Hydrologie : recherche actuelle

Creep of seawater intrusion in the nile delta aquifer

Abstract

Mohamed S. Taha, Asaad M. Armanuos and Bakenaz A. Zeidan

Background: The Nile Delta aquifer in Egypt subjected to a severe seawater intrusion problems because of the excessive pumping over the last several decades. The seawater has intruded the aquifer up to a distance more than 70.0 km measured from the shoreline along the bottom boundary of the aquifer. Climate change and the rise of sea level will affect the groundwater quality in the Nile Delta aquifer in two methods. First, low and flat lands along the shoreline will be submerged with seawater and the aquifer below these lands will be damaged. Second, pressure heads of sea water will increase causing more intrusion. Seawater intrusion is a process which seawater infiltrates into freshwater aquifers due to natural processes or human activities. Seawater intrusion is caused by decreases in groundwater levels as a result of excessive pumping or by rises in seawater levels as a result of climate change. The salt water rises 40 m for every 1 m of freshwater depression and forms a cone of salt water. The effects of intrusion on water quality not only belongs to the pumping well sites, but also at other well sites, and undeveloped parts of the aquifer. The problem of seawater intrusion is mainly conditioned by three factors: first, the difference between the densities of the fresh and salt water, second, the hydrodynamic properties of the aquifer and third, the flow that the aquifer discharges into the sea. The first two factors are intrinsic to the seawater intrusion problem regardless of the climate in the region. Furthermore, these two parameters are established, and cannot be affected by the usual human activities. The flow that the aquifers discharge into the sea is conditioned by natural conditions (from rainfall) or artificial recharge (mainly from irrigation and canals networks) and by pumping. Therefore, anthropogenic actions can make some modifications. The most prevailing technique is to increase the flow of groundwater from the aquifers towards the sea. In this paper (ARC GIS) program is used to prepare the required maps for the 3-D models (MODFLOW + SEWAT) which are used to simulate saltwater intrusion in the Nile delta aquifer. The amount of water pumped from the Nile delta aquifer through wells belongs to 2008. The recent shore line of the Mediterranean sea is used. The results of the simulation show that the Equi-concentration line 35 reaches 81 km in the east of the Nile delta, 93 km in the middle and 68.5 km in the west for base case. The Equi-concentration line 35 of this simulation is compared with the Equi-concentration line of 1960, 1980 and 1992. It is observed that the creep of the iso saline water occurs at the west and the middle of the Nile delta compared to these years.