The flood was caused by a cold drop (gota freda)[1] with heavy rain, overflowing the Llobregat and Besòs rivers.

[4] The geological characteristics of the area, with sedimentary and clayey terrain, meant that the bed of the stream was full of clay, pebbles and gravel.

[5] The economic development of Vallès in the 1940s and 1950s led to a population increase, which meant the construction of buildings close to the rivers, both homes and industries, with a marked lack of urban control.

The flood that affected the populations of Terrassa, Rubí, Sabadell, Sant Quirze, Cerdanyola del Vallès, Ripollet, Mollet del Vallès and Sant Adrià de Besòs caused between 617 and 1000 deaths, thousands of injured and economic damage of 2650 million pesetas being the largest natural catastrophe in the history of Spain.

People knew about the damage that occurred when the rivers receded, but the problem was that construction was allowed in their surroundings, making the catastrophe exponentially worse.

The flood devastated the factories located in the upper part, demolished several houses and dragged cars to the Rambleta.

On the other hand, the Arenes stream diverted its course in the blocks of the Sant Llorenç groups and flowed through an old channel, devastating the current Ègara neighborhood on the right bank, the triangle of death where it caused more than a hundred victims and demolished a large part of the houses.

The population of Sant Quirze del Vallès, then San Quirico de Tarrasa, was affected by the overflowing of the Sec river, that when flowing through Los Rosales neighborhood caused several victims and material damage.

[12] The entire Vallès area was declared in a state of emergency, with the consequent help of all types of public and private organizations such as the Red Cross, the Spanish army, administrations, associations, unions and the voluntary civilian population through material support or with the opening of accounts for aid to the affected Catalan population.