Coupling isotopic and piezometric data to infer groundwater recharge mechanisms in arid areas: example of Samail Catchment,Oman |
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| Authors: | Osman A E Abdalla Talal Al-Hosni Abdullah Al-Rawahi Anvar Kacimov Ian Clark |
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| Institution: | 1.Department of Earth Sciences,Sultan Qaboos University,Al-Khod P.C. 123,Oman;2.Water Research Center,Sultan Qaboos University,Muscat,Oman;3.Ministry of Regional Municipalities & Water Resources,Alkhwair,Oman;4.Department of Soil, Water and Agricultural Engineering,Sultan Qaboos University,Al-Khod P.C. 123,Oman;5.University of Ottawa,Ottawa,Canada |
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| Abstract: | Hydrochemistry and well hydrographs are coupled to assess groundwater recharge in the regional catchment of Samail, Oman. The complex geology comprises three aquifers: limestones of the Hajar Supergroup (HSG) at the highlands of North Oman Mountains (NOM); fractured/weathered ophiolites; and Quaternary alluvium. Groundwater flows south–north from the NOM to the coast. Samples from groundwater wells and springs (38) were analyzed for isotopes and major ions. Corrected 14C dating reveals modern groundwater across the entire catchment, while 87Sr/86Sr (0.70810–0.70895) shows greater homogeneity. Groundwater in the upper catchment is depleted in 2H and 18O, indicating a high-altitude recharge source (NOM), and becomes enriched downstream, with a slope indicating an evaporation effect. The hydrographs of nested piezometers located in the upper, middle and lower catchment show different recharge responses between deep and shallower depths. Head difference in response to recharge is observed upstream, suggesting a lateral recharge mechanism, contrary to vertical recharge downstream reflected in identical recharge responses. The homogeneous 87Sr/86Sr ratio, head changes, downstream enrichment of 2H and 18O, and the presence of modern groundwater throughout the catchment suggest that groundwater recharge takes place across the entire catchment and that the three aquifers are hydraulically connected. The recharge estimated using the chloride mass balance method is in the range of 0–43% of the mean annual rainfall. |
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