The Nile: A Lifeline in the Desert

Ellen Wohl
Tuesday, September 27, 2011

When not teaching geosciences at Colorado State University, Ellen Wohl is a river historian. This is an excerpt from her new book, A World of Rivers: Environmental Change on Ten of the World’s Great Rivers (Univ. of Chicago Press, 2011). 

The Nile
The Nile
The Nile River forms northern Africa’s tree of life. Waters from nearly three million square kilometers of Africa feed the Nile. Yet the river’s average yearly flow is less than 2% of the mighty volumes that gush into the Atlantic each year from the Amazon. Where the Amazon produces an average of 730,000 cubic meters of water per each square kilometer of its drainage basin, the Nile manages less than 30,000 cubic meters per square kilometer. But this seemingly poor flow is everything in a land as dry as northern Africa. People have clung to the lifeline of the Nile for at least 7,000 years. The earliest humans to live along the Nile relied on the yearly flood, just as do modern occupants of the river valley.

As it leaves Aswan, the Nile is less than a hundred meters above sea level, but it flows 1,200 kilometers through a labyrinth of irrigation works and canals before it reaches the Mediterranean. The lower river hosts odd juxtapositions of technology and appearance. The tall buildings, trains, traffic jams, high-tension lines, and twenty million people of Cairo abut without transition small villages with irrigated fields where farmers follow water buffalo dragging a wooden plough. As elsewhere along the lower river, everything is vividly green where there is water. Papyrus line the riverbanks, new crops sprout in the flooded fields, and date palms cast a scant shade over the dirt roads. Along the linear oasis of the river, simple wooden boats with graceful triangular white sails move quietly beside fishermen casting hand nets across the water. Immediately beyond the reach of the water, there is no apparent life. The orange-red sand and rock of the desert stretch toward a horizon lost in haze.

Seen in satellite images, the thin, dark line of the Nile meanders within a slender, jade-green band that crosses a corrugated landscape of tan, brown, and yellow desert mountains and plains. Just below Cairo the green band expands abruptly into the broad delta that the river has built over millennia.

Sand, salt marshes, lakes, and swamps intermingle across the 22,000 square kilometers of the delta, but the region still comprises two-thirds of Egypt’s fertile land. The sediments of the delta form an enormous freshwater aquifer that, along with the river’s annual flood, retains water in the wetlands. Among the wetlands live forty-five species of birds; more than half of the seventy-three species found throughout all of Egypt. The delta is also the gateway for birds migrating between Africa and Europe. The birds follow the green line of the Nile upstream to their winter homes and downstream to their summer habitat.

The not-so Blue Nile

The steeply dissected mountains surrounding Ethiopia’s Lake Tana are drenched by violent rains from March to September. The region was once covered in primary tropical rainforest, but deforestation has replaced much of the rainforest with secondary growth and shrublands. This rugged landscape supplies 98% of the sediment entering the Nile. Deforestation is increasing the volume of sediment eroded from the hill slopes.  

The countryside opens out as the river leaves the Ethiopian plateau. The river’s blue waters take on a heavier load of silt as they pass through the coffee-growing country at the borders of Ethiopia and Sudan. The last major rapids occur just before the river enters Sudan, when the turbid waters churn into a thundering white mass as they cut through the resistant rocks of the Blue Nile’s western gorge.

English explorer Samuel Baker wrote in the 1860s that during the dry season “the water is beautifully clear, and, reflecting the cloudless sky, its colour has given it the well-known name of Bahr el Azrak, or Blue River.” The river would be unlikely to receive that name today as it carries progressively more of the Ethiopian highlands downstream in the form of millions of tons of sand and silt.

A thousand kilometers downstream from Lake Tana, the waters of the Blue Nile encounter their first human-built obstacle in the form of Roseires Dam. From this point to its outlet in the Mediterranean more than 3,300 kilometers downstream, the river will be steadily dammed and diverted and used for all the thousand things that humans require of water.

Completed in 1966, Roseires was designed to supply irrigated agriculture in the Gezira region around the confluence of the Blue and White Niles. In satellite images of the region, the dense network of irrigation canals now resembles the intricate tunnels of boring insects in wood. Roseires dam was also built to supply hydroelectric power to downstream cities, including Khartoum. But deforestation in Ethiopia has allowed the torrential monsoon rains to steadily strip the hill slopes of soil, so that the reservoir has lost capacity to store water and to generate power as the sand and silt pile up behind the dam. These huge quantities of sediment have smothered and destroyed large beds of the Nile oyster. The reservoir was also the scene of heavy fish mortality during 1967 when water stratification in the newly filled reservoir created oxygen-deprived conditions.

The first megadam

The High Aswan Dam, completed in 1970, rises more than 100 meters above the river and backs water so far up the valley – almost 500 kilometers – that it can store almost two years’ worth of the Nile’s average yearly flow. Like other rivers draining dry regions, the Nile flow fluctuates substantially from year to year. During 1878-79 the great river poured more than 140 billion cubic meters down to the sea. During 1913-14 only 39 billion cubic meters flowed down from the highlands. The dam was designed to protect Egypt from such climatic fluctuations in water supply, as well as from limitations on water imposed by upstream countries. As Nasser phrased it, “After completion of the High Dam Egypt will no longer be the historic hostage of the upper partners to the Nile basin.”

The dam met its intended use when it helped to avert massive famines during droughts in the 1970s and ‘80s. Egypt’s irrigated area rose to nearly three million hectares by 2000 and Egyptian officials project that this will increase to 4.5 million hectares by 2020. It may have to; Egypt’s population has reached 70 million and is projected to reach 115 million by 2050. Half of the planned water addition from the High Dam, however, is lost to evaporation (10 billion cubic meters) and seepage each year. Egypt continues to import half or more of its annual food requirements.

Meanwhile, environmental deterioration caused by the High Dam began to appear. Many of the lakes associated with water-control structures along the Nile have aided the proliferation of introduced species of aquatic vegetation – principally water hyacinth, water fern and water lettuce. These plants impede water flow and navigation; reduce phytoplankton on which fish feed; lower dissolved oxygen levels as they decay, and increase water loss from the reservoirs. A hyacinth-covered water surface loses 3.5 times more water through evapotranspiration than a clear water surface in semitropical areas. In the desert, the increase can be up to eight times.
Prior to the closing of the Aswan High Dam, nearly 40% of the Nile’s total annual flow – approximately 30 billion cubic meters of water – entered the Mediterranean from the Nile Delta. This water transported 90% of the sediment washed down from the Ethiopian highlands – more than a hundred million tons of silt – onto the delta. The river spread the remaining 10% of sediment along its floodplain, creating the fertile soils that supported Egyptians for millennia. Once the dam closed, the annual river flow to the ocean dropped to less than 2 billion cubic meters. Sediment remained trapped upstream from the dam, where it diminishes the reservoir storage capacity.

Silt carried by the Nile nourishes plankton growing in the seawater offshore from the delta. The plankton in turn support sardines. When the water and sediment supply decreased, the abundant sardine fisheries collapsed. Contributing to this collapse was the pollution of the brackish lakes on the northern delta, which are connected to the sea, and into which most of the delta farmlands currently drain. Water quality in these lakes is now severely impaired by chemicals and sewage. The greatly reduced sediment supply also caused the delta to subside and erode. The former delta village of Borg-el-Borellos is now two kilometers off the coast.

Along the floodplain farmlands below the dam, soil fertility has diminished in the absence of the yearly influx of sediment and nutrients. Egyptian farmers rely increasingly on expensive chemical fertilizers that pollute surface and ground waters with excess nitrogen. The nearly constant flow level in the river also raises the regional water table (up to three meters per year in some parts of Egypt) and impedes drainage of irrigated lands. Egypt now has a severe problem with water-logging and soil salinization as salts dissolved in the irrigation water remain behind when the water finally evaporates. One study during the 1970s estimated that 35% of Egypt’s cultivated surface was affected by salinity and 90% by water-logging. Artificial land drainage systems are expensive and not always successful. As John Waterbury wrote in 1979, “No regime ever built a monument to itself with tile drains, but it is at that level that Egyptian planners must focus their attention.”

Bilharzia (schistosomiasis) has become endemic along the river’s course in Egypt and Sudan. Irrigation ditches filled with stagnant water and weeds host snails that serve as vectors to spread the disease to people who wade in the shallow ditches. Perennial irrigation eliminates the fallow periods during which the snail hosts would be killed as the canals dried out.

Egypt continues to aggressively expand its irrigation supplies and acreage. President Hosni Mubarak approved the New Valley project in 1997 to divert Nile water upstream from Lake Nasser and transfer it hundreds of kilometers to irrigate Egypt’s southwestern desert. Mubarak opened another canal to shunt Nile water beneath the Suez Canal in order to irrigate portions of the Sinai desert.

The source for all this irrigation water remains problematic. The flow of the Nile is anything but infinite. Egypt would like to continue its expansion, but neighboring countries that share the Nile’s waters are looking to their own growth. Although the Nile basin includes ten countries, the two downstream nations of Egypt and Sudan claimed most of the river’s flow in a 1959 treaty. Egypt wishes to expand beyond this allotment, but Ethiopia, where nearly 90% of the Nile’s flow originates, is ready to promote its own development. Only five percent of the potentially irrigable land in Ethiopia is currently under cultivation and the Ethiopian government is giving renewed attention to a 1964 U.S. Bureau of Reclamation plan that proposed 33 irrigation and hydropower projects in the upper Blue Nile. The plan also calls for four major hydroelectric dams on the Blue Nile that together could store nearly a year’s average flow of the river. The new reservoirs behind these dams would increase evaporation, as would the croplands under irrigation, thus reducing downstream water supply.

More people, less water

Three hundred million people in Africa, a third of the continent’s population, live under conditions of water scarcity at the start of the 21st century. The population of the Nile basin, which was 245 million in 1990, is projected to reach 859 million by 2025. By that time, Egypt is projected to have one of the lowest per capita availabilities of water in the world at less than 590 cubic meters per year.

By correlating long-term records of Nile flows with independent records of climatic conditions, hydrologists are beginning to understand how global climatic fluctuations translate into changes in water supply in the Nile drainage basin. Nile flows have become much more variable since the 18th century, with high and low flow sequences that are much more acute and persistent than sequences earlier in history. The 20th century in particular was characterized by exceptional droughts that climatologists relate to differential increases in ocean temperatures between the northern and southern hemispheres.

The Nile already rates a critical red color on a worldwide compilation of flow regulation along major river basins because its waters are among the most highly regulated and utilized of any major river basin. As human population soars upward in the Nile drainage, the margin of adaptability and survival during periods of water shortage decreases for both humans and every other form of life dependent on the river.

The historical details of the involvement of British, French, Germans, Italians, Belgians, and Americans in the Nile drainage amply illustrate the stunning arrogance and aggression behind 19th and 20th century colonialism. Contemporary uncontrolled population growth, and its implicit assumption that somehow the Nile will provide, seem equally arrogant and aggressive. It is only a matter of decades before we see how this episode of colonization reaches its crisis point.