Related news: Mallorca flooding: The four torrents with the greatest risk of disaster

The torrents of Mallorca are water courses that can be dry for much of the year but can fill, sometimes dangerously so, with torrential rains that typically fall in late summer and early autumn.

Naturally carved out across the island's landscape, some have had manmade interventions - concrete beds and walls. The concrete wasn't a decisive factor but it did contribute to the disaster of October 2018. Thirteen people, not all in Sant Llorenç , died as a consequence of torrential rain and flooding.

In the Torrent de ses Planes in Sant Llorenç there was water flow of some 400 cubic metres per second. To give this some context, the River Ebro, the longest river that is entirely in Spain, has an average flow of 426 cubic metres per second. This torrent is 12 kilometres in length, the Ebro is 930. It is very narrow whereas the Ebro, naturally enough, is wide. On October 9, 2018, almost as much water flowed through the torrent as the normal water flow of the Ebro .

According to the Balearic Islands hydrological plan, there are four torrents in Mallorca where an event similar to Sant Llorenç could occur once every fifty years.

These are the Almadrà , which rises in the area of the Cúber reservoir in Escorca and flows into Albufera on the Bay of Alcudia; Son Catlar , which meets the sea in Sa Rapita (Campos); Gros in Palma; and Na Borges , the longest of the island's torrents (forty kilometres) and which flows into the sea at Son Serra de Marina on the Bay of Alcudia.

The calculation for the Almadrà is the highest. Once every fifty years there could be 482.43 cubic metres per second; for every 25 years, 349.67 cubic metres per second every 25 years; once in 100 years, 638.40.

Potentially catastrophic calculations , they do of course depend on what lies in the immediate vicinity of a torrent bursting its banks. These calculations will come across as hypothetical, but they are the Balearic Government's own calculations and have to be considered relevant amidst what is a bitter political debate about permitting development in areas prone to flooding .

By the way, the Torrent de ses Planes ranks eighth among the calculations.

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