Geology and Geomorphological Evolution of the Ebro River Delta

Abstract

From a geological perspective, deltas are ephemeral geomorphic systems whose development is controlled by the sensitive equilibrium between fluvial sediment supply, global sea level, wave-induced energy and regional subsidence. Once this equilibrium is lost, the delta may start to retreat and eventually disappear. The ephemeral character of deltas is a serious threat to their lands, as well as to the economic activities developed in these areas for centuries. This is the case of the Ebro Delta, the third largest delta in the Mediterranean area, which is extensively used for agriculture and includes a Natural Park with special significance for migrating birds. Historically, the geomorphological features of the Ebro Delta have been controlled by the discharge of the Ebro River that used to supply large amounts of sediment during flood events. This sediment is redistributed along the coast in response to wave-induced sedimentary dynamics. However, the construction of dams during the twentieth century has drastically changed the equilibrium responsible for the previous morphological evolution of the delta. Nowadays, after the drastic reduction in sediment supply to the delta, the wave-induced processes cause strong erosion during storm events and rapid littoral drift affecting the shape of coastal landforms. This chapter shows the morphological evolution of the Ebro delta over the last 8000 years in response to the deceleration of Holocene sea-level rise, along with its most recent evolution and the predicted future morphology of delta according to the climate change scenario of the IPCC.