Análisis y modelización de la contribución de la erosión por cárcavas a la producción de sedimentos en la cuenca del Guadalquivir

Gully erosion is widely recognised as an important soil degradation process in many regions, causing important on-site (e.g. soil losses, environmental degradation, crop losses...) and off-site effects (e.g. muddy floods, water pollution, reservoir siltation...). In contrast to other erosion processes, as for instance sheet and rill erosion, where models have been successfully developed and tested extensively over the world, no widely accepted model exists for gully erosion. The reasons for this are the varied and complex subprocesses involved in gully erosion, the factors that control it and, its dependence on the spatial and temporal scale of study. Notwithstanding the above, gully erosion has been proved to be the major erosion process contributing to the total sediment yield in various regions, especially in the Mediterranean Region. This is particularly the case of the Guadalquivir River Basin, where the lithology added to the topography and the climate condition make of it a gully prone area. At present, very little information is available on gully processes and dynamics in this area. In this thesis, a complex gully network with a contributing area of 20 km2 was selected as a representative case of the gully prone agricultural landscape of the Campiña of the Guadalquivir River Basin, which land use consists mainly of herbaceous crops and live groves on Vertisols developed over soft parent material (marls and calcareous sandstone). The dynamics of the gully network was study over a period of 57 years by a combination of photointerpretation techniques in a GIS, field surveys and probabilistic approaches. Gully network evolution was derived from a dataset of 10 aerial orthophotos from the period 1956 to 2013. Field data and a Monte Carlo approach were then applied to estimate gully erosion rates dynamics over the study period. Modelling of gully erosion was then assessed by means of the study of the topographic thresholds for gully head initiation and by means of the gully widening rates dynamics. The results showed that gully erosion rate in the study area was 39 ton/ha/year on average, with peaks up to 591 ton/ha/year. However, these gully erosion rates were highly variable over the study period, and therefore the estimation through average values should be taking with caution. The variability on the gully erosion rates obtained highlights the importance of appropriately selecting the time scale on which gully erosion processes are assessed. For the first time, an important temporal variability in the topographic thresholds (TT) values for a given study area was demonstrated. In addition, this TT variability could be correlated to rainfall regime through various rainfall indexes, as for instance the Rainy Day Normal (RDN). A significant correlation between the gully widening rates and the runoff contributing area were found. Variability in gully widening rates were related to a rainfall index expressing the number of days exceeding a threshold rainfall depth of 13 mm. Land use present in the study area (herbaceous crops and olive groves) showed no significant effects on the TT and the widening rates.La erosión por cárcavas es un proceso de degradación del suelo que afecta gravemente a muchas regiones. Estos procesos causan importantes impactos tanto in-situ como ex-situ. A diferencia de lo que ocurre con otros procesos de erosión, como son la erosión laminar y la erosión por regueros, para la erosión por cárcavas no hay desarrollados en la actualidad modelos ampliamente aceptados. Sin embargo, distintos autores han demostrado que la contribución de las cárcavas a la producción total de sedimentos puede superar con creces la del resto de procesos en determinadas regiones, como ocurre por ejemplo en la cuenca del Mediterráneo. En esta tesis se ha analizado una cuenca de la Campiña representativa de las zonas más afectadas por la erosión por cárcavas en la Cuenca del Río Guadalquivir. Mediante técnicas de fotointerpretación de imágenes aéreas, se analizó la dinámica de la red de cárcavas en un periodo de 57 años. Para ello se utilizó una secuencia de 10 ortofotos del periodo comprendido entre 1956 y 2013, con el apoyo de datos de campo. Por último, se avanzó en la modelización de las cabeceras de las cárcavas y del ensanchamiento de las mismas a través de relaciones con el área de contribución, y con índices de precipitación. Los resultados obtenidos mostraron que las tasas de erosión durante el periodo de estudio fueron muy variables, siendo de 39 t ha-1 año-1 el valor medio para el conjunto del periodo y 591 t ha-1 año-1 el máximo obtenido. Por otro lado, se demostró que los umbrales topográficos para la formación de cabeceras pueden variar notablemente a lo largo del tiempo en un mismo área. Por último, se determinó que existe una correlación significativa entre la tasa de ensanchamiento de las cárcavas y el área de contribución aguas arriba. Tanto los umbrales topográficos como las tasas de ensanchamiento pudieron correlacionarse con índices de precipitación. Mientras que, los distintos usos del suelo presentes en la zona de estudio, resultaron poco relevantes para la modelización de los crecimientos en cabecera y en anchura

Characteristics of areas affected by fire in 2005 at Parque Nacional de Torres del Paine (Chile) as assessed from multispectral images

El uso de sensores remotos para la evaluación de la severidad es una de los aspectos más importantes en el estudio de grandes incendios, así como la aplicación de los resultados para el proceso de restauración. En este trabajo se ha estudiado la aplicación de imágenes de los sensores Landsat ETM+ y ASTER para evaluar la vegetación previa, la superficie recorrida por el fuego y los daños producidos por el incendio ocurrido en el año 2005 en el Parque Nacional de Torres del Paine (Chile). Los resultados obtenidos indican que el índice delta NBR es bastante versátil para evaluar la superficie afectada, estimada en este caso en 17.138 ha, así como la severidad de los daños (Fiabilidad = 81,5 %; κ = 0,73). Por otro lado, se ha confirmado la adecuación del uso de imágenes Landsat ETM+ para mejorar la calidad de los mapas de vegetación previa a la ocurrencia del fuego (Fiabilidad = 79,5 %; κ = 0,75). La combinación de esta información se ha podido aplicar para apoyar la restauración del área afectada por el incendio. Sin embargo, los resultados también han mostrado algunas limitaciones de los sensores, en particular en la definición de ecosistemas con representaciones superficiales pequeñas y/o fragmentadas, lo cual sugiere que el uso de sensores de mayor resolución espacial puede mejorar los productos cartográficos finales y, por tanto, la calidad de los trabajos de restauración.The use of remote sensors is one of the most important aspects in the study of large fires for an assessment of their severity, as well as the application of the results to the restoration process. This work has studied the application of images from the Landsat ETM + ASTER sensors in order to evaluate the prior vegetation, the surface burned and the damage caused by a fire occurring in 2005 in the National Park of Torres del Paine (Chile). The results obtained indicate that the delta NBR index is reasonably versatile for evaluating the affected surface, in this case estimated at 17.138 ha, as well as the damage severity (Reliability = 81.5 %; κ = 0.73). In addition, the suitability of using Landsat ETM+ images to improve the quality of maps of vegetation prior to the fire (Reliability = 79.5 %; κ = 0.75.) has been confirmed. It has been possible to apply a combination of this information to assist in the restoration of the fire-affected area. However, the results have also shown some limitations in the sensors, particularly in the definition of ecosystems with small and/or fragmented surface representations, which suggests that the use of sensors with a greater spatial resolution could improve the final cartographic products, and, therefore, the quality of the restoration works

Measuring, modelling and managing gully erosion at large scales: A state of the art

Soil erosion is generally recognized as the dominant process of land degradation. The formation and expansion of gullies is often a highly significant process of soil erosion. However, our ability to assess and simulate gully erosion and its impacts remains very limited. This is especially so at regional to continental scales. As a result, gullying is often overlooked in policies and land and catchment management strategies. Nevertheless, significant progress has been made over the past decades. Based on a review of >590 scientific articles and policy documents, we provide a state-of-the-art on our ability to monitor, model and manage gully erosion at regional to continental scales. In this review we discuss the relevance and need of assessing gully erosion at regional to continental scales (Section 1); current methods to monitor gully erosion as well as pitfalls and opportunities to apply them at larger scales (section 2); field-based gully erosion research conducted in Europe and European Russia (section 3); model approaches to simulate gully erosion and its contribution to catchment sediment yields at large scales (section 4); data products that can be used for such simulations (section 5); and currently existing policy tools and needs to address the problem of gully erosion (section 6). Section 7 formulates a series of recommendations for further research and policy development, based on this review. While several of these sections have a strong focus on Europe, most of our findings and recommendations are of global significance.info:eu-repo/semantics/publishedVersio

Reconstructing long-term gully dynamics in Mediterranean agricultural areas

Gully erosion is an important erosive process in Mediterranean basins. However, the long-term dynamics of gully networks and the variations in sediment production in gullies are not well known. Available studies are often conducted only over a few years, while many gully networks form, grow, and change in response to environmental and land use or management changes over a long period. In order to clarify the effect of these changes, it is important to analyse the evolution of the gully network with a high temporal resolution. This study aims at analysing gully morphodynamics over a long timescale (1956–2013) in a large Mediterranean area in order to quantify gully erosion processes and their contribution to overall sediment dynamics. A gully network of 20 km2 located in southwestern Spain has been analysed using a sequence of 10 aerial photographs in the period 1956–2013. The extension of the gully network both increased and decreased in the study period. Gully drainage density varied between 1.93 km km−2 in 1956, a minimum of 1.37 km km−2 in 1980, and a maximum of 5.40 km km−2 in 2013. The main controlling factor of gully activity appeared to be rainfall. Land use changes were found to have only a secondary effect. A new Monte Carlo-based approach was proposed to reconstruct gully erosion rates from orthophotos. Gully erosion rates were found to be relatively stable between 1956 and 2009, with a mean value of 11.2 t ha−1 yr−1. In the period 2009–2011, characterized by severe winter rainfalls, this value increased significantly to 591 t ha−1 yr−1. These results show that gully erosion rates are highly variable and that a simple interpolation between the starting and ending dates greatly underestimates gully contribution during certain years, such as, for example, between 2009 and 2011. This illustrates the importance of the methodology applied using a high temporal resolution of orthophotos.This research was funded under research project AGL2012-40128-C03-02.Peer reviewe

Caracterización de la situación posincendio en el área afectada por el incendio de 2005 en el Parque Nacional de Torres del Paine (Chile) a partir de imágenes multiespectrales Characteristics of areas affected by fire in 2005 at Parque Nacional de Torres del Paine (Chile) as assessed from multispectral images

El uso de sensores remotos para la evaluación de la severidad es una de los aspectos más importantes en el estudio de grandes incendios, así como la aplicación de los resultados para el proceso de restauración. En este trabajo se ha estudiado la aplicación de imágenes de los sensores Landsat ETM+ y ASTER para evaluar la vegetación previa, la superficie recorrida por el fuego y los daños producidos por el incendio ocurrido en el año 2005 en el Parque Nacional de Torres del Paine (Chile). Los resultados obtenidos indican que el índice delta NBR es bastante versátil para evaluar la superficie afectada, estimada en este caso en 17.138 ha, así como la severidad de los daños (Fiabilidad = 81,5 %; k = 0,73). Por otro lado, se ha confirmado la adecuación del uso de imágenes Landsat ETM+ para mejorar la calidad de los mapas de vegetación previa a la ocurrencia del fuego (Fiabilidad = 79,5 %; k = 0,75). La combinación de esta información se ha podido aplicar para apoyar la restauración del área afectada por el incendio. Sin embargo, los resultados también han mostrado algunas limitaciones de los sensores, en particular en la definición de ecosistemas con representaciones superficiales pequeñas y/o fragmentadas, lo cual sugiere que el uso de sensores de mayor resolución espacial puede mejorar los productos cartográficos finales y, por tanto, la calidad de los trabajos de restauraciónThe use of remote sensors is one of the most important aspects in the study of large fires for an assessment of their severity, as well as the application of the results to the restoration process. This work has studied the application of images from the Landsat ETM + ASTER sensors in order to evaluate the prior vegetation, the surface burned and the damage caused by a fire occurring in 2005 in the National Park of Torres del Paine (Chile). The results obtained indicate that the delta NBR index is reasonably versatile for evaluating the affected surface, in this case estimated at 17.138 ha, as well as the damage severity (Reliability = 81.5 %; k = 0.73). In addition, the suitability of using Landsat ETM+ images to improve the quality of maps of vegetation prior to the fire (Reliability = 79.5 %; k = 0.75.) has been confirmed. It has been possible to apply a combination of this information to assist in the restoration of the fire-affected area. However, the results have also shown some limitations in the sensors, particularly in the definition of ecosystems with small and/or fragmented surface representations, which suggests that the use of sensors with a greater spatial resolution could improve the final cartographic products, and, therefore, the quality of the restoration work

Can an appropriateness evaluation tool be used to prioritize patients on a waiting list for cataract extraction?

Objectives To determine whether a system originally developed to ascertain the appropriateness of cataract intervention may also be used to prioritize patients on cataract extraction waiting lists.Methods The IRYSS-appropriateness of indication for cataract surgery tool and the IRYSS-Cataract Priority Score were applied to a sample of 5448 patients consecutively placed on waiting lists for cataract surgery. Clinical data were gathered by ophthalmologists, and patients self-completed the Visual Function Index-14. The general linear model (GLM) was used to assign scores to the categories of the appropriateness and priority criteria. The relationship between both systems was evaluated by correlating scores. To assess the validity of the new appropriateness and priority scores, correlations with visual acuity (VA) and visual function were calculated.Results The GLM method generated highly similar scores for both appropriateness and prioritization systems. The correlation between scores was very strong (r = 0.96). The appropriateness scoring system correlated 0.29 with VA and 0.21 with gain in visual function. The priority system correlated -0.54 with VA and -0.28 with preintervention visual function.Conclusions The new appropriateness scoring system strongly correlates with the priority scoring system. This easy-to-use appropriateness rating could serve as a tool for simultaneously assessing the appropriateness of cataract surgery and assigning priority.Health priority Patient selection Cataract extraction Calibration Comparative study