The Ebro delta is the most important aquatic environment in the
western Mediterranean after the Camargue and the second largest in Spain after
the Coto Doņana National Park. Its 320 km2 form the most important wetland in
Evolution of the Delta alluvial plain
The current delta dates from the end of the last ice age when
eustatic changes lead to its growth. Sediment was transported by the Ebro river
and acted upon by marine, wind and river processes while successive changes in
sea level allowed progressive and rapid growth over the sediment platform. Thus
the delta is a relatively recent feature on the Mediterranean coastline. Indeed,
the old town of Amposta which is thought to have existed from Neolithic times
was a sea port in the fourth century. The period of most accelerated growth was
in the fifteenth and sixteenth centuries.
As the diagrams above show, the delta has continually changed
its form and many river mouths or goles have been created and abandoned.
Many of the previous distributaries provided the points from which the sediment
used to build the two extensive sand bars reached the sea and after their
abandonment these subsequently formed the freshwater lagoons.
Parts of the delta are now eroding as shown below and the 15%fall in sediment delivered from upstream, as a result of dam and reservoir
construction further up the river Ebro, has lead to widespread concern about
possible inundation by the sea. A certain amount of disagreement exists,
however, over the threat of coastal erosion.
Coastal Development induced by Wave Action.
The modern delta has been and is intensely transformed by human
activities and most of the area is now dedicated to agriculture -15,000ha. of
rice and 9,000ha. of market gardening and fruit orchards. Large expanses of
beaches, marshes and salt pans and lagoons still exist. Over 90km of unspoiled
beach remain in addition to two large open sea bays enclosed by sand bars. Both
of these sand bars enclose vast expanses of shallow water which are important
for waders and gulls. This last type of environment is rare in the Mediterranean
due to the low tidal range and is therefore of great importance.
Map of Ebro Delta showing the location of the Coastal Lagoons
and the Land Use
All of these environments suffer from intense hunting, fishing
and recently fish farming pressures.
Factors affecting Delta form
Where rivers reach the sea and are checked by the coastal
processes deposition may occur. In conditions where coastal erosion is slight or
sea level changes are taking place the formation of a delta may result. Such
coastal wetlands are environmentally diverse and have dynamic hydrological
systems where freshwater, brackish and sea water all contribute to the complex
underground layers of the groundwater. Zonation is common as are the processes
of natural vegetation succession and colonisation.
This is a diagram of the deltaic formations in accordance with
the relative importance of the river deposits (rios), the force of the waves
(olas) and the influence of tides (mareas). The shape of the Ebro River Delta
would be the consequence of a position of relative balance between the river
deposits and wave erosion, in an area uninfluenced by tides. This position can
change in time. This would be the case if, for example, the solid river deposits
diminish, due to the use of water for hydroelectric and irrigation purposes.