Impact of sea-level rise on groundwater salinity at the development area western delta, Egypt

Abstract

Climate change effects are expected to raise the average sea level. It is widely assumed that this raise will increase saltwater intrusion processes in coastal aquifers. There are four scenarios for sea level rise (RCP2.6, RCP4.5, RCP6.0, and RCP8.5), which were assumed in the year 2014 by the International Panel on Climate Change (IPCC, 2014). The two extreme scenarios (RCP2.6 and RCP8.5) are considered in this study to examine the impact of the expected changes in the Mediterranean Sea level on groundwater salinity at a relatively new development area in Egypt at the west of the Nile Delta. Rising in sea level would destroy parts of the protective offshore sand belt, which has already been weakened by reduced sediment flows resulting from the construction of dams in the Nile. Without this sand belt, water quality in coastal freshwater lagoons will be altered, and recreational tourism and beach facilities will be inundated. The tools of Geographic information systems and Numerical simulations, using the software “ArcMap” and “FeFlow” respectively are used. The simulations are conducted in 3D using digital elevation model. For three scenarios of sea level rise (RCP2.6, RCP8.5 and the scenario of no rise in sea level), two different ways for groundwater extraction rates are considered: the first is the actual extraction rate, and the second is the extraction rate at the initial condition in the year 1990. The simulations show that the effect of global sea level rise in the period from the year 1990 up to 2100 appears clearly through the coastal topography with relatively low level elevation adjacent to the shoreline. A shift of the interface is expected up to the year 2100 by a maximum of 43km covering an area of 1980km2 according to scenario RCP2.6, and by a maximum of 57km covering an area of 2870km2 according to scenario RCP8.5. Overexploitation of groundwater leads to an increase in salinity concentration up to 5000mg/l and covers about 10% of the study area.