Coupling isotopic and piezometric data to infer groundwater recharge mechanisms in arid areas: example of Samail Catchment, Oman

Abdalla, Osman A. E.; Al-Hosni, Talal; Al-Rawahi, Abdullah; Kacimov, Anvar; Clark, Ian

Coupling isotopic and piezometric data to infer groundwater recharge mechanisms in arid areas: example of Samail Catchment, Oman | Evaluation des mécanismes de recharge des eaux souterraines en région aride à partir d’une approche couplant des données isotopiques et piézométriques: exemple du bassin de Samail, Oman Acoplamiento de datos isotópicos y piezométricos para inferir mecanismos de recarga del agua subterránea en áreas áridas: ejemplo de Samail Catchment, Omán 综合同位素和测压数据推断干旱地区的地下水补给机理:阿曼Samail汇水区研究案例 Acoplando dados isotópicos e piezométricos para inferior sobre os mecanismos de recarga das águas subterrâneas em áreas áridas: exemplo da Bacia de Samail, Omã

2018

Abdalla, Osman A. E. | Al-Hosni, Talal | Al-Rawahi, Abdullah | Kacimov, Anvar | Clark, Ian

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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