Dendrogeomorphological Evidence of Flood Frequency Changes and Human Activities (Portainé Basin, Spanish Pyrenees)

Abstract

The Portainé mountain catchment, containing the Port Ainé ski resort (Lleida, Spanish Pyrenees), displays active erosional and depositional phenomena caused by periodic torrential floods. These events present a potential risk and incur significant economic losses. In ungauged remote catchments (like Portainé), trees might be the only paleohydrological source of information regarding past floods. Thus, we estimated the temporal and spatial distribution of torrential floods by dendrogeomorphological techniques to assess whether human impact (land-use changes and infrastructure works) affected their frequency and magnitude. One-hundred and sixty-six samples from 67 trees belonging to 10 different species were analyzed; past flood events of the last 50 years were identified by dating and relating evidence between them. Moreover, a detailed geomorphological study was performed and the available historical data compiled. Our multi-evidence analysis provides new insight into the occurrence of paleofloods. Changes in flood frequency since 2006, especially from 2008, suggest that the geomorphological equilibrium has been disturbed, coinciding with both major earthworks within the ski resort and intense but not extraordinary rainfall. This conclusion has important implications for land planning and the design of future projects in the mountain watersheds.

Flood Consequences of Land-Use Changes at a Ski Resort: Overcoming a Geomorphological Threshold (Portainé, Eastern Pyrenees, Iberian Peninsula)

“…Thus, the problem should not be considered exclusively by a single discipline, but in the wider context, by looking at relationships as a whole. Consequently, our approach is based on our previous, specifically focussed works carried out with different methods and with conclusive proofs and results [12][13][14][15][16][17][18][19][20][21][22] and also considers the complexity of the system as suggested by Kondolf and Piégay [23], by working with the convergence of evidence. From this scope, this paper integrates and synthesizes the results of multidisciplinary research carried out in the basin of Portainé, as only through this holistic approach can the hypothetical surpassing of the geomorphic threshold after flood events be detected and characterized.…”

“…The resulting decrease in the use of the land favoured the forest regeneration. Inferring from the ages estimated in [21] (see Section 6.3), most of the trees were progressively established in the Portainé alluvial cone since the beginning of the 1950s. During previous decades, the left bank of the stream was intensely cultivated and when this stopped, present vegetation colonized the area.…”

“…A dendrogeomorphological study was carried out in the cone, at the downstream stretch of Caners [21]. One hundred and sixty-six samples from 67 trees belonging to 10 different species were analysed, which are representative of the broadleaf forest in the downstream stretch ( Figure 12).…”

Improving Flood Maps in Ungauged Fluvial Basins with Dendrogeomorphological Data. An Example from the Caldera de Taburiente National Park (Canary Islands, Spain)

“…Ballesteros-Cánovas et al [13] and Benito and Díez-Herrero [14] provide an extensive review of the main contributions and future prospects of tree ring data analysis in flood record assessment. In addition to dating procedures from tree ring information [15][16][17][18][19][20], they have been used successfully for the estimation of flood magnitude in combination with paleo-hydraulic techniques [21][22][23]. Dendro-geomorphological data has also proved very useful for flood reconstruction in mountain areas (where data availability is scarcer), which, as a rule, are more prone to flash-floods [24][25][26], increasing the flood hazard of those events.…”

Geomorphic impact and assessment of flexible barriers using multi-temporal LiDAR data: The Portainé mountain catchment (Pyrenees)

“…Dendrogeomorphological studies have proved the occurrence of at least ten events from 1969/1970 to 2009/2010 (recurrence interval of 4.5 years), based on the dating of damage indicators on riverbank trees in different geomorphic positions (Génova et al, accepted;Victoriano et al, 2018). Torrential activity has intensified since 2006, with extraordinary flows occurring almost yearly.…”