Underground storage of drinking water in Oman
Oman features a beautiful landscape in the middle of the Arab world. But in the sultanate, which comprises about 80% desert. Rainfall is limited and irregular, and the capacity of aquifers is under pressure. Water scarcity is therefore increasingly a problem. Aquifer storage and recovery (ASR) could provide a cost-effective solution to Oman’s water management needs.
These days, drinking water for the population mainly comes from desalination plants, which makes the drinking water supply vulnerable to calamities and energy consuming. Aquifers have experienced long term declines in water levels due to heavy pumping to meet increasing urban and agricultural water needs.
What are the possibilities for temporarily storing large volumes of drinking water underground during times of low water demand, and recovering it later during emergencies or times of peak water demand? Acacia Water is working with other partners on a feasibility study of the application of ASR for the Omani drinking water company Nama Water Services.
Cost savings and resilience
Because water is scarce in Oman, the country relies largely on seawater desalination for drinking water supply. However, making drinking water from seawater is relatively expensive, mainly due to very high energy costs, and also vulnerable. If for example a cyclone or algal bloom brings production from one or more desalination plants to a halt, the drinking water supply is immediately jeopardized.
Map of the Arabian Peninsula, showing the four project sites in Oman: A’Bukrabah, Adam, Al Khoud and Jaalan.
Storing large water volumes deep underground, reduces or eliminates the need to construct large and expensive concrete surface reservoirs. Moreover, this underground buffer not only increases water resilience, it could also be a cost saving as peak production of desalination plants can be reduced, leading to lower energy costs, because seasonal variations in supply and demand can better be matched.
ASR enables utilities to store desalinated water in an aquifer when there is surplus and recover the water when it is needed, increasing drinking water security in Oman. By replenishing underground water supplies, the country is more climate resilient, as it can provide drinking water for its people even during persistently dry and hot periods when water demand is high.
Technical suitability and ASR system design
The technical suitability and economic feasibility of constructing large-scale ASR systems has been investigated at four sites in Oman. These are located near existing wellfields in Jaalan, A'Bukrabah and Al Khoud (in the capital city of Muscat) and a site near the city of Adam.
Jaalan wellfield located on the edge of the Sharqiya Sands desert.
ASR involves artificial infiltration of water into the subsurface. It is a proven method of actively replenishing groundwater. It has been used since the 1950s in the dunes of the Netherlands for drinking water supply. Large-scale underground storage of desalinated seawater to increase water security has also been successfully applied in Abu Dhabi (United Arab Emirates).
Since the start of the project, Acacia Water has taken the lead role in the groundwater system analysis of the four sites. Over two years, extensive geophysical investigations, exploration drilling, test pumping, and soil and water quality analyses were conducted. Based on those results, conceptual models were created that characterize the hydrogeology of each site.
Simulating scenarios
Using groundwater flow and density flow models, the operation and effects of large-scale infiltration and abstraction was simulated by Acacia Water. Several ASR systems designs were tested and optimized under different scenarios in order to determine the optimal operational mode and most effective design of an ASR system at each site.
The groundwater flow models, combined with hydraulic models and economic models, showed that of the four sites studied, Jaalan, located on the edge of the Sharqiya Sands desert, is the most suitable for ASR. Here the required investment costs are relatively low and the subsurface is most suitable for the infiltration ánd recovery of large volumes of water, within the set water quality requirements.
Pumphouse of one of the production wells in Jaalan.
Acacia Water has extensive experience with managed aquifer recharge projects around the world, including in the Netherlands, Bangladesh and Lebanon. Because of our expertise with ASR, and with groundwater systems in arid and semi-arid areas, Acacia Water was asked to cooperate in this ASR project in Oman.
Harmen van den Berg, hydrogeologist at Acacia Water, is involved from the start of the project in 2021. "The scale on which Oman wants (and can!) store water underground is unprecedented. That makes this project extremely interesting."
This is not the moon landing, but a geophysical survey in the blazing Omani sun.
During a two week field trip in September 2021, all four sites were visited and measurements were taken. "That was quite a challenge at 40+ degrees Celsius and in the blazing sun," says Harmen.
Underground channels
The project also brought personal enrichment. Harmen became fascinated by the ancient aflaj water systems, which are historic irrigation systems that have been used in Oman for centuries to distribute water from the mountains to villages for small-scale agriculture and drinking water.
"In the middle of the dry desert, you suddenly find underground canals with running water! Despite their ancient origins, the oldest aflaj systems date back to around 2,500 B.C., thousands of aflaj systems remain functional, underlining their enduring value to Oman's agricultural and domestic water supply. Unfortunately, due to growing water demand and unregulated overabstraction, aflaj systems are no longer sufficient to provide water to all Omanis. New techniques like desalination and ASR are therefore essential to ensure water security in arid areas like Oman," Harmen says.
Harmen at the project site in Jaalan.
ASR pilot in Jaalan
The next step for Oman is to do a pilot with a small-scale ASR system in Jaalan. In this way the ASR system design can be tested, and performance and cost efficiency can be optimized, prior to the implementation of a full-scale ASR system.
A pilot also provides insights into operational risks, allowing them to be minimized, and helps to improve the design to ensure maximum efficiency and desired water quality.
Other participating companies in this project are Consulaqua Hamburg (Germany) and AZD Engineering (Oman). In addition to the collaboration with the drinking water specialists of Nama Water Services, there was considerable local cooperation with experts from Ministries and Sultan Qaboos University in Muscat.
Read more about what we are doing on water security and addressing drought and water quality. Contact person: Harmen van den Berg
Cover photo: Like ASR, the camel knows how to store water when and where it is available, to meet water demand in arid conditions.
