J.M.Alveirinho Dias * R. Gonzalez * Ó. Ferreira * * Universidade do Algarve Faculdade de Ciências do Mar e do Ambiente

4ª bacia hidrográfica (em área) da Península Ibérica Area: 66 960 km 2 Comprimento: 810 km

Discharges Escoamentos extremamente irregulares Relação inter-annual entre os maiores e os menores escoamentos anuais Guadiana - 55 Tejo - 17 Douro - 6 É o rio mais irregular da Península Ibérica

Irregularidade caudais

Variação da frequência das cheias durante os tempos históricos Ice Age

Evolução Evolution during the last 2000 years Present sedimentary distribution and main urbanizations

Delta Accordingly to descriptions by Plato and others, 2000 years ago Guadiana delta had two distributaries The eastern distributary was filled in due to natural evolution and man influences (mainly agriculture) At Present is a tipical wave dominated delta (the only oceanic delta in existence in Portugal)

Barra Evolução Sands stemming from river basins are deposited in the vicinity of the river mouths Channels and sand banks can quickly change their location. The O Bril Sand Bank at the mouth of the Guadiana River is a good example

O bril Through the interaction of waves, tides, and the outflow of the River, the sand is redistributed either further towards east by the littoral drift, or onto the inner shelf. O Bril bank has been in existence at least since the 16 th century. It reached a minimum extension after the catastrophic flood of January 1876, when it was almost completely flushed out onto the shelf.

Landsat

Mining Main man induced factors disturbing sedimentary processes: Mining loose materials dredgings railroad construction slope destabilization Deflorestation mainly for ore pre-processing Wheat Campain first half 20th century deflorestations agriculture Damming electricity production irrigation populations

Vapores Number of cargo steam ships per year in the harbour of V.R.Sto. António

Fisrt d ams First dams in the Iberian Peninsula built by Romans during 2nd century in the Guadiana River Basin Proserpina Dam in river Pardillas Cornalbo Dam in river Albarregas

Dams Sketch map of dams in the Guadiana river basin

Erosão / a cumulação The construction of jetties at the Guadiana River Mouth during the period 1972-1975, to stabilize the O bril bank mobility, led to wide coastal accumulation at the western side and strong coastal erosion at the eastern side

Armazenamento Storage capacity in the Guadiana River Basin

NAO The NAO (North Atlantic Oscillation is the dominant mode of winter climate variability in the North Atlantic region The NAO index is based on the surface pressure difference between the Subtropical (Azores) high and the Subpolar (Iceland) low Positive NAO Index - Induced by a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low. - The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track Negative NAO Index - Induced by a weak subtropical high and a weak Icelandic low. - The reduced pressure gradient results in winter storms crossing on a more west-east pathway. -Bring moist air into the Mediterranean and cold air to northern Europe

NAO-Guadi total Correlation between winter NAO index and Guadiana discharge

NAO-Giadi a ntes Correlation before the dam construction period

NAO-G iadi depois Correlation after the dam construction period

Esc 21 anos Modification of annual discharges (using 21 year windows)

Anos humidos Variation in the number of wet and dry years due to river damming

Future The Future For the foreseeable future an increase in the positive NAO index through global warming is expected. The immediate consequence of this will be a reduction in the frequency and magnitude of flood events. Additionally the influence of the human factor can only be expected to rise, as water is needed up-river for irrigation, human consumption, and electricity. The consequence will be a further decrease of sand export from the Guadiana River basin to the shelf and the coast, with severe consequences for ecosystems, and the economy.

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