Vulnerability Assessment of Elbe-Weser-Triangle Coastal Aquifer Using GALDIT Method

Tanvir Ehsan1, M. Azizur Rahman2, Eva González3, Helga Wiederhold2, Monika Sester1
1 Leibniz Universität Hannover
2 Leibniz Institut für Angewandte Geophysik
3 Landesamt für Bergbau, Energie und Geologie

1.15 in Wasserqualität in Grundwasser und Flusseinzugsgebieten

Elbe-Weser-Triangle costal aquifer (~1700 km2) is located at the North of Germany and surrounded by the sea at the West and by the Elbe River at the North and East. The source of aquifer pollution is not only the surface sources (e.g., agricultural activities) but also the saline water intrusion from the sea (chloride value ~16000 mg/L) and the downstream of the Elbe River (ranges between 9000 mg/L and 700 mg/L at the North boundary). Hence, the aquifer system is significantly vulnerable to the saline water intrusion from these sources. This poster assessed the study area aquifer vulnerability to seawater intrusion using GALDIT method. Basic information on thematic maps of six major factors: (1) Groundwater occurrence, (2) Aquifer hydraulic conductivity, (3) Level of Groundwater depth above sea level, (4) Distance from the shore, (5) Impact of existing status of the seawater intrusion in the area, (6) Thickness of the aquifer, were obtained from secondary sources. All the maps were normalised to a score between 0 to 10 using step-wise transformation function, and relative weights were assigned according to the significance of each thematic layers to vulnerability assessment. Finally, the vulnerability index has been generated by combining six thematic layers using weighted linear combination (WLC) method. ArcGIS has been used to process the thematic maps and overlay of these. In addition to the nearby area to the sea and upstream of the Elbe River, the marsh areas where the topography is below mean sea level and the groundwater elevation is low are significantly vulnerable to seawater intrusion. The result is in consistent with the regional groundwater flow pattern within the upper aquifer. The groundwater from the Elbe River flow towards the marsh and thus carry the saline water towards the relatively fresh aquifer. The aquifer water quality status (e.g., salinity due to early age flooding) also plays a significant role in vulnerability index. Therefore, this study also have assessed the sensitivity of thematic map’s weight by varying one weight and keeping the others equal.