Review status: this preprint is currently under review for the journal HESS.
Dynamics of hydrological and geomorphological processes in
evaporite karst at the eastern Dead Sea – a multidisciplinary study
Djamil Al-Halbouni1,Robert A. Watson2,Eoghan P. Holohan2,Rena Meyer3,Ulrich Polom4,Fernando M. Dos Santos5,Xavier Comas6,Hussam Alrshdan7,8,Charlotte M. Krawczyk1,9,and Torsten Dahm1,10Djamil Al-Halbouni et al.Djamil Al-Halbouni1,Robert A. Watson2,Eoghan P. Holohan2,Rena Meyer3,Ulrich Polom4,Fernando M. Dos Santos5,Xavier Comas6,Hussam Alrshdan7,8,Charlotte M. Krawczyk1,9,and Torsten Dahm1,10
Received: 19 Jan 2021 – Accepted for review: 27 Jan 2021 – Discussion started: 01 Feb 2021
Abstract. Karst groundwater systems are characterised by the presence of multiple porosity types. Of these, subsurface conduits that facilitate concentrated, heterogeneous flow are challenging to resolve geologically and geophysically. This is especially the case in evaporite karst systems, such as those present on the shores of the Dead Sea, where rapid geomorphological changes are linked to a fall in base level by over 35 m since 1967. Here we combine field observations, remote sensing analysis, and multiple geophysical surveying methods (shear wave reflection seismics, electrical resistivity tomography [ERT], self-potential [SP] and ground penetrating radar [GPR]) to investigate the nature of subsurface groundwater flow and its interaction with hypersaline Dead Sea water on the rapidly retreating eastern shoreline, near Ghor Al-Haditha in Jordan. Remote-sensing data highlight links between the evolution of surface stream channels fed by groundwater springs and the development of surface subsidence patterns over a 25-year period. ERT and SP data from the head of one groundwater-fed channel adjacent the former lakeshore show anomalies that point to concentrated, multidirectional water flow in conduits located in the shallow subsurface (< 25 m depth). ERT surveys further inland show anomalies that are coincident with the axis of a major depression and that we interpret to represent subsurface water flow. Low-frequency GPR surveys reveal the limit between unsaturated and saturated zones (< 30 m depth) surrounding the main depression area. Shear wave seismic reflection data nearly 1 km further inland reveal buried paleochannels within alluvial fan deposits, which we interpret as pathways for groundwater flow from the main wadi in the area towards the springs feeding the surface streams. Finally, simulations of density-driven flow of hypersaline and under-saturated groundwaters in response to base level fall perform realistically if they include the generation of karst conduits near the shoreline. The combined approaches lead to a refined conceptual model of the hydrological and geomorphological processes developed at this part of the Dead Sea, whereby matrix-flow through the superficial aquifer inland transitions to conduit-flow nearer the shore where evaporite deposits are encountered. These conduits play a key role in the development of springs, stream channels and subsidence across the study area.
Overall, I considered this manuscript as a well written paper that is based on substantial hard work by the authors. The paper investigates the nature of subsurface groundwater flow and its interaction with hypersaline Dead Sea water. The authors conducted a multidisciplinary scientific study combining field observations, remote sensing data analysis, multiple geophysical surveying methods (shear wave reflection seismic, electrical resistivity tomography, self-potential and ground penetrating radar) and Hydrogeological modelling. The research design is so appropriate and the methodological approach adopted is adequately described and suitable for karst environment studies. The results obtained are very interested and very well presented. This manuscript contains significant scientific information and is very interesting for the readers and for the scientific community in general. The manuscript constitutes a suitable study that I recommend to be accepted for publication in Hydrology and Earth System journal after minor revisions.
Below are some comments and suggestions:
Could you please present the results of regional and local geological summary that you used for geophysical data interpretation? This would help readers get a sense of how you calibrated geophysical data.
Page 5: The Figure 1 (b).It is difficult to identify Ground penetrating Radar and S-Wave reflection seismic profiles
Page 6: Figure 2. Could you please indicate on the field photos the limits of alluvial fans, halite cover, silt-clayey marl deposits, and alluvial deposits?
Page 8: Table 1. Could you please provide the Spring Id with logical numeration? Or provide the missing information for (4,5,6) Spring Id.
Page 10: line 28: Pansharpening pre-processing: What were the results? Did you obtain the same spatial resolution for all the satellite images you used? These could help readers understand the smallest fluvial and karst features you were able to identify and extract on remote sensing data.
Page 10: lines 32-34: What were the band combinations you chose for aerial and satellite images on which you manually digitalize the fluvial and karst features? Which bands did you choose? What was the base on which you chose these bands? Did you notice any band combination which highlights better the fluvial and karst features? Please provide more details.
Page 11: Lines 17-19: Please provide spatial distance between each SP point measurements.
Page 16: Figure 6: Please indicate the limits of CS (with a box).
Pages 20-21: Figure 7-8: Could you please provide the name of satellite and the band combination for aerial and satellite imagery presented on the left column of these Figures?
thank you very much for reviewing the paper and for the constructive comments. We will upload a point-by-point detailed response together with the revised manuscript once the review has been completed.
The rapid decline of the Dead Sea by over a meter per year leads to dynamic changes of the water system, with physical and chemical processes rapidly creating voids and conduits into the geologic underground. This work uses a combination of remote sensing, geophysical methods and numerical modeling to link groundwater flow patterns and stream-channel formation at the eastern shore to occurence of sinkholes & subsidence. Better understanding of this system will improve regional hazard assessment.
The rapid decline of the Dead Sea by over a meter per year leads to dynamic changes of the water...
