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Variability in the characteristics of depth-induced wave breakers along a non-uniform coastal topography and its impact on the morpho-sedimentary processes is examined at the island sheltered wave-dominated micro-tidal coast, Karwar, west coast of India. Waves are simulated using the coupled wind wave model, SWAN nested in WAVEWATCH III, forced by the reanalysis winds from different sources (NCEP/NCAR, ECMWF, and NCEP/CFSR). Impact of the wave breakers is evaluated through mean longshore current and sediment transport for various wave energy conditions across different coastal morphology. Study revealed that the NCEP/CFSR wind is comparatively reasonable in simulation of nearshore waves using the SWAN model nested by 2D wave spectra generated from WAVEWATCH III. The Galvin formula for estimating mean longshore current using the crest wave period and the Kamphuis approximation for longshore sediment transport is observed realistically at the sheltered coastal environment while the coast interacts with spilling and plunging breakers. 相似文献
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The extreme 2013/2014 winter storms: hydrodynamic forcing and coastal response along the southwest coast of England 
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下载免费PDF全文 Gerd Masselink Tim Scott Tim Poate Paul Russell Mark Davidson Daniel Conley 《地球表面变化过程与地形》2016,41(3):378-391
The southwest coast of England was subjected to an unusually energetic sequence of Atlantic storms during the 2013/2014 winter, with the 8‐week period from mid‐December to mid‐February representing the most energetic period since at least 1953. A regional analysis of the hydrodynamic forcing and morphological response of these storms along the SW coast of England highlighted the importance of both storm‐ and site‐specific conditions. The key factor that controls the Atlantic storm wave conditions along the south coast of southwest England is the storm track. Energetic inshore wave conditions along this coast require a relatively southward storm track which enables offshore waves to propagate up the English Channel relatively unimpeded. The timing of the storm in relation to the tidal stage is also important, and coastal impacts along the macro‐tidal southwest coast of England are maximised when the peak storm waves coincide with spring high tide. The role of storm surge is limited and rarely exceeds 1 m. The geomorphic storm response along the southwest coast of England displayed considerable spatial variability; this is mainly attributed to the embayed nature of the coastline and the associated variability in coastal orientation. On west‐facing beaches typical of the north coast, the westerly Atlantic storm waves approached the coastline shore‐parallel, and the prevailing storm response was offshore sediment transport. Many of these north coast beaches experienced extensive beach and dune erosion, and some of the beaches were completely stripped of sediment, exposing a rocky shore platform. On the south coast, the westerly Atlantic storm waves refract and diffract to become southerly inshore storm waves and for the southeast‐facing beaches this results in large incident wave angles and strong eastward littoral drift. Many south coast beaches exhibited rotation, with the western part of the beaches eroding and the eastern part accreting. © 2015 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
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Spatio-temporal cross-shore profiles and textural characteristics are the key parameters for understanding dynamics of the inter-tidal sedimentary environment.This study describes short-term dynamics of the inter-tidal sedimentary environment at beaches along the micro-tidal coast.Further a correlation is estimated in cross-shore morphodynamics and textural characteristics of surface sediments.The sedimentary environment is examined for a complete annual cycle using monthly collected cross-shore profiles and sediment samples.The Devbag beach（northern side） and Ravindranath Tagore beach（southern side） at the Kali river mouth,Karwar,west coast of India are characterized from extremely gentle to average slope,and broadly composed of unimodal sands.The sedimentary environment is significantly composed of textures having fine to medium sand,well to moderately sorted,fine to coarse skewed,and platykurtic to leptokurtic in nature.During the annual cycle a reversal pattern is observed between the two adjacent beaches,where a slower rate of sediment accretion is observed at Devbag beach while Ravindranath Tagore beach exhibited erosion.The beach dynamics along with the propagation of south-west（SW） and south-west-west（SWW） waves towards the coast significantly exhibit a dominance of northward sediment transport with the existence of a northerly alongshore current.In addition,the study reveals that an eroded beach may not be significantly identified composed of coarse grains.The poor correlation in morpho-sedimentary characteristics reveals the prediction of grain characteristics based on beach profile and vice-versa is unrealistic. 相似文献
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The cross-shore variation of long-term average longshore current velocity was investigated on the basis of a 15-year data set of longshore current, wave and wind. The longshore current velocities were measured once a day along a 427-m-long pier. The results show that the direction of the long-term average longshore current velocity away (>200 m) from the shore was the opposite to that near the shore. The southward current was dominant offshore, whereas the northward current was dominant near the shore. The cross-shore variation of the long-term average longshore current velocity was formed owing to a difference between the wave and wind conditions when the northward and southward currents developed. When the northward current developed, the offshore wave height was relatively small and the frequency of the southward wind velocity was almost equal to that of the northward one. As a result, the northward current developed only near the shore and decayed outside the narrow surf zone. On the other hand, when the southward current developed, the offshore wave height was relatively large and the southward wind velocity was predominant, which resulted in the southward current developing not only in the wide surf zone but also outside the surf zone. The superposition of the two cross-shore variations produced a cross-shore variation of the long-term average longshore current velocity with a northward velocity near the shore and a southward velocity away from the shore. 相似文献
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Katsuto Uehara Pramot Sojisuporn Yoshiki Saito Thanawat Jarupongsakul 《地球表面变化过程与地形》2010,35(14):1701-1711
Seasonal variation in seabed elevation in the muddy intertidal zone of the Chao Phraya River delta, an area of serious coastal erosion for 40 years, was assessed using information on waves and tides predicted by numerical simulations. The study area is under the influence of the Southeast Asian monsoon climate and lies in the innermost part of a sheltered gulf, across which a low‐gradient slope has developed. Observations, aimed at evaluating the effectiveness of a prototype breakwater on mitigating coastal erosion, indicated that the seasonal variation in the seabed elevation, typically about 30 cm, was caused primarily by seasonal changes in wave direction and height. The breakwater seems to have contributed to a net rise in the seabed level at sites behind the structure. Seabed erosion was most apparent during the northeast monsoon, when waves are weak. Erosion under this low wave energy state was attributed to the combined effect of wave breaking and the low tidal level. A difference in the observed seabed accretion rate between the transitional intermonsoon period and the succeeding southwest monsoon period was attributed to the direction of the wave energy flux; offshore sediments seem to have been supplied efficiently to the study area by waves during the transitional period. Another potential cause of seabed erosion and accretion during the wet southwest monsoon season was the discharge of water and sediments from local canals associated with intense tropical rainfall; this discharge seems to be linked to land use in the coastal area. The results of this study show the importance of monitoring across‐shore sediment transport for better understanding of coastal erosion processes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Hydrodynamic constraints and storm wave characteristics on a sub‐horizontal shore platform 下载免费PDF全文
下载免费PDF全文 Few studies of wave processes on shore platforms have addressed the hydrodynamic thresholds that control wave transformation and energy dissipation, especially under storm conditions. We present results of a field experiment conducted during a storm on a sub‐horizontal shore platform on the east coast of Auckland, New Zealand. Small (<0.5 m) locally generated waves typically occur at the field site, whereas during the experiment the offshore wave height reached 2.3 m. Our results illustrate the important control that platform morphology has on wave characteristics. At the seaward edge of the platform a scarp abruptly descends beneath low tide level. Wave height immediately seaward of the platform was controlled by the incident conditions, but near the cliff toe wave height on the platform was independent of incident conditions. Results show that a depth threshold at the seaward platform edge > 2.5 times the gravity wave height (0.05–0.33 Hz) is necessary for waves to propagate onto the platform without breaking. On the platform surface the wave height is a direct function of water depth, with limiting maximum wave height to water depth ratios of 0.55 and 0.78 at the centre of the platform and cliff toe, respectively. A relative ‘platform edge submergence’ (water depth/water height ratio) threshold of 1.1 is identified, below which infragravity (<0.05 Hz) wave energy dominates the platform energy spectra, and above which gravity waves are dominant. Infragravity wave height transformation across the platform is governed by the relative platform edge submergence. Finally, the paper describes the first observations of wave setup on a shore platform. During the peak of the storm, wave setup on the platform at low tide (0.21 m) is consistent with measurements from planar sandy beaches, but at higher tidal stages the ratio between incident wave height and maximum setup was lower than expected. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Jeffrey A. Lee K. Evan Moffett B. L. Allen Richard E. Peterson James M. Gregory 《地球表面变化过程与地形》1994,19(5):437-449
Blowing dust is a common phenomenon at Lubbock, Texas, on the Southern High Plains. The directional variability of blowing dust estimated with the ‘sand rose’ technique, using wind speed and direction data, suggest that dust transport occurs from all directions. An empirical method of determining directional variability using meteorological data on visibility reductions due to blowing dust, however, indicates that most dust comes from the west and south-west. In addition to wind speed and direction, other environmental factors must be considered in explaining the spatial pattern of dust transport. Soil erodibility is variable in the region, with the most extensive area of highly erodible soils to the west and south-west of Lubbock. Rangeland dominates land use to the east, while agriculture is extensive to the north, west and south. Local farming techniques leave bare soil during the winter and spring, when most airborne dust is produced and also when strong winds are common from the west and south-west. Soil moisture is lowest to the southwest of Lubbock, which leads to a decrease in soil structure and an increase in the potential for wind erosion in that direction. Relative humidities affect threshold wind speeds and are lowest during March and April, when winds are common from the west and south-west. The spatial and seasonal variability and interactions between many factors, both natural and human-controlled, must therefore considered in explaining the directional variability of aeolian sediment transport at Lubbock. 相似文献
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Future shoreline changes on a sandy beach with a structure such as a jetty or groin can be estimated when wave time series is known (i.e. sequence of wave height, period, and direction). This paper presents an extension of an existing solution (Pelnard-Considere, 1956) for the linearized partial differential equation for shoreline change at an infinite jetty where waves are time varying and when the angle of the shoreline is small with respect to the waves breaking at the shoreline. The novel solution provided in this paper allows the previous constant wave condition solution to be extended to the case where wave properties (i.e. wave direction, wave height, and wave period) are time varying. Example usage of the method presented shows that shorelines may be of different final plan form shape for time varying wave conditions even though the sediment transport along adjacent beaches is not spatially varying (i.e. spatially constant) from time step to time step. Although this difference in shape may have been known previously using numerical models, it could not be proved analytically. Reversals of wave height, period, and direction time series are shown to provide different final shoreline shapes even though the time series consists of the same waves although in different ordered time. The solution provided will allow one line numerical shoreline models to be tested using an analytic solution. 相似文献
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Janusz Krzyścin 《Pure and Applied Geophysics》1990,132(3):481-493
In this paper we solve analytically wave kinematic equations and the wave energy transport equation, for basic long surface gravity wave in the coastal upwelling zone. UsingGent andTaylor's (1978) parameterization of drag coefficient (which includes interaction between long surface waves and the air flow) we find variability of this coefficient due to wave amplification and refraction caused by specific surface water current in the region. The drag coefficient grows towards the shore. The growth is faster for stronger current. When the angle between waves and the current is less than 90° the growth is mainly connected with the waves steepness, but when the angle is larger, it is caused by relative growth of the wave phase velocity. 相似文献
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Rafael Almar Alexandre Nicolae Lerma Bruno Castelle Timothy Scott 《Ocean Dynamics》2018,68(7):899-909
The reflection of incident gravity waves over an irregular swash zone morphology and the resulting influence on surf zone dynamics remains mostly unexplored. The wave-phase resolving SWASH model is applied to investigate this feedback using realistic low-tide terraced beach morphology with well-developed beach cusps. The rhythmic reflection generates a standing wave that mimics a subharmonic edge wave, from the superimposition of incident and two-dimensional reflected waves. This mechanism is enhanced by shore-normal, narrow-banded waves in both direction and frequency. Our study suggests that wave reflection over steep beaches could be a mechanism for the development of rhythmic morphological features such as beach cusps and rip currents. 相似文献
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The wave energy loss as waves break on nearshore bars is an important geomorphological process as it controls the stability of the adjacent beaches and dunes. The effect is particularly important during storms as it serves to guard against severe shoreline erosion. Field measurements from Florida and Ireland of waves crossing both single and multiple bar bedforms, indicate that where bar-breaking occurs, between 78 and 99 per cent of wave energy may be dissipated from individual waves. However, a further 20 per cent energy may reach the shore if wave frequencies increase during the reformation process. This latter effect was not noted at the multiple bar site where spilling mode breakers dominate. The level of energy dissipation is related to the time taken to cross that section of the submerged bar below the critical depth, d < 1.28H. In the field this may be approximated by the ratio of wave speed to the width of the bar breaker zone. 相似文献
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Shari L. Gallop Ana Vila-Concejo Thomas E. Fellowes Mitchell D. Harley Maryam Rahbani John L. Largier 《地球表面变化过程与地形》2020,45(15):3854-3868
Many estuaries contain sandy beaches that provide habitats and offer protective buffers for wetlands and infrastructure, alongside cultural and recreational resources. Research underpinning coastal management tends to focus on tide- and swell-dominated sandy beaches, but little attention is given to beaches in estuaries and bays (BEBs) that exist along a continuum of wind/swell wave, tide and riverine influence. BEBs are subject to less wave energy than open coast locations because of the generally narrow window of directions for which ocean waves can propagate through the entrance. However, when storm wave direction coincides with the orientation of the estuary or bay entrance, waves can penetrate several kilometres inside. Here we focus on eight BEBs in two major bays/estuaries in Sydney, Australia and present observations from before and after a major extratropical storm with waves from an atypical direction in June 2016. We quantify magnitudes of beach erosion and recovery rates for 3 years post-storm. We show that when high-energy storm waves penetrate bays and estuaries, BEBs can undergo up to 100% of subaerial beach erosion. Three years after the storm, only 5 of the 29 (17%) eroded subaerial beach profiles had recovered to their pre-storm volume. This is likely due to the lack of low-frequency, beach-building waves at BEBs under modal weather conditions in between storms, in contrast to open coast beaches. We also show that the recovery of BEBs may be limited by the absence of adjacent sediment reservoirs due to the dominance of tidal processes mid-channel. Our study highlights the unique behaviour of BEBs relative to beaches on the open coast, and that shifting wave direction needs to be considered in long-term beach resilience under climate change. © 2020 John Wiley & Sons, Ltd. 相似文献
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Multiple breaches of a dam resulting from wind-generated waves and wave overtopping are studied for a hypothetical long non-cohesive earthen dam with an uneven crest. Both wind speed and direction affect breach locations and outflow for a particular reservoir surface geometry. Locations on the dam with longer fetches along the wind direction are more subject to wave overtopping and breaching than other locations. Higher wind speeds lead to wave overtopping and dam breaches under larger freeboards than lower wind speeds. For a specified inflow hydrograph and spillway configuration, there exists a location at which the smallest estimated peak outflow occurs among all possible breach locations and the pool drops too quickly for additional breaches to develop. Using this location for a fuse plug or a pilot channel could minimize downstream impact, perhaps as an interim or emergency measure for a dam with inadequate spillway capacity. 相似文献
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Mud deposits near sandy beaches, found throughout the world, are of scientific and societal interest as they form important natural sea defenses by efficiently damping storm waves. A multi-national field experiment to study these phenomena was performed offshore Cassino beach in southern Brazil starting in 2004. This experiment aimed to investigate the formation of an offshore mud deposit, to characterize wave attenuation over potentially mobile muddy bottoms, and to evaluate the performance of models for wave transformation over heterogeneous beds through the measurement of water waves, near-bottom currents, bathymetry, and changes in bottom sediment characteristics. The main instrumentation was a set of wave sensors deployed in a transect from the shoreline across sandy and muddy deposits offshore to a depth of 25 m. Additional sensors, including current meters and optical backscatter sensors, were concentrated at stations in the middle of the mud deposit and in the surf zone to document aspects of the wave boundary layer and lutocline dynamics. This fieldwork also involved the geological and geotechnical characterization of the mud deposit using seismic equipment, echo-sounders, cores, surficial sampling and an in-situ density meter. These sediment samples were subsequently analyzed for density, grain size distribution, mineralogy, rheology and sedimentary structures. In addition, video and radar monitoring equipment were installed to measure the long-term aspects of surf zone damping by fluid mud and any associated morphodynamic responses. This paper provides a summary of environmental conditions monitored during the experiment and describes the major findings of the various investigations. Although data collection was more difficult than anticipated and dramatic wave attenuation involving the onshore transport of fluid mud into the surf zone region was not observed during the instrumented interval, the new methodologies developed and comprehensive observations obtained during this effort are being used to improve our understanding of shoaling wave dynamics and sediment transport in the coastal zone in regions with significant cohesive sediment deposits. 相似文献
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Modelling the wave phenomena in acoustic and elastic media with sharp variations of physical properties using the grid‐characteristic method 下载免费PDF全文
下载免费PDF全文 Alena V. Favorskaya Michael S. Zhdanov Nikolay I. Khokhlov Igor B. Petrov 《Geophysical Prospecting》2018,66(8):1485-1502
This paper introduces a novel method of modelling acoustic and elastic wave propagation in inhomogeneous media with sharp variations of physical properties based on the recently developed grid‐characteristic method which considers different types of waves generated in inhomogeneous linear‐elastic media (e.g., longitudinal, transverse, Stoneley, Rayleigh, scattered PP‐, SS‐waves, and converted PS‐ and SP‐waves). In the framework of this method, the problem of solving acoustic or elastic wave equations is reduced to the interpolation of the solutions, determined at earlier time, thus avoiding a direct solution of the large systems of linear equations required by the FD or FE methods. We apply the grid‐characteristic method to compare wave phenomena computed using the acoustic and elastic wave equations in geological medium containing a hydrocarbon reservoir or a fracture zone. The results of this study demonstrate that the developed algorithm can be used as an effective technique for modelling wave phenomena in the models containing hydrocarbon reservoir and/or the fracture zones, which are important targets of seismic exploration. 相似文献
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Interactions between waves, current, mud and turbulence are very complicated in the coastal and estuarine turbid waters. It is still necessary to improve our understanding of the fundamental physical processes governing the cohesive sediment transport in the coastal and estuarine waters. A numerical model is developed to study the interactions among waves, current, and mud. An eddy viscosity model for wave and current is proposed in order to close the equations of wave motion or of current motion in a combined flow, respectively. The equations of mud transport are derived based on the visco-elastic properties of mud. Coupling the equations of wave motion or of current motion for water layer with those of mud layer can give (1) wave height; (2) distributions of current velocities in the water layer; (3) distributions of transport velocities at the water–mud interface; and (4) distributions of mass transport velocities within the mud layer. These modeled results are in a reasonable agreement with experimental results. Results suggest that (1) the rate of wave attenuation increases in the opposing currents (currents against in the direction in which the waves propagate) and decreases in the following currents (currents in the same direction as that in which the waves propagate); (2) the opposing currents would have more significant effects on the rate of wave height attenuation than the following currents; (3) the effect of current on the rate of wave attenuation on the muddy bottom is larger than that on the rigid bottom; (4) mud transport rate increased in the following currents but decreased in the opposing currents; and (5) the rate of wave height attenuation on the mud bottom is one order of magnitude larger than that on the rigid bottom. 相似文献
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The on–offshore (cross-shore) transport of sand on beaches is highly time-variable, which has made it difficult to model or predict. In this paper, simple energetics modelling is used to compare velocity moment predictions with field observations of suspended sand transport rates. Separate consideration is given to transport associated with the three main frequency-dependent cross-shore transport processes: that associated with the short (incident) waves, that due to the long (infragravity) waves, and transport associated with the mean flow. Direct comparison between the depth-averaged model predictions, and the in-situ point measurements was facilitated by making the first order assumption that the time-averaged suspension profile is exponential and the wave velocity profile is vertically uniform. An appropriate rippled bed roughness was used to provide the drag coefficient in the energetics model and the vertical length scale of the exponential suspension profile. Despite these simple assumptions, comparison of the velocity moment predictions with the field observations of suspended sand fluxes reveals that this approach has the capacity to predict transport magnitudes due to short wave, long wave, and mean flow components to within about one order of magnitude. However, owing to the limitations of the model, the transport direction of the short wave component could not, on occasion, be correctly determined, probably due to ‘reverse’ transport over ripples. © 1998 John Wiley & Sons, Ltd. 相似文献