Most (semi-)arid regions are characterized by limited surface water and hence rely on other sources. While unconventional resources such as desalinated seawater can be a valuable option for domestic supply in coastal areas, groundwater withdrawal is still the only relevant option to produce volumes that can satisfy the demand of water-intensive sectors, above all irrigated agriculture.In many areas, however, groundwater resources are over-exploited, i.e., more water is abstracted from the aquifers than is naturally replenished. Considering global changes such as population and economic growth, and the predicted expansion of dry areas due to climate changes (e.g. in the Circum-Mediterranean region), the pressure on groundwater resources will be even amplified.This situation calls for a better water management, which is in turn dependent on an adequate hydrogeological understanding comprising both, available quantities and water quality. We hence envisage a session that covers a broad spectrum of hydrogeological aspects of (semi-)arid environments. Sub-topics could include, but are not limited to, groundwater recharge estimations, flow modelling, hydrochemical studies, and isotope applications. Interdisciplinary contributions, linking hydrogeology to neighboring disciplines, are encouraged.
1:30pm - 2:00pmSession Keynote
Groundwater resources in northern Namibia
The transboundary Cuvelai-Etosha Basin (Namibia/ Angola) is a semi-arid region. Rising population and water demand increase the stress on already scarce water resources. The local aquifers, the perched KOH-0 and the deeper KOH-1 are of limited use, the former due to low yields and microbiological issues, the latter due to often brackish water. A previously unknown deep freshwater aquifer, KOH-2, with high yield and good water quality was discovered at the end of the 1990s. This new resource is a game changer for the region. Therefore, the geological framework of the CEB and its hydrogeological conditions were investigated by detailed geological (core drilling), geophysical (TEM) and hydrogeological studies.
The geological background of the KOH-2 is an inland mega-fan system, reaching from the Angolan highlands in the north down to the Etosha Pan. A 400 m cored borehole revealed three distinct depositional sequences, which cover the last 60 Ma. The lower Olukonda Formation (270-400 m) has poor well yields due to a high degree of heterogeneity. It is overlain by the Andoni Formation, of which the KOH-2 (170-270 m) forms the lower part. The transition between the formations is marked by distinct geochemical changes, indicating different source areas. The KOH-2 is overlain by a sequence of aquitards and aquifers (KOH-1 (80-110 m), KOH-0).
The sedimentology of mega-fans strongly affects the distribution and hydraulic properties of aquifers and aquitards. This knowledge will be useful for the further exploration and sustainable development of the KOH-2.
2:00pm - 2:15pm
Reasons and implications of fossil hydraulic gradients in large-scale aquifer systems
1Technische Universität Darmstadt, Institute of Applied Geosciences, Hydrogeology Group, Germany; 2Technische Universität Dresden, Faculty of Environmental Sciences, Department of Forest Sciences, Germany
Due to limited availability of surface water, many arid and semi-arid countries have to rely on their groundwater resources. Despite the quasi-absence of present-day replenishment, some of these aquifers contain large amounts of water that was recharged during wetter periods in the past. Although these recharge events often occurred several thousand years ago, some of these so-called fossil aquifer systems exhibit considerable hydraulic gradients and flow towards their discharge areas, even without pumping. As a result, these systems have more discharge than recharge and are therefore not in steady state, which makes their modelling, in particular the calibration, very challenging. Probably the most relevant explanation for this phenomenon is the long groundwater residence time and the associated long-term head decay of the paleo-recharge mounds.
In this study, we propose a possible approach to deal with this phenomenon during model calibration. Moreover, we analyse the effect of considering and ignoring fossil gradients on aquifer parameterization for the Upper Mega Aquifer system on the Arabian Peninsula.
Further details can be found in a related publication (Schulz et al., 2017).
Schulz S, Walther M, Michelsen N, Rausch R, Dirks H, Al-Saud M, Merz R, Kolditz O, Schüth C. 2017. Improving large-scale groundwater models by considering fossil gradients. Advances in Water Resources 103: 32–43 DOI: 10.1016/j.advwatres.2017.02.010
2:15pm - 2:30pm
The Yarmouk basin, an essential transboundary water resource
1Helmhotz-Zentrum für Umweltforschung UFZ, Germany; 2Geological Survey of Israel; 3Bundesamt für kerntechnische Entsorgungssicherheit BfE, Germany; 4Deutsches Geoforschungszentrum – GFZ, Germany; 5National Agricultural Research Centre of Jordan; 6Thüringer Landesamt für Umwelt, Bergbau und Naturschutz – TLUBN, Germany
The Yarmouk River is the primary tributary to the Jordan River and a strategic transboundary freshwater resource of Syria, Jordan, and Israel. In the past decades, the Yarmouk watershed has been extensively exploited by the riparian with the construction of dams including the Al-Wehda and Adassiyeh dams. The operation of the dams is guided by international water agreements between Jordan and Israel and Jordan and Syria and control the flux of the Yarmouk River.
Repeated sampling over 16 years revealed variable flow paths towards certain wells over time as documented by variable REE-pattern and δ18O, δD and 87Sr/86Sr signatures of groundwater and lead to new insight with respect to sources of groundwater, their flow patterns and salinization in the Yarmouk basin. The conjoint interpretation of water table fluctuations indicate unexpected interactions of the river with the major groundwater resources of the entire region. 2D transient numerical simulations of coupled fluid flow and heat transport processes are used to investigate the impact of (i) a zone of hydraulic anisotropy and (ii) abstraction on hydraulic heads and temperature profiles in the shallow aquifers. The models support the geochemical indicated 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.