How the Roman dam that saved a village from flooding in Spain is made and how it works

A video is currently making the rounds showing an ancient Roman dam from the 1st century AD protecting the village of Valencia from the tragic flood that devastated Valencia. Almonacid de la Cuba in the province of Aragon in Spain, not far from the city of Zaragoza. Here the bad weather produced by the arrival of a DANA (i.e. a low pressure “cold drop” at high altitude) caused the river to flood Aguasvivas and a resulting flood, which however was partially contained by the Roman dam, which is part of a group of dams built by the Romans in Spanish territory, to limit problems relating to the availability of water in the areas of interest which, at the time of construction, suffered scarce – or in any case uneven – rainfall during the year.

The structural system of the dam that fought the flood in Spain

The dam has a height of 34 meters and represents, to date, the highest still existing Roman dam in the world. From a structural point of view, it presents a peculiarity, as it is the only one in the group of works that has undergone a reconstruction (the one that later reached the present day) which it differed radically from the original work. In fact, originally the dam was made up of a structure of three arches, while in its reconstruction (necessary following some fractures generated on the arches themselves) it became a so-called gravity dam.

What does gravity dam mean? Let’s talk about one structure equipped with such a geometry and mass capable of counteracting the hydrostatic pressures of the water (i.e. those that the water transfers when it remains still inside a container, so to speak) which is located on the back of the wall facing. In essence, a gravity dam is capable of “transform” a horizontal force, that is the push of the waterin an inclined force with a preponderant vertical component. In these conditions, the structure does not overturn or slide under the pressure of the water, but rather brings its weight and the indirect effect of the thrust back onto the foundation soil. Having a large surface area available to distribute these large forces at play, the foundation of the dam structure easily guarantees the balance of the entire work and, therefore, the ability of the dam itself to store a suitable quantity of water.

Geometry and materials of the Roman dam

The load-bearing wall facing of the arched structure (i.e. that of the pre-intervention dam) reaches thicknesses between 10 and 12 meters in the central partinterspersing various types of building materials typical of Roman engineering and architecture, such asOpus Caementicium (i.e. a fluid mixture of lime, sand and water, possibly mixed with crushed stone) e Opus Incaertum (wall facings made with irregularly shaped stones and exposed faces, completed with mortar). In the subsequent gravity reconstruction, the thickness of the load-bearing wall also reached approximately 40 m, adding in the outermost part Opus vittatum (wall facings made up of bands of bricks interspersed with blocks of tuff, all horizontally). while the original wall also had to guarantee an important hydraulic seal of the work, the added part – especially towards the valley – only had the task of strengthening the structural section of the wall and could therefore have poorer waterproofing characteristics.

How did the Roman dam counteract the inundation of Almonacid de la Cuba from the flood

Simply, the dam resumed/continued to perform its functionor what it was designed for. The presence of a wall still solidand capable of containing the water coming from‘enlargement of the river due to the significant atmospheric precipitation, made it possible to obtain a partial commissioning of the damwhich therefore has possessed water and slowly brought it back downstream, avoiding disasters for the surrounding towns. In the videos circulating online you can see a part of the water which in any case flows laterally to the barrier: in that area the wall facing is not present throughout the entire height, this therefore becomes a preferential path for the motion of the water which, as happens in an overflow, falls towards the valley, flowing freely, but with quantities limited by the presence of the reservoir produced by the dam.

The Almonacid de la Cuba dam: the historical context

Together with other dams built in the basin Ebro riverthe Almonacid de la Cuba dam served to diverge and control the flow of water in this region of central-eastern Spain which at the time was the province of Hispania Tarraconensis. Together with the dams La Pared of the Moros, Muel And the Ermita de la Virgen del Pilarthe Almonacid de la Cuba dam was a part of the Roman hydraulic system aimed at rationalizing water consumption in an area of ​​Spain not particularly rich in waterways. These dams were built in the Roman imperial era, between the 1st and 2nd centuries AD. The Almonacid de la Cuba dam has been dated more precisely (thanks to carbon-14 taken from some preserved wooden elements of the structure) to the time of Emperor Augustus (31 BC – 14 AD), who among other things founded the nearby city of Cesaraugustathe current one Zaragoza.