Geoelectrical investigation of seawater intrusion in the coastal urban area of Çanakkale, NW Turkey
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Seawater intrusion (SI) constitutes one of the major concerns most commonly encountered in coastal areas. The city of Çanakkale, which is situated in the northwestern part of Turkey and built on an alluvial coastal plain, has the second longest coastline in the country. Thus, SI poses a serious threat to shallow freshwater resources in the plain. Direct current resistivity method is the most widely used geoelectrical method for determining low-resistivity zones that usually correspond to the presence of SI. A total of 78 vertical electrical sounding (VES) measurements covering the entire coastal urban area were conducted in 2004 for groundwater exploration. In the present study, 61 soundings displaying an alignment along 13 lines in the direction of E–W were re-interpreted using a two-dimensional (2D) inversion technique based on a smoothness-constrained least squares method to delineate the extend of SI landward. The produced geoelectrical cross-sections successfully revealed an undulating seawater–freshwater interface. The reliability of the estimated solutions was demonstrated by a sensitivity analysis performed by calculating model resolution matrix. The results obtained via 2D inversion of VES data were also correlated well with those obtained from hydrogeological and borehole information within the study area. Consequently, the results of this study indicated that SI characterized by low resistivity (<5 Ωm) is mainly observed in the southern part of the Sarıçay stream which passes through the city center and flows into the Çanakkale Strait (Dardanelles). Moreover, seawater input extends several hundred meters landward.
Keywords2D inversion Coastal urban area Çanakkale Seawater intrusion Electrical resistivity VES
We thank Savaş Gürçay (MSc), Dr. Alper Demirci and Dr. Yunus Levent Ekinci for their efforts and contributions to the field study. We also thank Dr. Ozan Deniz for kindly providing us his works. We are grateful to two anonymous reviewers for their helpful and constructive comments which greatly improved the paper. Generic Mapping Tools (GMT) (Wessel and Smith 1995) was used to generate location maps.
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