Abstract
A numerical model of variable-density groundwater flow and miscible salt transport is applied to investigate the extent of seawater intrusion in coastal aquifer of Ras El-Hekma, northwestern coast, Egypt. The SEAWAT 2000 code is used to solve the density-dependent groundwater flow and solute transport governing equations. Seventeen groundwater samples were collected in 2015 for routine chemical analysis and water level monitoring were carried out and interpreted. The model was calibrated using data measured for heads (m) and TDS (mg/L) in 2009 compared with data collected in 2015. Three scenarios of pumping and fourth scenarios of sea level rise by 0.5 m were applied. The results of three scenarios of pumping revealed that there was a general trend of drawdown in water table (~5 m) of observed wells located at about 1 to 1.5 km from the coast at the end of 20 years of simulation. At the same time there was replenishment from rainfall and surface runoff caused a water table rise in some observed wells that were located inland. For the proposed fourth scenario of sea level rise, the seawater/freshwater interface will migrate more inland (0.5 to 2 km) than its current position. The result of the numerical model shows a transgression of seawater inland and along the coast. The model and chemical results recommend a decrease in pumping to the drilled wells should not exceed 40 m3/day in order to avoid further seawater intrusion along the coast and upwelling of deep saline groundwater with continuous monitoring of the groundwater level and salinity measurements in north coast of Mediterranean Sea. Key words: Seawater intrusion, groundwater modeling, SEAWAT code, Ras El-Hekma, Egypt.
Highlights
Coastal areas are important for human settlement and development
Soliman et al (2013) mapping of seawater/freshwater interface at Ras El-Hekma city by 2-D resistivity imaging and transient electromagnetic soundings, concluded that the upper aquifer represented by Oolitic limestone of Pleistocene age and the lower aquifer represented by Middle Miocene age were affected by seawater, but the lower one showed larger effect than the upper one
The groundwater flow is directed toward Mediterranean Sea with a steep groundwater gradient
Summary
Coastal areas are important for human settlement and development. It is estimated that more than half the world’s population lives within 60 km of the shoreline, and this number could increase up to three quarters over a decade (UNCED, 1992). Over exploitation of groundwater in coastal aquifers may result in intrusion of saltwater. Youssief and Bubenzer (2013) studied groundwater at Ras El-Hekma area and clarified the relationship between depth to water, sea level and salinity of water. The last decade has seen the appearance of several density-dependent simulation codes that are based on the commonly used groundwater model, MODFLOW, developed by the U.S Geological Survey (McDonald and Harbaugh, 1998; Harbaugh et al, 2000). These codes include SEAWAT (Guo and Bennett, 1998a, b; Guo and Langevin, 2002; Langevin et al, 2003)
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