Posted by: chrismaser | August 23, 2012


While I was working as a vertebrate zoologist with the Yale University Peabody Museum’s prehistoric expedition in Egypt in 1963 and 1964, a representative of the Egyptian Ministry of Agriculture spent time with us as we worked just north of the Sudanese border along the Nile. One day, three of us from the expedition tried to help this man understand that building the Aswan High Dam across the Nile at Abu Simbel was an ecological mistake. He could not, however, see beyond the goal of generating electricity for the Nile Delta, which was the official reason given by the government for constructing the dam.

We explained to the government representative that building the dam would increase the geographical distribution of the snails that carry the tiny blood fluke, which causes the debilitating disease Schistosomiasis (also called “Bilharzias”) from below the original, modest Aswan Dam (built by the British at the town of Aswan in the early 1930s) south to at least Khartoum in the Sudan, several hundred miles above the new, yet to be completed dam. At that time, it was still safe to swim above the Aswan Dam, where the water was too swift, deep, and cold for the snails to live, but it was not safe to swim, or even catch frogs, in the water below the dam, where the snails already lived.

We told him further that the Nile above the High Dam would fill with silt, which would starve the Nile Delta of its annual supply of nutrient-rich sediment and affect farming in a deleterious way, as well as degrade the Mediterranean end of the Nile Delta. We also told him that the dam could easily become a military target for the Israelis, as German dams were targets for the British during World War II.


The engineers building the Aswan High Dam had intended only to store more water and to produce electricity, which they did. However, when the dam was completed in 1970, it began intercepting the nutrient-rich sediments destined for the Mediterranean Ocean. Deprived of the nutrient-rich silt of the Nile’s annual floodwaters, which nourished organisms at the base of the food chain in estuaries and near-shore water, the population of sardines off the coast of the Nile Delta diminished by 97% within two years. In addition, the rich delta, which had been growing in size for thousands of years, is now being rapidly eroded by the Mediterranean, because the Nile is no longer depositing silt at its mouth. And the Nile is not alone.1

The Ebro River and its tributaries in Spain have 187 dams that trap almost all of the sediment that would otherwise reach the river’s delta. This loss has led engineers to truck in more than 110 million tons of sediment since 1983 in order to replenish the beaches.2

Until the Aswan Dam was built, the annual sediment-laden waters of the Nile added a millimeter (a little less than a sixteenth of an inch) of nutrient-rich silt to the farms along the river each year. Now that the floods have been stopped by the new dam, the silt not only is collecting upriver from the dam, where it’s diminishing the dam’s water-holding capacity, but also is no longer being deposited on the riverside farms, thus decreasing their fertility. If it hasn’t already, the time will come when the farmers will have to buy commercial fertilizer, something most of them probably cannot afford. In addition, because irrigation without flooding causes the soil to become saline, the Nile Valley, which has been farmed continuously for 5,000 years, may have to be abandoned within a few centuries.

Moreover, schistosomiasis has indeed spread southward to the Sudan, raising the question: Does one nation have the right to knowingly cause the spread of a highly infectious disease into another nation in the name of economic self-interest, or any other reason for that matter, without the receiving nation’s permission?


There is another consequence of the Aswan High Dam, one I would never have thought of, even though I had studied the mammals along the Nile. The Nile annually flooded the many nooks, crannies, and caves along its edge, killing the rats whose fleas carry bubonic plague. Because the floods no longer occur, the rat population has soared, and bubonic plague is once again a potential threat.

I learned about this unexpected consequence of the Aswan Dam from Dr. Wulf Killmann of the Deutsche Gesellschaft für Technische Zusammerarbeit, whom I met in Malaysia. As we visited about the effects of dams on rivers and oceans, I told him about my experience in Egypt. Dr. Killmann then told me that he had been part of a project to figure out how to control the ever-growing population of rats, which had become a serious health problem.

But that is not all. The saga of the Aswan Dam continues, according to R.G. Johnson of the Department of Geology and Geophysics at the University of Minnesota. “If the Mediterranean Sea continues to increase in salinity,” says Johnson, “shifting climatic patterns throughout the world may cause high-latitude areas in Canada to glaciate within the next century.”3</span


The Mediterranean is starving for fresh water because of human activities, such as the Aswan High Dam, cut off most of the annual flow of the Nile River, which is now used for irrigation and no longer enters the sea. In addition, evaporation from the surface of the Mediterranean is increasing due to global warming. Consequently, a larger amount of fresh water is being lost to human activities and evaporation than is being replaced by rainfall and the inflowing of freshwater rivers. All of which means the Mediterranean is becoming more saline and that salinity is being modified at the Strait of Gibraltar, where the waters of the Atlantic and Mediterranean mix. Barring a significant change in the regional circulation of the atmosphere, Johnson contends two human-caused losses of fresh water from the Mediterranean (the Aswan Dam and global warming) will cause the salinity to increase for some time because of the influence burning fossil fuels has on global warming.

The higher salinity in the Mediterranean will lead to more of the Mediterranean flowing into the Atlantic through the Strait of Gibraltar, which will modify the high-latitude oceanic-atmospheric circulation and, in effect, initiate new glaciation. This hypothesis, says Johnson, arises from his 1997 study of the climatic conditions and inferred changes in the oceanic-atmospheric circulation that probably triggered the last glaciation.

The hypothesis, which is presented here in a simplistic form, works something like this: Leaving Gibraltar, the more saline and thus heavier water of the Mediterranean sinks and mixes with the very cold, deep water of the Atlantic, moving northward until it enters the northern gyre, a great circular vortex. As the fast-flowing water of the Mediterranean approaches the shallow banks north and west of Ireland, it comes to the surface by upwelling. The upwelling apparently acts like a fluidic switch that deflects the relatively warmer surface water of the Atlantic past Greenland into the colder Labrador Sea off the eastern coast of Canada. That water in turn becomes warmer and, in connection with cloudy, cooler summers, causes more precipitation around Baffin Island and other regions in northern Canada, thereby causes sheets of ice to grow while cooling the Nordic seas and northern Europe.

Johnson says, “Today’s climate may be close to the threshold for new glaciation,” because the large plateau areas of Baffin Island are already covered with semi-permanent snowfields that expanded during the historic Little Ice Age 150 to 350 years ago, a time during which summers were cool and extremely severe winters frequented northern Europe. Initiation of new growth in the ice sheet is of grave concern, says Johnson, because of the strong, self-reinforcing feedback from the enhanced electromagnetic radiation reflected by a growing ice sheet (termed albedo effect), and denser cloud cover could ostensibly “lock in” the beginnings of an ice age despite global warming. (Albedo, which is Late Latin for “whiteness,” from the Latin albus, “white,” already exists today over the Greenland Ice Sheet.) The ultimate consequence, warns Johnson, might be a combination of two extremes in which strong global warming in the lower latitudes would nourish the rapid expansion of ice sheets in Canada and Eurasia.

Although there are many unknown variables (such as the current warming of the Arctic and the consequential melting ocean’s ice, which is endangering the polar bears), Johnson says that if his conceptual model is “approximately correct, a new ice age can be avoided if a partial dam is constructed on the sill across the strait 25 miles west of Gibraltar.” The idea, which again is presented in simplistic form, is to limit the outflow of the Mediterranean to something like twenty percent of today’s rate of flow, which would remove the faster flowing water of the Mediterranean from traveling northward to the shallow banks off Ireland and thus diminish the upwelling. With the upwelling diminished, the warm surface water, now diverted into the Labrador Sea, would once again enter the Nordic seas. Canada would remain dry, and Europe’s climate would remain mild and stable.4

Regardless of the eventual outcome, a fundamental question arises: Can an environmental error—the myopic construction of a dam—be corrected with more of the same symptomatic consciousness (such as another dam to offset the effects of the initial dam, which created the problem in the first place)? The answer is an emphatic “No.” We must raise our level of consciousness of cause and effect by unequivocally honoring the guidance of Nature’s inviolable biophysical principles in their totality—which means systemic thinking with all generations in mind.

Related Posts:

• Levees—An Ignored Lesson In “Conduit 101”

• Principle 1: Everything is a relationship

• Principle 6: All relationships are self-reinforcing feedback loops

• Principle 7: All relationships have one or more tradeoffs

• Principle 9: All relationships are irreversible

• Principle 11: All systems have cumulative effects, lag periods, and           thresholds


1. The foregoing discussion is based on: (1) My personal experience while working in Egypt in 1963-1964; (2) C.J. George. 1972. The Role of the Aswan Dam in Changing Fisheries of the South-Western Mediterranean. In: The careless technology. M.T. Farvar and J.P. Milton (eds.). Natural History Press, New York, NY, and (3) James P. M. Syvitski, Charles J. Vörösmarty, Albert J. Kettner, and Pamela Green. Impact of Humans on the Flux of Terrestrial Sediment to the Global Coastal Ocean. Science 308 (2005):376-380.

2. Sid Perkins. Muddy Waters. Science News 167 (2005):328-329.

3. The foregoing discussion is based on: R.G. Johnson. Climate Control Requires a Dam at the Strait of Gibraltar. EOS, Transactions, American Geophysical Union 78 (1997):277-281.

4. The foregoing discussion is based on: R.G. Johnson. Ice Age Initiation by an Ocean-Atmospheric Circulation Change in the Labrador Sea. Earth Planetary Science Letters 148 (1997):367.

Text © by Chris Maser 2012. All rights reserved.

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  1. […] extreme precipitation patterns (Hossain and Jeyachandran, 2009) and global circulation patterns (Maser, Aug 23 2012).  Dams also increase coastal erosion by depriving deltas of sediment.  This, coupled with sea […]

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