ABSTRACT
The impacts of high-stage fluvial discharge events on the Upper Guadalquivir River (Southern Spain) as well as the Guadalbullón and Guadiana Menor tributaries are studied in this work. Better insight into the recent morphological evolution of the rivers was derived from consideration of the association of sediment deposits, modelled two-dimensional hydraulic conditions, riparian vegetation and instrumental data. We alert on the continuous channel narrowing of Guadalquivir River and the colonisation of bars by non-flexible riparian vegetation as observed in high-resolution orthophotos from 1956 up to present days, opposite to non-regulated tributary widen (e.g. Guadabullón river). Highly-accurate two-dimensional numerical simulations in the presence of riverbank defences and dams, which are verified with radar images from Terrasar-X satellite, show that the predominant mode of sediment transport (bedload) can be impeded by actual dams promoting sedimentation, higher water surface elevation during floods and higher risk. The main anthropogenic factors identified in the present study that increase the flood potential are: the land use legacy in the basin since Roman period, soil management and destruction of the vegetation cover in rural areas, owing to larger runoff and contributing to reservoir sedimentation, soil and gully erosion processes; non-optimised hydraulic structures that promote aggradation in the main channel and the formation of slackwater deposits that are later colonised by non-flexible riparian vegetation, decreasing consequently the water drainage capacity of the Guadalquivir River.
