Bed improvement and bank upgrading of Torrent Gros, Manacor Highway–Vella de Sineu Highway. Municipality of Palma

The project

There was only one river in the Balearic Islands until the late 19th century. Located on the island of Ibiza, water was always flowing through it until it finally disappeared due to increased exploitation of the aquifers around it as tourism boomed.  

However, there are plenty of wadis in the Balearic Islands known as torrentes. These are beds that remain dry for most of the year and become discontinuous channels of surface water at times of heavy rainfall or sudden thaws.

Spain has regions that are highly affected by drought problems and other areas that suffer the hardships of highly localised heavy rainfall events. The Balearic Islands enjoy a typically Mediterranean climate.  It is characterised by scant and irregular rainfall that is usually heavy at the end of the summer. The water-channelling torrentes have open beds and sometimes a high erosion and transport capacity, which is why there are frequent deposits of sand, gravel and other sediments of diverse origin.

The course of Torrent Gros is quite straight and runs for a total of 23.55 km. Its hydrographic basin is one of the largest on the island, 208 km², hence its name, which means Large Wadi. It results from two other wadis merging together, Esporles and Bunyola, which means its source is in the Serra de Tramuntana mountains. It runs through the municipalities of Marratxí and Palma before flowing into the Bay of Palma at Coll d’en Rebassa.

Along the stretch where there are two 90º changes in direction, the banks of Torrent Gros divide the urban area from cropland in the countryside with no containment measures and, therefore, there is a high risk of the wadi overflowing and causing flooding.

The work to be performed entails the construction of a low-water channel bordered by walls comprising gabions in electro-welded mesh, the containment of the edge of flood terraces by forming berms with unused excavated soil and the use of hydroseeding on the terraces and the bed, formed by perforated concrete slabs.