Fossil Aquifers are large underground reserve of water that were established under past climatic and geological conditions. They can underlie present-day semi-arid environments, provide key source of groundwater in otherwise water scarce regions.
What are Fossil Aquifers
The water in fossil aquifers accumulated under past environmental conditions, with subsequent geological change sealing the water and preventing further recharge or significant outflows (Soos, 2011). These aquifers are often ‘geologically confined’, bounded at their upper and lower limits by impermeable rocks. This geological setting results in the water being stored under pressure, with the pressure, or peizometric head, of water in the aquifer above the actual height of the water (Tsur, Park and Issar, 2007). This means that water can be abstracted in part using the aquifer’s pressure, rather than pumping from the water table which may be at considerable depth. In confined aquifers, as water is pumped, there is a gradual reduction in the pressure of water remaining in the aquifer. In unconfined aquifers the water table falls. In both cases this results in a greater pumping head being required, and a corresponding increase in energy and cost of water abstraction.
Fossil aquifers often exist below the level of other recharge aquifers. This makes them difficult to identify. Recent analyses in the middle east have used airborne sounding radar to measure electromagnetic changes in the landscape that indicates water (Soos, 2011).
Examples of Fossil Aquifer use and development
Fossil aquifers have been used across the world as the basis for key irrigation-based agricultural development. Over time, the finite nature of these resources is being realised, posing a challenge to established agricultural behaviour.
The Ogallala aquifer underlies the great plains of the United States. It has underpinned large areas of irrigated development in Texas, New Mexico, Oklahoma, Colorado, Kansas, and Nabrasca. Its waters supply 20% of irrigated land in the United States (BBC, 2003). Significant development of the resource started with the introduction of improved pumping technologies in the 1940s, and large-scale irrigation applications. Withdrawal rates exceed recharge rates by 50:1, and decreased pressure heads in the aquifer, and consequentially higher pumping costs are increasingly forcing farmers to return to dryland agriculture. This change has implications for global food supply, due to the significant volume of grain for the North American and Global Market grown using Ogallala water (Overmann, 2005).
In the 1970s, inspired by the success of oil drilling technology, Saudi Arabia extended the technology to mine fossil aquifers under their territory (Polycarpou, 2011). Their aim was to achieve food self sufficiency. In 2008, the Saudi Government announced a tapering off of the wheat industry, with a policy to increase imports and abandon wheat production by 2016, in the face of rapidly declining fossil water resources (Laumer, 2008). Between 2008 and 2011, domestic wheat production decreased by 2/3 (Polycarpou, 2011). The abandoning of aspired food self sufficiency in Saudi Arabia and other gulf countries reliant on fossil aquifers has led to their dependence on global markets to meet the needs of their growing populations. The depletion of fossil aquifers has also resulted in these countries increasingly turning towards investment in land and agriculture in other regions, notably sub-Saharan Africa to ensure their long-term food security. This is leading to a new wave of ‘land grabs’ by foreign investors. Despite this shift in focus, there remains a need for new water supplies in Saudi Arabia, and increased efforts have been targeted at identifying new reserves of fossil groundwater to meet population water needs, increasingly with the help of outside expertise, including from Europe with GIZ having funded exploration in recent times (Shafy, 2010).
Potential for productive and sustainable use
Assessment of fossil aquifers is not absolute, but dependent on the quality and scope of measurement techniques. New measurement technologies can reveal recharge that was previously undetectable. In 2013 a significant volume of water previous considered fossil under the Northern Sahara Desert was found through satellite measurements to be recharging at a rate of 1.4km3/yr. At abstraction rates of the early 21st century of around 5km3/yr, the aquifer was being significantly over-abstracted however the existence of recharge, open avenues for long-term sustainable use of the resource (Science Daily, 2013).
In 2012 it was announced that significant quantities of fossil groundwater existed in otherwise water-scarce areas of north and central Africa (MacDonal, et al, 2012). The water was recharged 5000 years ago under previous, wetter, climate regimes in the continent. These reserves are estimated to be 100 times larger than the annual renewable freshwater in Africa (McGrath, 2012). The fragmented nature of these fossil resources means that they have the potential to meet growing population needs and improve local water access to 300 million Africans without access to safe water, helping to alleviate poverty and poor health.
While providing significant resource, the researchers were at pains to emphasise the potential for small-scale development, using low-yielding hand pumps for village supplies, and the unsuitability of the identified resource for large-scale exploitation. This argument is related both to the geological conditions and to a desire to use the fossil water for long-term sustainable social and economic improvement (MacDonald et al. 2012). This recommendation aviods the short-termism and over-development that has characterised fossil water use during the 20th century, including the Middle East and the United States discussed above. Such sustainable small scale use of fossil aquifers offers a future development avenue for these finite resources.
BBC, 2003. Water Hotspots: Ogallala Aquifer. Available at: http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/ogallala_aquifer.stm
Laumer, J., 2008. Groundwater Mining for Wheat to be Phased Out in Saudi Arabia. Available at: http://www.treehugger.com/corporate-responsibility/ground-water-mining-for-wheat-to-be-phased-out-in-saudi-arabia.html
MacDonal, A. M., Bonsor, H. C., Dochartaigh, B. E. O., and Taylor, R. G., 2012. Quantatitive maps of Groundwater Resources in Africa. Environmental Research Letters, 7. 19 April 2012. Available at: http://iopscience.iop.org/1748-9326/7/2/024009/article
McGrath, 2012. ‘Huge’ water resource exists under Africa. BBC News Website. Available at: http://www.bbc.co.uk/news/science-environment-17775211
Overmann, S. R., 2005. The High Plains Aquifer. Regional Updates, Southeast Missouri State University. Available at: http://wps.prenhall.com/wps/media/objects/1373/1406592/Regional_Updates/update23.htm
Polycarpou, L., 2011. The Middle East Dries up – Another Case study in the Water-Energy-Food Nexus. Water Matters. State of the Planet. Available online: http://blogs.ei.columbia.edu/2011/04/26/the-middle-east-dries-up—another-case-study-in-the-water-energy-food-nexus/
Science Daily, 2013. Sub-Saharan Water: Not Just Fossil Water. 22 July. Available at: http://www.sciencedaily.com/releases/2013/07/130722123014.htm
Shafy, S., 2010. Ice Age Aquifers: Searching for Water Under the Sands of Saudi Arabia. Spiegel Online. 19 March 2010. Available at: http://www.spiegel.de/international/world/ice-age-aquifers-searching-for-water-under-the-sands-of-saudi-arabia-a-684360.html
Soos, A., 2011. Ancient Fossil Aquifers and Nasa. Environmental Science News, September 19. Available at: http://www.enn.com/sci-tech/article/43271
Tsur, Y., Park, H., and Issar, A., 2007. Fossil Groundwater Resources as a basis for arid zone development? International Journal of Water Resources Development v5(3) 191-201.