NS004-11
Stream-channel processes at the eastern Dead Sea from combined surface and subsurface observations

Tuesday, 15 December 2020: 06:00
Virtual
Djamil Al-Halbouni1, Robert A Watson2, Eoghan Patrick Holohan2, Fernando M Santos3, Rena Meyer4, Ulrich Polom5, Hussam Alrshdan6, Charlotte M Krawczyk1,7 and Torsten Dahm1,8, (1)Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, (2)University College Dublin, UCD School of Earth Sciences, Dublin, Ireland, (3)Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal, (4)University of Copenhagen, Department of Geosciences and Natural Resource Management, København K, Denmark, (5)Leibniz Institute for Applied Geophysics, Hannover, Germany, (6)Jordanian Ministry of Energy and Mineral Resources, Amman, Jordan, (7)Technical University Berlin, Berlin, Germany, (8)University of Potsdam, Potsdam, Germany
Abstract:
A dynamic reaction of the hydrogeological system at the Dead Sea (DS) has led to the formation of new springs, stream channels, depressions, and sinkholes. The connection between surface and sub-surface processes presents methodological challenges that we address by a novel combination of methods. Focusing on the eastern shoreline, near Ghor Al-Haditha in Jordan, we use satellite image analysis, close-range photogrammetry, shear wave (SH) reflection seismics, electric resistivity tomography (ERT), self-potential (SP) and hydrogeological modelling to reveal and understand these dynamic hydro-morphological processes.

The development of a stream channel system in the DS mud deposits is intricately linked to that of the nearby karstic features. Moreover, the system has localised from several small channels to one ‘main channel’ over time. In the main depression zone, the subsurface traces of these channels are identified by SH reflection. Complemented by ERT, we identify clearly bordered, several meters wide channels within the alluvial sediments at shallower depths. The most destructed area surrounds these channels. At the former stable shoreline, a network of complex active flow zones is identified by self-potential and ERT, with a predominantly upflow regime. At the mud-alluvium contact we find an extremely low resistivity layer beneath resistive cover and indications of fracture zones. At the surface of the former Dead Sea lakebed, these channels partly appear as active drainage conduits.

A 2D hydrogeological density driven flow model simulating DS regression reveals a complex head distribution and development of a strong hydraulic gradient towards inland. A fresh-saline water interface of different levels develops, with salt water intrusion reaching widely inland. From local transformation equations between salinity and electric conductivity implemented in the hydrogeologic modelling, we find that both alluvium and mud sediments can reach extremely low resistivities ) when saturated by DS brine. Alluvial sediments saturated by relatively fresh water show higher resistivities of .

Finally, we formulate a new conceptual model for the hydro-morphological processes in a karstic network, to support hazard assessment in this area.

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