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.