Geotimes - September 2002

Geotimes

Geophenomena

Soggy soil sours Egyptian sandstone
Southern Africa drought

Soggy soil sours Egyptian sandstone

The ancient monuments of Egypt are in danger. Rising groundwater is bringing salts into the pores within the sandstone and limestone foundations. As the water evaporates, these salt crystals cause blisters in the structures and flaking on their surfaces.

The problem was first identified as afflicting the great Sphinx of Giza in the early 1980s. When the government provided a sewage system for the neighboring village, the water table below the Sphinx dramatically dropped and the salts stopped their intrusion. But elsewhere the problem continues.

Egypt’s rising water table is an especially serious concern in the north along the Nile Delta, as well as in the city of Luxor in the Nile Valley. But lowering the water table may not be easy. For Luxor, its low topography indicates to some researchers that another method is needed to remove the salts.

Egyptologists suspect multiple causes for the damage the salt is doing to Egypt’s historical treasures. The problem mainly results from the rise of Egypt’s water table over the last 30 years; the prevention of freshwater floods through the cities where the monuments stand; and leaking or non-existing sewage systems.

Ahmed Ismail measures the height of water rise in the foundation of the Luxor Temple. He is a researcher at the National Institute of Astronomy and Geophysics in Egypt and a Ph.d. student at the University of Missouri-Rolla. Photo courtesy of R. Stephenson.

“There is no question about the fact that water is seeping into the ground from cities or human activities,” says Farouk El-Baz, director of the Center for Remote Sensing at Boston University and Chief Advisor to Egypt’s Supreme Council of Antiquities (SCA). The case of the Sphinx points to a need for improved sewage systems wherever feasible, he adds. “That same month the sewage system became functional in the village, the level of the water in the well at the tail of the Sphinx began going down. It went down 9 meters below the surface and has been there since.” For the Sphinx at least, “Now there is no danger anymore.”

In November 2001, antiquities inspectors discovered a tomb of three burial chambers in a neighborhood in Cairo. Sewage from the neighborhood had damaged one of the burial chambers. Zahi Hawass, Secretary General of SCA, proposed building a new sewage system for that area, similar to the one installed in 1990 for the village of Nazlet el-Samman near the Sphinx. “We are working closely with the sewage organization to create a plan to manage the sewage and protect the monuments,” Hawass says. “We are now in the process of installing similar systems in the area near the Karnak and Luxor temples.”

But lowering the water table might be difficult under Luxor, say researchers from the University of Missouri-Rolla (UMR). Unlike the Sphinx, which sits on a plateau, the Temple of Luxor rests in a low spot near the Nile. Instead of tackling the water table to protect Luxor’s antiquities, the researchers suggest attacking the salts.

In Luxor, samples of the groundwater show it loaded with 36 parts per thousand of chloride, on par with seawater, says Richard Stephenson of UMR. The salts are derived from the surrounding soil and rocks, which have a chemical attraction to water. This attraction also enables the soil to draw the groundwater back up. Pore spaces within the soil act like straws, pulling water from below via capillary action. Once within the soil, the groundwater begins to evaporate as it seeps toward the surface.

Adam Sevi, Stephenson’s student who conducted his master’s thesis on this subject, found the accumulating salt left behind after the water evaporates contributes to the capillary ability, “effectively accelerating water transport up into the foundation stones,” he says.

Salt accumulation is a problem that farmers in arid regions, including Israel and the United States, have always struggled to control. Often more water is used to help flush the salt away, or crops are planted in rows away from where the salt reaches the surface.

The Nile Valley and Delta are formed from flood deposits of the river’s fine-grained soil. Before the construction of the Aswan High Dam in the 1960s, freshwater floods inundated the region annually. Today, farmland irrigation occurs almost year-round. SCA is working with the Ministry of Agriculture to reduce the impact irrigation methods have on the water table, Hawass says. Adding that “The High Dam has nothing to do with the rising water table.”

But El-Baz maintains that the dam, finished in 1970, exacerbated the problem of the water table adding salts to the monuments and destroying them bit by bit. The dam regulates the Nile’s flow to the Mediterranean, preventing devastating fluctuations between wet and dry seasons. Instead of depending on a yearly flood — which often wrought devastation to cities along the Nile, but prepared agriculturalfields for planting — farmers use the water from the regulated river to flood their fields more often and have multiple harvests throughout the year.

The added irrigation, however, raises the water table without flushing salts out of the soil around the monuments as the floods did in the past. “What is to be done,” El-Baz suggests, “is to make certain that surrounding temples are separated from the excessive water from the water level in the soil and kept constant, not fluctuate with the cropping cycles.” He proposes fluid-injecting cement under monument foundations through small drill holes. Stephenson agrees, adding that similar sealant techniques have been used to stabilize bad soils under highways in the southwest United States.

Another option Sevi proposes in his master’s thesis is to bring back the effect the Nile flooding had around the monuments, by introducing freshwater in the areas of salt buildup. He proposes a combination of controlled surface flooding, to wash salts away from the surface, and a slow drip method, to wash salts from the soils back to the Nile. “In effect simulating the historic floods that occurred in the area,” he says. “The problem didn’t occur for 5,000 years because of that flooding and my estimate is that the salt pitting of the monuments is only going to accelerate in the future. We have noticed 30 years accumulation of salt at the surface and every year of adding salt to the problem only makes the problem grow.”

Christina Reed

back to top

Southern Africa drought

Latest estimates by the United Nations World Food Program are that 13 million people in Southern Africa may starve between now and April 2003. This year heralds the worse food crisis in a decade and the situation will continue to degrade as drought conditions are expected to intensify with the onset of El Niño.

Drought is common in the semiarid to arid Southern Africa regions and this year has hit Malawi, Zimbabwe, Zambia, Mozambique, Lesotho and Swaziland hardest. “What might have been a normal drought 50 years ago is now a major crisis,” says Michael Glantz, a political scientist from the National Center for Atmospheric Research (NCAR) in Boulder, Colo. Exacerbating the situation, he says, are growing population and decreasing arable land.

Donald Wilhite, director of the National Drought Mitigation Center in Lincoln, Neb., agrees. “Drought is the important trigger in famine and in food insecurity, but it’s not the only trigger. Food and land policies have set the stage, and drought pushed it over the edge.”

Heavy rains affected the December 2000 to January 2001 maize planting season in many parts of Southern Africa, decreasing agricultural productivity. In contrast, drought conditions affected the December 2001 to January 2002 planting season and countries saw a decline in crop yields. This year, Zimbabwe’s maize crop yield is 50 percent of what it was last year. “The other countries face similar problems,” says Heidi Cullen, a climatologist from NCAR. “There have been two years of bad crops. The economies and climates of these countries are all tied to each other, and they’re going down together.”

Glantz and Cullen explain the situation as a “drought+ factor.” Politics have played a large role, Glantz says, citing the example of Zimbabwe. Previously known, along with South Africa, as one of Southern Africa’s chief food exporters, Zimbabwe has suffered from policies framed by its new government. Redistributing large tracts of white-owned farm lands to small-scale subsistence farmers without providing training or infrastructure has badly hurt and weakened the economy. Poor planning and mismanagement plague all governments in the region. Decisions by international donors such as the World Bank and the International Monetary Fund to cut agriculture subsidies and have Southern Africa compete in world markets has also had adverse effects, Glantz explains.

The issue is complicated further by the HIV/AIDS epidemic that is sweeping across the region — an estimated 25 to 45 percent of the population is believed to be infected. The disease is undermining the working capacity of the people and jeopardizing the rate of economic recovery (Geotimes, March 2001).

“It’s only in the last couple of decades that drought is being looked at as a multidisciplinary problem,” Cullen says. Governments in the region have shown interest in drought monitoring. It is one of the functions of the Southern Africa Development Committee, a consortium of all the countries in the region. “There’s information on what should be done, but there’s a lack of focus on implementing the recommendations,” Wilhite says.

Despite implementation setbacks, Cullen, Glantz and Wilhite all emphasize the importance of promoting mitigation responses to drought. “The main thing is they need to look at and learn from the experience, need to document the way forecast information was used or not used, what food and land policies created the situation and correct these things so they are prepared the next time around,” Wilhite says. The Famine Early Warning System, supported by USAID, has helped determine the evolution and severity of the situation. Combining this with a drought early warning system will help, he explains.

Currently, the situation in Southern Africa is beyond simple mitigation. The United Nations World Food Program has declared it an emergency and appeals for US$507 million from international donors to provide relief food to the people of the region. “A drought is not a drought,” Glantz says to emphasize that meterological drought can become much more with added factors. “In a rich country like the United States, drought is primarily an economic problem. In a third-world country it becomes a matter of life and death.”

Salma Monani

back to top

© 2024 American Geological Institute. All rights reserved. Any copying, redistribution or retransmission of any of the contents of this service without the express written consent of the American Geological Institute is expressly prohibited. For all electronic copyright requests, visit: http://www.copyright.com/ccc/do/showConfigurator?WT.mc_id=PubLink