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The Tagus is the largest river of Iberian Peninsula, ending
in a large tidal estuary covering an area of 320 km2.
About 110 km2 are intertidal areas; being 20 km2
occupied by salt marsh vegetation and 80 km2 by
mudflats. Morphologically the estuary can be divided into
three parts: upstream, middle and downstream sections. The
upstream part, between Vila Franca de Xira and the Alcochete
– Sacavém, has an average depth of 2 m and includes most
mudflats. The middle part is deeper (average of 7 m), and
the dowstream part reaches depths of 46 m and is the main
navigation channel of the estuary.The combined effects of
low average depth, strong tidal currents, and low input of
river water make the Tagus a globally well-mixed estuary,
with stratification being rare and occurring only in
specific situations such as neap tides or after heavy rains.
The Tagus estuary is meso-tidal and its circulation is
mainly tidally driven. The amplitude of the tide is the
controlling variable of the flowand is responsible to a
large extent for the turbidity of the Tagus, which in
shallow areas of upstream part of the estuary is enhanced by
small high frequency wind waves. The wind is however of
secondary importance for estuarine circulation. |
