An estuary is the typically funnel-shaped part of a river near its mouth where fresh- and seawater mix and which is affected by the tides. At ebb tide both tide and river current
assist in the erosion of the estuary. Estuaries
may also form by local subsidence of the coast. As well as the mouths of
rivers, estuaries may include bays, salt marshes, and lagoons.
These brackish water ecosystems shelter and feed marine life, birds, and
wildlife, but are particularly vulnerable to damage as a result of human
actions. Many estuaries provide important harbors.
|Lisbon, the capital of Portugal, is observable north
of the Tagus River estuary in this photo taken from the Space Shuttle.
The estuary of the Tagus River, the longest river in the Iberian Peninsula,
is 19km long and is considered one of the best harbors in Europe.
Visible south of the Tagus River estuary are the cites of Almada,
Barreiro, and Montijo; farther south are Setúbal Bay and the
Sado River estuary.
AND PLANETARY SCIENCE