Optimal water resources management model for Ash Sharqiyah region domestic water supply, Oman

Abstract

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, most of the readily accessible fresh groundwater 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 therefore 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. Thus, a numerical simulation model of Ash Sharqiyah Sands Aquifer was developed in this study and used to assess the long-term impacts on piezometric heads of supplying the eight Wilayats of Ash Sharqiyah Region with water from the 29 operational wells located in two regional groundwater fields- the Jaalan and the Al Kamil. The simulation results showed that the existing provision from the two wellfields will be inadequate by the 1st of September 2025 to meet domestic water supply needs without creating excessive drawdown and the cessation of flow in some of the existing operational Aflaj, which are artificial, surface channels that tap and convey by gravity groundwater for diversion into various uses along its route. Supplementing the abstraction from the wellfields with the more costly desalinated water of the Sur Desalination Plant offers the prospect for combating the problem; consequently, a constrained optimization problem was formulated to find the least cost blending of groundwater and desalinated water to meet demands while satisfying various constraints including the need to maintain Aflaj flow. The optimisation revealed increasing contribution of desalination to future total water supply for the Region, as desalination water replaces pumping from wells that affect Aflaj flow, with implications for the project cost. However, significant reduction in the long-term total production cost was achieved by increasing up to 50% the existing pump capacity at the Jaalan, made possible because its associated Aflaj are located upstream of the wellfield and are hence only minimally affected by the current abstractions