In floods, it not only damages the water; also the mud

The torrential rains due to the recent passage in Spain of a DANA (Isolated Depression at High Levels), which has killed more than 200 people, the majority in the Valencian Community, overflowed the river beds in a few minutes, flooded fields, streets and houses, hundreds of vehicles were swept away and bridges were demolished. 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 damage caused by the speed of the flow itself and by the materials carried by the current can also be very important.

On numerous occasions, the damage to people, buildings and infrastructure caused by these floods is due, not to the depth or time of submersion in the water, but to the impacts and burial under floating elements (such as wood and plant remains). , vehicles, containers and street furniture), or sediments mobilized in suspension or dragged along the bed (such as clay, silt, sand, gravel, pebbles and blocks).

The repercussions of flooding on homes, businesses and industries are usually associated, more than with the temporary wetting of belongings, with the mud deposited by the flood, which renders household appliances useless and deteriorates furniture. However, most flood risk studies and flood zone maps are prepared assuming that what circulates through our channels and banks is clean, almost distilled water, devoid of mud.

Hence the importance of investigating how erosion, transport and sedimentation of soil influences aggravating the danger of floods and floods. And a first step in this research should always be to collect, analyze and draw practical conclusions from the few studies and maps that have considered the role of sediments in flooding.

That is precisely what a team of scientists and professors from various research centers have done in a bibliographic compilation and review work published in the international scientific academic journal Geomorphology, in which we analyzed 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. This review of previous studies also suggests that mountain channels are perhaps more sensitive to this problem.

Flood area affected in Utiel after the DANA on October 29 captured by satellite. (Photo: Copernicus)

In conclusion, the authors of the work affirm that it is necessary to transfer this information obtained by previous scientific research work into practice and consider the sediment transport processes in a more explicit way in the risk maps due to river flooding. The new modeling tools that have been developed and widespread in the last decade can help in this work.

Therefore, when flood risk studies for a town or risk maps for the banks and banks are made, it is advisable to take more into account how much sediment and what type that river will be capable of eroding, transporting and depositing. (Source: Daniel Vázquez Tarrío, Andrés Díez Herrero, Ana Lucía Vela, Geological and Mining Institute of Spain (IGME) / CSIC)