Abstract
The Dahab watershed comprises three aquifers; the alluvial Quaternary, the Early Cambrian sandstone, and the fractured Pre-Cambrian basement aquifers. The Dahab watershed is located in the southeastern part of the arid Sinai Peninsula, where low precipitation and groundwater over-exploitation deteriorate the groundwater quality in the alluvial coastal plain aquifer located downstream. Multi-isotopes including δ18O and δ2H, 87Sr/86Sr, δ81Br and δ11B coupled with groundwater geochemistry were utilized to assess the recharge source(s), water-rock interaction, and seawater mixing to aid sustainable groundwater management strategies. Br and Cl concentrations, used to measure groundwater salinity, were low in the upstream groundwater, while higher concentrations were observed in the deep drilled wells located downstream, in the main well field. The δ18O and δ2H isotopes were depleted in the upstream aquifers, but enriched in the shallow coastal aquifer, indicating slight evaporation and seawater intrusion. Higher mean values of 87Sr/86Sr and δ81Br were observed in the fresh groundwater from high in the watershed (87Sr/86Sr = 0.707716 and δ81Br = +2.05‰), while lower mean values were observed in the saline groundwater located downstream in the main well field (87Sr/86Sr = 0.706631 and δ81Br = +0.11‰). The cumulative mass balance mixing curves and the geochemical NETPATH model confirm the change of groundwater quality from the upper to lower watershed caused by the leaching and evaporation processes, as well as mixing with seawater. The corrected 14C age dating and stable isotopes show that the Quaternary and Pre-Cambrian basement aquifers contain modern groundwater, while the Early Cambrian aquifer holds paleo-groundwater, which has received considerable recharge from recent precipitation. The mixing ratiosin the Quaternary coastal aquifer range between 5% and 13% seawater to 95% and 87% fresh groundwater, respectively. These results indicate that future groundwater withdrawal must be well managed in order to limit further salinization. Groundwater withdrawal from the Quaternary coastal aquifer must be below the natural average recharge in order to be sustainable.
Highlights
The Dahab watershed is located in the Southeastern Sinai Peninsula, part of an arid coastal zone where scarce rainfall and high summer temperatures dominate the climate (Figure 1)
This study examined the chemistry and the stable isotopic composition of groundwater in the Dahab watershed of the Southern Sinai Peninsula
The stable isotopes δ18 O and δ2 H indicate that recent precipitation is the main source of groundwater recharge for the Quaternary and Precambrian aquifers, and mixing with seawater and water–rock interaction are considered the main salinization source for coastal groundwater
Summary
The Dahab watershed is located in the Southeastern Sinai Peninsula, part of an arid coastal zone where scarce rainfall and high summer temperatures dominate the climate (Figure 1). The groundwater processed in desalination plants is considered one of the main sources of fresh water groundwater salinization [9,10,11,12]. Historical records drilled wells used for feeding these desalination plants exceeds 25,000 m /day [13], which is of groundwater salinityHistorical in the main well field low in salinity the Dahab watershed considered substantial. The Dahab basin (Figure 1) drains east toward the Gulf of Aqaba and is considered to be one of the most important watershed systems in the South Sinai Peninsula. Dahab watershed contains three main aquifers: the Quaternary, Quaternary, Early Cambrian, and Precambrian. They are recharged by flash floods when the area. Catchment receives an average annual rainfall of about 76 mm/year [57], and the potential evaporation exceeds 2400 mm/year [58]
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