Flood Hazard Management in Public Mountain Recreation Areas vs. Ungauged Fluvial Basins. Case Study of the Caldera de Taburiente National Park, Canary Islands (Spain)

Las Angustias River is an ungauged stream in the Caldera de Taburiente National Park (Spain), where frequent intense flash-flood events occur. The aim of this research is to analyze the flood hazard at the Playa de Taburiente. Based on the limited information available (short time-series of daily precipitation), a statistical frequency analysis of 24 h rainfall was completed and the precipitation results were transformed into surface runoff. To determine if the model underestimates the flows that are generated in the basin, the dendro-geomorphological information available was used to calibrate results. The results of the HMS model were significantly lower. At this point, both the rainfall data and the rainfall-runoff model were re-analyzed to maximize the rainfall intensity values and the runoff generated (increasing the CN value for the basin). For the 1997 flood event, a 1250 m3·s−1 flood minimizes the RMSE for the disturbed tree sample; this flow value also clearly exceeds any peak flow derived from the rainfall-runoff analysis. It is only when rainfall intensity and surface runoff are maximized that the peak flows obtained approximate those associated with dendro-geomorphological data. The results highlight the difficulties of flood hazard management in ungauged torrential basins in mountain recreational areas (such as National Parks). Thus, in the absence of flow records, when considering the maximum rainfall intensity scenario may be a useful and effective tool for flood risk management

Hydrological Alteration Index as an Indicator of the Calibration Complexity of Water Quantity and Quality Modeling in the Context of Global Change

Modeling is a useful way to understand human and climate change impacts on the water resources of agricultural watersheds. Calibration and validation methodologies are crucial in forecasting assessments. This study explores the best calibration methodology depending on the level of hydrological alteration due to human-derived stressors. The Soil and Water Assessment Tool (SWAT) model is used to evaluate hydrology in South-West Europe in a context of intensive agriculture and water scarcity. The Index of Hydrological Alteration (IHA) is calculated using discharge observation data. A comparison of two SWAT calibration methodologies are done; a conventional calibration (CC) based on recorded in-stream water quality and quantity and an additional calibration (AC) adding crop managements practices. Even if the water quality and quantity trends are similar between CC and AC, water balance, irrigation and crop yields are different. In the context of rainfall decrease, water yield decreases in both CC and AC, while crop productions present opposite trends (+33% in CC and -31% in AC). Hydrological performance between CC and AC is correlated to IHA: When the level of IHA is under 80%, AC methodology is necessary. The combination of both calibrations appears essential to better constrain the model and to forecast the impact of climate change or anthropogenic influences on water resources

Procesos geomorfológicos activos en cárcavas del borde del piedemonte norte de la Sierra de Guadarrama (Provincia de Segovia, España)

Dos localizaciones situadas cerca del borde del piedemonte norte de la Sierra de Guadarrama (provincia de Segovia) ofrecen formas erosivas en cárcavas bien desarrolladas: (a) un conjunto de barrancos encajados sobre arenas arcósicas del Mioceno, en un relieve de lomas y vaguadas del suroeste provincial; (b) cárcavas sobre arenas silíceas del Cretácico Superior, en un relieve de laderas de mesas y cuestas de la zona centro sur de la Provincia. En este trabajo se caracteriza la actividad geomorfológica de esos barrancos y cárcavas, y se inicia su cuantificación. El objetivo está encaminado a conocer qué procesos movilizan sedimentos, y a evaluar sus tasas de actuación, intensidad, frecuencia de ocurrencia y conectividad entre los mismos. Los procesos de erosión hídrica por salpicadura, arroyada laminar y concentrada en rills, junto con la actividad gravitacional observada, movilizan materiales desde las cabeceras de las cárcavas hasta los colectores, rellenándolos; éstos son evacuados mediante procesos de encajamiento en los canales efímeros, y sedimentados en pequeños conos aluviales. En los barrancos sobre arcosas, los eventos de precipitación poco intensos y de alta frecuencia tienden a rellenar los lechos arenosos, mientras que la fusión nival y las precipitaciones de alta intensidad y baja frecuencia vacían los canales, sedimentando en zonas apicales de los conos aluviales. En las cárcavas sobre arenas silíceas, los primeros datos obtenidos apuntan a unas tasas de erosión y producción de sedimentos muy elevadas, ya que sobre ellas se produce escorrentía y erosión hídrica de manera casi instantánea; por ello, los eventos de precipitación de baja intensidad son capaces de sedimentar en las zonas apicales de los conos, mientras que los eventos de alta intensidad originan lóbulos telescópicos sobre conos aluviales existentes en pedimentos. [ABSTRACT] Two areas located at the edge of the North piedmont of the Guadarrama Mountains (province of Segovia) show a conspicuous development of gullies. A series of valley side gullies, or ravines, cut on arkosic sand sediments of Miocene age at the Río Chico Valley (southwest of the Segovia province); and slope gullies, cut on silica sand, shale and gravel sediments of Upper Cretaceous age, on the slopes of a set of mesas and cuestas at the río Cega piedmont (Pedraza region, south centre of the Segovia province). This paper characterizes the geomorphic activity of both types of gullies. In addition, the quantification of their current activity is initiated. The objectives are: to know which processes are eroding and mobilizing the sediments within the gullies, and to evaluate their rates, intensity, frequency and connectivity. A detailed field survey shows that weathering processes (sandstone sheeting, and the formation of popcorn structures on shale layers), and splash, sheet and rill erosion, along with sand and mud falls, slides and flows move sediment from the gully slopes and internal divides to the dry washes. These materials are temporary stored in ephemeral stream channels (filled with sandy bed material), evacuated by stream-bed scour and fill processes, and deposited in alluvial cones. In order to get a first approximation of the amount of erosion and sediment movement, a set of field methods have been applied to these areas. These methods include: erosion pins, measurement of pedestals, system of rods and washers, pit traps (box and gabion check-dam types), and topographic surveys after extensive sedimentation on alluvial cones, along with the installation of pluviographs. The results show how on the arkosic valley side gullies, the precipitation events of low intensity and high frequency tend to fill the sandy stream-beds, whereas the snowmelt and the high intensity and low frequency precipitation events scour the sandy stream-beds. The sedimentation occurs here at the apex part of the alluvial cones, which rest directly on the nearby floodplain of the Chico River. On the silica sand slope gullies, the first gathered data point at very high rates of erosion and sedimentation (44.1 tons/ha for a single event), which is interpreted due to the fact that runoff and water erosion occurs here almost instantaneously after precipitation. Here, the precipitation events of low intensity and high frequency produce sedimentation at the apex part of the alluvial cones, whereas the high intensity and low frequency precipitation events sediment in the form of telescopic lobes, on existing alluvial cones, which rest on pediments

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

Flash floods represent one of the more usual natural hazards in mountain basins, and, combined with the lack of reliable flow data and the recreational use of the drainage basin by tourists and hikers, there is a significant risk of catastrophe. Here, we present a dendro-geomorphological reconstruction of a past flash flood event in the Caldera de Taburiente N.P. (Canary Islands, Spain), an ungauged drainage basin in the SW side of the volcanic island of La Palma. We couple two-dimensional hydraulic modelling in a highly-resolved topographic environment (LiDAR data) with (1) peak flow data for various Tyear return periods from an uncalibrated hydrological model and (2) a data set of scars on trees, to investigate the magnitude of a 1997 dated flash-flood. From the results, flood hazards and associated risks would be clearly underestimated by using only the unique available hydrological data (a rainfall gauge station downstream of the study area). Hydraulic models using scars data show a higher flood hazard scenario, improving the flood hazard map by using all available flood evidence. Moreover, all this will allow for better implementation of appropriate adaptation policies by National Park managers, and therefore the mitigation of future disasters

Improvement of resilience of urban areas by integrating social perception in flash-flood risk management

In urban areas prone to flash floods, characterization of social resilience is critical to guarantee the success of emergency management plans. In this study, we present the methodological approach that led to the submission and subsequent approval of the Civil Protection Plan of Navaluenga (Central Spain), in which the first phase was to analyse flood hazard by combining the Hydrological Modelling System (HEC-HMS) and the Iber 2D hydrodynamic model. We then analysed social vulnerability and designed measures to put into practice within the framework of the Civil Protection Plan. At a later phase, we assessed citizens’ flash-flood risk perception and level of awareness regarding some key variables of the Civil Protection Plan. To this end, 254 adults representing roughly 12% of the population census were interviewed. Responses were analysed descriptively, comparing awareness regarding preparedness and response actions with the corresponding information and behaviours previously defined in the Civil Protection Plan. In addition, we carried out a latent class cluster analysis aimed at identifying the different groups present among the interviewees. Our results showed that risk perception is low. Specifically, 60.8% of the interviewees showed low risk perception and low awareness (cluster 1); 24.4% had high risk perception and low awareness (cluster 2), while the remaining 14.8% presented high long-term risk perception and high awareness (cluster 3). These findings suggest the need for integrating these key variables of social risk perception and local tailored information in emergency management plans, especially in urban areas prone to flash-floods where response times are limited.This research has been funded by the MARCoNI Project (MINECO, CGL2013-42728-R) of the Spanish National Plan for Scientific and Technical Research and Innovation, and previous projects of this research team by MAS Dendro-Avenidas (MINECO, CGL2010-19274; www.dendro-avenidas.es) and MIDHATOVenero (IGME 2013/2313)

Investigaciones dendrogeomorfológicas aplicadas a la gestión de los impactos por erosión hídrica acelerada de suelos en las sendas del parque nacional de Monfragüe

En muchos espacios naturales protegidos, el flujo peatonal de visitantes se concentra en determinados sectores del área de uso público, sobre todo en la proximidad de las principales vías de acceso (carreteras, núcleos de población...) y en un reducido número de sendas y caminos peatonales que comunican los elementos más visitados. Es el caso del camino hacia la Cola de Caballo en el parque nacional de Ordesa y Monte Perdido; el camino a la ermita de San Frutos en el parque natural de las Hoces del río Duratón; o la senda que comunica el Salto del Gitano con el castillo y la ermita en el parque nacional de Monfragüe, por citar algunos ejemplos. Esta concentración de actividades de senderismo produce en determinados tramos de estos caminos y sendas (zonas con suelos arenosos o limosos y altas pendientes) una erosión hídrica acelerada por el efecto físico del pisoteo, compactación y continua fricción. En ocasiones se llegan a formar regueros, pequeños barrancos y se pierden grandes cantidades de suelos fértiles, que además fosilizan y aterran aquéllas zonas donde va a parar la escorrentía, produciendo importantes impactos en estos espacios singulares. Existen numerosos ejemplos de ingentes partidas económicas que los gestores de estos espacios protegidos tienen que destinar a la reparación y recuperación de estas sendas y su entorno. Para ayudar a los gestores es básico disponer de metodologías y herramientas que cuantifiquen esta erosión hídrica (en mm/año) delimitando qué tramos de estas sendas y caminos tienen los mayores problemas erosivos, para así determinar cuáles deben ser prioritarios en su corrección, o qué acciones de restricción de paso o determinación de capacidad de acogida, son necesarias adoptar. Para esta cuantificación son muy útiles, desde hace décadas, las técnicas dendrogeomorfológicas aplicadas a las raíces de árboles que han quedado expuestas a la intemperie por la erosión acelerada en las sendas. En este trabajo se propone una nueva metodología de medición del suelo denudado en relación con la raíz, basado en el estudio microtopográfico de la superficie utilizando moldes y réplicas de alta resolución realizados en diferentes tipos de siliconas, latex y escayolas, y su posterior escaneo tridimensional. La zona piloto donde se ha ensayado esta metodología son los senderos y caminos del parque nacional de Monfragüe (Cáceres), que presentan raíces expuestas debido a la intensa erosión hídrica acelerada como consecuencia de la elevada concentración de visitantes. Los estudios son financiados por el proyecto de investigación IDEA-GesPPNN, del OAPN (MAGRAMA)

Ensayos metodológicos para la cuantificación de procesos geomorfológicos activos asociados a la hidrología de superficie en las sierras de Guadarrama y Gredos

Esta tesis doctoral parte de la hipótesis según la cual es posible cuantificar procesos geomorfológicos activos utilizando metodologías variadas en función de la escala espacio-temporal del fenómeno hidrológico asociado. Con el fin de verificar esta hipótesis, se han ensayado una serie de metodologías, al objeto de establecer y cuantificar las interacciones existentes entre algunos procesos geomorfológicos activos presentes en sectores de las sierras de Guadarrama y Gredos y la escorrentía superficial y subsuperficial. La selección de los procesos se hizo sobre la base de la consideración de aquéllos que pertenecen a distintas fases del proceso lluvia-escorrentía, y cuya actuación está muy condicionada por las características geomorfológicas existentes a escala de cuenca hidrográfica. Se ha llevado a cabo una evaluación cuantitativa de cinco escenarios diferenciados de las Sierras de Gredos y Guadarrama, cuya definición y ubicación ha venido dada por la información disponible. Para llevar a cabo dicha caracterización, se han aplicado una serie de técnicas y herramientas, tales como los geoindicadores y los modelos matemáticos. Igualmente, aparte de abordar las distintas problemáticas desde un enfoque geológico, también se ha aplicado los principios asociados a otras ciencias, tales como: dendrocronología; hidrología; hidráulica, geotecnia y estadística..

Enhancing flash flood risk perception and awareness of mitigation actions through risk communication: A pre-post survey design

Flood risk management is gradually shifting from a risk-based approach to an integrated one that, among other elements, considers risk communication (RC) as a means of boosting resilience. Regardless of the above, few scientists have tackled up to now the integration of RC into flood risk management. In this connection, this particular study seeks to check out the potential of a risk dialogue approach (based on an ad hoc RC strategy) to change attitudes and behaviours in relation to flash flood risk. Via a pre-post survey design, we evaluated risk perception and awareness regarding a Civil Protection Plan (CPP) implemented locally (i.e., in the municipality of Navaluenga, central Spain). For this particular objective, a questionnaire survey was created, and 201 adults (representing more than 10% of the population census) were interviewed twice in a one-year period. Before the second survey, an RC strategy was created. The RC strategy comprised briefings, quiz answers, storytelling, a contest of videos and photographs about past floods, and an intergenerational workshop. A t-test for paired sample analyses and a general linear model (GLM) repeated measures ANOVA were applied to identify changes in risk perception and awareness. Our results indicate that the RC strategy did increase flood risk perception in Navaluenga in the long term (lifetime). Also, it increased the level of awareness of the various features that comprise the CPP, enabling people to be more competent in facing a flash flood. Some cognitive biases detected in the perceptual process of human beings may shed some light on the results obtained. The implementation of well-thought-out RC strategies can play a role in improving resilience, particularly in geographic areas such as the Iberian Peninsula, in which climate change scenarios indicate a likely increase in the severity and frequency of flooding.This research was funded by the projects MARCoNI (CGL2013-42728-R) and DRAINAGE (CGL2017-83546-565 C3-1-R), both funded by the Spanish National Plan for Scientific and Technical Research and Innovation (MINEICO)

Hazard Zoning for Landslides Connected to Torrential Floods in the Jerte Valley (Spain) by using GIS Techniques

The Jerte Valley is a northeast-southwest tending graben located in the mountainous region of west central Spain (Spanish Central System). Mass movements have been a predominant shaping process on the Valley slopes during the Quaternary. Present day activity is characterized as either ‘first-time failure’ (shallow debris slides and debris flows) or ‘reactivations’ of pre-existing landslides deposits. A delineation of landslide hazard zoning within the Valley has been carried out by using the detailed documentation of a particular event (a debris slide and a sequel torrential flood, which occurred on the Jubaguerra stream gorge), and GIS techniques. The procedure has had four stages, which are: (1) the elaboration of a susceptibility map (spatial prediction) of landslides; (2) the elaboration of a map of ‘restricted susceptibility’ in the particular case of slopes that are connected to streams and torrents (gorges); (3) the elaboration of a digital model which relates the altitude to the occurrence probability of those particular precipitation conditions which characterized the Jubaguerra event and (4) the combination of the probability model with the ‘restricted susceptibility map’, to establish ‘critical zones’ or areas which are more prone to the occurrence of phenomena that have same typology as this one

Searching for useful non-systematic tree-ring data sources for flood hazard analysis using GIS tools

Tree-ring analysis has been demonstrated to be a useful tool for palaeohydrology. Selecting suitable study areas is the first step in palaeoflood research using tree-ring techniques. Objective methods are needed to facilitate exploration and subsequent location of basins where sediment-laden flash floods are likely and that also have tree species suitable for dendrogeomorphological research in a palaeohydrological context. This paper presents a novel methodology for selecting preliminary suitable watersheds for dendrogeomorphological palaeoflood research in central Spain. Geographical information systems (GIS) provide decision-makers with a powerful set of tools for the manipulation and analysis of spatial information. Using GIS tools and basic thematic maps, we defined three different indexes concerning the occurrence of dendrogeomorphological evidence. A Consensus Decision Making procedure (CDM) was carried out in order to weight each factor individually prior to combining the factors. As a result, we obtained information about the most appropriate watersheds for palaeoflood research using tree-ring analysis. A total of 189 watersheds appeared to be highly interesting for tree-ring studies. Of these only 17 have flow gauges, so data concerning frequency and magnitude of floods in basins without gauges could potentially be provided by dendrogeomorphological studies. In order locate such sites and to carry out such studies more efficiently, a more objective methodology for selecting watersheds for tree-ring studies is presentedDepartamento de Infraestructura Geocientífica y Servcios, Instituto Geológico y Minero de España, EspañaDepartamento de Ingeniería Geológica y Minera, Universidad de Castilla-La Mancha, Españ