Recharge, timescale of groundwater flow, and geochemical evolution of the groundwater system in the Najd area, Dhofer Governorate, Sultanate of Oman
Final Report Abstract
The main goal of the proposed study was to assess key aspects of the water balance in order to obtain a comprehensive and reliable understanding about recharge, flow, as well as transport processes and geochemical evolution in the Najd aquifers. To reach this goal, we focused the investigation on the hydrogeological, hydrochemical and isotope geochemical characterization of the Najd aquifers. In three field campaigns, groundwater from the four main aquifers A to D over the Najd area as well as spring water (five important springs) from the Dhofar mountains region were collected and analysed for stable isotopes and 14C, for concentrations of noble gases, and for hydrochemistry. Based on measurements of the groundwater levels manually and by newly installed automatic pressure deducers we could construct the hydraulic conditions of the groundwater flow system. We report new data on the isotopic composition of water (2H, 18O), of dissolved inorganic carbon (13C and 14C) from the groundwater of the four aquifers A to D. Using the water isotope data we determined the recent recharge process initiated by the annual monsoon and sporadic cyclonic events (here: cyclone Keila). Mixing processes of young recharge with old groundwater were assumed for aquifer D – the most relevant aquifer for recharge. Along the flow path of the groundwater, we measured the noble gas concentrations for reconstruction of climatic conditions (noble gas temperature) during past recharge periods. Depending on the He concentration three different groups were detected with temperature differences of 5.1 to 6.8 K between cold and warm climate periods. Based on these results and our research hypothesis we developed a conceptual model that identifies three processes that are mainly controlling the groundwater evolution and quality in the Najd region: (i) modern water input by monsoon events, (ii) runoff and recharge generation by cyclonic events in past and present, and (iii) interactions between the aquifers by hydraulic exchange. Based on the isotope and hydrochemical results in combination with the conceptual model, we came to the conclusion that the groundwater in the Najd region belongs to an active flow system which is fed by recent monsoon and cyclonic events mainly in the Dhofar mountains, but was formed by past recharge processes during periods of climatically favourable conditions. Radiocarbon analyses of the Najd groundwater give only an age of up to 35,000 years. However, the analyses of 4He in groundwater and aquifer material and the calculation in connection with the groundwater flow yielded a completely new insight into the groundwater evolution of the Najd aquifers: the water residence time in the lower and northern part of the Najd groundwater system extends to more than 2 million years. The results of our investigation contribute to a comprehensive understanding of the groundwater evolution in the Najd region as an important area for groundwater usage in the southern part of Oman. Particularly, further groundwater flow modelling along with paleoclimatic recharge models benefits from the data achieved during this study. As announced by the Ministry of Municipalities and Water Resources, spring water studies will be intensified to improve the knowledge about their recharge, and as a valuable resource for human usage in the Salalah region.
Publications
- Isotope and hydrochemical signature of groundwater in the Najd aquifers, Sultanate of Oman. 9th Gulf Water Conference, Muscat, 22-25 March 2010
K. Al-Mashaikhi, G. Strauch, S. Oswald, S. Attinger, K. Knöller
- Modelling study to quantify the groundwater resources in the Governate of Dhofar, Sultanate of Oman. 9th Gulf Water Conference, Muscat, 22-25 March 2010
Müller, T.H., Strauch, G., Al-Mashaikhi, K., Oswald S.
- Using a large scale groundwater model to quantify water resources availability in an arid aquifer system. GeoDarmstadt2010, SDGG, Heft 68, S.405- 406
T. Müller, G. Strauch, S. Oswald
- (2011): Evaluation of groundwater dynamics and quality in the Najd aquifers located in the Sultanate of Oman. Environ. Earth Sci.
K. Al-Mashaikhi, S. Oswald, S. Attinger, G. Büchel, K. Knöller, G. Strauch
(See online at https://doi.org/10.1007/s12665-011-1331-2) - 2011. Evaluation of Groundwater Recharge in Najd Aquifers. PhD thesis, Friedrich-Schiller-Universität Jena, UFZ-Report 09/2011, Helmholtz Centre for Environmental Research UFZ, Leipzig, Germany
Al-Mashaikhi, Khalid Salim Ahmed
- Groundwater characteristic of the Najd aquifers, Oman, derived from isotope and hydrochemical signatures. GQ10: Groundwater Quality Management in a Rapidly Changing World, (Proc. 7th International Groundwater Quality Conference, ed by M. Schirmer, E. Hoehn, T. Vogt, Zurich, Switzerland, 13–18 June 2010), IAHS Publ 342, 11-14 (2011)
A-Mashaikhi, K., Strauch, G., Osenbrück, K., Müller, T., Knöller, K., Oswald, S.
- Sulphate reduction in deep groundwater. Proc. ESIR conference, Budapest, June 2011, in: Central European Geology 54, 148 (2011)
G. Strauch, K. Al-Mashaikhi, K. Knöller
- Use of Helium as a tracer for groundwater flow-model calibration of the Dhofar region of southern Oman. American Geoscience Union Fall Conference San Francisco, 05.-09.12.2011
T. Müller, W. Sanford, K. Osenbrück, W. Aeschbach-Hertig, C. Herb, G. Strauch
- 2012. Recharge and residence times in an arid area aquifer. PhD thesis, TU Dresden, 150 pp.
Müller, Thomas
- Assessment of Groundwater Recharge in an Arid Zone Using Several Approaches. Proc. Gulf Countries Conference 2012, Muscat, March 2012
K. S. Al-Mushaikhi; G. Strauch, S. Attinger, T. Müller, K. Osenbrück, W. Aeschbach-Hertig, K. Knöller
- Stable H & O isotope signatures reveal sources of recharge in Dhofar, Oman. JESIUM 2012, Leipzig, Sept 2012
G. Strauch, K. Al-Mashaikhi, A. Bawain, K. Knöller, A. Hildebrandt, J. Friesen, T. Müller
- Use of Helium as a Tracer for Groundwater-Model Calibration of the Dhofar Region of Southern Oman. Proceedings “Hydrogeology of Arid Environments”, Poster Abstract, Stuttgart, March 2012, 2012 Gebr. Borntraeger, Stuttgart, Germany
T. Müller, W. Sanford, K. Osenbrück, W. Aeschbach-Hertig, C. Herb, G. Strauch
