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3D Groundwater Modeling of the Upper Mega Aquifer System (Arabian Peninsula) using OpenGeoSys

Stephan Schulz1, Randolf Rausch2, Olaf Kolditz1, Christian Siebert1, Ralf Merz1, Nils Michelsen3, Mohammed Al-Saud4, Christoph Schüth3
1 Helmholtz–Centre for Environmental Research UFZ
2 GIZ International Services and TU Darmstadt, Institute of Applied Geosciences
3 TU Darmstadt, Institute of Applied Geosciences
4 Ministry of Water & Electricity of the Kingdom of Saudi Arabia

P 10.11 in Hydrogeologie arider Gebiete

A 3D groundwater flow model merges all relevant hydrogeological information. Thus, it became a powerful management tool, which serves the purpose of understanding a system and calculating scenarios. Especially for the countries on the Arabian Peninsula, which heavily rely on groundwater resources, those models became important in order to achieve a better water management. During this study a transient (10,000 years BP to present) groundwater flow model of the Upper Mega Aquifer (UMA) system using the open source model OpenGeoSys is setup.

The lateral extent of the UMA system corresponds almost to the extent of the Arabian Shelf. It comprises a sedimentary succession from the Early Cretaceous to the present. As a computer model is an approximation of the reality, several geological formations are merged to single hydrogeological units. Ten units plus the sealing Hith aquiclude, which represent the boundary at the bottom of UMA, resulted. All these units consist of clastic or chemical sediments and dip slightly eastwards.

Due to (i) the basin structure and related conditions of sedimentary deposition, (ii) tectonic processes and (iii) different expositions over longer time periods, the hydraulic properties vary within each hydrogeological unit. In order to take this into consideration these units are separated into hydrofacies zones. These hydrofacies zones are projected on each hydrogeological unit in the geometric model by means of specially designed Matlab-Routines. Relevant aquifer properties (hydraulic conductivity, specific yield and specific storage coefficient) for these hydrofacies zones are from 223 pumping tests. Additionally, laboratory analyses of drilling cores are integrated in order to make these values (especially anisotropy of hydraulic conductivity) more certain.

The water fluxes of a groundwater flow model are driven by sink and source terms. Due to a falling water table over the whole modelling period (and especially since the anthropogenic water withdrawal from the aquifer system increased), these terms are not constant over space and time. Relevant sink terms are: (i) Springs, (ii) Paleo rivers, (iii) Agricultural water abstraction, (iv) Domestic and industrial water abstraction, and (v) Discharge into Euphrates and the Arabian Gulf. Major source terms are: (i) Groundwater recharge, and (ii) Wadis as bypass for the leakage from underlying aquifers.

Finally, the model will be calibrated with the classical approach of fitting the modelled hydraulic heads to the observed ones. For the validation a multi response approach will be applied. First method will be the comparison of modelled groundwater ages (backward particle tracking or transport modelling) with ages determined by isotopic investigations (e.g. 14C). The second method will be a comparison of the overall water balance with satellite gravimetry (GRACE). 

Letzte Änderung 08.10.2013