scholarly journals Beach Morphodynamic Response to a Submerged Reef

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 340 ◽  
Author(s):  
Douglas Duarte Nemes ◽  
Francisco Fabián Criado-Sudau ◽  
Marcos Nicolás Gallo
Keyword(s):  
Wave Energy ◽  
Wave Breaking ◽  
Seasonal Cycle ◽  
High Energy ◽  
Morphological Features ◽  
Energy Conditions ◽  
Vector System ◽  
Coastal Processes ◽  
Physical Mechanisms ◽  
Physical Functions

To develop beach engineering, the submerged structure’s primary physical functions have to be understood. This study focuses on submerged structures in order to understand the strategy of reduced wave energy, stabilizing the shoreline and not generating erosion or adversely modifying coastal processes. Important developments have been made since the 1990s, taking into account the functions of recreational amenity. However, non-dimensional models cannot explain the physical mechanisms that generate accretion or erosion morphological features in the lee of the submerged structure. The present study aims to collaborate with the understanding of the mechanism of beach response to a submerged structure. For this, 26 surveys were made using topographic, Lagrangian, and Eulerian hydrodynamic measures during one seasonal cycle of a beach system from Rio de Janeiro (Brazil) with a natural submerged reef or rocky bank V-shape in the plan. This beach system is energetic and intermediate when referring to wave energy conditions and beach states, respectively. The wave breaking vector system on the rocky bank’s geometry was examined in the intermediate and dissipative beach morphodynamic organization. The variability of the wave breaking vector system determines the establishment, deformation, and erosion features in the lee of the structure. During high-energy waves, the submerged structure’s hydrodynamic and morphodynamic processes are transparent. When the submerged structure combines with the dissipative beach state, the surfing wave conditions are improved. These results provide the dimensional and positional references for an engineering proposal for a beach system.

scholarly journals Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems

2021 ◽  
Vol 13 (10) ◽  
pp. 1874
Author(s):  
Isaac Rodríguez-Padilla ◽  
Bruno Castelle ◽  
Vincent Marieu ◽  
Philippe Bonneton ◽  
Arthur Mouragues ◽  
...  
Keyword(s):  
Optical Flow ◽  
Wave Breaking ◽  
Surf Zone ◽  
High Energy ◽  
Energy Conditions ◽  
Surface Currents ◽  
Pass Filter ◽  
Current Profiler ◽  
Low Pass

This paper examines the potential of an optical flow video-based technique to estimate wave-filtered surface currents in the nearshore where wave-breaking induced foam is present. This approach uses the drifting foam, left after the passage of breaking waves, as a quasi-passive tracer and tracks it to estimate the surface water flow. The optical signature associated with sea-swell waves is first removed from the image sequence to avoid capturing propagating waves instead of the desired foam motion. Waves are removed by applying a temporal Fourier low-pass filter to each pixel of the image. The low-pass filtered images are then fed into an optical flow algorithm to estimate the foam displacement and to produce mean velocity fields (i.e., wave-filtered surface currents). We use one week of consecutive 1-Hz sampled frames collected during daylight hours from a single fixed camera located at La Petite Chambre d’Amour beach (Anglet, SW France) under high-energy conditions with significant wave height ranging from 0.8 to 3.3 m. Optical flow-computed velocities are compared against time-averaged in situ measurements retrieved from one current profiler installed on a submerged reef. The computed circulation patterns are also compared against surf-zone drifter trajectories under different field conditions. Optical flow time-averaged velocities show a good agreement with current profiler measurements: coefficient of determination (r2)= 0.5–0.8; root mean square error (RMSE) = 0.12–0.24 m/s; mean error (bias) =−0.09 to −0.17 m/s; regression slope =1±0.15; coherence2 = 0.4–0.6. Despite an underestimation of offshore-directed velocities under persistent wave breaking across the reef, the optical flow was able to correctly reproduce the mean flow patterns depicted by drifter trajectories. Such patterns include rip-cell circulation, dominant onshore-directed surface flow and energetic longshore current. Our study suggests that open-source optical flow algorithms are a promising technique for coastal imaging applications, particularly under high-energy wave conditions when in situ instrument deployment can be challenging.

scholarly journals Geotechnical Approach to Early-Stage Site Characterisation of Shallow Wave Energy Sites

2021 ◽  
Vol 9 (6) ◽  
pp. 605
Author(s):  
Craig Heatherington ◽  
Alistair Grinham ◽  
Irene Penesis ◽  
Scott Hunter ◽  
Remo Cossu
Keyword(s):  
Wave Energy ◽  
Early Stage ◽  
Breaking Waves ◽  
Time Frame ◽  
High Energy ◽  
Specific Information ◽  
Terrain Analysis ◽  
Site Suitability ◽  
Site Characterisation ◽  
A Site

Marine renewable energy is still in its infancy and poses serious challenges due to the harsh marine conditions encountered for wave or tidal installations and the survivability of devices. Geophysical and hydrodynamic initial site surveys need to be able to provide repeatable, reliable, and economical solutions. An oscillating water column wave energy converter is to be installed on the west coast of King Island, Tasmania. The location is in a high-energy nearshore environment to take advantage of sustained shoaling non-breaking waves of the Southern Ocean and required site-specific information for the deployment. We provide insight into scalable geophysical site surveys capable of capturing large amounts of data within a short time frame. This data was incorporated into a site suitability model, utilising seabed slope, sediment depth, and water depth to provide the terrain analysis needed to match deployment-specific characteristics. In addition, short-term hydrology and geotechnical work found a highly energetic seabed (near seafloor water velocities <1 m/s) with sufficient bearing capacity (6 MPa). In a highly energetic environment, care was taken to collect the relevant data needed for an assessment of critical information to an emerging technology companies primary project. This is in addition to the malleable methodology for a site suitability model that can incorporate various weighted parameters to prioritise the location for shallow wave energy sites in general.

scholarly journals Diverse floodplain deposits of reworked loess in a monsoon climate (Hanzhong Basin, central China)

2021 ◽  
pp. 1-17
Author(s):  
Jef Vandenberghe ◽  
Xun Yang ◽  
Xianyan Wang ◽  
Shejiang Wang ◽  
Huayu Lu
Keyword(s):  
Soil Formation ◽  
High Energy ◽  
Central China ◽  
Energy Conditions ◽  
Middle Pleistocene ◽  
Sedimentary Sequences ◽  
Varied Intensity ◽  
Floodplain Deposits ◽  
Flooding Events ◽  
Floodplain Sediments

Abstract This paper describes an assemblage of diverse floodplain facies of reworked loess (facies b, c) in a Middle Pleistocene monsoonal setting of the Hanzhong Basin, central China. The vertical and lateral sedimentary sequences show changing energy conditions. Apart from the highest energy in the channel facies (facies a), a relatively high energy floodplain environment (facies b) prevailed in waterlogged conditions, with small, laterally migrating (sub)channels. Facies b generally interfingers with aggrading horizontal sheets of overbank deposits in alluvial pools and swamps in a floodplain with much lower energy (facies c), in which phases of stability (soil formation) occasionally interrupted overbank deposition. Reworked loess forms the main part of the floodplain deposits. The paleosols are considered to have been formed under low hydrodynamic conditions in an interglacial environment. These interglacial conditions follow the commonly assumed glacial conditions of channel facies a. The sedimentary successions in the floodplain show a recurrent composition and cyclicity between wet and dry floodplain sedimentation terminated by stability with soil formation. The cyclic rhythm of stacked high- and low-energy floodplain sediments is attributed to varied intensity of different hydrodynamic flooding events that may have been due to changing monsoonal rainfall or simple intrinsic fluvial behavior.

On characteristics of the water-particle velocity in a plunging breaker

1983 ◽  
Vol 126 ◽  
pp. 251-268 ◽  
Author(s):  
Takeo Nakagawa
Keyword(s):  
Wave Energy ◽  
Wave Breaking ◽  
Separate Flow ◽  
Transverse Flow ◽  
Two Dimensional ◽  
Frequency Range ◽  
Flow Component ◽  
Flow Components ◽  
Flow Drag ◽  
Plunging Breaker

Three velocity components of water particles in a plunging breaker over a horizontal step on the bed of a two-dimensional laboratory wave tank have been determined simultaneously by means of an elaborate flowmeter that measures the flow drag on three ‘tension threads’, with each recording a separate flow component.It is found that all three of the r.m.s. values in the plunging breaker become maximum at x/L ≈ 0·7, where x is the distance from the breaking point to the shore and L is the wavelength. It is found that both the velocity and r.m.s. values of the transverse flow component generated by the shoaling and wave breaking become comparable to those of the other two flow components.On the basis of spectral analyses it is found that major wave frequencies in both the longitudinal and vertical flow components of the original two-dimensional wave survive even after experiencing relatively strong shoaling and wave breaking, and part of the original wave energy is transferred to the transverse flow component and is located at these major frequencies. It is found that the majority of the higher-harmonic-frequency components (or turbulent fluctuations) are generated in the shoaling process and that the wave breaking provides a relatively minor contribution to the generation. Finally, it is found that, through the shoaling and wave breaking, the original wave energy is transported to a frequency range lower than the primary wave frequency (negative cascade), as well as to the higher frequency range (positive cascade) in each flow component.

scholarly journals Involvement of Progranulin in Hypothalamic Glucose Sensing and Feeding Regulation

Endocrinology ◽  
2011 ◽  
Vol 152 (12) ◽  
pp. 4672-4682 ◽  
Author(s):  
Hyun-Kyong Kim ◽  
Mi-Seon Shin ◽  
Byung-Soo Youn ◽  
Churl Namkoong ◽  
So Young Gil ◽  
...  
Keyword(s):  
Neuropeptide Y ◽  
Energy Condition ◽  
Physiological Role ◽  
High Energy ◽  
Glucose Sensing ◽  
Energy Conditions ◽  
Related Peptide ◽  
Feeding Regulation ◽  
Nocturnal Feeding ◽  
Hypothalamic Regulation

Progranulin (PGRN) is a secreted glycoprotein with multiple biological functions, including modulation of wound healing and inflammation. Hypothalamic PGRN has been implicated in the development of sexual dimorphism. In the present study, a potential role for PGRN in the hypothalamic regulation of appetite and body weight was investigated. In adult rodents, PGRN was highly expressed in periventricular tanycytes and in hypothalamic neurons, which are known to contain glucose-sensing machinery. Hypothalamic PGRN expression levels were decreased under low-energy conditions (starvation and 2-deoxy-D-glucose administration) but increased under high-energy condition (postprandially). Intracerebrovetricular administration of PGRN significantly suppressed nocturnal feeding as well as hyperphagia induced by 2-deoxyglucose, neuropeptide Y, and Agouti-related peptide. Moreover, the inhibition of hypothalamic PGRN expression or action increased food intake and promoted weight gain, suggesting that endogenous PGRN functions as an appetite suppressor in the hypothalamus. Investigation of the mechanism of action revealed that PGRN diminished orexigenic neuropeptide Y and Agouti-related peptide production but stimulated anorexigenic proopiomelanocortin production, at least in part through the regulation of hypothalamic AMP-activated protein kinase. Notably, PGRN was also expressed in hypothalamic microglia. In diet-induced obese mice, microglial PGRN expression was increased, and the anorectic response to PGRN was blunted. These findings highlight a physiological role for PGRN in hypothalamic glucose-sensing and appetite regulation. Alterations in hypothalamic PGRN production or action may be linked to appetite dysregulation in obesity.

scholarly journals The Seasonal Cycle of Blocking and Associated Physical Mechanisms in the Australian Region and Relationship with Rainfall

2013 ◽  
Vol 141 (12) ◽  
pp. 4534-4553 ◽  
Author(s):  
M. J. Pook ◽  
J. S. Risbey ◽  
P. C. McIntosh ◽  
C. C. Ummenhofer ◽  
A. G. Marshall ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Seasonal Cycle ◽  
Seasonal Temperature ◽  
Ocean Fronts ◽  
Temperature Changes ◽  
Physical Mechanisms ◽  
Australian Region ◽  
Continental Antarctica ◽  
Positive Correlations ◽  
Blocking Index

Abstract The seasonal cycle of blocking in the Australian region is shown to be associated with major seasonal temperature changes over continental Antarctica (approximately 15°–35°C) and Australia (about 8°–17°C) and with minor changes over the surrounding oceans (below 5°C). These changes are superimposed on a favorable background state for blocking in the region resulting from a conjunction of physical influences. These include the geographical configuration and topography of the Australian and Antarctic continents and the positive west to east gradient of sea surface temperature in the Indo-Australian sector of the Southern Ocean. Blocking is represented by a blocking index (BI) developed by the Australian Bureau of Meteorology. The BI has a marked seasonal cycle that reflects seasonal changes in the strength of the westerly winds in the midtroposphere at selected latitudes. Significant correlations between the BI at Australian longitudes and rainfall have been demonstrated in southern and central Australia for the austral autumn, winter, and spring. Patchy positive correlations are evident in the south during summer but significant negative correlations are apparent in the central tropical north. By decomposing the rainfall into its contributions from identifiable synoptic types during the April–October growing season, it is shown that the high correlation between blocking and rainfall in southern Australia is explained by the component of rainfall associated with cutoff lows. These systems form the cyclonic components of blocking dipoles. In contrast, there is no significant correlation between the BI and rainfall from Southern Ocean fronts.

scholarly journals A Review of the Morphology, Physical Processes and Deposits of Modern Straits

2021 ◽  
pp. SP523-2021-76
Author(s):  
Robert W. Dalrymple
Keyword(s):  
High Energy ◽  
Energy Conditions ◽  
Physical Processes ◽  
Content Type ◽  
Fluvial Deposits ◽  
Sediment Waves ◽  
Contourite Drifts ◽  
Supplementary Material ◽  
Maximum Flooding Surface ◽  
Oceanic Currents

AbstractThis study reviews the morphology, hydrodynamics and sedimentology of 33 modern straits, including examples from diverse tectonic and climatic settings. Strait morphology ranges from short, simple straits to long, tortuous passages many 100s of kilometers long; depths range from 10 m to >1 km. The morphological building block of strait sedimentation is a constriction flanked by open basins; a single strait can contain one or several of these. Currents accelerate through the constrictions and decelerate in the basins, leading to a spatial alternation of high- and low-energy conditions. Currents in a strait can be classified as either ‘persistent’ (oceanic currents or density-driven circulation) or ‘intermittent’ (tidally or meteorologically generated currents). Constrictions tend to be bedload partings, with the development of transport paths that diverge outward. Deposition occurs where the flow decelerates, generating paired subaqueous ‘constriction-related deltas’ that can be of unequal size. Cross-bedding predominates in high-energy settings; muddy sediment waves and contourite drifts are present in some straits. In shallow straits that were exposed during the sea-level lowstand, strait deposits typically occur near or at the maximum flooding surface, and can overlie estuarine and fluvial deposits. The most energetic deposits need not occur at the time of maximum inundation.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5746061

scholarly journals The correlative behavior of sandbars and shoreline along Sulina – Sf. Gheorghe beaches (Danube Delta Coast)

2016 ◽  
Vol 18 (1) ◽  
pp. 19-31
Author(s):  
Florin TĂTUI
Keyword(s):  
High Energy ◽  
Sandy Beaches ◽  
Energy Conditions ◽  
Danube Delta ◽  
Dune System ◽  
Migration Rates ◽  
System Protection ◽  
Main Driver ◽  
Southern Central

Longshore sandbars along wave-dominated sandy beaches are important for beach-dune system protection during storms. Our analysis is based on 6 years of seasonal and annual bathymetric surveys along 16 km of erosive, stable and accumulative low-lying non-tidal beaches northward of Sf. Gheorghe arm mouth (Danube Delta – Romanian Black Sea coast). Our results show significant correlations established between longshore sandbar crest positions and morphology with more intense coupling between the inner and outer sandbar sub-systems during high-energy conditions and more frequent along the northern erosive sector in comparison with the southern/central accumulative/stable ones. There is a good connection between the long-term shoreline mobility and sandbars offshore migration rates along different sectors of the study area, with faster sandbars movement and shorter cycle return periods along the northern erosive sector in comparison with the central (stable) and southern (accretionary) sectors. The longshore variations of the nearshore slope are the main driver of the relationship between long-term sandbars dynamics and shoreline variability along the study site.

scholarly journals LOS ARRECIFES DE LA ISLA DE SAN ANDRÉS (MAR CARIBE, COLOMBIA)

2016 ◽  
Vol 7 ◽  
Author(s):  
Jörn Geister
Keyword(s):  
Wave Energy ◽  
Maximum Degree ◽  
Caribbean Sea ◽  
High Energy ◽  
Reef Crest ◽  
Acropora Palmata ◽  
Reef Complex ◽  
Western Caribbean ◽  
The Caribbean ◽  
San Andres

The windward reef complex NE and E of San Andrés Island is briefly described in terms of submarine topography, sediments and the distribution of corals and other benthonic organisms. The breaker zone of the San Andrés barrier and other exposed Western Caribbean reefs characteristically exhibits a profuse growth consisting almost exclusively of Millepora. In this respect they are different from most other described West Indian reef localities, where Acropora palmata is the dominating species in this part of the reef. The replacement of Acropora palmata by Millepora is interpreted as an adaptation of the reef crest community to high energy environments due to long swell prevailing at the Western end of the Caribbean Sea. A few short reef sections exposed to the maximum degree of wave energy show conspicuous algal ridges.

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