73 towns underwater at once: the scale of the Valencia flood

73 towns under two metres of water at once

On 29 October 2024, the Poyo ravine turned a strip of about 20 by 10 kilometres of the Valencia metropolitan area into a sea. It was not the usual half-metre puddle in a square: 73 towns were flooded simultaneously, with up to two metres of water for some six hours. The capital emerged unscathed. Everything around the new Turia channel did not.

The debate in the trinc weeks split in two. Some argue that no engineering work could have channelled that volume; others believe something could — and should — have been done beforehand. In between, dozens of videos, maps and documents circulate that should be sorted without fuss.

The real scale: channels that widened by 500%

The Poyo ravine rises in the Sierra de Chiva and flows into the Albufera. Its basin, together with those of the Pozalet and Saleta ravines, covers about 450 km², with a drop of over 1,000 metres in just 50 kilometres of channel. Little surface area and a steep gradient: the perfect recipe for turning torrential rain into a brutal flow.

Downstream of Chiva, in Cheste, the flood was of such magnitude that the channel widened by up to 500% compared to what it measured the day before. The road that crossed it disappeared, asphalt included, leaving hardly any debris. And that was not an isolated episode: at the same time, Manises airport was flooded, the V-30 poured water into the new Turia channel, the Silla track at Catarroja became a river and the AP-7 bypass at Calicanto swept away everything in its path. All at once, in a strip that in some places exceeded 40 kilometres.

Utiel and Turís recorded the highest rainfall accumulations. Turís drains into the Magro, not the Poyo. Had it drained into the Poyo, the human toll would have been even greater.

Could the Poyo flood have been prevented?

This is the core of the dispute. One side argues that the Poyo, with an estimated flow of 1,800 m³/s for a 500-year return period, lacks the physical capacity to evacuate such a volume. The comparison repeated: the Turia was flowing that day at over 2,200 m³/s and was already overflowing in Quart de Poblet. Adding an extra channel of 700 m³/s would have caused, according to this calculation, water to back up into the upper area and devastate Manises, Xirivella or Paterna before solving anything.

Against that, another side recalls that dams, weirs and flood detention dikes exist precisely to slow the peak flow before it reaches urban areas. Dutch and French systems are cited, with equally flat plains managed by regulation reservoirs. "I don't agree that it can't be done; in France they channel water in a brutal way with hardly any height differences," summarises someone with first-hand knowledge of those works.

One detail dismantles part of the noise: the surrounding terrain is not flat. Even a minimal slope — the new Turia channel drops only 0.3% — is enough to generate flows of several metres per second when the discharge is enormous. That is why laboratory models, with their slides, do not reproduce what happens at real scale.

The new Turia channel and the shadow of 1957

Valencia city was spared. And not by luck. After the 1957 flood, the Turia channel was diverted through the so-called Plan Sur, a project designed in Franco's era that moved the river away from the city centre. Thousands of homes and much of the city's layout now rest on that decision.

That same fact is used in both directions. For some, it proves that when works are carried out, they work. For others, it marks the limit: the Plan Sur managed a river with a known regime, not a ravine torrent that overflows any historical record. The new channel itself overflowed at its mouth, flooding Pinedo.

Reservoirs, alerts and the fine print of dams

Much of the public anger was directed at the opening of reservoirs. The narrative of massive releases over towns without warning has little basis in the Poyo channel: there are no dams there that can spill. There are at other points, such as the Magro, where releases are blamed for the deaths of about ten people, a figure that should be treated with caution until officially confirmed.

What does command broad consensus is the late alert. That the warning to the population came when water was already flowing through the streets of Paiporta is a failure difficult to dispute. Most analyses agree that a timely warning and road closures would have saved lives, even if they would not have prevented the flooding.

Urban development in flood zones: the wound of Paiporta

The other major reproach points to bricks and mortar. Paiporta and several municipalities in southern Valencia grew right next to ravines and at elevations that risk plans marked as floodable. The question is why those rezonings were approved and why no one reviewed them.

Here the nuance matters: much of the flooded area was farmland, not housing developments. The water swept away entire plots of orchards. That leaves open the debate over whether the problem was building where one shouldn't or whether, simply, the event exceeded any foreseeable risk category.

What the Júcar Confederation already warned

One of the most widely circulated documents is a 2006 report by the Júcar Hydrographic Confederation. Even then it described the Poyo, Pozalet and Saleta basin and estimated the expected flow. The report, according to those who cite it, proposed defence measures that were never implemented.

The conclusion drawn is not that a complete solution existed, but that the risk had been identified for two decades. That no one moved on the ravine or in urban plans is the reproach that survives all versions.

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Could this flood have been prevented? Probably not. Could the death toll have been reduced with a timely warning? Almost certainly, yes. The question is why that answer was sought after the water and not before.