[en] Flood forecasting in mountain areas is limited by the complexity of triggering meteorological instabilities (convective storms with high orographic influence), the rapid hydrological response of the watersheds (flash floods) and the variable sediment load of the resulting torrential flows (stream, hyperconcentrated or debris flows). Thus, in order to define fluvial and torrential activity for an adequate hazard assessment, a research for different alternatives needs to be done. Systematic and paleohydrological methods have additional drawbacks when applied to mountain environments lacking complete and accurate data sources. At this point, a comprehensive understanding of a system could be reported by adopting a holistic approach that combines all the available evidences in the area and their potential analysis methods, correlating the obtained results according to their reliability and uncertainty. The main objective of this work was to develop and integrate as many methods as possible to characterize the hydrogeomorphological activity of the Portainé catchment (Eastern Pyrenees), which shows high torrential risk. Given the scope of the study, it was divided in two stages depending on the subject under consideration: basin-scale and channel-scale assessments. On the one hand, the catchment was investigated in its entirety through widely tested structural, sedimentological, geomorphological, historical, dendrocronological, pluviometric and land-cover mapping methods. This allowed us to collect and analyse torrential flows and anthropogenic alterations that played out during last decades. On the other hand, temporal changes and extraordinary events along main torrents were reconstructed in detail using multi-temporal airborne LiDAR data and hydraulic modelling, respectively. In this case, large uncertainties arise from conventional techniques as long as mountain catchments lack of reliable discharge and rainfall time series. Two novel methodological approaches were developed so as to face this challenge. First, sequential digital elevation models (DEMs) were analysed accounting the spatial variability of errors on a section-by-section basis along channels. Second, a more consistent paleoflood reconstruction was obtained by combining geomorphology, dendrogeomorphology, flow hydraulics and hydrodynamics. This research involves new paleohydrological contributions for ungauged and densely forested torrential catchments. In the field of remote sensing, an effective appreciation of DEM errors and real geomorphic changes was achieved, which allowed magnitude and pattern of erosion-deposition phenomena to be quantified and sediment budget volumetric calculations to be optimized. Moreover, the geomorphic impact of flexible sediment retention barriers was also estimated, providing new tools for a high-resolution assessment of the behaviour, effectiveness and stability of engineering structures in remote areas that are hardly reached in the field. Regarding the dendrogeomorphic paleoflood reconstruction, the distribution of external disturbances was analysed in terms of their geomorphological position and flow energy. Differences between scar height and modelled water surface were also compared. This revealed that, while most reliable scars for peak discharge estimations are those from trees located on intermediate energy forms (alluvial terraces and fans), the riverbed and lateral slopes are prone to greater errors. The results achieved confirm that small mountain catchments are highly sensible to human activities. The study case shows that there has been an intensification of torrential processes in the 21st century, with an annual recurrence of torrential flows present-day. This tendency differs from the approximately 5-year interval recorded during the 20th century. Considering the non-variability in time of triggering rainfalls, this phenomenon must be related to changes in soil conditions, essentially resulting in lower rainfall interception and higher surface runoff. Those factors have provoked the geomorphological threshold to be exceeded and the transport capacity of the torrents to be increased. Their evolution is now strictly conditioned by the interaction of the natural river dynamics and debris flow protection measures. In conclusion, the integration of multidisciplinary methodologies enables a robust approximation to hydrogeomorphic behaviour in catchments lacking direct data or with limited indirect evidences. Even if such a study requires a thorough interpretation of the results according to site characteristics, it can also be adapted and extrapolated to other mountain torrential systems.

[eu] Mendi inguruneetan garatzen diren uholdeen iragarpena oso mugatua da, batez ere ezegonkortasun meteorologiko sortzaileen konplexutasuna (efektu orografiko handiko ekaitz konbektikoak), arro hidrografikoen erantzun bizkorra (bat-bateko uholdeak) eta fluxuen sedimentu kontzentrazio aldakorra (urtsuak, hiperkontzentratuak edo debris flow motatakoak) direla eta. Hortaz, beste alternatiba batzuk bilatu behar dira arroetako mendi- erreken jarduera eta honi lotutako uholde-arriskugarritasuna zehaztu ahal izateko. Metodo sistematiko eta paleohidrologikoek, ordea, zailtasun handiak erakusten dituzte eremu hauetan aplikatzen direnean, ez baitago datu iturri zehatz edota osorik. Gauzak horrela, sistema baten ulermen integrala lortu nahi izanez gero beharrezkoa da ikuspuntu holistiko bat hartzea, tokian eskuragarri dauden ebidentziak eta dagozkien analisi-metodo guztiak erabiliz, eta lortzen diren emaitzak euren fidagarritasun eta ziurgabetasunaren arabera erlazionatuz. Lan honen helburua uholde-arrisku handia erakusten duen Portainé arroa (Ekialdeko Pirinioak) hidrogeomorfologikoki aztertzeko ahalik eta metodologia gehien garatzea eta integratzea izan da. Ikerketaren zabaltasuna kontuan izanik, bi fasetan burutu da: arro eskalara eta drainatze-sare eskalara. Alde batetik, arroa bere osotasunean ikertu da metodo estruktural, sedimentologiko, geomorfologiko, historiko, dendrokronologiko eta plubiometrikoetaz baliatuz, baita lurrazal-estalkiaren kartografiaren bitartez ere. Honi esker, azken hamarkadetako mendi- uholdeak eta eraldaketa antropogenikoak biltzea eta ezaugarritzea lortu da. Bestetik, LiDAR hegaldietako datuak eta modelizazio hidraulikoak erabiliz, ibaibideetako aldaketa tenporalak eta ohiz kanpoko uraldiak zehaztasunez aztertu dira, hurrenez hurren. Kasu honetan, ikuspegi klasikoek ur-emari eta prezipitazio datu-serie zehatz gabeko mendi arroetan ziurgabetasun ugari sortzen dituztela igarri da. Erronka horri aurre egiteko, bi prozesu metodologiko berri garatu dira. Lehenengoa lurzoruaren eredu digital (LED) sekuentzialen azterketa sakon bati dagokio, non euren erroreak ibilguaren zeharkako profiletik profilera espazialki aldakortzat jotzen diren. Bigarrenak geomorfologia, dendrogeomorfologia, hidraulika eta hidrodinamika bateratzen ditu modelizatutako uholdeen berregite zintzoago bat lortu nahian. Garatutako ikerketek pausu paleohidrologiko nabarmenak dakartzate landaredi dentsodun, emari estazio gabeko eta bat-bateko uholde izaeradun arroetarako. Teledetekzioaren alorrean, LEDen erroreen eta aldaketa geomorfologiko errealen arteko bereizketa eraginkorra lortu da, higadura-metaketa prozesuen magnitude eta banaketa hobeto kuantifikatzea ahalbidetuz, eta era berean, balantze sedimentarioaren kalkulu bolumetrikoak optimizatuz. Gainera, sedimentua atxikitzeko diseinatutako sare deformagarrien inpaktu geomorfologikoa zenbatu da. Honek, iristeko zailak diren tokietan kokatzen diren neurri estrukturalen eraginkortasuna eta egonkortasuna balioztatzeko irizpide berriak dakartza. Iraganeko uholdeak seinale dendrogeomorfologikoen bidez berreraikitzeari dagokionez, landarediak erakusten dituen kanpo-kalteen sakabanaketa euren posizio geomorfologikoaren eta ur korrontearen energiaren arabera aztertu da. Enborretako zaurien eta modelizatutako ur mailaren arteko altuera diferentzia ere neurtu da. Honela, muturreko emaria kalkulatzeko erabilitako zaurien artean fidagarrienak energia ertaineko formetan kokatzen direla ikusi ahal izan da, ubide eta magalek errore handiagoak ekartzen dituztelarik. Lortutako emaitzek mendi arro txikiek giza jarduerekiko duten kalteberatasun altua uzten dute agerian. Ikerketa tokian, XXI. mendean zehar uholdezko prozesuak zeharo biziagotu direla nabarmentzen da. Izan ere, gaur egun fluxuak urtero garatzen dira. XX. mendean, ostera, hauen maiztasuna 5 urte ingurukoa zen. Prezipitazio eragileen patroi aldaketarik ez dela eman kontuan izanda, gertakari honek lurzoruaren baldintzekin lotuta egon behar du. Hain zuzen ere, azken urteetan gauzatutako lurzoru erabilerek infiltrazio gaitasuna txikitu eta azaleko isurketa areagotu dute. Faktore guzti hauek oreka geomorfologikoa gainditzea ekarri dute, baserreken higadura ahalmena handituz. Beren egungo eboluzioa ibai-dinamika naturalaren eta defentsa neurrien arteko interakzioaren emaitza da. Ondorioz, metodologia multidisziplinarrak integratzea aukera ezinhobea da datu zuzen gabeko eta zeharkako-datu eskaseko arroen funtzionamendu hidrogeomorfologikoa era sendoan aztertzeko. Horrelako ikerketa bat gauzatu ahal izateko, ezinbestekoa da emaitzak ingurunearen ezaugarrien arabera arreta handiz interpretatzea. Hala ere, aurkeztutako lana gainerako mendi-sistemetara egokitu eta estrapolatu daiteke.