Evolución y dinámica geomorfológica actual del río Ebro en la Reserva Natural Dirigida de los Sotos y Galachos (Zaragoza)

Abstract

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Nature-Human-River Relationships at the Ebro River and its Delta (Spain)

“…On the outer riparian/floodplain fringes, brambles and meadows with an abundance of nitrophilic species dominate. In the border near the water flow and on the sediment bars, different species of Salix are being replaced by Populus nigra and particularly Tamarix gallica and T. canariensis, all of which have expanded in the last 40 years (Najes et al 2019). The enormous aesthetic and bioclimatic values of the Ebro riparian forests are remarkable, providing a humid belt of atmospheric freshness in the midst of the arid Depression.…”

“…Another significant feature are the galachos or ancient cut-off meanders, for their dynamics and ephemeral nature. The most prominent, still preserving a surface sheet of water, are those of Boquiñeni, Juslibol, La Cartuja, La Alfranca and Osera (Najes et al 2019, Peño 2019. Galachos that were disconnected from the river between 50 and 100 years ago generally lack surface water, or it is too shallow to be seen under the dense tapestry of helophytes (reeds and cattails).…”

“…30.21) is strikingly similar to that of other river basins (see, e.g., chapter on Loire, this volume), namely: i) simplification (reduction of branching and morphologies), ii) stabilization and reduction of lateral dynamics, iii) plant colonization within the channel, iv) narrowing of the channel and v) incision of the riverbed (by up to 2 m). This tendency is very well documented for the Ebro (Ollero 2010, Cabezas et al 2009, Magdaleno and Fernández Yuste 2011, Magdaleno et al 2012, Najes et al 2019) and a slow-down has yet to be observed.…”

“…An extreme example is the cutting of the natural meanders and total channeling of the last 13 km of the Arga River (Acín et al 2011). The situation of the floodplain forests is worrying, evidenced by losses of biodiversity and complexity, drought symptoms, and high tree mortality (Najes et al 2019).…”

Updated knowledge on floods and risk management in the Middle Ebro River: The “Anthropocene” context and river resilience

“…As a result of these works, the fear to the river is lost and the crops are moved towards the banks, gradually reducing the river space (Horacio et al, 2019) and increasing the exposure to risk. A new period of floods (June 1977, winter-spring of 1978, December 1980and January 1981 generates significant damage and a new wave of defense actions takes place that complete the dikes, avoiding totally the dynamics of any meander (Ollero, 1992;Najes et al, 2019), considerably simplifying the channel (Ollero et al, 2015). With all this, a defense system has been created that destroys the fluvial dynamics, but it is ineffective and requires continuous maintenance, although the scarcity of floods between 1981 and 2003 seems to consolidate it and gives security to the riverside population, completing the vicious circle by increasing once more the agricultural and urban exposure in a flood zone (Ollero et al, 2017).…”