demands. Since this body is considered an essential aquifer in the northern region of the Western Desert, it should be well managed to ensure its adequacy for sustained development. Groundwater contamination can be caused by many factors (Allam et al., 2019; Mansour et al., 2018), the most common of which is seawater intrusion (SWI). This factor is a natural phenomenon by which the salt water of the sea can replace the freshwater of the aquifer (Badaruddin et al., 2017). Badaruddin and Morgan (2017) categorize the SWI into active and passive. It depends on the direction of the freshwater direction if toward the sea or the land.

Many studies on SWI based on monitoring systems and modeling have been conducted. The simulation of SWI is considered to be a complex process, and the results differ among aquifers according to their natures (Sefelnasr and Sherif, 2014). Pool et al., 2014, Pool et al., 2015 showed the difference of homogeneity and heterogeneity in the hydraulic conductivity on SWI and solute spreading. Modeling is a useful tool for defining an aquifer, simulating its phase, and predicting its behavior under various conditions (Sobeih et al., 2017). Two approaches can be used for simulating SWI. The first is the sharp interface approach, which depends on the Ghyben–Herzberg relation assuming that the fresh water and saltwater are not miscible and are separated by a sharp interface. The second is the transition zone approach, which assumes a diffusion interface between the two water types (Sakr, 1992; Sherif et al., 2014). Sakr et al. (2004) used an analytical model using the sharp interface approach to determine the thickness of the freshwater that occupies the Nile Delta Aquifer. Guo and Langevin (2002) used the FEFLOW computer program to develop a groundwater flow and solute transport numerical model to test the effects of pumping on SWI. In their study, many scenarios were applied, which considered pumping rate, number of wells, and well location to determine the optimal case with the least intrusion. Sherif et al. (2014) used a numerical model using the FEFLOW software to simulate a coastal aquifer under various pumping scenarios. The model showed that reducing the pumping rate could mitigate SWI, whereas increasing the pumping rate could accelerate SWI toward the freshwater zone and reduce the volume of fresh water in the aquifer. Nofal et al. (2015) used the SEAWAT software program to build a detailed conceptual regional model that illustrated the effect of SWI on the Nile Delta aquifer. The model showed that SWI mainly occurred in shallow and medium depths. Abu-Bakr et al. (2016) used numerical modeling to investigate the effect of groundwater abstraction from a coastal aquifer. The model predicted the salinity and water levels under various scenarios and showed a direct relationship between the wells arrangement and the enhancement of groundwater quality. Chang et al. (2018) simulated the SWI for coastal aquifers using a 2D SEAWAT model to predict the interface between the brine and freshwater for specific forecasting as well as the changes in water level caused by pumping. Farooq (2020) presented an explanation for the SWI phenomenon and its controlling factors and discussed several methods for mitigating its effect. Kazakis et al. (2018) used a six parameters-dependent method for modifying the standard method for the GALDIT-F method which explains the seawater intrusion assessment in a coastal aquifer. Many other studies were discussed in SWI Meetings as a review for the groundwater quality influenced by the SWI phenomenon (Sarker et al., 2018; Stein et al., n.d.; Langevin et al., 2016; Polemio and Zuffianò, 2013; Oude Essink and Boekelman, 1998; Verkaik et al., 2018). Abdel Mogith et al. (2013) investigated the Moghra aquifer to determine the best physical, chemical, and hydrological configurations. The salinity of the aquifer in the study area was 5000–10,000 mg/L; this wide range is attributed to changes in the depositional environment of the Moghra Formation from continental to marine.

The previous studies help to explain the mechanism of SWI simulation in aquifers and the geological and hydrogeological settings of the Moghra aquifer. However, very little has been reported on the effect of SWI on the Moghra aquifer. Also, there are not many researches to discuss the active SWI studies, which is the same situation in Moghra aquifer case. Therefore, the objective of the present study is to assess the impact of groundwater extraction from the Moghra aquifer considering the SWI phenomenon under many different scenarios.

Section snippets

Site description

The study area is located in the northern part of the Western Desert in Egypt. It extends between the geographical coordinates of 28°10′, 29°20′ E longitude and 29°50′, 31°10′ N latitude. The development area for the pumping wells is about 60 km from the coast; looking south (Fig. 1). The study area is located in the northwestern coastal zone of the subtropical Mediterranean climate, which includes mild and wet winters and hot and dry summers. Matrouh receives average annual precipitation of

Data analysis and sampling

In this research, about 450 wells drilled in 2018 by the Ministry of Water Resources and Irrigation in only two aquifers from the previously stated aquifers were analyzed (Table 1). For the collected data, groundwater levels in the Moghra aquifer were between −10 m and −60 m, and the main groundwater flux is directed from the northeast to southwest. About 96 samples were taken from Moghra aquifer's screens to measure the salinity of the aquifer water. Their salinity is 1200–9800 mg/L. On the

Results and discussion

The mechanism of the solution was to start with the baseline condition, which describes the current situation without any groundwater extraction because the wells had not been pumped yet. Thus, groundwater extraction during the last 40 years was performed by only 20 wells inside the modeled area domain with very low and non-continuous pumping rates. The baseline condition of the designated model was the year 2018 as the data are available for this year.

To delineate the salinity concentration

Conclusion

  • In this research, a 3D groundwater flow and solute transport model was set up to describe the current situation of the aquifer system flow and salinization and its behavior under different pumping conditions.

  • The procedure performed for that aspect was unconventional. The first approach succeeded in defining the dividing line between the saline water and brackish water of the aquifer in the northern coastal zone for which the observation data was rare. The second approach achieved the best

CRediT authorship contribution statement

The study is part of an MSc. research conducted by S.M.G, under the supervision of E.H., T.M.H. The paper is conducted as a joint effort of all authors. Conceptualization, S.M.G, E.H., and T.M.H.; methodology, S.M.G., E.H. and T.M.H.; software, S.M.G; analysis, S.M.G; data curation, S.M.G; writing—original draft preparation, S.M.G; writing—review and editing, S.M.G., E.H, and T.M.H.; supervision, E.H, T.M.H.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The activities of this research were supported by the Research Institute for Groundwater (RIGW) and the Ministry of Water Resources and Irrigation (Groundwater Sector). The authors would like to thank the review and constructive comments of the reviewers.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability statement

Research data are available from the corresponding author by request.

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