Valencia spared but the diversion of a river worsened the consequences

SPAIN – A solution that reaches its limits. If the south-east of Spain has suffered massive floods since Tuesday due to torrential rains, the city of Valencia has been spared by the waters. An astonishing contrast, which can be explained by a choice made in the 1960s to divert the river which crossed the city, the Turia. But this movement of the river, thought of at a time when urbanization and extreme climatic events were less, today shows its limits.

This deviation was motivated by the catastrophic flood of 1957, when torrential rains dumped 300 liters of water per square meter in 24 hours on Valencia, the equivalent of a year of rain. The rising waters, which reached up to 3 meters in certain streets, caused the death of at least 81 people and the destruction of 1,700 houses.

In response to the tragedy, authorities decided to remove the bed of the Turia from central Valencia and completely reshape its course, moving it to the southern edge of the city. The colossal project was approved in 1962, and the work was completed ten years later. Since the 1970s, several episodes of flooding have been avoided thanks to this infrastructure, but this week the neighborhood of Pinedo, located right next to the mouth of the new bed of the Turia river, was flooded impressively, reports The World.

“The worst solution is to want to channel the rivers. » Clément Gaillard, urban planner specializing in bioclimatic projects in The Parisian.

“When we divert watercourses, that is to say we try to control them, we increase the speed of the flows, since when a river is straight or in the form of a canal, the water goes well faster than if there were meanders”, analyzes Amandine Richaud, urban planner specializing in the environment, on franceinfo this Friday. As a result, this deviation causes “torrents over areas that should be buffer zones to absorb water”, she summarizes.

“The worst solution is to want to channel the rivers”also said in The Parisian Clément Gaillard, urban planner specializing in bioclimatic projects.

Make soils permeable to avoid flooding

Instead, it is better to turn to the renaturation of waterways, and the establishment of buffer zones in cities: infiltration basins, rain gardens, green roofs. Thanks to these developments, the water will not run off and create powerful torrents as is currently the case in the Valencia region, but rather will infiltrate deep into the ground, which considerably limits floods.

Build this canal south of the city, “it was undoubtedly a good idea at the time when in this part of Valencia there were only orchards which formed the interface between the risky flood zone and the rest of the city. Except that today, this part of the city has been totally urbanized,” underlines Clément Gaillard.

According to his calculations, in 55 years, the agglomeration of Valence has destroyed 9,000 hectares of orchards (almost the surface area of ​​Paris) under the influence of urbanization. However, these areas are impermeable, and therefore more easily flooded.

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