Effect of wind and atmospheric pressure variations on the mean sea level of salt marshes and estuaries

Se presentan tres formulaciones para predecir las variaciones de largo periodo en el nivel del mar debidas no a la marea astronómica, sino a fenómenos meteorológicos como el viento y los cambios de presión tanto de carácter estacionario como dinámico. Para validar estas fórmulas, se analiza una serie de datos del nivel del mar de tres meses de duración tomada en dos puntos del caño de Sancti Petri separados 5 km entre sí. Se advierten importantes variaciones del nivel medio diario y se demuestra que dichas variaciones son causadas por cambios en la presión atmosférica. Las diferencias son tan importantes (llegan a ser de 26 cm en cuatro días y de 50 cm en un mes y medio) que no pueden ser explicadas únicamente por el factor barométrico invertido (FBI) estático y debemos acudir a la hipótesis dinámica. Los valores ajustados del FBI real oscilan entre 1.9 y 2.2 cm/mb, el doble de lo generalmente utilizado. Se proporciona una acotación superior de la fórmula, de fácil aplicación, para el FBI dinámico. Debido a la morfología y dimensiones del caño, el efecto del viento fue despreciable en este caso. Como conclusión, debe destacarse que cualquier estudio que persiga encontrar la determinación de niveles máximos del mar en estuarios y marismas, con vistas a la delimitación del dominio público marítimo terrestre o de zonas inundables, deberá considerar series de datos de un año mínimo de duración. En caso contrario, la predicción será siempre inferior a los valores reales.The article presents three formulas to predict long-term variations in sea level due not to astronomical tide but to weather effects such as the wind and changes in pressure of both seasonal and dynamic nature. In order to validate these formulas, an analysis was made of a series of sea level data recorded, over a period of three months, at two points in the Sancti Petri Channel spaced 5 km apart. Considerable variations were noted in the daily mean sea level and these variations have been shown to have been caused by changes in the atmospheric pressure. The differences are so large (as much as 26 cm in four days and 50 cm in six weeks) that they cannot be purely explained by the static inverted barometer effect (IBE) and we must then resort to a dynamic hypothesis. The adjusted values of the real IBE vary between 1.9 and 2.2 cm/mb, twice that generally employed. An easily applicable upper limit of the formula for the dynamic IBE is provided. On account of the form and the dimensions of the channel, the wind effect is negligible in this case. By way of conclusion it is indicated that any study attempting to establish the maximum sea levels in estuaries and salt marshes, in order to mark the boundaries of public-owned coastal zones or floodable areas, would require an examination of a series of data covering at least one year. If this is not the case, the forecast will always be lower than the real values

Monitoring of the water particle velocity field near the seabed under different wave and tidal scenarios: a real case

Monitoring of water particle velocity on the sea bed is crucial to study morphological shore changes in a coast at intermediate and shallow water depth under progressive surface waves and tidal flow current. Therefore, 3-D particle velocity was monitored continuously at the bottom of Santa Maria del Mar (SMM) beach (SW Spain) by means of a single point current meter during 3 weeks in 2007 since August 28. The current meter was placed at 0.45m above the seabed in order to acquire instantaneous velocity. Wave properties (height and period) were taken from the nearby wave buoy and tidal data were taken from a tidal gauge station. Wave-induced bottom particle velocities were obtained during spring and neap tides at a d/L (depth over wave length) parameter ranging from 0.06 to 0.3. Bottom water particle velocity near the seabed ranges from 0 to ± 0.5 m/sec of which about 82% does not exceed 0.2 m/sec during monitoring. Therefore, only 18% of the surveyed water particle velocities exceed the critical Shield parameter of the beach sand (d50 = 0.23mm) which is about 0.05-0.2 depending on Reynolds number. Results show that maximum horizontal speed is obviously lower during the slack tide (high or low tide) in comparison with flood tide and ebb tide. Moreover, speed is higher during ebb tide in comparison to adjacent flood tide, with steady wave climate. Finally and among other conclusions, the maximum real values of the bottom current surveyed in SMM, as well as the Shield parameter, substantially coincide with the theoretical estimates calculated for a given wave and tidal climate

Short term variability of reef protected beach profiles: an analysis using EOF

Victoria beach (SW Spain) has a rocky flat at the northernmost zone. This has allowed to choose one profile and monitoring the changes induced by a single day storm. Topographic data taken during 21 days and different tendencies of the beach profile, as the accretion rate, were identified. The analysis is carried out by means of Empirical Orthogonal Function (EOF) techniques, in order to separate the spatial from the temporal variability of the beach profile data. Among the conclusions, it should be highlighted that a swing or oscillation point of the profile was found around the intertidal zone. Furthermore, the erosion has been irreversible in a short term, and the recuperation consisted only in a modification of the slopes of the emerged part, trying to assimilate them to the ones before the storm. Read More: http://ascelibrary.org/doi/abs/10.1061/40855%28214%29

Comentario sobre Avila-Serrano et al. “Variaciones sedimentarias y transporte litoral en Playa de la Victoria, Cádiz, España”

The article published by Avila-Serrano et al. (2009) presents an interesting analysis of the sediment dynamics at Victoria Beach based on a series of samples taken together with fortnightly topographic profiles between February and October 2004. The authors of this comment, directors of this beach’s regeneration and monitoring programs over the past 20 years, believe some observations are relevant. We aim to provide a series of constructive comments that complement Avila-Serrano et al.’s commendable study

Beach Nourishment: A 21st Century Review

Long-term erosion is experienced by most of the coastlines worldwide, and it is usually attributed not only to sea level rise but also to the retention of sand in dams, the occupation of dry beaches by urbanized areas, the disturbance of the natural patterns of longshore drift, the mining of sand as building material for construction, and so on. Beach nourishment has evolved as the favored erosion-mitigation strategy in many areas of the world. The increasing number of people living on the coast, the safety of those people, and the high values of coastal property are all factors that have made beach nourishment a cost-effective strategy for managing erosion in many locations. However, a new scenario of sand scarcity and environmental care has arisen in recent decades. There have been a number of different and interesting cases of various aspects of beach nourishment in the last years. The purpose of this Special Issue has been to publish the different experiences and research related to this topic. After a careful review process, nine papers were included. Their thematic contributions include the use of field methods such as the use of remotely piloted aircraft systems (RPAS) or un-manned aerial vehicles (UAV) for faster and automated mapping of the coastal area or the acquisition of geomagnetic data in marine environments; the use of multi-approach methodologies to assess the interaction between coastal structures and beaches and in particular of submerged pipelines; the need to adopt a plan for the optimal use of limited resources of available sediment from a regional perspective and the assessment of the effectiveness of beach nourishments; the understanding of the role of submerged geological control of beach profiles together with the implementation of innovative beach nourishment strategies while facing the non-trivial challenge of visualizing and communicating mesoscale modeling assumptions, uncertainties and outcomes to both coastal specialists and decision makers; and the influence of sea-level rise and erosion on diminution of beach habitats

Ondas regulares y su aplicación en la ingeniería de costas

Pronto se cumplirán 20 años desde mis primeras clases en la Facultad de Ciencias del Mar de la Universidad de Cádiz. Por aquel entonces, los catedráticos Luis Tejedor y Paco López Aguayo decidieron asignar la docencia de la asignatura de Ingeniería de Costas a un joven ingeniero de caminos del Estado. Siempre les estaré agradecido por la confianza que me mostraron al principio, al permitirme acceder al gratificante mundo de la enseñanza, y por la desinteresada amistad con que me honraron después.102 págs

Influence of coastal structures on equilibrium beach

An equilibrium beach profile model for a beach affected by a coastal structure is presented. The model is based on the well-known energy flux approach proposed by Dean (1977). The effect of the structure is taken into account by considering the modification that the structure generates on the wave energy flux. The model is then applied to several cases that are usually found along the littoral, namely a perched beach and a reefprotected beach. Several field and laboratory data are used to analyze the merit of the proposed model for describing the equilibrium condition of a beach profile affected by a coastal structure. A good comparison is obtained

A return to the "Rules of Thumb" in Maritime Engineering for digital native students

Engineering and technical degrees are difficult to teach and, consequently, have always been characterized by a large number of academic failures. That is the reason why different methodologies have been applied to classes of similar content in different countries [1]. Among these methodologies, it is noteworthy to mention audio/visual resources as a useful tool to improve the teaching of coastal engineering [2], which means more students that pass the coastal engineering courses [3]. Moreover, use of GPS and Google Earth have also shown to be useful tools to improve the learning process [4]. Nevertheless, the authors have not found anything about the use of “rules of thumb” as a better way for students to improve their comprehension of the basic knowledge of an engineering subject. This paper shows the teaching experience on Maritime Engineering for undergraduate students of Civil Engineering in the School of Engineering at the University of Seville (Spain). The application of new information technologies in classrooms and advanced training in the use of finite element software tools and programming languages gives our students extremely powerful tools for solving very complex engineering problems with excellent results. However, the enormous effort invested by the students in acquiring this advanced knowledge and to be up to date in using and commanding on these technologies leads them to focus their main efforts, attention and skills just toward the numerical resolution of the problem, the efficiency of the implemented algorithm, and the programming language difficulties. This puts aside the essential and the critical sense of the accuracy of the results obtained by the algorithm. The students do not get the physical ‘feeling’ of what’s happening in the algorithm. We have included a teaching sequence in our lesson programs that always starts with an historical review of the different approaches used by engineers in their times in order to solve engineering problems from the seventeenth through the nineteenth century to today. This method makes the students to appreciate the importance and wits required by those men in the past in facing a difficult task when they didn’t have a PC or powerful software. The “rules of thumb” in engineering become a powerful tool for the digital native students which helps them make sense and enjoy the study and programming when they finally find out that their algorithm responds with reasonable accuracy and orders of magnitude to the result expected beforehand. Simply applying "rules of thumb" and well-known approximations of the past, perhaps obsolete from a technical point of view, will help the student learn the process. Some examples will be given in this paper in order to show the use of these “rules of thumb” or simplified models in class for teaching Maritime Engineering subject. Among them: the dimensionless stability number of Vicente Negro [5] for the design of the armour layer blocks in breakwaters, the Iribarren’s wave drawings [6], the US Army Corps of Engineers Shore Protection Manual Graphs and plates, etc

Non-dimensional analysis of experimental pressure drop and energy dissipation measurements in Oscillatory Baffled Reactors

An experimental study is performed to characterize the pressure drop and the power consumption in Oscillatory Baffled Reactors, using dimensionless numbers: the oscillatory Fanning friction factor (f osc ) and the Power number (Po), respectively. Two baffle geometries (one-orifice and three orifices) are tested, for different fluids and oscillating amplitudes. The range of oscillatory Reynolds numbers (Reosc ) tested is 10–1000. Data reduction based on the statistical fitting and the FFT of the pressure drop and velocity signals is introduced to assess the maximum pressure drop and the phase lag between both signals. The new set of experimental data proves the limitations of the conventional models available in the open literature. f osc and Po provide consistent dimensionless results for the different working fluids tested and their trends are clearly related to different flow behaviours: laminar or chaotic flow. Correlations for f osc and Po as a function of Reosc and dimensionless amplitude are obtained.The authors gratefully acknowledge the financial support of the project DPI2015-66493-P by Ministerio de Economía y Competitividad (MINECO, Spain) and the European Regional Development Fund (ERDF)

Characterization of wind-blown sediment transport with height in a highly mobile dune (SW Spain)

The Valdevaqueros dune is located at one of the windiest points of Europe, where the frequent occurrence of strong easterly winds has generated a highly mobile dune. Several rotating cup anemometers in vertical array and a self-designed vertical sand trap, were placed to retain the drift sands at different heights over the surface in order to determine theoretical and actual sand transport rates in the Valdevaqueros dune system. General results show that 90% of the wind-blown sand is transported within the first 20cm above the dune crest surface. Theoretical transport rates based on different empirical formulae were 0.33 to 0.78 times the in-situ sand transport rate detected, which was 2.08·10-2kgm-1s-1 under moderate wind power (mean speed ranging from 8.4 to 17.9ms-1). Analysis of different statistical grain-size parameters helped to understand sand transport distribution at different heights