At the base of the great sand dune, at the exact point where the slopping wall of white sand shoulders its way into the oasis, an old man, his white robe tucked up around his waist, bends ankle-deep in water and thumbs fresh, lime-green rice shoots into the black earth of a small garden. In the narrow lane adjoining the garden a white, orange flanked donkey plods by a slow-moving automobile. A frog, startled, leaps into an irrigation ditch and splash in hand, backs through a gate in the frond fence.
He pauses for a moment, looking up toward the top of the dune where a hot wind off the desert ceaselessly piles its millions of tiny pin-sharp specks of sand upon the crest. With a wave of his hand at the old man he slips out of his sandals and lunges exuberantly up the steep bank. Halfway to the crest he passes what was once a palm tree, but is now a black skeleton protruding from the dune like a single brunt piling from the waters of the sea. As he climbs, his feet scrabbling for purchase, the sand yields and, grain by grain, rolls down the shimmering flank to the base and there trickles forward into the oasis a fractional part of an inch. So, imperceptibly but relentlessly, the desert invades as-Hasa..
In 1961 in Saudi Arabia, villagers in an oasis called al-Hasa dispatched to the central government's Ministry of Agriculture an urgent appeal for help. The desert, they said, is upon us.
It was indeed. Along a nine-mile front, nearly the entire eastern wing of the oasis, a great mass of sand was advancing on the oasis at an estimated average rate of 30 feet annually. Each year some 230,000 cubic yards of sand were ebbing into the oasis, and near 14 villages in the al-'Umran section, the dunes were looming over the very roofs of the houses. Investigators assigned by the ministry reported after an aerial survey that the active dune field—the dunes that were moving—measured five and a half miles by 100 miles and that it was advancing so fast that it would bury the village of al-'Umran ash-Shimaliyah within seven years if immediate action were not taken. Furthermore, they added ominously, huge sections of the whole oasis would vanish beneath the sand within the lifetimes of youngsters living there now.
For the farmers of al-Hasa's 50 villages, it was a catastrophe and it was obvious that something had to be done. But what? The encroachment of dunes is no new problem in Saudi Arabia; excavations have shown that the dunes near al-Hasa had been moving toward the oasis since the time of the Prophet Muhammad. Yet it is only in comparatively recent times that science and industry have begun to seek answers to the basic questions affecting the movement of dunes: What causes the dunes to move? What can be done to control or halt them?
To the first question the answer is obvious: wind. Be it the monsoon of the Indian Ocean, the simoon of Syria, the sirocco of North Africa, the khamsin of Egypt or the shamal of Saudi Arabia, it is wind, fundamentally, that makes the desert move, sometimes lifting the sand and carrying it along suspended above the ground; sometimes rolling it along the ground; or, most commonly, bouncing it forward in an erratic hop, skip and jump called "saltation." It is wind too that shapes and molds the sand into streamlined domes, stars, pinwheels and tear drops and into the most familiar shape—the barchan, a high-crested quarter moon with the two horns sloping down to ground level.
Whenever the stream of wind is broken, however, or when it slows or twists into turbulence and so can no longer support the sand, the "saltation" process stops. Thus in the lee of any object imposed in the windstream—a tree, a fence, a bush or a rail, no matter how small—the sand begins to accumulate as though the object is casting a downwind shadow of sand. This is the core of a dune and around it forms the mass of sand which slowly assumes the characteristics of dunes.
Those characteristics, noted by R.A. Bagnold, the British authority on sand movement, involve differing steepnesses between the windward side and the lee side of a dune. The angle on the windward side, Mr. Bagnold reported, is less steep—generally a 22-degree slope as compared to 32 to 33 degrees on the lee side. Because the windward angle is shallow, oncoming winds can sweep easily up the slope, driving grains of sand to the crest, where they spill over into the lee of the dune and roll to the bottom. The dune, in effect, moves much like a wave breaking on shore, the base moving to the crest and tumbling over itself.
Wind, then, is the essential force in the creation and movement of dunes, and nowhere in the world does it have more freedom to mold and move mountains of sand than it does on the Arabian Peninsula. More than 1,000,000 square miles in area, the peninsula contains many great deserts, one of which, the Rub' al-Khali (The Empty Quarter), a basin some 400 by 700 miles in area, contains approximately 250,000 square miles of sand, the largest continuous body of sand in the world. In the Rub' al-Khali, dunes form parallel ridges 125 miles long, a mile wide and up to 300 feet high. These sinuous 'umq (veins) or snyuf (swords) streaming away from the prevailing wind are so mighty that smaller, transverse dunes 100 feet high march along their backs. In other parts of the desert, shifting winds from all points of the compass beat upon the sands from all directions and pile up great pyramidal massifs 700 to 1,000 feet high.
The smothering advance on al-Hasa, however, was caused not by the Rub' al-Khali, but by the Great Nefud, a desert roughly the size of West Virginia (26,500 square miles) stretching over the northwestern part of the peninsula. In the Great Nefud the prevailing winds blow in from the Mediterranean, scouring upland sandstone outcrops and winnowing sand and dust from the ancient alluvial deltas where the great dry wadis once poured their spring floods onto the plain. Scooping up the crumbled grains of quartz and basalt, the winds swing east and south in a great crescent and then west, connecting the Great Nefud and the Rub' al-Khali with several arching sand "rivers," a particularly appropriate term which describes their ability to literally inundate anything that stands in their path—roads, pipelines, gardens and whole villages. The longest of these "rivers," the Dahna, famed for its red sand (due to a high iron oxide content), "flows" 60 miles east of the capital city of Riyadh. Further east, another, the Jafura, picks up the white coral sand of the Arabian Gulf beaches and also advances south and southeast to the storehouse of the Empty Quarter. It was an arm of the Jafura field which threatened al-Hasa.
The threat of moving dunes is not, of course, limited to Saudi Arabia. Dunes have wiped out many communities in the Sahara and Libyan deserts. In the United States, dunes along the Atlantic seaboard and the Gulf of Mexico are constantly pushing inland. On the south shore of Lake Michigan they have marched across entire forests. In the Bay of Biscay, coastal winds press dunes forward up to 100 feet a year and have buried French vineyards, villages and even church steeples.
In such humid coastal areas, however, control is relatively easier because there is usually sufficient moisture to nourish the grass and shrubs that can slow the movement of sand. Near Lebanon's Beirut International Airport, for example, creeping beach grass from the United States and young pine trees were planted and because of Lebanon's ample rainfall not only survived, but flourished, and are turning the dunes into green parklands. At al-Hasa where the annual precipitation is rarely more than two and a half inches, the same approach would not, without modifications, have been feasible. The magnitude of the problem, furthermore, wasn't comparable, simply because of the sheer size of the mass which threatened al-Hasa. There was, moreover, a particular problem in al-Hasa that was of much more immediate concern: the effect of the sand on drainage.
Al-Hasa has an abundance of ground water, and much of the excess must be drained away. Ditches to carry part of it off crisscross the oasis and lead eastward into a chain of shallow depressions or salt flats (sabkhah) called Birkat al-Asfar. The shallows, in turn, empty through a narrow neck about six miles north of the plantations. With the advance of the dunes, drifting sand had slowly choked off the narrow outlet in two places. Water backed up, creating an artificial lake which at times was two miles square and six feet deep. The lake quickly turned into a malodorous and unsanitary swamp which, in the hot sun of Saudi Arabia, began to evaporate. The evaporation soon began to raise the salinity of the water to levels fatal to nearby plant life. Drifting sand also posed a distinct threat to the vital springs on which not only the crops, but the people themselves, depended for life.
Thus in al-Hasa the answer to the second question—what can be done to control or halt the movement of dunes?—had to be found immediately. With the sources of drinking water threatened, it was clear that al-Hasa could not wait. In 1961 the Ministry of Agriculture began to assess the weapons available for a counterattack, many of which were originated by the Arabian American Oil Company (Aramco) in 25 years of experiments with ways of protecting oil installations from the onslaughts of sand.
According to Aramco's experience there are many ways to cope with dunes, each with multiple techniques, particular advantages and definite drawbacks. There is channeling or diverting the dunes by fencing, much as a jetty deflects wave action on a sea coast. There is trenching or oiling in strips, which can deflate or flatten a dune by destroying its symmetry. There is the transposing of sand physically. There is asphalting which so smooths a surface that the wind-borne grains skid across and beyond an area, rather than pile up around it. There is designing which might, for example, tilt the downwind edge of a road six inches upward so that grains of sand would skid over the traveled surface and land on the lee side. There is also solid oiling of whole dunes. And there is the planting of trees.
Although each of those techniques had been used successfully in other areas, they had limitations with regard to al-Hasa. Channeling, in the face of the sheer mass of dunes, was inadequate. So were trenching and oiling in strips. Moving the sand by conveyor belt, bulldozer, or other earth-moving equipment, is prohibitively expensive and could be used in al-Hasa only on the fringe of villages, near roads and buildings, where the cost could be justified. Stabilizing by applying a solid coat of oil is unsightly and can be technically difficult. To be effective, the coating must be applied and maintained in a carefully controlled way. A high-gravity, waxy, penetrating oil must be sprayed from heavy-duty trucks. Using a low-flying plane to spray oil is unsatisfactory because the crust—which must sink in three or four inches—would be too thin and could be torn up by a heavy wind. On the other hand, a heavy truck can tear up a dune surface and destroy the streamlined form which is easiest to stabilize. And even though Saudi Arabia is an oil-producing country, solid oiling is expensive. To achieve an effective coating requires three gallons of crude oil per square yard, a ratio that would, along a nine-mile front, add up to an estimated 600,000 barrels.
The final alternative—trees—seemed, in al-Hasa, to offer the most advantages. To begin with, the large number of laborers which would be needed (500 in the first year the program got started) could be drawn right from the villages of the oasis. These men would only need a minimum of training—agriculture, after all, was their business—and they would be more likely to work in earnest since it was their own homes and those of their friends that they would be striving to save (which was, one man reported later, exactly what happened. "I've never seen people more interested in doing a job.")
The most important advantage, however, was that it worked efficiently. Past experience had shown that with the right approach, tree-planting could provide an effective barricade against encroaching sand swiftly and could fix the sand in place. On the Libyan coast on the southern Mediterranean, where there are but five to six inches of rainfall every year, a new technique developed by Standard Oil Company (N.J.) made possible a vast forestation project on top of the dunes. That technique was to plant seedlings immediately after a shower and then spray the surface with a special formulated petroleum product that would hold the sand down, yet admit moisture.
Even with this plan, however, al-Hasa presented special problems. If planting were to work at al-Hasa, a species of tree would have to be found which would require a minimum of water and care, which could reach deep into the sand for water, yet stand tall enough to fend off sand, which had horizontal branches for maximum wind resistance, and which could thrive in an arid, salty environment. To find such a tree the Ministry of Agriculture sought the advice of Aramco's agricultural specialist, Dr. Grover Brown.
Dr. Brown, a blunt man with a gift for exact expression, immediately dismissed the idea that any tree "thrived" in such an environment.
"Plants are like people," he said. "Some require more or less water and heat than others. But that doesn't mean that they thrive under poor conditions. For example, date palms have the happy faculty of tolerating rather wet land, but they can suffocate if stagnant water covers their roots. At the same time they can tolerate fairly dry conditions, their roots reaching down maybe 40 feet to search for water. But the palm still grows better under ideal conditions of air, moisture and fertility.
"Now the same thing applies to this question of salt," he went on. "People can drink water with up to 3,000 parts of mineral salts per 1,000,000. Some plants are like camels and can tolerate up to 4,000 or more parts per 1,000,000—the approximate level of salinity in the drainage ditches at al-'Umran—so it was not a question of finding a tree that thrives, but one that has a high level of toleration." The tree that met those requirements, he said, turned out to be the tamarisk—five varieties of the tamarisk tree, actually—which, depending on the variety, covers the ground densely, grows quickly, can send its roots down for water a distance equivalent to its own height and holds onto moisture greedily.
Before deciding how to tackle the problem, the Ministry of Agriculture weighed many proposals, including a plan offered by an Egyptian agriculturist, Ezz ed-Din Rashad, that was built around proposals from Aramco and based to a large extent on data supplied by Aramco's original surveys of the problem.
According to Mr. Bagnold's formula, it was calculated that if the great sand mass looming over al-Hasa were impounded in a single mighty dune by constructing a nine-mile barrier and raising it over the years, eventually a linear ridge roughly five miles long, 600 feet high and half a mile wide at the base would be built up. It was calculated too that it would take 2,700 years, long-range planning in the extreme. Furthermore most of the sand mass—61 per cent—would be upwind of the crest and the rest—39 per cent—would be downwind. That would mean that if the barrier were built on the present front, another 670 acres of farmland and several villages would still be buried.
To avoid further loss of land, yet still block the whole dune field's advance, Ezz ed-Din Rashad offered a plan which, he said, could be completed economically in a year and a half plus three years of maintenance. The logical solution, he said, consists of a multiple system of barriers: one on the front for immediate relief, one about five miles upwind to impound the mass of the field, and one in between for support and in case of a break in the barrier upwind. If the front were completely stabilized within five years and the rest of the program were faithfully carried out, only an additional 50 acres would succumb.
With a speed rare in governments, the Supreme Planning Board of Saudi Arabia gave its approval and the mechanics of the plan were set in motion. So rapidly did it progress that although actual work did not begin until the summer of 1963 the initial effects are already visible: a barrier, nine miles long and 150 feet wide, studded with some 3,000,000 seedlings, some nearly six feet high already; a canal along the base, to supply water for tree nurseries and for terraces on what was formerly the face of the dune; a road on the barrier, shielded by palm fences, running along the dune as much as 50 feet above the gardens.
At the top of the dunes on the windward side is the second barrier, also nine miles long but 300 feet wide. The third line, five miles to the rear, will be the most important eventually but has had to wait until the immediate encroachment has been blocked.
As do most projects that fire man's imagination, the al-Hasa project brought forth unexpected benefits. To meet the demand for approximately 1,000,000 pots to transplant young seedlings from the nursery to the dunes, a small factory was established at the project side to turn out 3,000 concrete pots daily. Surplus coarse gravel, produced by a stone crusher bought to help in making the concrete, was employed to make bricks to line the small reservoirs and to build sluice gates on the canal. To enrich the soil Mr. Rashad mixed loam, mud and waste oil, added chemicals available locally, and threw in nitrogen-rich algae from irrigation ditches. The result was a product so rich in chemical value and so cheap to produce that its commercial prospects are being studied.
Since 1961, when the government and Aramco answered the villagers' call for help, there has been a dramatic change in al-Hasa, not only in the movement of the desert, but in the minds of the people. Despair has given way to hope, weakness to strength.
For al-Hasa is not only being saved from extinction; it is looking forward to a much more promising future than it had before. A 1962 survey showed that enough water is available to increase total cultivation by 15 to 20 per cent. The artificial lake in the salt flats to the north will be drained and a huge conduit will be constructed so that shifting sand can move across the narrow neck without plugging it. Even longer-range plans call for the establishment of a sand control board with complete authority in al-Hasa to take steps to control the restless sands, to conduct research programs and to pass laws to safeguard trees and other barriers.
For villagers who faced destruction just four years ago this is a startling change, and they are as grateful as they are hopeful. "They know how close they came," explained Dr. Brown. "The village would certainly have been destroyed. It was only a matter of time. Once that drain was plugged they would have been finished. Now they have a future."
In describing that future Mr. Rashad's eyes sparkled as he pointed upward to the crests of the dunes. "That's where they'll live, up there," he said, "and around the new village lemons and oranges and mangoes will grow, and there will be a mosque with a little public garden, and a hospital and a school and houses ... Oh, it will be a wonderful thing to see."
"In fact," he added, "it already is," and he pointed upward where the ranks of tough, green trees stood like sentinels against the sky, their roots deep in a mountain of sand that will move no more.
William Tracy, who lives in Beirut, is a free lance writer who contributes regularly to Aramco World.