Geoparque Unesco

9 Braided rivers (La Serreta de Aínsa)

Braided rivers (La Serreta de Aínsa)

Localización La Serreta de Aínsa., Detrás del Castillo de Aínsa, hacia el cementerio y con vistas al río Cinca.

Coordenadas. 264497 4701151 31 N

Textos Esperanza Fernández (Geopage)

Historically, rivers have provided elements which are vital for human beings: water for drinking, operating watermills, washing and irrigating; food in the form of fish and crustaceans; wood, willow for wickerwork and medicinal plants on their banks; gravel and sand for building; transportation of people and goods, etc. However, it is only recently that we have begun to understand that rivers have their own dynamics which are changed, sometimes drastically, by these human activities. An example is the Cinca River.

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The Cinca River

Like many rivers in Pyrenees, the Cinca is a braided river: when not in flood, the water flows through multiple channels separated by accumulations of sediment (bars or islets) which may be colonised by vegetation. Braided rivers are unstable and unpredictable, often subject to floods that in just a few days can modify the size and shape of the channels and bars.

They are formed when the water carries large amounts of coarse materials with a diameter greater than 2 mm, known as gravel. In the Cinca, this gravel comes from two places: 1 / deposits left by the ancient glaciers that occupied what is now the head of the river, and 2 / sediments produced by erosion of the soft rocks (marl) that form the substrate around Aínsa.

The river transports coarse materials during floods. In the Cinca, these can occur in spring but above all they happen during the autumnal rains; winter and summer are times of drought.

El río Cinca desde La Serreta de Aínsa. Fotografía: Ander Gómez.

Canales y barras, algunas colonizadas por vegetación, en el río Cinca. Al fondo de aprecian los materiales turbidíticos (gris) donde el río ha excavado su cauce y la terraza (tonos ocres y rojos) que está formada por depósitos del propio río en una época anterior a la actual. Fotografía: Esperanza Fernández.

The Cinca River and human history

A braided river requires two elements: sediments and floods. Any change in either of these will alter the river's dynamics. An example can be seen in the recent history of the Cinca River.

Did you know that...?

Successive aerial photos of this area, the first of which was taken in 1957, are analysed to study the changes in the River Cinca. In this way, changes in the shape, size and location of bars can be visualised. Above all, it can be seen that since 1990 there has been a dramatic increase in the number of bars colonised by vegetation. This indicates that the river is unable to move the sediments forming these bars and that, therefore, it is losing the dynamics of a braided river.

Barras colonizadas por vegetación en el río Cinca. La presencia de esta vegetación indica incapacidad del río para mover los sedimentos que forman las barras y, por tanto, pérdida del modelo de río trenzado que ha caracterizado el Cinca en épocas históricas anteriores. Fotografía: Esperanza Fernández.

Ortofoto del río Cinca en las proximidades de Aínsa. Las fotos aéreas y las ortofotos se utilizan para estudiar la evolución del río en las últimas décadas (aproximadamente desde 1950, momento en que comenzaron a hacerse las primeras fotos aéreas). Fuente: Centro Nacional de Información Geográfica.

Recomentations in your visit to Sobrarbe-Pirineos Geopark

  • Safe visits, unforgettable experiences. There are companies who collaborate with the Geopark where you can hire specialized guides to make your tour a unique and safe experience.
  • Respect the geological outcrops. Do not break off samples of rock, mineral or fossils.

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