The environmental impact of the Spanish national hydrological plan on the lower Ebro river and delta

Abstract

The main goal of the Spanish National Hydrological Plan is the implementation of an inter-basin water transfer of a maximum of 1050 hm 3 /year from the lower Ebro River to the north and south Mediterranean coast. The plan also includes an additional list of public works of about 100 new dams and the infrastructure for new irrigation areas, as well as water treatment plants and river canalizations, etc. Taking into accout that the planned Ebro transfer would take 50 m 3 /s during 8 months, and that river flow is mostly in the interval of 150-250 m 3 /s during this period, the abstraction would repesent between one-third and one-fifth of the Ebro flow. This plan, if implemented, would have a strong negative environmental impact on the fluvial ecosystem, as well as on the estuarine and marine ecosystems, but these impacts have not been properly considered in the environmental assessment. This paper principally deals with the environmental effects of the water transfer on the area that supplies the water, downstream from the diversion point. The impact of an inter-basin water transfer on the mouth area is based on three aspects: (1) there is an increase in salinity in the delta and estuary; (2) there is a decrease in the biological productivity, mostly due to the decrease of nutrient inputs, and there are also changes in the species distribution; and (3) the river carries less sediment, which affects the geomorphology of the system. The possible effects of lower water quality and changes in the fluvial system have also to be considered. The sustainability of deltas can only be guaranteed with the allocation of an appropriate flow regime, which must include not only a liquid flow, but also a solid flow (sediment), given that deltas and coastal systems need sediment inputs (and nutrients) from the river to maintain their structure and dynamics. The classical methods of determining environmental flows in rivers are neither designed nor adequate for the objective of maintaining the deltas and estuaries in a good ecological state. The determination and implementation of an environmental flow regime not only for the river but also for the coastal and marine systems represent a new challenge for scientists and managers.