On August 18, 2008, the Kosi, a Nepalese river four times larger than the Ebro, suddenly changed its course. The official count speaks of 42 deaths, hundreds of people swept away by the current and more than three million displaced people. It is a bestiality, yes; but everything seems to indicate that it is a conservative estimate because no one has been able to accurately quantify what that hell entailed. It is the most well-known recent avulsion in the world, but it is not the only one and, of course, it will not be the last. That’s the problem.
When the river changes its course. It doesn’t happen very often, but sometimes a river abruptly changes its course. The process can take decades or even centuries, yes; but also hours or a few days. The result is the same: devastating floods and untold damage. I don’t know if it’s a coincidence that, in medical terminology, “avulsion” means “removal”.
These phenomena have been responsible for some of the deadliest floods in human history, including the Yellow River floods of 1887 and the China floods of 1931, which together claimed an estimated six million lives. Therefore, in recent years, engineers have devoted enormous efforts to build diversion channels and dams that counteract the dangers of a river avulsion. The problem is that, according to new research, those avulsions could happen where we least expect them.
50 years of wild rivers. Sam Brooke and his team (from the University of California, Santa Barbara and Texas at Austin) realized that we knew very little about how these kinds of sudden events work. Therefore, they decided to collect 50 years of satellite images to study in detail why this happened (and how to prevent it). In total, they discovered 113 large avulsions in the last half century.
Not surprisingly, the researchers found that most of them occurred in areas near the mouth of rivers. I say that it is not surprising because the “little” we knew about this process was related to the creation of deltas. However, Brooke and his team discovered that there were other types of avulsions (“located higher than would normally be expected”) that were of concern.
An increasing risk. They are avulsions produced by the erosion of the Earth. Therefore, they occur more frequently in steep rivers rich in sediments (especially in tropical environments and, be careful because this is important, desert). This is a huge problem. Basically, because what the model predicts is that, as the effects of climate change increase, the avulsions will become more and more frequent.
Desertification has been a pressing problem for a long time. 20% of Spain is already desertified and nothing suggests that this will go less. But, without a doubt, the most disturbing thing about all this is that the consequences of this process are still unknown. This is just one example, but in view of what is to come… there will be many more.
Image | POT
George is Digismak’s reported cum editor with 13 years of experience in Journalism