2. Cultural systems
From 1836 to 1839 Helmuth von Moltke, future Prussian Chief of Staff, performed the duties of military adviser and cartographer to the Turkish army, which afforded him the opportunity to make several journeys in Mesopotamia and to descend the Euphrates on a raft. In his correspondence are many detailed descriptions of the river which played so great a part in the history of Babylon and in the Old Testament. He writes dramatically of the whirlpools, rapids, outcropping reefs and great rocks which made such a journey so dangerous. In this very Euphrates valley brilliant civilizations had flourished thousands of years earlier; populous towns rose up, terraced with hanging gardens, watered by aqueducts, canals and various hydraulic machines.
Von Moltke pondered the vanished irrigation systems of the Babylonians, at that time known only from ancient texts, and he ended his report with these words:
One day when an English engineer was asked why God had made the rivers, he replied: 'To feed the canals!' I think he ought to have added: 'And to water the fields."
The quotation reveals the spirit of nineteenth-century technology, ever mindful of material progress. Man was vigorously setting about the 'correction' of nature. Streams and rivers were no longer to flow as they had done hitherto; they were to be mastered by the regularization of their courses, to be confined between embankments, transformed into drainage ducts; their waters were to be made to supply intricate canal systems. But von Moltke's own stipulation went unheeded: the regularization of river courses has often robbed fields and forests of the water upon which they depend.
When he was in the Near East von Moltke remarked: 'How much natural energy is still unused in these parts!' Since then people have wherever possible tamed and exploited the energy of rivers and torrents. But, necessary though it may have been, such intervention has often proved ill fated. To harness one form of energy is usually to release another; when one danger has been removed a second, often more serious, quickly shows itself. Communities that took pride in imposing their wants upon nature, have often paid the price for their presumption.
Today many watercourses illustrate the unfortunate consequences of clumsy or excessive interference. The Rhine is only too good an example of this process. Until 1817 its upper valley was a broad wetland basin with marshy soil, dotted with woods and copses, through which the river meandered sluggishly, enclosing more than two thousand isles and islets. Capricious and unpredictable, the Rhine left its bed at every thaw, overflowed its banks and threatened towns and villages. That might be described as the normal behaviour of a river. All rivers emanating from mountains obey the same laws when they debouch into a plain: they tend to wander as they will and to spread themselves before heading for the sea.
In 1817 there came upon the scene a man commemorated on his monuments as one who had 'subdued the wild Rhine'. Johann Gottfried Tulla, a native of Karlsruhe, was engineer in charge of the rivers, bridges and roads of the Grand Duchy of Baden, and he determined to set right the vagaries of the Upper Rhine. As early as 1812 he had drawn up a plan for deepening and straightening the river; work began five years later, but its promoter did not see it finished. Tulla died in 1828 and the work continued until 1872. During those fifty years the bed of the Rhine between Basel and Mannheim was shortened by over one third; marshes, forests, copses, obsolete channels disappeared, and in some places the river dug its bed twenty feet lower than before. From that time the waters flowed freely northward, floods were no more than a memory, barges could ascend as far as Basel and the reclaimed ground became fertile fields. In such circumstances it is easy to understand why Tulla was proclaimed, after his death, the greatest hydraulic engineer of modern times.
This enthusiasm lasted until about the end of the century, when the disadvantages of the 'corrected' course of the Rhine began to appear. The embanked waters could no longer vent their spleen upon the meadows, and the now swift current scoured the river bed ever deeper. At the same time the water-table was lowered because underground ducts now trickled into the drainage system into which the Rhine had been transformed; the roots of trees and the reclaimed land were deprived of the moisture they needed. The former swamp between the Black Forest and the Vosges dried out; everywhere wells had to be dug deeper, the climate underwent a gradual change, and the fish formerly abundant in the slowly meandering river disappeared.
Despite such revelations the Rhine was again attacked. Its waters were diverted when the French began in 1932 to cut the great Alsace Canal, which was to produce hydro-electric power. The economic and political reasons behind this undertaking need not concern us: the fate of the Rhine landscape is what interests us here. At present the information to be gleaned from the partial completion of the works is that the opening of this canal has greatly hastened the deterioration inaugurated by the earlier'improvements' to the Rhine.
Since 1932 the level of the river has sunk by from six to twelve feet according to the locality; after the canal branches off half a dozen miles below Basel the Rhine has become a narrow thread, to be crossed on foot at times of low water. The water- table has suffered a similar dereliction: wells dug by the Romans to a depth of fifty feet are now dry, many orchards have been abandoned, and in long stretches on either side of the river, where there were dense forests a hundred and fifty years ago, even the sallow thorn, one of the less exigent plants, is in jeopardy.
The Rhine is but one example of what is happening almost throughout the world. Man interferes with the watercourses and subterranean reserves: he drains, canalizes, dries up marshes and bogs, isolates streams and tributaries from their natural cycle, transforming some into stagnant backwaters whose polluted water cannot even serve to irrigate the ground and in which, often enough, no life stirs. Where once the drop of water took weeks or months to cover the distance between source and mouth, a day or two suffices in rivers which have been 'improved'.
Water cannot play its part in the economy of nature, as engineers have long known, unless it follows its natural course:.the spring becomes a brook and then a river, as a tributary it joins a greater stream which flows into the sea. During its journey from the source to the ocean each drop of water takes on diverse duties. It makes a course in the soil, alters the landscape, brings water to vegetals and aquatic creatures, moistens and fertilizes the valleys; absorbed and then returned by the animals, it must often make its round more than once without quitting nature's cycle.
When man began to organize himself into civilized communities, he was compelled to interfere with the water cycle, just as he had made war upon the forests and the wastes. To exploit the soil for growing crops, to protect his fields and settlements from flooding, to make use of the watercourses for the transport of heavy goods— such were his objects. At a later stage he was obliged to draw off large quantities for drinking water, for the needs of industry and agriculture and to provide himself with fresh sources of power. Hydrology is an essential part of civilization, but the requirements and schemes of the water engineers conflict harshly with water's role in nature.
Will it be possible to reconcile the needs of a rapidly expanding human race with those of the planet on which it lives? It can be done, and several systems of irrigation and barrage construction in the United States, Canada, the Soviet Union and China are there to prove it. The main thing is to slow down as much as possible the journey of the drop of water to the sea. To achieve this, great rivers must be provided with barrages and reservoirs holding back the water of the upper courses, slowing the rate of flow so that they deposit some of their silt; slopes must be afforested and eroded areas replanted; there must be belts of trees to slow down surface evaporation, the volume of floods must be reduced by storing the water and distributing it according to need rather than by carrying it off uselessly to the sea through artificial canals. Have these principles any prospect of world-wide acceptance? This most crucial problem is one that man must settle promptly.
If river water took a smooth straight course downhill it would empty into the sea without having much effect on the land once it had swept away the top-soil. But the bed and banks of any normal river are irregular and offer obstacles which turn the water aside, create rapids, set up whirlpools and cross currents. In a fairly straight, deep, swift-flowing stretch the water along the banks follows the most turbulent course while water at the centre has the strongest current. Rivers continuously change direction and character as the nature of the terrain dictates, suddenly cascading where the land falls abruptly and remorselessly attacking the rocks and soil and deepening or widening their valleys.
Many of the world's highest waterfalls and most spectacular cataracts are today tourist attractions or have been harnessed to provide hydro-electricity. To the explorers of earlier generations they were not only awe-inspiring natural wonders but also hazards and hindrances to be faced as those intrepid men sought, for example, the sources of the Nile or the headwaters of the Zambezi. The origins of numerous waterfalls are attributable to the Pleistocene Ice Ages. Glaciers filling the main valleys of high mountains were joined by those of side valleys; but as the ice retreated the lesser ones were divorced from the shrinking main glacier, which had also probably deepened its own bed, and eventually their courses became the characteristic hanging valleys, over which today in many cases rivers leap dramatically to plunge into the valley below.
In the course of time waterfalls move backwards by eroding the rock behind the fall face, especially where this consists of the exposed ends of more or less horizontal strata of different degrees of hardness; the water eats into the softer stratum, eventually undermining the harder cliff above. This is the case at the Horseshoe Falls of Niagara, which formerly cut back the crest an average of 2 feet 3 inches every year. However, careful regulation of the flow of the Niagara river and agreement between Canada and the United States about the amount of water taken from it to provide power have ensured the preservation of the Horseshoe and American Falls at Niagara as one of the great scenic splendours of the world.
The erosive power of running water is enormous and has been shaping the Earth's features ever since the planet's first rains. In its natural development a mature river is both destroyer and builder. The spring soon becomes a stream, swollen at times to a torrent by rainwash or melting snow. In this swift-flowing upper course the water, seeking the shortest path downhill, carries with it large and small stones, particles of soil and humus, and shifts and abrades boulders in its bed. When the stream, now grown into a river, emerges from the high land it loses its sense of urgency. The current slows and the waters begin to drop their load: first the larger stones and gravel, then the finer sediments as the river winds through an open valley or across a wide plain to join a greater stream or receive lesser ones as tributaries. In times of flood the river in its lower reaches overtops its banks and spreads a fertilizing ooze across its plain. But not all rivers have extensive flood plains, and when in their lower courses the current is still strong the fertile silt is carried to the sea. Man's intervention can help or hinder the loss of valuable alluvium: if, in seeking to limit the extent of floods, he confines the lower reaches of a meandering river to a course too straight and swift, he hastens the impoverishment of the land; on the other hand he can impede the flow by building barrages and dams and complex irrigation systems.
The fate of vast areas depends upon the activities of big rivers. The first great civilizations arose upon the fertile alluvial lands of the Euphrates, the Tigris, the Nile, and the Indus. The fine particles of mud settle mainly where dense forests edge the river, being held back by the roots of trees. Such mud feeds the virgin forests and great woodlands of the equatorial regions. At Abidos, in the middle reaches of the Amazon, the river is carrying away each year over 600 million tons of mud. The Mississippi, the Nile, the Hwang-Ho, whose banks are without or almost without trees, carry down masses of sediment greater than those of the Amazon and its tributaries. The Nile, most famous of the mud-laden streams, has one of its sources in the mountains of Ethiopia. During the rains, that is from the end of May until the middle of September, the tributaries of the Blue Nile carry the red earth of Ethiopia across the Sudan to Egypt. Seven thousand years ago Neolithic husbandmen already knew how to use this mud as fertilizer.
Modern Egypt has an area of over 386,000 square miles, but only a small proportion is cultivable land, the Nile Valley being bordered by deserts or semi- deserts. The periodic rises of the Nile have shaped the whole history of the country. In the times of the Pharaohs the day on which the flood water reached the lower Nile was a day of rejoicing. The red alluvium from the mountains of Ethiopia was of such importance that, as Diodorus Siculus records, the ancient Egyptians believed that 'the first men were born of the mud of the Nile'. The amount of taxation was settled by the marks left by the water on the river banks'. The higher the level', Strabo pointed out, 'the greater will be the yield from the fields.' The volume of loess carried by the Hwang-Ho in its journey across northern China is enormous, adding an estimated 2,000 million tons of alluvium to its delta each year. Since 1950 the Chinese have been building barrages and irrigation systems designed to retain the precious mud, but the eroded plateaux of the river's upper reaches defy all man's efforts to re- establish productive soil.
In contrast to natural flooding, barrages have the disadvantage that the water held back drops its load of precious silt, so that the irrigation channels fed by them carry very little to enrich the fields. Such systems confer their greatest benefits only when they form part of large-scale schemes which include conservation of land in a river's upper courses and thus reduction of the amount of top-soil carried down by rainwash. In many parts of the world the terracing of steep slopes has for generations served this end; in others the urgent need for action is due to man's heedless felling of trees and overcropping of land, which accelerate natural processes. Artificial fertilizers can do little to compensate for the millions of tons of fertile soil lost annually by water erosion.  Indeed, the Egyptian experience after the creation of the Asswan dam has been that the closed irrigation systems have accumulated salts with losses of formerly fertile land at the desert edge.
Much engineering work has been done to control the waters of the Mississippi and its tributaries. But so gigantic a system, draining over a third of the area of the United States, is not easily confined, and periodically the 'Father of Waters', as the American Indians call it, bursts through the levees and inundates hundreds of square miles of territory. When this happens the damage to farmland and towns is enormous; but at the same time the great alluvial flood plain which the river has created provides much good arable land.
When a large river carries alluvium to the ocean, or to a lake or inland sea, it often turns architect, building new land out of its sediments if the currents and tides are not too strong and the gradient of the sea bed is slight. The name delta was first given to the mouth of the Nile which, seen from the sea, resembled the fourth letter of the Greek alphabet. There are other kinds: some rivers are producing long narrow deltas by filling in former outlets which have been submerged in past ages; the Mississippi has a remarkable 'bird's-foot' delta, forming embankments above sea level for its main channels and advancing some 200 feet a year into the Gulf of Mexico.
In some cases the increases of land are considerable. The joint delta of the Ganges and the Brahmaputra extends to 16,000 square miles: alluvium is deposited in the Gulf of Bengal over an area as large as France. Every year new and fertile land is emerging, and man hurries to take possession. In Italy, the Po gains up to 200 feet a year upon the sea, a process hastened by the protective embankments which have been built along the river's course through its extensive plain. The ancient port of Adria, to which the Adriatic owes its name, is now fourteen miles from the sea. In the sixth century waves still lapped the walls of Ravenna, which is now six miles inland.
As he did with the sea, man has celebrated and personified rivers, making them the heroes of his myths and legends. Poets and writers have striven not only to extol the beauty and poetry and to recount the perils of the rivers; they have also described life on their shores and in their waters. The Rhine, the Danube, the Rhone, the Loire, the Volga, the Don, the Nile, the Tigris, the Euphrates, the rivers of India and China, all have their place in the literature of the world. The Mississippi Sketches, in which Mark Twain described life on the banks of the river and in the boats which plied upon it, are a hymn to the great water artery of America.
Twelve hundred years ago the Chinese poet Li T'ai-po described many a waterside scene:
Butterflies with lilac-dusted wings dip their velvet heads into the flowers. Motionless, the boat is like an island in the pool. The fisherman carefully lets slip his net, shattering the fragile silver mirror.
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