Publicaciones sobre hidromorfología

The Ebro River in the 20th century or the ecomorphological transformation of a large and dynamic Mediterranean channel

In the first decades of the 20th century, the Ebro River was the Iberian channel with the most active fluvial dynamics and the most remarkable spatial-temporal evolution. Its meandering typology, the dimensions of its floodplain, and the singularities of its flow regime produced an especially interesting set of river functions.

The largest dynamics of the Ebro River are concentrated along the meandering profile of the central sector. During the 20th century, this sector experienced a large alteration of its geomorphological structure. We present here an analysis of this evolution through the cartographic study of a long segment of the river (~250 km) in 1927, 1956 and 2003. The results show a large reduction in bank sinuosity, a progressive loss of fluvial territory, and a large decrease in channel width. These changes are especially clear in the areas previously most ecologically connected with the active channel. The fluvial territory of the river in 2003 was approximately half that found during the first decades of the 20th century. Forest plantations, which were non-existent in 1927, occupied more than 1500 ha of the study area in the last decade.

This intense geomorphological transformation becomes ecologically visible in (i) a 35% reduction of the area occupied by riparian vegetation; (ii) a loss of the heterogeneity of riparian forest spots, which were formerly structured in an irregular mosaic far from the river thalweg; and (iii) a modification of the riparian forest structure, which is currently linear, uniform, thin and very close to the river axis. The ecomorphological alteration was intensified by the remarkable reduction in bank length (13%) and the reduced dynamism of the present river system, indicated by an increase in the percentage of fluvial territory occupied by riparian forests and a reduction in the area occupied by the active channel.

  • Autores: Fernando Magdaleno, José Anastasio Fernández y Silvia Merino
  • Publicado en la revista Earth Surface Processes and Landforms  •  Diciembre 2011
  • Descargar: primera página del artículo (PDF)
Meander dynamics in a changing river corridor

In the first decades of the twentieth century, the Ebro River was the Iberian channel with the most active fluvial dynamics and the most remarkable spatial–temporal evolution. Its meandering typology, the dimensions of its floodplain (with an average width > 3.0 km), and the singularities of its flow regime produced a especially interesting set of river functions from the perspective of the fluvial geomorphology of the largest Mediterranean channels.

The largest dynamics of the Ebro River are concentrated along the meandering profile of the central sector. During the twentieth century, this sector experienced a large alteration of its geomorphological structure. We present here an analysis of this evolution through the cartographic study of a long segment of the river (~ 250 km) in 1927, 1956, and 2003. The study is focused on a wide set of geomorphic parameters and indicators that represent the forms of the meander belt, its lateral dynamics, and the overall mobility of the river corridor. The results of the analysis show a large transformation of the meander dynamics, as well as a massive loss of the river lateral activity, most of which occurred in the second half of the twentieth century. This intense geomorphological transformation becomes visible in (i) the large reduction of the bankfull width and the active channel area; (ii) the decrease in the rate of lateral channel migration; (iii) the loss of channel activity; and (iv) the large reduction of coincidence of the active channel areas. However, the most traditional form parameters (i.e., wavelength, amplitude, radius of curvature, and meander length) do not show significant differences throughout the time interval analysed. The study reinforces the necessity of integrating a wide range of dynamic indicators, which may complement the classical form parameters and represent the real functioning of the river corridor, in the geomorphological analyses of meander dynamics.

This work also shows the most important procedures for the recuperation of the ecomorphological processes of the meander belt. It highlights the most urgent measurement for ecological recovery and illustrates the management scenarios that have led to the present-day situation of the river system. This work further highlights the management scenarios that could be most important for the continued good status of the meander dynamics in this changing river corridor.reduction in the area occupied by the active channel.

  • Autores: Fernando Magdaleno y José Anastasio Fernández
  • Publicado en la revista Geomorphology  •  Volumen 130  •  Julio 2011  •  páginas 197-207
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Hydromorphological alteration of a large Mediterranean river: Relative role of high and low flows on the evolution of riparian forests and channel morphology

This paper evaluates the causes and effects of the hydrogeomorphological alteration of the central reach of the Ebro River (NE Spain). The Ebro River is one of the largest Mediterranean rivers. In this reach, it develops a meandering planform in a wide floodplain. Geographic Information System (GIS) analyses of historic aerial photographs, analysis of hydrologic data and measurement of various indicators linked to the fluvial morphology and the structure and distribution of the riparian vegetation led to the establishment of the prevailing processes in the dynamics of this river.

Statistical analyses conducted on some of the main components of the flow regime, including floods, droughts and flow duration curves, showed a role for these components in river dynamics. Similarly, a thorough analysis of the evolution of the aforementioned indicators was performed to identify and measure the effects of the hydrological regulation of the river. These indicators were measured in 1927, 1956 and 2003 for a 106 km reach.

The geomorphic dynamics of the Ebro River in its central reach reflect a remarkable tendency for stabilization and rigidification of the channel. The active river corridor has largely been modified, primarily in the second half of the twentieth century. The corridor lost a huge portion of its width and extension, the channel suffered an intense narrowing and the natural mobility of the meander train decayed proportionally. The structure and distribution of the riparian vegetation were completely transformed. The riparian forest lost its original function, behaving as a linear corridor and was notably continuous and very close to the channel thalweg. The vegetation colonized most of the previously active channel, contributing to the loss of the natural dynamics of the river.

The hydrological analyses suggest that the large morphological modification of the river planform and the parallel alteration of the riparian forests are not to be seen as a consequence of a loss of the attributes of natural floods. On the contrary, these extreme hydrological events only generate slight alterations due to river regulation and are not capable of enhancing the aforementioned evolution. Nevertheless, a profound change in the attributes of the low (summer) flows was found. The modification of the low flows was studied through its relationship with the global evolution of the geomorphic indicators and the riparian forest indicators. The results show the relative role played by high and low flows in the evolution of the river dynamics. These results are used to propose a future scenario of ecohydrological management in the central reach of the Ebro River. This scenario is intended to improve its ecological status and recover, at least partially, its natural dynamics.

  • Autores: Fernando Magdaleno y José Anastasio Fernández
  • Publicado en la revista River Research and Applications  •  Volumen 27  •  Marzo 2011  •  páginas 374-387
  • Descargar: primera página del artículo (PDF)
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