The effect of hydraulic anisotropies on intensely exploited groundwater resources: the numerical evaluation of a hydrothermal transboundary aquifer system in the Middle East

Previous investigations postulate the presence of a zone of high hydraulic anisotropy parallel to the principle axis of the Lower Yarmouk Gorge (LYG) in the Middle East. Driven by mixed convection, heated fresh groundwaters ascend within the gorge from confined Cretaceous units through artesian wells and Hammat Gader springs. Two-dimensional transient numerical simulations of coupled fluid flow and heat transport processes are used to investigate the impact of (1) a zone of hydraulic anisotropy and (2) abstraction on hydraulic heads and temperature profiles in the shallow aquifers. The models successfully reproduce hydraulic head distribution pre- and post-groundwater abstraction; dominance of conductive and advective heat transport processes is also shown. The models further support the existence of a structural feature along the principle axis of the gorge, which hydraulically connects groundwaters in both flanks, while cross flow of groundwaters is prevented. That implies a subsurface anisotropic zone, which lets the gorge act as a complex conduit-barrier system where adjacent N–S and S–N flow-fields confluence and get drained towards the Jordan Rift. The present numerical investigations support the hypothesis that, most likely, structural features that represent physical anisotropies control the hydrothermal system of the LYG. Furthermore, the study provides an example of numerical investigation of a complex transboundary aquifer system, with emphasis on existent anisotropies, structural ambivalence and restricted field accessibility.