Long-term entrenchment and consequences for present flood hazard in the Garona River (Val d'Aran, Central Pyrenees, Spain)

Abstract

Abstract. On 18 June 2013, a damaging flood of the Garona River (Val d'Aran, Central Pyrenees, Spain) caused losses exceeding EUR100 million. Few studies have related flood events to the geologic, tectonic and geomorphologic context. This study deals with both short-and long-term processes by studying the upper reach of the Garona River on different timescales and space scales. There has been a clear entrenchment tendency of the drainage network since the Miocene. Post-orogenic exhumation and uplift of the Axial Pyrenees determines the recent and active tectonics of the area and leads to fluvial incision. The last Upper Pleistocene glaciation affected Val d'Aran and gave rise to a destabilization period during the glacial-interglacial transition, marked by a postglacial incision tendency. Mean entrenchment rates between 0.68 and 1.56 mm yr −1 since deglaciation have been estimated. The assessment of the 2013 flood, characterized by the predominance of vertical incision and bank erosion, suggests that the long-term tendency of the fluvial system is reflected in short-term processes. The study of the geologic and geomorphologic evolution, combined with the analysis of this 30-50-year return period flood event, helps to improve flood risk management by providing contextual information that can constrain predictions and help guide choices and decisions. In fact, the millennial entrenchment tendency is shown at the human scale, which is considered useful for river management, but could be imperceptible in detailed hydrodynamic and channel morphology studies that describe river dynamics mostly at the 10-15-year timescale.

Impacts of future climate and land cover changes on landslide susceptibility: regional scale modelling in the Val d’Aran region (Pyrenees, Spain)

“…On June 17 th and 18 th 2013, multiples landslides and important flooding occurred in the Val d'Aran region due to a combination of both heavy rainfall and snowmelt causing a total economic loss of more than 100 M€ (Oller et al 2013;Victoriano et al 2016;Shu et al 2019). Rainfall of 124.7 mm in 48 h and 101.2 mm in 24 h were measured at the meteorological station of Vielha, while reports from the meteorological and water agencies indicate significant amount of snowmelt before and during the rainfall episode (CHE 2014).…”

Evidencias dendrogeomorfológicas de inundaciones en la cuenca alta del río Noguera Pallaresa (Pirineos, España)

“…On 17-18/June/2013, there were significant rainfalls and snowmelt in the Val d'Aran and the headwaters of the Noguera Pallaresa and Flamisell, which caused significant flooding in the Val d'Aran (Victoriano, et al, 2016). At gauging station 9267 -Capdella, a significant flow peak was observed, higher than those of 2007, 2008, 2011, and 2015, although no flooding is documented for that occasion.…”

First Captive Breeding Program for the Endangered Pyrenean Sculpin (Cottus hispaniolensis Bacescu-Master, 1964)

“…During the summer of 2013, there was a devastating flood in the Garona River-caused by heavy rainfall and a big fast snow melt-with an estimated return period (RP) of 30-50 years [22][23][24]. Changes in the river course and the subsequent arrangement by the machinery led the Pyrenean sculpin populations to a limit situation: only 16 individuals were captured during several samplings along most of the Spanish distribution area in 2014 [17].…”