The Effects of High River Discharges on the Morphodynamics of the Guadiana ebb-tidal delta

Abstract

López-Ruiz, A.; Garel, E., and Ferreira, Ó., 2020. The effects of high river discharges on the morphodynamics of the Guadiana ebb-tidal delta. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 558-562. Coconut Creek (Florida), ISSN 0749-0208.This work analyses the role of high river discharges upon the morphodynamics of an ebb-tidal delta at a jettied inlet (the Guadiana river mouth, at the southern border between Portugal and Spain). The analysis is performed using a numerical model to simulate the effects of synthetic single high river discharge events with return periods ranging from 3 to 670 years. This model was calibrated and validated both for hydro- and morphodynamics. Results show that the area with mobile sediment over the delta varies strongly with the magnitude of the river discharge. Events peaking over 7,500 m3/s produce significant bathymetric variations at the delta, including scouring of the inlet channel, along with the offshore migration and volumetric growth of the outer shoal. Observations have indicated that the delta does not recover from these sudden morphological changes. However, the recent strong river flow regulation by dams has limited the maximum river discharges to 2,500 m3/s. Such vanishing of unusually high discharge events has affected both the short-term and long-term morphodynamics of the Guadiana ebb-tidal delta.