Intertidal finger bars at El Puntal, Bay of Santander, Spain: observation and forcing analysis

A system of 15 small-scale finger bars has been observed, by using video imagery, between 23 June 2008 and 2 June 2010. The bar system is located in the intertidal zone of the swell-protected beaches of El Puntal Spit, in the Bay of Santander (northern coast of Spain). The bars appear on a planar beach (slope = 0.015) with fine, uniform sand (D50 = 0.27 mm) and extend 600 m alongshore. The cross-shore span of the bars is determined by the tidal horizontal excursion (between 70 and 130 m). They have an oblique orientation with respect to the low-tide shoreline; specifically, they are down-current-oriented with respect to the dominant sand transport computed (mean angle of 26° from the shore normal). Their mean wavelength is 26 m and their amplitude varies between 10 and 20 cm. The full system slowly migrates to the east (sand transport direction) with a mean speed of 0.06 m day-1, a maximum speed in winter (up to 0.15 m day-1) and a minimum speed in summer. An episode of merging has been identified as bars with larger wavelength seem to migrate more slowly than shorter bars. The wind blows predominantly from the west, generating waves that transport sediment across the bars during high-tide periods. This is the main candidate to explain the eastward migration of the system. In particular, the wind can generate waves of up to 20 cm (root-mean-squared wave height) over a fetch that can reach 4.5 km at high tide. The astronomical tide seems to be important in the bar dynamics, as the tidal level changes the fetch and also determines the time of exposure of the bars to the surf-zone waves and currents. Furthermore, the river discharge could act as input of suspended sediment in the bar system and play a role in the bar dynamics

Influence of a rocky platform in the profile morphology: Victoria Beach, Cadiz (Spain)

The equilibrium profile concept is a useful tool for the knowledge and management of the coastline. This concept is based on several assumptions that rarely are satisfied in nature. One of these considers that the geologic setting has no influence in the profile morphology. The Victoria beach is a good example that questions this hypothesis. Muñoz-Pérez (1996) and Muñoz-Pérez et al. (1999) proposed an analytical expression of equilibrium beach profile for reefprotected beaches. In this work, data measured at Victoria beach are used to confirm the goodness of this model. The results obtained show that the occurrence of a horizontal rocky platform in subtidal zone modifies the beach slope and the seasonal evolution of the profile.Xunta de Galici

Morphodynamics of a microtidal sandbar beach under storm condition: case of the Mahdia nearshore, Tunisia

L?effet du changement climatique s?illustre dans l?élévation du niveau de mer et l?agressivité ascendante des évènements météo-marins sur les milieux côtiers, voué à une accélération extrêmement forte (IPCC 2007). L?action des tempêtes marines va entraîner des réponses morphologiques rapides et des impacts importants sur les littoraux sableux particulièrement l?érosion des plages et le recul du trait de côte. Certains rivages tunisiens sont déjà touchés par cet aléa notamment la baie de Ras Dimas-Cap Africa (Mahdia), objet de cette étude. L?objectif de ce travail consiste à suivre la réponse de deux profils de plage sableuse dissipative à barres subtidales sous des conditions de forçages hydrodynamiques de tempête au niveau de Mahdia au Golfe de Hammamet en Tunisie. La méthodologie adoptée s?est basée sur des mesures bathymétriques de l?avant côte acquises lors de deux campagnes de mesures en 2004 et 2006, complétées par la simulation numérique grâce à un nouvel modèle morphodynamique: Système de Modélisation côtière (SMC). Cet outil a été développé et validé en Espagne par la Direction Générale des Côtes et le Groupe d?Ingénierie Océanographique et Côtière (GIOC) de l?Université de Cantabrie. La modélisation côtière appliquée fournit une estimation de l?évolution spatiale de la hauteur de la houle en fonction de la bathymétrie, un suivi de la surélévation de la masse d?eau ainsi que le déplacement des barres sédimentaires engendré par les courants de fond (courant de retour). Soumises à des conditions de haute énergie d?une houle de tempête, les barres sableuses migrent vers le large puis reviennent vers la côte. Le rapprochement des barres du rivage est associé à un engraissement de la plage sous des conditions de forte houle au niveau du centre de la baie où la plage est à faible pente et à deux barres sableuses. Néanmoins au sud de la baie, où une seule barre est présente, le bilan sédimentaire s?oriente vers une érosion et un recul de la ligne de rivage lors d?événements météo-marins de forte énergie et il est marqué par une migration vers le large de la barre subtidale.The effects of global climate change are illustrated by rising sea level and the increase of intensity of storm events. The highest waves generated attack the upper beach. This combination of the two factors would produce severe erosion, threatening the coastline. The Ras Dimas-Cape Africa (Mahdia, Tunisia) coastline and adjacent areas are particularly exposed to such impact. The aim of this study is to assess the response of wave-dominated sandbar beach under storm events in two different cross shore cases in the Mahdia beaches. The methodology adopted is based on the surveyed bathymetry of the nearshore (2004-2006), completed with the morphodynamic numerical model SMC (Tunisian SMC software, Hispano- Tunisian project of coastal rehabilitation, TUNEROSION). The model has been developed and validated by the Spanish Government and the Ocean and Coastal research Group (GIOC) (University of Cantabria, Spain). Coastal modelling provides the wave high and wave induced set-up created by breaking wave and the sediment transport volume calculated as a function of local conditions. The response of sandbars to storm condition is moving onshore and migrates seaward. The morphodynamic result is however an accretion of the nearshore under the storm wave at the center of the bay (two sandbars with gentle slope). Nevertheless, in the southeast beach, where we find single sandbar, the sediment budget is characterized by shoreline retreat during high wave energy and the migration offshore of this sanbar beach

Flow Prediction in Ungauged Catchments Using Probabilistic Random Forests Regionalization and New Statistical Adequacy Tests

Flow prediction in ungauged catchments is a major unresolved challenge in scientific and engineering hydrology. This study attacks the prediction in ungauged catchment problem by exploiting advances in flow index selection and regionalization in Bayesian inference and by developing new statistical tests of model performance in ungauged catchments. First, an extensive set of available flow indices is reduced using principal component (PC) analysis to a compact orthogonal set of ?flow index PCs.? These flow index PCs are regionalized under minimal assumptions using random forests regression augmented with a residual error model and used to condition hydrological model parameters using a Bayesian scheme. Second, ?adequacy? tests are proposed to evaluate a priori the hydrological and regionalization model performance in the space of flow index PCs. The proposed regionalization approach is applied to 92 northern Spain catchments, with 16 catchments treated as ungauged. It is shown that (1) a small number of PCs capture approximately 87% of variability in the flow indices and (2) adequacy tests with respect to regionalized information are indicative of (but do not guarantee) the ability of a hydrological model to predict flow time series and are hence proposed as a prerequisite for flow prediction in ungauged catchments. The adequacy tests identify the regionalization of flow index PCs as adequate in 12 of 16 catchments but the hydrological model as adequate in only 1 of 16 catchments. Hence, a focus on improving hydrological model structure and input data (the effects of which are not disaggregated in this work) is recommended

Multivariate wave climate using self-organizing maps

ABSTRACT: The visual description of wave climate is usually limited to two-dimensional conditional histograms. In this work, self-organizing maps (SOMs), because of their visualization properties, are used to characterize multivariate wave climate. The SOMs are applied to time series of sea-state parameters at a particular location provided by ocean reanalysis databases. Trivariate (significant wave height, mean period, and mean direction), pentavariate (the previous wave parameters and wind velocity and direction), and hexavariate (three wave parameters of the sea and swell components; or the wave, wind, and storm surge) classifications are explored. This clustering technique is also applied to wave and wind data at several locations to analyze their spatial relationship. Several processes are established in order to improve the results, the most relevant being a preselection of data by means a maximum dissimilarity algorithm (MDA). Results show that the SOM identifies the relevant multivariate sea-state types at a particular location spanning the historical variability, and provides an outstanding analysis of the dependency between the different parameters by visual inspection. In the case of wave climate characterizations for several locations the SOM is able to extract the qualitative spatial sea-state patterns, allowing the analysis of the spatial variability and the relationship between different locations. Moreover, the distribution of sea states over the reanalysis period defines a probability density function on the lattice, providing a visual interpretation of the seasonality and interannuality of the multivariate wave climate.The work was partially funded by projects GRACCIE (CSD2007-00067, CONSOLIDERINGENIO 2010) from the Spanish Ministry of Science and Technology, MARUCA(200800050084091) from the Spanish Ministry of Public Works, and C3E(E17/08) from the Spanish Ministry of Environment, Rural and Marine Environs. The authors thank Puertos del Estado (Spanish Ministry of Public Works) for providing the reanalysis database

Identification of Dominant Hydrological Mechanisms Using Bayesian Inference, Multiple Statistical Hypothesis Testing, and Flexible Models

ABSTARCT: In hydrological modeling, the identification of model mechanisms best suited for representing individual hydrological (physical) processes is of major scientific and operational interest. We present a statistical hypothesis-testing perspective on this model identification challenge and contribute a mechanism identification framework that combines: (i) Bayesian estimation of posterior probabilities of individual mechanisms from a given ensemble of model structures; (ii) a test statistic that defines a ?dominant? mechanism as a mechanism more probable than all its alternatives given observed data; and (iii) a flexible modeling framework to generate model structures using combinations of available mechanisms. The uncertainty in the test statistic is approximated using bootstrap sampling from the model ensemble. Synthetic experiments (with varying error magnitude and multiple replicates) and real data experiments are conducted using the hydrological modeling system FUSE (7 processes and 2?4 mechanisms per process yielding 624 feasible model structures) and data from the Leizarán catchment in northern Spain. The mechanism identification method is reliable: it identifies the correct mechanism as dominant in all synthetic trials where an identification is made. As data/model errors increase, statistical power (identifiability) decreases, manifesting as trials where no mechanism is identified as dominant. The real data case study results are broadly consistent with the synthetic analysis, with dominant mechanisms identified for 4 of 7 processes. Insights on which processes are most/least identifiable are also reported. The mechanism identification method is expected to contribute to broader community efforts on improving model identification and process representation in hydrology.The authors from IHCantabria acknowledge the financial support from the Government of Cantabria through the FÉNIX Program (ID 2020.03.03.322B.742.09)

Estructura flotante e instalación para el aprovechamiento de la energía del oleaje utilizando un catamarán flotante con varias cámaras de columna de agua oscilante.

Una estructura flotante para el aprovechamiento de la energía del oleaje, que comprende múltiples cámaras independientes de columna de agua oscilante (CAO) alineadas, abiertas por el fondo, estando cada cámara comunicada por la parte superior con la atmósfera a través de un grupo turbo-generador formado por un conducto de aire, en cuyo interior se ubican una válvula de control del flujo de aire y una turbina de aire auto-rectificadora conectada a un alternador.Solicitud: 201100242 (28.02.2011)Nº Pub. de Solicitud: ES2387492A1 (24.09.2012)Nº de Patente: ES2387492B2 (26.03.2013

A contribution to the selection of tsunami human vulnerability indicators: conclusions from tsunami impacts in Sri Lanka and Thailand (2004), Samoa (2009), Chile (2010) and Japan (2011)

After several tsunami events with disastrous consequences around the world, coastal countries have realized the need to be prepared to minimize human mortality and damage to coastal infrastructures, livelihoods and resources. The international scientific community is striving to develop and validate methodologies for tsunami hazard and vulnerability and risk assessments. The vulnerability of coastal communities is usually assessed through the definition of sets of indicators based on previous literature and/or post-tsunami reports, as well as on the available data for the study site. The aim of this work is to validate, in light of past tsunami events, the indicators currently proposed by the scientific community to measure human vulnerability, to improve their definition and selection as well as to analyse their validity for different country development profiles. The events analysed are the 2011 Great Tohoku tsunami, the 2010 Chilean tsunami, the 2009 Samoan tsunami and the 2004 Indian Ocean tsunami. The results obtained highlight the need for considering both permanent and temporal human exposure, the former requiring some hazard numerical modelling, while the latter is related to site-specific livelihoods, cultural traditions and gender roles. The most vulnerable age groups are the elderly and children, the former having much higher mortality rates. Female mortality is not always higher than male mortality and not always related to dependency issues. Higher numbers of disabled people do not always translate into higher numbers of victims. Besides, it is clear that mortality is not only related to the characteristics of the population but also of the buildings. A high correlation has been found between the affected buildings and the number of victims, being very high for completely damaged buildings. Distance to the sea, building materials and expected water depths are important determining factors regarding the type of damage to buildings