Beschreibung:    The area of study lies at the northeastern part of Nile Delta. Global shoreline regression and sea-level rise have their own-bearing on the groundwater salinization due to seawater intrusion. A new adopted approach for vulnerability mapping using the hydrochemical investigations, geographic information system and a weighted multi-criteria decision support system (WMCDSS) was developed to determine the trend of groundwater contamination by seawater intrusion. Six thematic layers were digitally integrated and assigned different weights and rates. These have been created to comprise the most decisive criteria used for the delineation of groundwater degradation due to seawater intrusion. These criteria are represented by the total dissolved solids, well discharge, sodium adsorption ratio, hydrochemical parameter (Cl/HCO 3 ), hydraulic conductivity and water types. The WMCDSS modeling was tried, where a groundwater vulnerability map with four classes ranging from very low to high vulnerability was gained. The map pinpointed the promising localities for groundwater protection, which are almost represented by the very low or low vulnerability areas (53.69 % of the total study area). The regions having high and moderate groundwater vulnerability occupy 46.31 % of total study area, which designate to a deteriorated territory of groundwater quality, and needs special treatment and cropping pattern before use. However, the moderate groundwater vulnerability class occupies an area of about 28.77 % of the total mapped area, which highlighted the need for certain management practices to prevent the saltwater intrusion from expanding further to the south. There was a good correlation of the constructed vulnerability map with the recently gathered water quality data and hydrochemical facies evolution. The plotting of water quality data on Piper trilinear diagram revealed the evolution of freshwater into the mixing and the saline zones as an impact of seawater intrusion, which validates the model results. Content Type Journal Article Category Original Article Pages 1-19 DOI 10.1007/s12665-012-1740-x Authors Hossam H. Elewa, National Authority for Remote Sensing and Space Sciences (NARSS), P.O. Box 1564, 23 Jozef Brows Tito St., El Nozha El-Gedida, Alf-Maskan, Cairo, 11769 Egypt Ragaa E. Shohaib, Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt Atef A. Qaddah, Geological Hazards Research Unit, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia Ahmad M. Nousir, Geology Department, Faculty of Science, Zagazig University, Zagazig, Egypt Journal Environmental Earth Sciences Online ISSN 1866-6299 Print ISSN 1866-6280