The National Hydrological Plan and the Ebro: the environmental problems
1. Increased Salinisation
The transfer of water from the Ebro to increase areas under
irrigation will increase the salinisation of the Delta, according to the
biologist Carles Ibáñez. The reduction in the volume of fresh water as a
result of the National Hidrológico Plan, will lead to an increase in the
penetration of salt water in the estuary of this river. The expansion of
irrigated land in the river basin will also increase the concentration of salt
in the river due to reduced flow levels. The risk is that in time the
salinisation will lead to reduced crop yields, because the rice fields and other
crops are irrigated with river water.
2. Erosion of the Delta
The regression of coastline will worsen as less sediment
arrives at the river mouth. The river now no longer floods and the 60 dams
constructed upstream have retained sediments. There is always a balance between
erosion and deposition in a delta, which affects its shape. This balance has
shifted in favour of marine erosion, which is now threatening the
ecologically-important island of Buddha. Sands deposited in the river mouth are
transported towards the end of the Banya and the Fangar, (the Delta lobes). The
Delta is not losing any surface area for the moment, but changes are taking
place in its form. This instability is a danger for the natural and agricultural
zones located close to the sea.
This loss of new sediment is also contributing to the sinking
of the delta.
3. Sinking of the Delta
Half of the Delta has already sunk to the height of sea level.
The Delta loses five millimeters in height each year, (three millimeters due to
compaction and two by the rise of the level of the sea by the global warming).
In one hundred years half of the plain will be a half metre below the level of
the sea. The consequence is the immediate entrance of salt water through the
subsoil by the hydrostatic pressure exerted by sea water.
4. Marine intrusion of sea water in the estuary
The marine intrusion of water in the estuary of the Ebro is an
impact considered only briefly in the Hidrológico Plan. The salt water entrance
in the estuary is a natural phenomenon that has increased as the volume of the
Ebro in the last decades has reduced. The marine intrusion now reaches 32
kilometers inland. If water is transferred as anticipated by the hidrológico
plan, the saline water which currently averages six months will then remain for
nine months. In dry years the phenomenon will last even longer. In 1989 the
saline wedge lasted for more than 20 months. When this water remains for a long
time, the wells near the river are salinised, which affects the citrus fruit and
other crops grown near the zones.
5. Contamination of the water
When the wedge of marine water in the river estuary remains a
long time, the water of the river rots. Salt water, that is located in the lower
level, does not mix with the better oxygenated fresh water above and the
accumulation of organic matter that this causes leads to the consumption of
oxygen and that the water ends up rotting. The lower the volume of the river,
the greater the phenomenon of rotten water. In the past, there was a thriving
fishing industry in the river estuary. Today, however, it is fished very little,
because most of the water lacks oxygen.
6. Effects upon the food chain
The fresh water arriving from the river has a fertilizing
effect on the sea through the contribution of nutrients (nitrogen, phosphorus),
that, when mixed with salt water, encourages the growth of plankton, the bases
of the marine food chain. A reduced flow will affect the plankton growth and the
food chain dependent upon it.
In addition, the estuary is an ideal location for the mixing of
sea bed organic matter through wave and river turbulence. If less turbulence
takes place due to reduced river flow, less mixing will occur and there will be
less biological wealth in the coastal strip. Furthermore, the delta of the Ebro
is very productive because the irrigation water that passes through the
fertilised rice fields arrives nutrified in the bays where a significant marine
aquaculture (oysters, mussels) has developed. If the volume of river water is
not guaranteed, this production may suffer.