La turbulencia en los flujos en cauces con lecho vegetado. Estudio teórico-experimental con aplicación del "Acoustic Doppler Velocimeter" ADV

Los cálculos hidráulicos sobre flujos en canales se fundamentan en coeficientes de resistencia al flujo de los diferentes materiales de construcción. Estos coeficientes son un modelo simplificado de todos los procesos hidrodinámicos que tienen lugar en el interior del flujo, y vienen caracterizados fundamentalmente por un valor, la rugosidad absoluta. Los valores de los coeficientes de resistencia asociados a cada uno de los materiales son conocidos y están descritos en tablas. Las rugosidades flexibles son una excepción, entre ellas encontraríamos la vegetación presente en ríos y canales, se trata de materiales que tienen una respuesta elástica o semi-elástica a las cargas dinámicas provocadas por el agua, esto hace que la rugosidad absoluta dependa de las condiciones del flujo. En consecuencia para conocer en cada caso el estado de la rugosidad flexible es necesario conocer en cada caso las cargas que están actuando sobre esta, es decir no basta con las macrovariables utilizadas en la hidráulica sino que hay que realizar una descripción interna del flujo

Tsunamis generated by fast granular landslides: 3D experiments and empirical predictors

Landslides falling into water bodies can generate impulsive waves, which are a type of tsunamis. The propagating wave may be highly destructive for hydraulic structures, civil infrastructure and people living along the shorelines. A facility to study this phenomenon was set up in the laboratory of the Technical University of Catalonia. The set-up consists of a new device releasing granular material at high velocity into a wave basin. A system employing laser sheets, high-speed and high-definition cameras was designed to accurately measure the high velocity and geometry of the sliding mass as well as the produced water displacement in time and space. The analysis of experimental data helped to develop empirical relationships linking the landslide parameters with the produced wave amplitude, propagation features and energy, which are useful tools for the hazard assessment. The empirical relationships were successfully tested in the case of the 2007 event that occurred in Chehalis Lake (Canada).Peer ReviewedPostprint (author's final draft

Versatile image-based measurements of granular flows and water wave propagation in experiments of tsunamis generated by landslides

Landslides falling into water bodies can generate destructive waves, which can be classified as tsunamis. An experimental facility to study this phenomenon has been set up. It consists of a landslidegenerator releasing gravel at high-speed into a wave basin. A non-intrusive system has been designed ad-hocto be able to measure the high velocity and the geometry of the landslide as well as the generated waves characteristics. The measurement system employs the treatment of images captured by a high-speed camera which records the launched granular material illuminated by a laser sheet. A grid of laser sheets marks thebasin water surface. The water has been filled by a small amount of kaolin to properly reflect the laser lightat water surface. Thus, by filming with high definition cameras the perturbed water surface and successively processing the resulting images, it has been possible to measure the generated waves. The measurement framework employs a versatile camera calibration technique which allows accurate measurements in presence of: (1) high lens distortions; (2) pronounced non-parallelism condition between camera sensor and plane of measurement coincident with the laser sheet. The maximum resolution of the measurement tool is0.01 mm, while the maximum uncertainty due to systematic error has been estimated to be 15% for theworst-case scenario. This work improves the suitability of image-based measuring systems in granular flows and free surface hydraulics experimentsThis work was funded by GITS and the 3 years’ national project DEBRIS FLOW (CGL 2009-13039) ofthe Spanish Ministry of Education. Francesco Bregoli has been supported by the 4-years grant FPU2009-3766 of the SpanishMinistry of Education. Authors want to thank Dr. Cecilia Caldini (IDOM Consulting, Barcelona) for the 3D reconstruction ofthe laboratory setup.Peer ReviewedPostprint (published version

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

The final publication is available at Springer via http://dx.doi.org/10.1007/s10346-021-01775-6It is widely accepted that future environmental changes will affect rainfall-induced shallow slides in high-mountain areas. In this study, the Val d’Aran region located in the Central Pyrenees was selected to analyze and quantify the impacts of land use and land cover (LULC) and climate changes on regional landslides susceptibility. We analyzed 26 climate models of the EURO-CORDEX database focussing on the future rainfall conditions. The IDRISI TerrSet software suite was used to create the future LULC maps. These two inputs were analyzed individually and in a combined way defining 20 different scenarios. All these scenarios were incorporated in a physically based stability model to compute landslides susceptibility maps. The results showed that both environmental conditions will considerably change in the future. The daily rainfall will increase between 14 and 26% assuming a return period of 100 years. This intensification of precipitation will produce an overall decrease of the stability condition in the study area. Regarding the LULC prediction, the forest area will significantly increase, while in particular grassland, but also shrubs decrease. As a consequence, the overall stability condition improves, because the root strength is higher in forest than in grassland and shrubs. When we analyzed the combined impacts, the results showed that the positive effect of LULC changes is larger than the negative influence of rainfall changes. Hence, when combining the two aspects in the future scenarios, the stability condition in the study area will improve.This study was funded by the national research project EROSLOP (PID2019-104266RBI00/AEI/10.13039/501100011033) of the Spain Government. Zizheng Guo acknowledges the financial support of China Scholarship Council for his research at UPC BarcelonaTECH, and Fundamental Research Funds for National Universities, China University of Geosciences (Wuhan).Peer ReviewedPostprint (author's final draft

Quantitative analysis of the effects of incorporating laser powder bed fusion manufactured conformal cooling inserts in steel moulds over four types of defects of a commercially produced injected part

The introduction of additively manufactured conformal cooling inserts in steel moulds for plastic injection is becoming a recommended standard. Fine adjustment of the temperatures in the mould has demonstrated potential to reduce cycle times and to increase production volumes. Within this context, the present article explores the historical production data of a commercially produced part, before and after the incorporation of an LPBF conformal cooling insert, to analyse what is the quantitative real effect on the efficiency of the production runs. The article analyses the change in the global rejection rates, and its effect over four different product defect types, i.e.: optical (surface), part integrity (bubbles, transparency, geometry), incomplete fill-in (interior), and breakages during extraction. The results demonstrate a specific decrease on the average appearance (from 20.53% to 13.48%; reduction of 7.05%) and variability (standard deviation from 14.16% to 6.81%; reduction of a 7.35%), of the global scrap rates, and a significant decrease in the scrap rates generated by optical defects and extraction part breakages. The article also characterises the former and the new processes by adjusting two distribution functions (Pareto Type-I and Weibull) and compares different estimates for the global expected scrap rates in past and future production runs.Peer ReviewedPostprint (published version

A Framework to Project Future Rainfall Scenarios: An Application to Shallow Landslide-Triggering Summer Rainfall in Wanzhou County China

Fatal landslides are a widespread geohazard that have affected millions of people and have claimed the lives of thousands around the globe. A change in climate has significantly increased the frequency and magnitude of rainfall, which affect the susceptibility of slopes to shallow landslides. This paper presents a methodological framework to assess the future changes in extreme and seasonal rainfall magnitudes with climate model projections. This framework was applied to project summer rainfall over Wanzhou County, China, using an ensemble of four regional climate models (RCMs) from the East Asian domain of the Coordinated Downscaling Experiment (CORDEX) under the Phase 5 Coupled Intercomparison Modeling Project (CMIP5). The results find that extreme daily rainfall was projected to decrease in the mid-21st century, with an uncertainty measured by a coefficient of variation between 5% and 25%. The mean seasonal rainfall is projected to increase in the mid-21st century up to a factor of 1.4, and up to a factor of 1.8 in the late-21st century. The variation in the mid21st century ranged from 10% to 35%, and from 30% to 50% in the late-21st century. This case study delivered a proof-of-concept for a methodological framework to derive shallow landslide-triggering rainfall scenarios under climate change conditions. The resulting spatially distributed climate change factors (CCFs) can be used to incorporate future rainfall scenarios in slope susceptibility models and climate impact assessments.Peer ReviewedObjectius de Desenvolupament Sostenible::13 - Acció per al ClimaPostprint (updated version

Morpho-fluvial analysis of headwater catchments: an example from the Central-Eastern Pyrenees

Geomorphometry of headwater catchments has been poorly reported in the Central-Eastern Pyrenees. This study presents a series of parameters obtained for Central-Eastern Pyrenean headwater catchments. The database consists of 3,005 first-and 655 second-order catchments. These catchments have been digitalised, identified, and attributed a value for each parameter. The parameters investigated are divided into three groups: relative to catchments, relative to streams and morpho-hydrological ratios. Histograms reveal similarities between orders for some parameters such as mean slope or orientation, while stream orders seem to condition metrical parameters (area, perimeter, stream length). Streams have been fragmented to assess different values for slope. Values for slope over a small portion of the stream near the outlet seem to show clearer differences between orders. With regard to morpho-hydrological ratios, catchments show better distinctions between orders for the Melton and Lemniscate ratios than for the form factor or the basin elongation. The power-law relationship between catchment area and stream length recognised for large fluvial systems is shown here to follow a linear trend at small values. An attempt to identify the morpho-structural regionalisation differentiating the Axial Pyrenees from the pre-Pyrenees is made based on the parameters. However, applying the methodology to other environments could improve the context of the current results. Similar studies could also benefit from the development of such databases.Postprint (author's final draft

Development of preliminary assessment tools to evaluate debris flow risks

In the framework of the IMPRINTS European Research Project (FP7), a toolbox for fast assessment of debris flow hazard has been developed. The aim of this toolbox is to implement different existing models inside a common package useful for a fast evaluation of potential hazard. The initiation and propagation of the debris flow is included. One of the requirements of the projects is to define different scenarios with different detail levels in data input. As an example of this, the results could be obtained just using topographical data or improve accuracy by adding geological and hydrological data.Postprint (published version

Analysis of river bed dynamic evolution following a landslide dam

Landslides and debris flows can strongly interact with the river network and its mass transport processes, determining modifications of the river pattern with consequent effects on the hydrodynamic phenomena, alterations of the existing morphologies and possible interferences with anthropic works. Modifications of the cross section geometry and channel slope may produce changes in the sediment budget, with consequent repercussions on the stream evolutionary dynamics and its equilibrium configuration, leading to a new river branch arrangement. In this paper, investigations were carried out on a gravel-bed reach in the middle valley of the Noce River in Basilicata (Italy), which in 2007 suffered a progressive morpho-hydrodynamic change caused by a landslide. Because of the phenomenon complexity, mainly due to the mutual interaction between the landslide and the river transport dynamics, an integrated approach that combines field observations and numerical modelling in a spatial scale and natural environment, rarely available in literature, is suggested. The results highlight a satisfying correspondence between the altimetric profiles obtained through the numerical models and those deriving from the field surveys.Peer ReviewedPostprint (published version

Análisis de susceptibilidad de deslizamientos superficiales a escala regional: efecto de futuros cambios en el Val d’Aran (Pirineo Central)

Los deslizamientos superficiales desencadenados por precipitaciones intensas pueden causar daños importantes en diferentes tipos de infraestructuras e incluso provocar pérdidas de vidas humanas. La ocurrencia de estos deslizamientos está directamente relacionada con futuros cambios (climáticos y de usos de suelo). Por ello es necesario disponer de herramientas para planificar el territorio y de esta manera contribuir a la reducción del riesgo asociado a estos procesos. En este estudio, se presenta un nuevo modelo de susceptibilidad llamado FSLAM basado en la teoría del talud infinito. El modelo calcula las presiones de agua en el suelo mediante dos modelos hidrológicos que incorporan la lluvia antecedente y la lluvia desencadenante. FSLAM es un modelo de código abierto que se ha implementado en un plugin de QGIS para su uso. El modelo FSLAM se ha aplicado y validado en cuatro áreas de centenares de kilómetros cuadrados del Pirineo (Andorra y Val d’Aran), del Pre-Pirineo (Berguedà) y de la Cordillera Prelitoral Catalana (Montseny). Se ha evaluado su eficiencia mediante el análisis ROC (Receiver Operating Characteristic) mostrando unos valores de precisión (accuracy) altos y satisfactorios a pesar de las incertidumbres de muchos parámetros de suelo. Mediante FSLAM se ha analizado la influencia de los efectos del cambio climático y de futuros cambios en los usos y cubiertas del suelo en la susceptibilidad a generar deslizamientos en la zona de la Val d’Aran. Los resultados indican que los cambios en las cubiertas del suelo, especialmente la transformación de prados y arbustos a bosques, aumenta la estabilidad global en la zona de estudio. Por el contrario, el aumento de precipitación diaria para un periodo de retorno de 100 años provoca una reducción de la estabilidad. Sin embargo, el efecto del cambio de las cubiertas del suelo es más importante que el cambio en las condiciones pluviométricas y, por ello, la estabilidad global en esta zona de estudio aumentará en el futuro.El presente estudio ha sido financiado por dos proyectos nacionales: SMuCPhy (BIA 2015-67500-R) y EROSLOP (PID2019-104266RB-I00/AEI/10.13039/501100011033).Postprint (published version