Barcelona Field Studies Centre

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.