Guadiana


The Guadiana River, or Odiana, is an international river defining a long stretch of the Portugal-Spain border, separating Extremadura and Andalucia from Alentejo and Algarve. The river's basin extends from the eastern portion of Extremadura to the southern provinces of the Algarve; the river and its tributaries flow from east to west, then south through Portugal to the border towns of Vila Real de Santo António and Ayamonte, where it flows into the Gulf of Cádiz. With a course that covers a distance of, it is the fourth-longest in the Iberian peninsula, and its hydrological basin extends over an area of approximately .

Etymology

The Romans referred to the river as the Flumen Anas, the "River of Ducks". During the Moorish occupation and settlement, the name was extended and referred to as Wadi Ana, later passed on to Portuguese and Spanish settlers as the Ouadiana, and later just Odiana. Since the 16th century, due to Castilian influences, the name has slowly evolved to take on the form Guadiana, a cognitive variation that developed from many Moorish-Arab river place-names using the prefix guad-.

Watershed

The Guadiana flows east to west through Spain and south through Portugal, then forms the Spanish-Portuguese border; it flows into the Gulf of Cádiz, part of the Atlantic Ocean, between Vila Real de Santo António and Ayamonte. It is long, of which are within Spanish territory, within Portugal, while are shared between the two nations. About 82 percent,, of its basin is in Spain, while about 17 percent, is in Portugal.

Course

From its origin/spring runs from the southern Iberian plain in a direction east to west, to near the town of Badajoz, where it begins to track south leading to the Gulf of Cádiz. The Guadiana marks the border of Spain and Portugal twice as it runs to the ocean: first, between the River Caia and Ribeira de Cuncos, then later from the River Chança until its mouth. The river is not used to completely mark the boundary between the two states; between the Olivenza ravine and the Táliga ravine, the border still remains a disputed section claimed de jure by both countries and administered de facto by Spain.
For the most part, the Guadiana is navigable from the Atlantic Ocean until Mértola, a distance of. North of Mértola on the Guadiana is the highest waterfall is Southern Portugal called Pulo do Lobo.
The ecosystem has Mediterranean hydrological characteristics, including high variation in intra- and inter-annual discharge, large floods and severe droughts. This variability is a consequence of considerable variation in rainwater supply averaging around an annual mean of. The climate is semiarid with an average annual temperature of.

Estuary

The river empties into the Gulf of Cadiz between Ayamonte and Vila Real de Santo António, the two highly touristic regions of the Algarve and the sea-side of Andalusia There it forms a saltmarsh estuary. The estuary has a maximum width of, and its depth ranges from. Tides are semi-diurnal, ranging from ; their upriver propagation is limited by falls situated from the mouth at Moinho dos Canais. In the lower estuary there are nature reserves covering a total of ; in Spain, the Marismas de Isla Cristina and, in Portugal, the Reserva Natural do Sapal de Castro Marim e Vila Real de Santo António ; they give a valued nature conservation character to the region.

Human impact

In Spain, three autonomous communities, are crossed by the Guadiana. Meanwhile, in Portugal the river crosses the regions of Alentejo and Algarve, and the districts of Portalegre, Évora, Beja and Faro.

Dams

There are over 30 dams on the river basin. The following are the dams on the Guadiana river itself: