Assut de Xerta, Diversion dam in Cherta, Spain

Assut de Xerta is a diagonal dam built across the Ebre River between Xerta and Tivenys, about 3 km upstream of Xerta. It is 310 m long, 3.50 m wide at the crest and 6 m high, with a foundation 35 m wide. A central spillway runs its full length, and gates at each abutment feed the Right and Left Ebre canals. The Renaissance flour mill of 1575 stands on the right bank.

Medieval documents show no dam existed before the 1440s, when Tortosa built it using the lost-stone technique with masters Domingo Xies, Antoni Alcanyiç and Bernat Gual. It was declared a Cultural Asset of National Interest in 2002, but the Supreme Court annulled that status in 2005; it is now protected as a Local Cultural Asset.

This dam showcases traditional Catalan water management skills through its hand-built construction and design. It represents generations of knowledge about directing river flow for agricultural needs.

The best views of the dam structure can be seen from both riverbanks, where the water channels and distribution systems are clearly visible. Access is relatively straightforward since the site sits along the main route through the region.

The structure uses a system of ancient water channels that works entirely without modern pumps, relying only on natural slope to move water. This principle shows how engineers over centuries understood and used the river's natural geography.