Mud and destruction. These two words are the common denominator right now in the areas affected by DANA that devastated several parts of Valencia and eastern Castilla-La Mancha last week. An event for which more than two hundred people have already died and which has affected more than 9,000 hectares of land in which 74,000 people live, according to data calculated by the Copernicus Program, which tracks the scope of this type of catastrophes. thanks to images from space.
In that area, the same system estimates that some 900 kilometers of roads and more than 4,000 hectares of buildings have been affected. Chaos and damage that, however, has not been solely caused by water. In fact, there has been an even more damaging factor: mud. This is what scientists from the Geological and Mining Institute of Spain (IGME-CSIC) Daniel Vázquez Tarrío, Andrés Díez Herrero and Ana Lucía Vela point out, who sign a statement in which they point out that these sediments are not usually taken into account in risk studies by floods and maps of flood zones despite their enormous destructive capacity.
“It is enough to observe the shocking images of this tragedy, which has especially affected several towns south of Valencia, to realize that what is dangerous is not exclusively the water and its depth,” the authors point out. «The damage caused by the speed of the flow itself and by the materials carried by the current can also be very important (…) In floods, it not only damages the water; “It damages the mud more.”
The researchers explain that the damage in this type of events occurs “not to the depth or time of submersion in the water,” but to the impacts produced by the materials contained in the flood, such as wood, plant remains, vehicles, containers or urban furniture, in addition to the sediments themselves that come down the torrent, “such as clay, silt, sand, gravel, stones and blocks,” they indicate.
And although damage to home furniture is usually attributed more to water that wets household goods or appliances, the truth is that it is mud that renders them useless and deteriorates. Even so, “most of the flood risk studies and maps of flood zones are prepared assuming that what circulates through our channels and banks is clean, almost distilled water, devoid of mud,” they indicate. That is, the models take into account as if a torrent of pristine water were flowing down the areas likely to flood, although that is not reality.
The sediment difference
Geologists emphasize the importance of “investigating how erosion, transport and sedimentation of land influences aggravating the danger of floods and floods”, and using “the few studies and maps that have considered the role of sediments” in this type of episodes to draw conclusions.
In fact, the researchers are members of a team that has compiled all these scientific works and has published the summary in the journal ‘Geomorphology’, in which they analyze more than a hundred scientific and technical studies. «Our results allow us to interpret that sediment transport processes are associated with sudden morphological changes in the channel, which in many cases aggravates the danger due to flooding -they indicate-. “This review of previous studies also suggests that mountain channels are perhaps more sensitive to this problem.”
Finally, geologists urge “taking more into account the sediment” that can be transported in each river, as well as the amount and type of materials that the torrent could erode, transport and deposit. Because, for example, a riverbed that passes through a clayey area is not the same as a calcareous area, or a terrain with large rocks or, on the contrary, gravel. “It is necessary to transfer this information obtained by previous scientific research work into practice and consider sediment transport processes in a more explicit way in risk maps due to river flooding,” they conclude.
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