Research papers A Comprehensive evaluation of groundwater vulnerability to saltwater up-coning and sea water intrusion in a coastal aquifer (case study: Ghaemshahr-juybar aquifer) Alireza Motevalli a , Hamid Reza Moradi a,⇑ , Saman Javadi b a Department of Watershed Management Engineering, Faculty of Natural Resources, Tarbiat Modares University, Iran b Department of Irrigation and Drainage, Aburaihan Campus, University of Tehran, Iran article info Article history: Received 25 June 2017 Received in revised form 8 December 2017 Accepted 17 December 2017 Available online 18 December 2017 Keywords: Saltwater up-coning Seawater intrusion Aquifer salinization Groundwater management Vulnerability optimization abstract Aquifer salinization has recently increased significantly due to human activity and has caused irreparable environmental and economic effects. In this research, a new method is proposed for modeling the vulner- ability to salinity for the Ghaemshahr-juybar aquifer. Specifically, the GALDIT (Sea water intrusion) and TAWLBIC (Saltwater up-coning) indices were combined to produce a map of vulnerability (Comprehensive Salinity Index or CSI) to seawater intrusion of a region near the coast and saltwater up-coning away from the coast, respectively. Single parameter and removal layer sensitivity analysis were performed in order to identify the sensitive parameters and achieve optimal weights (through the single-parameter method) of contributing factors in all three methods. The three optimized methods produced were GALDIT-Opt, TAWLBIC-Opt and CSI-Opt. To assess the accuracy of the original maps and optimal ones, the Pearson correlation was used. Results indicated that the Pearson correlation of the opti- mized GALDIT, TAWLBIC and CSI model was better than GALDIT, TAWLBIC and CSI. The results show that the increase in correlation between EC (Electrical Conductivity), TDS (Total Dissolved Solids) and SAR (Sodium Adsorption Ratio) from the GALDIT model to the CSI-Opt model from values of 0.64, 0.56 and 0.68 has improved to values of 0.81, 0.88 and 0.91, respectively. The highest concentration of EC, with a value of 7050 ms/cm, is sampled in the areas of the east and northwest of the Ghaemshahr-juybar aqui- fer, which are classified in the CSI-Opt model as high and very high vulnerability levels. The highest con- centration of TDS and SAR has been found in the east, northwest and northeast of the Ghaemshahr-juybar aquifer with a value of 4724 ppm for TDS and 14 mg/l for SAR that have been modeled in the CSI-Opt index as highly vulnerable areas. Eventually, CSI mapping can be used as an efficient tool in prioritizing in terms of the vulnerability to aquifer salinity, carrying out adjustments, recharge, and adaptation poli- cies for this issue. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction Groundwater is considered as one of the most important water resources in the world (Gholami et al., 2010; Sherif et al., 2012; Neshat et al., 2015; Javadi et al., 2017). In northern Iran, some of the well’s consumption for agricultural, industrial and drinking purposes are supplied from groundwater sources. Aquifer salinity has been identified as a major constraint for the use of water resources (Kura et al., 2014a,b; Gautam et al. (2015); Gholami et al., 2016; Gholami et al., 2015a; Mastrocicco et al., 2012). Unau- thorized and uncontrolled exploitation of groundwater resources and climate change (Sherif and Singh, 1996; Sherif and Singh, 1999; von Gunten et al., 2015; Luoma et al., 2017; Moller et al., 2008; Zhang et al., 2012), has thereby reduced the amount of groundwater flow and has led to contaminated transports from sea to groundwater resources (Werner, 2010; Yu et al., 2010; Sefelnasr and Sherif, 2014; Kura et al., 2014b; Gholami et al., 2015b; Arezoomand et al., 2016; Michael et al., 2017). In addition, solute transport and aquifer salinity is not limited to areas near the coast (Werner et al., 2013; Jakovovic et al., 2016). The saltwater up- coning process, unlike seawater intrusion, is not limited to the shores and occurs as a result of indiscriminate exploitation in all of the plains (Diersch and Prochnow, 1984; Bower et al., 1999) (See Fig. 1). Presumably, the saltwater up-coning process is much broader than the seawater intrusion. Understanding salinity mechanisms is extremely difficult and there are various scientific https://doi.org/10.1016/j.jhydrol.2017.12.047 0022-1694/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail addresses: Ar.motevalli@modares.ac.ir (A. Motevalli), hrmoradi@ modares.ac.ir (H.R. Moradi), javadis@ut.ac.ir (S. Javadi). Journal of Hydrology 557 (2018) 753–773 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol