sábado, 6 de março de 2010

The São Francisco Delta

The São Francisco river delta is widely considered as a paradigm of a wave-dominated delta.
Deltaic Depositional Systems (Galloway 1975)

São Francisco Delta Depositional Model (Dominguez 1996 - The São Francisco strandplain: a paradigm for wave-dominated deltas?. Geological Society Special Publication no. 117, p.217-231) (click to enlarge)
 The São Francisco Delta - Landsat-5 Image

During the last decade widespread erosion has affected the delta's shoreline as a result of extensive river damming. Erosion has resulted in the complete destruction of a small village named Cabeço (see pictures below). Last week I had a chance to flyover the river mouth and take some pictures (see clip).

It is interesting to see that although the shoreline is eroding there  is still a lot of sand available at the river mouth (see clip). Sometime in the future waves might move all this sand landward mitigating shoreline erosion.

Photo taken 28/02/2010 during overflight

Photo taken 1994 during overflight (compare with previous photo)

Photo taken 1998 when the Cabeço village was destroyed. The lighthouse is the same shown on clips and overflight photos.

Shoreline erosion is a major concern on all modern dammed rivers. Dams retain riverborne sediments that otherwise would nourish the shoreline.

Sobradinho reservoir (Source: http://www.eosnap.com/)

The Sobradinho reservoir, built on the São Francisco river,  is one of the largest artificial reservoirs in the world, with an area of 4,214 square kilometres (1,627 sq mi). Its  storage capacity is 34.1 billion m3 of water. Note in the satellite  image above the sediment plume trapped in the reservoir.

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