Browsing by Author "Almar, Rafael"
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- ItemA new breaking wave height direct estimator from video imagery(ELSEVIER SCIENCE BV, 2012) Almar, Rafael; Cienfuegos, Rodrigo; Catalan, Patricio A.; Michallet, Herve; Castelle, Bruno; Bonneton, Philippe; Marieu, VincentBreaker height is a key parameter of nearshore processes and the demand for a continuous remote estimator is pressing. In this paper we present a standalone remote video-based method that estimates wave height at the breakpoint. Individual breaking events are first identified from changes in optical properties and wave height is further derived from the optical signature at the onset of breaking. An extended validation is performed using a dense wave basin dataset. The results show the ability of the method to measure individual breaker heights (9% of mean error, 18% RMS). In addition, the unique combination of in situ and remotely sensed data allows the estimation of two other breaking-related parameters, the height-to-depth ratio and wave front face slope, which show a substantial amount of dispersion. Because nearshore video systems are rapidly spreading over world coasts, this low-cost remote breaker height estimator should encounter large interest in coastal engineering studies. (C) 2011 Elsevier B.V. All rights reserved.
- ItemA new remote predictor of wave reflection based on runup asymmetry(2019) Almar, Rafael; Blenkinsopp, Chris; Almeida, Luis Pedro; Catalán, Patricio A.; Bergsma, Erwin; Cienfuegos Carrasco, Rodrigo Alberto; TrungViet, Nguyen
- ItemAssessing the Performance of a Low-Cost Method for Video-Monitoring the Water Surface and Bed Level in the Swash Zone of Natural Beaches(2018) Ibaceta, Raimundo; Almar, Rafael; Catalan, Patricio A.; Blenkinsopp, Chris E.; Almeida, Luis P.; Cienfuegos Carrasco, Rodrigo Alberto
- ItemDétection de courants marins côtiers à partir de séquences vidéo(2014) Larnier, Stanislas; Almar, Rafael; Cienfuegos, Rodrigo; Lejay, Antoine; Dhersin, Jean-StéphaneLes courants marins à proximité d’une côte contrôlent le transport de sédiment et son évolution. Or leur estimation par des instruments sur site est difficile et coûteuse. Les systèmes de télédétection reposant sur des observations constituent une alternative prometteuse lorsque la mousse dérivante laissée après le passage de vagues déferlantes est visible. Pourtant, seules quelques méthodes ont été proposées à ce jour dans la littérature.Dans cet article, nous décrivons deux nouvelles méthodes : l’une basée sur les images vidéos considérées dans leur globalité et l’autre basée sur des timestacks le long de la côte. La première approche est une extension de la méthode Particle Image Velocimetry (PIV). La seconde approche produit une estimation de la composante parallèle à la côte des courants de surface en utilisant la transformée de Radon sur des séries temporelles de données en une dimension. Cette dernière nécessite moins de données.Les vidéos utilisées dans cet article proviennent d’une campagne menée sur la zone de l’embouchure de Mataquito dans la région de Maule au Chili. Elles font partie d’une étude sur l’évolution côtière de la zone de Mataquito après le tsunami chilien de 2010. Une comparaison a été également réalisée avec les mesures d’un courantomètre prises lors de la campagne du Truc Vert de 2008 en Aquitaine, France. Elle a eu lieu lors d’une tempête qui a provoqué l’évolution d’une barre sableuse.
- ItemField Survey of the 27 February 2010 Chile Tsunami(2011) Fritz, Hermann M.; Petroff, Catherine M.; Catalán, Patricio A.; Cienfuegos Carrasco, Rodrigo Alberto; Winckler, Patricio; Kalligeris, Nikos; Weiss, Robert; Barrientos, Sergio E.; Meneses, Gianina; Valderas-Bermejo, Carolina; Ebeling, Carl; Papadopoulos, Athanassios; Contreras, Manuel; Almar, Rafael; Domínguez, Juan C.; Synolakis, Costas E.On 27 February 2010, a magnitude M-w = 8.8 earthquake occurred off the coast of Chile's Maule region causing substantial damage and loss of life. Ancestral tsunami knowledge from the 1960 event combined with education and evacuation exercises prompted most coastal residents to spontaneously evacuate after the earthquake. Many of the tsunami victims were tourists in coastal campgrounds. The international tsunami survey team (ITST) was deployed within days of the event and surveyed 800 km of coastline from Quintero to Mehuin and the Pacific Islands of Santa Maria, Mocha, Juan Fernandez Archipelago, and Rapa Nui (Easter). The collected survey data include more than 400 tsunami flow depth, runup and coastal uplift measurements. The tsunami peaked with a localized runup of 29 m on a coastal bluff at Constitucion. The observed runup distributions exhibit significant variations on local and regional scales. Observations from the 2010 and 1960 Chile tsunamis are compared.
- ItemObservations and Modeling of the 27 February 2010 Tsunami in Chile(ASCE Library, 2011) Fritz, Hermann M.; Synolakis, Costas E.; Petroff, Catherine M.; Catalán, Patricio A.; Cienfuegos Carrasco, Rodrigo Alberto; Winckler, Patricio; Kalligeris, Nikos; Weiss, Robert; Meneses, Gianina; Valderas-Bermejo, Carolina; Ebeling, Carl; Papadopoulos, Athanassios; Contreras, Manuel; Almar, Rafael; Domínguez, Juan C.; Barrientos, Sergio E.On February 27, 2010, a magnitude Mw = 8.8 earthquake occurred off the coast of Chile's Maule region causing substantial damage and loss of life. Ancestral tsunami knowledge from the 1960 event combined with education and evacuation exercises prompted most coastal residents to spontaneously evacuate after the earthquake. Many of the tsunami victims were tourists in coastal campgrounds. The international tsunami survey team (ITST) was deployed within days of the event and surveyed 800 km of coastline from Quintero to Mehuín and the Pacific Islands of Santa María, Mocha, Juan Fernández Archipelago, and Rapa Nui (Easter). The collected survey data include more than 400 tsunami flow depth, runup and coastal uplift measurements. The tsunami peaked with a localized runup of 29 m on a coastal bluff at Constitución. The observed runup distributions exhibit significant variations on local and regional scales.
- ItemOn the use of the Radon Transform in studying nearshore wave dynamics(2014) Almar, Rafael; Michallet, Herve; Cienfuegos Carrasco, Rodrigo Alberto; Bonneton, Philippe; Tissier, Marion; Ruessink, GerbenIn the nearshore, describing the complex individual wave dynamics remains a key challenge. In this paper we test the ability of the Radon Transform to produce estimates of individual wave celerities and to separate incoming and outgoing waves conserving the temporal characteristics. The Radon Transform is a projection of a two-dimensional field into polar space. Oblique features such as propagating crests in a spatio-temporal space are identified with density peaks in the polar space. In this paper, the Radon Transform is applied to synthetic test cases including a wide range of beach slopes and wave conditions. The Radon Transform shows good skills at estimating individual celerity and separating incoming and outgoing components with a relative RMS error lower than 10%, even a standing wave node. The accuracy is fairly insensitive to wave characteristics whereas the main limitations rise from the sampling scheme and are the number and density of wave gauges. The distance between gauges should be less than one third of the shortest wavelength, while the set of gauges should cover more than one third of the longest wavelength.
- ItemSWASH ZONE BASED REFLECTION DURING ENERGETIC WAVE CONDITIONS AT A DISSIPATIVE BEACH: TOWARD A WAVE-BY-WAVE APPROACH(2014) Almar, Rafael ; Catalán, Patricio ; Ibaceta, Raimundo; Blenkinsopp, Christopher; Cienfuegos Carrasco, Rodrigo Alberto; Villagrán, Mauricio ; Aguilera, Juan Carlos; Castelle, BrunoThis paper presents a 11-day experiment conducted at the high-energy dissipative beach of Mataquito, Maule Region, Chile. During the experiment, offshore significant wave height ranged 1-4 m, with persistent long period up to 18 s and oblique incidence. Wave energy reflection value ranged from 1 to 4 %, and results show that it is highly linked to both incoming wave characteristics and swash zone beach slope, and is well correlated to a swash-slope based Iribarren number. The swash acting as a low-pass filter in the reflection mechanism, our results show that thecut-off period is better determined by swash slope rather than incoming wave's period. A new low cost technique for observing high-frequency swash hydro-morphodynamics is introduced and validated using LIDAR measurements. A good agreement is found. Separation of uprush and backswash components using the Radon Transform illustrates the low-frequency filtering effect. These results show the key role played by swash mechanism in the reflection rate andfrequency selection. More investigation is needed to describe the reflection process and its link with shoreface evolution, moving toward a swash-by -swash approach.
- ItemSWASH-BASED WAVE ENERGY REFLECTION ON NATURAL BEACHES(2015) Almar, Rafael; Ibaceta, Raimundo; Blenkinsopp, Christopher; Catalán, Patricio; Cienfuegos Carrasco, Rodrigo Alberto; Trung Viet, Nguyen; Hai Thuan, Duong; Van Uu, Din; Lefebvre, Jean Pierre; Sowah Laryea, Wahab; Laibi, Raoul; Castelle, Bruno; Senechal, Nadia; Anthony, Edward J.Can wave reflection be remotely described from swash dynamics and the shoreface slope inversely from reflected waves? In this paper, we revisit the link between swash dynamics and reflection using contrasting field datasets: swell waves on steep and flat beaches and wind waves on an intermediate beach. Reflection ranges from less than 1% to up to 25%. Analyses are conducted from ~10-m depth directional wave spectra measurements, daily beach surveys and video swash measurements. Our results show that swash saturation can be linked to the offshore reflection cut-off frequency (shortest reflected waves) with a strong dependence on swash zone slope, underlining the importance played by swash processes in nearshore dynamics. Moving towards a more process-based approach, an ensemble-average analysis indicates that swash flow asymmetry and skewness are strongly linked to reflection.
- ItemTsunami du Chili 2010 : destruction du système littoral et retour vers un équilibre sédimentaire?(Editions Paralia CFL, 2012) Villagrán Valenzuela, Mauricio Felipe; Cienfuegos Carrasco, Rodrigo Alberto; Almar, Rafael; Catalán, Patricio; Camano, AndrésLe 27 février 2010, un mégaséisme de magnitude 8.8 au large du Chili a généré un tsunami qui a atteint des hauteurs de 10 m sur les côtes chiliennes. Les conséquences humaines et environnementales ont été lourdes. Nous détaillons ici les observations qui ont été réalisées d'abord ponctuellement pour évaluer l'impact du tsunami sur la morphologie littorale et ensuite sur la reconstruction naturelle au moyen d'un suivi bimensuel. Les relevés montrent que le littoral a subi une nette érosion associée à la destruction des structures sableuses (barres, plages, dunes). La réponse du littoral a ensuite été rapide (~mois) avec la reconstruction de la plupart des structures, avec cependant des évolutions vers des états souvent différents de ceux observés antérieurement au tsunami. En particulier, pour expliquer cette différence, les effets du changement d'élévation terrestre sur la zone et le déficit fluvial sont supposés avoir joué un rôle prépondérant. Les observations suggèrent que la dynamique de la flèche sableuse du rio Mataquito est particulièrement sensible à ces réajustements. Ces résultats sont riches d'enseignements, en particulier en considérant les effets tectoniques sur le littoral, notamment dans le cadre des échelles de temps des effets liés au changement climatique
- ItemWave runup video motion detection using the Radon Transform(2017) Almar, Rafael; Blenkinsopp, C.; Almeida, Luis Pedro; Cienfuegos Carrasco, Rodrigo Alberto; Catalán, Patricio A.