The race of the riversUncategorized
The Nile is the longest river on earth. Or is it not? Some researchers doubt this record and claim that the Amazon is longer. But it is not so easy to measure a river precisely.
The previous leader was the African Nile with a length of 6,671 kilometres. It has its source in two headwaters: The Blue Nile from the Ethiopian highlands and the White Nile from the mountains of Rwanda and Burundi. On its way, it flows through Tanzania, Uganda and Sudan and flows into the Mediterranean Sea in Egypt. So long, so good. But some researchers now claim that the Amazon is longer. Until now, South America’s most gigantic river had an official length of 6,437 kilometres.
If, however, one were to add its tiniest source river, one would arrive at around 7,000 kilometres. That would make the Amazon clearly longer than its African competitor. And now? Scholars cannot agree. Textbooks and reference books still rank the Nile first among the longest rivers, the Amazon only second. But there is one thing that cannot be disputed about the Amazon: It is by far the most water-rich river on earth: two-thirds of all the river water on earth flows through its bed. At its mouth, 200,000 cubic metres of water flow into the Atlantic Ocean every second – the equivalent of about a million full bathtubs!
The life of the ancient Egyptians, who lived around 5,000 years ago, was determined by the Nile. It probably didn’t matter to them whether their river was longer than all the others. What was important, however, was that they could cultivate crops on its banks – and that in the middle of Egypt, a land of desert.
Once a year, the Nile overflowed its banks and spread black and fertile mud over meadows and fields – a perfect fertiliser. Because the river and its water level were so crucial to their lives, the ancient Egyptians built Nilometers: They could read from these markers whether the water level was falling or rising. Even taxes were assessed according to the Nilometer: A high water level promised good harvests and meant high taxes. If the Nile had little water, the taxes that the farmers had to pay also decreased.
From trickle to stream – flowing waters
Bubbling groundwater emerges from a spring and flows down the slope as a thin trickle or a small stream: a watercourse has been created. All flowing waters start out small. On their way towards their mouths, they merge with other watercourses and continue to grow until they have become a river or even a broad stream. At its lower end, the watercourse flows into another river, a lake or the sea.
Streams, rivers or creeks – terms that come to our lips fluidly are precisely distinguished from one another by scientists (geographers). They can be classified by their water volume, their length or their width: If the watercourse is less than half a metre wide, it is called a trickle; if it is more than 2 metres wide, it is called a stream. If the watercourse swells to a width of 10 metres, it is a river. And if it gets even wider, the river can be called a stream. The Amazon or the Nile, for example, are called rivers, but the Rhine and the Danube are also streams.
The amount of water in the flowing water increases from the source to the mouth. Nevertheless, it flows slower and slower downhill. This is because the slope down which it flows is steeper at the top than at the bottom. And because the water flows faster at the top and slower downstream, it can carry more sand and debris along the upper course than the lower. Thus, more sand and debris is removed from the upper course of a river, and more is deposited in the lower course.
Catchment area and watershed
When a raindrop falls to earth in Furtwangen in the Black Forest, it flows down the small river Breg into the Danube. After a long journey, it finally lands in Romania in the Black Sea. If, on the other hand, the drop falls only a few kilometres north of Furtwangen, it will – if it does not evaporate or seep away – eventually wash into the Atlantic Ocean. This is because this area is drained via the Elz River into the Rhine and the North Sea.
Every river has a land area that – like a funnel – guides the water towards it. The region from which a river feeds is called the catchment area. Because the water always flows from higher elevations to lower elevations, the catchment area is bounded by mountains and ridges. These separate the catchment area from other river systems. So it can happen that raindrops that fall from the sky only a few centimetres apart are washed in another direction and end up in seas far away from each other.
The boundary that separates one river basin from another is the watershed. The catchment areas of the Danube and Rhine, for example, are separated by the European watershed. However, this thousands of kilometres long watershed also delimits many other catchment areas: In France, it separates the Rhône, which flows into the Mediterranean, from the Loire, which flows into the Atlantic.
A watershed does not have to run along the same line for all eternity. If a mountain range rises or is eroded by glaciers and weathering, this changes the landscape and the gradient. Also, a river that digs deep into the terrain can “drain” the water from another river. In the southern Black Forest, for example, the Wutach, a tributary of the Rhine, has tapped into some of the Danube’s headwaters over time, thus shifting the watershed between the Danube and the Rhine. Or as a result of plate movement, a landscape can even tilt in a different direction in some places, so that the water eventually drains into another river.
The cycle of water
The water on earth is always on the move. Huge quantities of it are constantly moving – between sea, air and land – in an eternal cycle in which not a drop is lost.
The motor of the water cycle is the sun: it heats the water of the oceans, lakes and rivers so much that it evaporates. Plants also release water vapour into the atmosphere through tiny openings. The moist air rises, tiny water droplets gather at high altitudes and form clouds. As rain, hail or snow, the water falls back into the sea or onto the earth. If it falls to earth, it seeps into the ground, feeds plants or flows through the ground, via streams and rivers back into the sea. The eternal cycle of evaporation, precipitation and runoff starts all over again.
The water cycle has existed almost as long as the earth has. It ensures that living beings on our planet are supplied with fresh water. And not only that: without the water cycle, the weather as we know it would not exist.
What the Karlsruhe engineer Johann Gottfried Tulla began in 1817 was completed this year: The river loops of the Upper Rhine have been pierced, the Rhine straightened and shortened. With the correction, the bed of the river was also deepened. The Rhine is now navigable as far as Basel.
For decades, construction workers had been working on the river with shovels, wheelbarrows and horse-drawn carts. The bed of the Rhine north of Karlsruhe had to be partially re-excavated: A total of 18 cuttings now shorten the original path of the water through its numerous meanders. The old river loops were filled in at their inlets. The result: the Rhine no longer flows in many branching tributaries, but is concentrated in a dead-straight main bed. In addition, dams were built along the river. These are intended to protect the residents from flooding. It is also hoped that draining the swamps will reduce the dreaded swamp fever, malaria.
The straightening of the Rhine initially met with fierce resistance from farmers and fishermen, some of whom used force of arms to break it up. However, when the straightened areas were spared from the floods after a flood, the project found more supporters and the work was accelerated.
Since the Rhine has been straightened, its course between Basel and Mannheim is 90 kilometres shorter than before. Because the river bed has also been lowered, heavy cargo ships can now reach as far as Basel.
On risks and side effects …
Tulla had only wanted the best: “…In cultivated lands, streams, rivers and creeks should be canals and the management of the waters should be in the power of the inhabitants.” The advantages of river correction were clear: one wanted to facilitate navigation, to de-sump the land for agriculture and animal husbandry, and at the same time to curb the danger of epidemics and floods.
But Tulla’s project was controversial from the start. Farmers and fishermen feared economic disadvantages. Moreover, the further development of the Upper Rhine showed the unforeseen consequences of this intervention in nature: the Rhine no longer flowed leisurely through the loops, but flowed much faster on a straight path. As a result, it dug deeper into the ground, the groundwater level sank and species-rich wetlands dried up.
In addition, during floods, the excess water masses could no longer spread out in the Rhine floodplains. Instead, they flowed quickly downstream and threatened the towns and countryside there. So Tulla did not really eliminate the flood danger, but only shifted it downstream.
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