Continuously increasing water demand in various sectors is intensifying the water scarcity problem particularly in arid and semi-arid regions like Oman. In many areas of the Sultanate, demand for water far exceeds its current availability. This presents logistical challenges in overcoming this situation or at least keeping the water deficit as low as possible. In Oman, the majority of accessible fresh water resources have already been extensively developed in order to attempt to meet the increasing demand for water, and any further intensification of groundwater abstraction is not sustainable. Attention has therefore turned to desalination of sea water to supplement the available groundwater resources. Desalination is expensive and energy intensive; hence it cannot realistically be the sole source of drinking water in Oman. Rather, a conjunctive use of groundwater and desalination optimally operated to meet water demands while ensuring the sustainability of the groundwater resources is the best option in this arid to semi-arid region. To achieve this, a numerical simulation model of Ash Sharqiyah Sands Aquifer was first developed and used to assess the long-term impacts of supplying the eight Wilayats of Ash Sharqiyah region with water from the 29 operational wells of the two groundwater wellfields by predicting the long-term behaviour of the piezometric heads until the year of 2030. The simulation results showed that the existing 29 operational wells of the two groundwater wellfields will be inadequate by the 1st of September 2025 to meet the domestic water supply needs for the eight Wilayats of Ash Sharqiyah Region without creating extensive drawdown and negative environmental impact and the cessation of flow in existing operational Aflaj. Supplementing the abstraction from the well fields with processed water from the Sur Desalination Plant offers the prospect for combating the problem; However, given the relatively high cost of desalination in comparison with the cost of treating fresh groundwater, the blending strategy to be adopted must be such that the aggregated cost is minimal. Thus, for the second part of the study, a constrained optimization problem was set up to find the least cost combination of groundwater and desalinated water while satisfying environmental constraints imposed by the need to keep the Aflaj continuously flowing. The results are presented and discussed and recommendations are made about how the study could be extended to other equally water stressed Regions of Oman.

Continuously increasing water demand in various sectors is intensifying the water scarcity problem particularly in arid and semi-arid regions like Oman. In many areas of the Sultanate, demand for water far exceeds its current availability. This presents logistical challenges in overcoming this situa...