Variety Of Wave Conditions Research Articles

Applicability of a Long-Term Wave Hindcast System in the Inner Bay Areas and Seto Inland Sea of Japan Using SDP Measurement-Based Winds

A 45-year wave hindcast system on a nested grid with high space resolution is applied to investigate the long-term wave conditions in the inner bay areas and inland sea of Japan from Tokyo Bay to the western Seto Inland Sea. The system is driven station by station by hourly sea wind distributions evaluated using both the typhoon-embedded analysis wind data archive in the open ocean and the land-based measurement(SDP) wind data in the bay areas. Reasonable agreement between the hindcasts and measurements for wave statistics in each bay area shows that the system is sufficient to closely reproduce the long-term wave conditions in the concerned sea areas but that use of other types of wind data archives with temporal homogeneity may be desirable to more properly evaluate the long-term variation of wave conditions.

Fecal production by sea urchins in native and invaded algal beds

To examine the role of fecal production by the sea urchin Strongylocentrotus droe- bachiensis in native and invaded algal assemblages in Nova Scotia, Canada, we examined the quan- tity (production rate by urchin feeding aggregations, or 'fronts') and quality (organic carbon and nitro- gen content) of feces egested on 3 diets: (1) a native kelp Saccharina longicruris, (2) kelp encrusted with the invasive bryozoan Membranipora membranacea, and (3) an invasive green alga Codium fragile ssp. fragile. Relatively low absorption of clean and encrusted kelp resulted in high fecal output from urchins grazing native and invaded kelp beds (74 and 81 g feces m -1 front d -1 , respectively). In contrast, high absorption of C. fragile resulted in low fecal output from urchins grazing meadows of the invasive alga (31 g feces m -1 front d -1 ). Low C:N ratios of feces obtained from grazing C. fragile (8.5) or encrusted kelp (11.4), compared to clean kelp (30.7), suggest that feces from invaded assemblages are a higher quality food source for microbes and detritivores. To compare dispersal characteristics of feces from each diet, we measured pellet shape, size, density, and settling and critical erosion veloci- ties. Using a wave model, we estimated the depth at which feces would be deposited under seasonally varying wave conditions. We found that pellets of C. fragile are likely deposited at the greatest depths (33 to 55 m), pellets of clean kelp at intermediate depths (28 to 47 m), and pellets of encrusted kelp at the shallowest depths (22 to 40 m). Our findings suggest a smaller amount of higher quality feces enters the detrital food web at greater depths from Codium meadows than from native kelp beds.

Identification of breaking events from the responses of a data buoy

Conventional data buoys record wave spectral parameters such as the significant height, peak period, and mean direction. Information about the existence of wave groups and breaking waves is also important for the design of ocean structures. To derive such information from data buoy measurements, understanding of the motion characteristics of data buoys under a variety of wave conditions is essential. In the present study, the motion characteristics of a scale-modelled discus data buoy were tested under the action of deep-water breaking waves of different intensities, covering spilling to steep plunging types. The laboratory generation of breaking waves was based on the constructive wave—wave interaction method. The buoy heave and pitch motions were measured using potentiometers and non-contact motion-capturing cameras. The measured time series of the breaking-wave surface elevation and the resulting buoy motions were analysed by continuous wavelet transformation and phase—time methods. A closer insight into the wavelet phases reveals that the breaking events leave a constant phase variation over a wider range of higher frequencies. Through appropriate filtering of the localized frequencies, the phase—time method could also be adopted to detect breaking events in the time histories of the measured wave elevation and motion response. The details of the model, instrumentation, testing conditions, and analysis are presented and discussed in this paper.

Littoral sediment transport and shoreline changes along Ennore on the southeast coast of India: Field observations and numerical modeling

The newly constructed port in 2001 at Ennore, on the southeast coast of India near Chennai, with breakwaters on either side (north and south) has been causing large-scale changes in nearshore morphology. Beach profiles and shoreline positions along 25 km coastline of Ennore were measured at regular intervals during 2001–06 to understand the sediment transport patterns in the region. At the same time the results of wave hind-casting and wave transformation modeling were incorporated in LITDRIFT model to compute the sediment transport rates along Ennore coast. The model results are compared with the sediment transport values obtained from beach profile measurements. The performance of the model at different locations within the study area with variable wave conditions has been examined. The annual net sediment loss (−) versus accumulation (+) were estimated for two smaller study areas (cells) containing ten regularly spaced beach profiles numbered from north to south, BP1-5 in cell I and BP6-10 in cell II. For the cell I region, which is protected by the Ennore shoals and where human interference is minimum, the annual net sediment supply is + 0.02 × 10 6 m 3 as obtained from beach profile measurements while the model gave a value of + 0.014 × 10 6 m 3. For the cell II region where there is large human intervention by way of Ennore port development and breakwater construction, the annual net sediment movement as obtained by the beach measurements is − 0.14 × 10 6 m 3 while the model gave a value of − 0.154 × 10 6 m 3. It is found that the performance of the model is satisfactory and the model may be used successfully to study sediment dynamics along any coastline provided one has detailed understanding of the coastline orientation, nearshore topography, cross-shore bathymetry and prevailing annual wave climate. Based on the sediment transport data and beach profile measurements the beach and shoreline changes for transect locations BP-1 to BP-10 are also critically examined in this paper.

Patterns of surface sediment grain size distribution under the influence of varying wave conditions on a mixed sediment beach at Pevensey Bay, southeast England

Surface sediment distributions, derived using a new DGPS based survey technique, are described from three sections of a mixed sediment beach (MSB) at Pevensey Bay, southeast England. Spatial patterns of the distribution and size composition are related to antecedent hydrodynamic conditions and beach topography. Results indicate that higher energy waves produce a beach surface with a relatively homogenous grain size distribution, whilst lower energy waves produce surfaces with a more mixed size distribution. Under storm conditions, a 'type' beach response was recorded, comprised of a fine upper beach face and coarse lower beach face. Management practices, especially beach renourishment, also influence beach surface sediment distribution patterns

Dislodged but not dead: survivorship of a high intertidal snail following wave dislodgement

Waves breaking on rocky shorelines impart large forces on intertidal organisms, sometimes dislodging individuals. Dislodged individuals may be deposited in habitats that have a greater risk of predation or that prevent return to preferred regions on the shore. Thus, dislodgement is often assumed to be lethal. We experimentally dislodged Littorina keenae snails from high in the intertidal zone to test the likelihood of survival. Under a variety of wave conditions, we measured return rates to the high shore of 54–90%, so in this species, dislodgement is not equal to death. Snails showed a strong preference for returning to the approximate tidal height from which they were dislodged, but we found no evidence of widespread homing behaviour back to the original site of dislodgement.

Climate Controls on US West Coast Erosion Processes

Erosion along the West Coast of the United States is affected by climate controls that include a trend of increasing wave heights during at least the past 25 years that might be related to global warming and the El Niño Southern Oscillation (ENSO) range between El Niños and La Niñas that affects both annual wave conditions and monthly mean water levels that raise tidal elevations. These processes are analyzed for sites from Washington to south-central California, revealing a latitude dependence of the individual processes and how their combinations affect total water levels at the shore, which is important to beach and property erosion. Particularly significant on the coast of the Pacific Northwest (Washington and Oregon) has been the progressive decadal increases in deep-water wave heights and periods, which have increased breaker heights and elevated storm wave runup levels on beaches. Along the entire West Coast, the annual variations in wave conditions above and below any progressive decadal increase are controlled by the North Pacific index (NPI), the atmospheric pressure difference between the Hawaiian High and Aleutian Low, and the ENSO range, as demonstrated by a strong correlation with the multivariate ENSO index (MEI), with the highest wave conditions occurring during El Niños. In addition, the ENSO range is particularly important in controlling mean water levels, causing tides to reach their highest elevations during El Niños, again shown by correlations with MEIs along the entire West Coast. With El Niños producing increased deep-water wave heights, runup levels on beaches, and elevated tides, the total water levels at the shore from the combined processes are significantly higher compared with normal or La Niña years, resulting in episodes of major property erosion along the entire US West Coast.

Morphodynamics of intertidal bars on a megatidal beach, Merlimont, Northern France

The morphology, bedforms and hydrodynamics of Merlimont beach, in northern France, characterised by intertidal bars and a spring tidal range of 8.3 m, were surveyed over a 10-day experiment with variable wave conditions that included a 2-day storm with significant wave heights of up to 2.8 m. The beach exhibited two pronounced bar-trough systems located between the mean sea level and low neap tide level. Waves showed a cross-shore depth modulation, attaining maximum heights at high tide. The mean current was characterised dominantly by strong tide-induced longshore flows significantly reinforced by wind forcing during the storm, and by weaker, dominantly offshore, wave-induced flows. Vertical tidal water-level variations (tidal excursion rates) showed a bimodal distribution with a peak towards the mid-tide position and low rates near low and high water. The two bar-trough systems in the mid-tide zone remained stable in position during the experiment but showed significant local change. The absence of bar migration in spite of the relatively energetic context of this beach reflects high macro-scale bar morphological lag due to a combination of the large vertical tidal excursion rates in the mid-tide zone, the cross-shore wave structure, and the pronounced dual bar-trough system. The profile exhibited a highly variable pattern of local morphological change that showed poor correlation with wave energy levels and tidal excursion rates. Profile change reflected marked local morphodynamic feedback effects due mainly to breaks in slope associated with the bar-trough topography and with trough activity. Change was as important during low wave-energy conditions as during the storm. Strong flows in the entrenched troughs hindered cross-shore bar mobility while inducing longshore migration of medium-sized bedforms that contributed in generating short-term profile change. The large size and location of the two pronounced bars in the mid-tide zone of the beach are tentatively attributed respectively to the relatively high wave-energy levels affecting Merlimont beach, and to the cross-shore increase in wave height hinged on tidal modulation of water depths. These two large quasi-permanent bars probably originated as essentially breakpoint bars and are different from a small bar formed by swash and surf processes in the course of the experiment at the mean high water neap tide level, which is characterised by a certain degree of tidal stationarity and larger high-tide waves.

Un modèle morphologique côtier pour la création de barres rythmiques

ABSTRACT A hydrodynamic and morphodynamic model for sandy beaches is presented. One interesting point is that the effects of the undertow and the wave asymetry are computed, which are the main factors in the creation of the bar. A study of the position and the initial vertical growth of the bar has been made with varying wave conditions and beach slope. This model is integrated in a commercial 2DH software. And it has also been coupled with a model of linear stability which gives the initial bottom, perturbations be added to an initial plane beach. The complete model allows the creation of a rythmic bar.

Sediment resuspension on beaches: response to breaking waves

Field data of time-averaged suspended sediment concentration (ssc) are presented from three different UK beaches and a variety of wave conditions. The data are collated into a single analysis to examine the mechanisms associated with sand resuspension in the surf zone. Emphasis is placed upon the relative contribution of bottom and surface generated turbulence in controlling suspended sediment concentration distribution. Inside the surf zone, vortices induced by breaking waves and bores are the main mechanism for sediment resuspension; this process dominates over bottom boundary layer processes. Time-averaged reference concentration, defined as the ssc at 3.5 cm above the bed, does not correlate with bottom-induced shear stress or predicted ripple steepness. Both reference concentration and vertical distribution of sediment are controlled by the breaking wave (plunging, spilling) characteristics. Within the inner surf zone, hydraulic jumps (associated with strong offshore flows) are responsible for sediment resuspension. Vertical distribution of sediment is parameterised using a convective type time-averaged suspended sediment concentration profile. Reference concentration is highly correlated with wave breaking type, as defined by the local breaker parameter. The mixing parameter depends also on the wave breaking type and may be expressed as a fraction of the local water depth.

Flow resistance in the coastal zone

The apparent bed roughness, the roughness value experienced by a mean flow outside the wave-boundary layer, is deduced from the physical bed roughness and the wave–current interaction mechanism. Both the physical bed roughness and the wave–current interaction are described by a (combination of) model(s). Modelling of the apparent bed roughness leads to realistic results, however, the final results are rather sensitive to the particular choice of these models. Four bed form models and two wave–current interaction models were implemented in a 1-DV flow model to calculate near-bed velocities. A comparison between measured and predicted velocities shows that reasonable results can be obtained in this way. A constant bed roughness of 0.1 m, however, leads to even better results at this site during all conditions. This can be explained by the reversed influence of the form roughness and the wave–current interaction on the apparent bed roughness value for varying wave conditions.

Modelización del comportamiento morfodinámico de las playas mediante el estudio de la profundización de removilización

This paper concerns with a description of the variations in the disturbance depth across four open mesotidal beaches in the Cadiz littoral (SW Spain), along single tidal cycles, using rods and cores of marked beach sands inserted in the foreshore. The studied beaches show a quite wide range of morphologies, from reflective and barred dissipative to pure dissipative ones. Nevertheless, the energetic conditions of the coast remain more or less constant along its length. In this work the recorded disturbance depths have been compared with parameters like wave height, beach gradient and grain size distribution. As a conclusion, it has been obtained that the morphodynamic regime is the characteristic that better explains the spatial variation of the disturbance depth, as well as the different response of the beaches under broadly similar energetic conditions. In each case the morphodynamic situation controls the distribution and relative intensity of wave processes acting across the beach profile and, hence, the different rate of disturbance depth. The morphodynamic study of a beach permits an initial prediction of its morphological response under variable wave conditions.

Progression and Variability of Damage on Rubble Mound Breakwaters

As a first step to develop a probabilistic method for the maintenance and repair of breakwaters, one 28.5-h test and two shorter tests, which were repeated twice, were conducted in a wave flume. Damage progression and variability were measured on a conventional rubble mound exposed to depth-limited breaking waves in sequences of storms with varying wave conditions and water levels. Measurements were made of 16 or 32 damage profiles every 30 min of irregular wave action. Each measured profile was characterized by the eroded area, depth and length of the armor layer, and the remaining cover depth. The mean and standard deviation of these statistical variables changed with damage progression, whereas the probability distributions of the normalized variables were practically invariant. The mean and standard deviation of the damage variables are shown to be represented empirically by the mean eroded area alone. The damage variability along the breakwater was significant. Finally, an empirical formula is proposed to predict the mean eroded area in sequences of storms for these three tests.

Progression and Variability of Damage on Rubble Mound Breakwaters

As a first step to develop a probabilistic method for the maintenance and repair of breakwaters, one 28.5-h test and two shorter tests, which were repeated twice, were conducted in a wave flume. Damage progression and variability were measured on a conventional rubble mound exposed to depth-limited breaking waves in sequences of storms with varying wave conditions and water levels. Measurements were made of 16 or 32 damage profiles every 30 min of irregular wave action. Each measured profile was characterized by the eroded area, depth and length of the armor layer, and the remaining cover depth. The mean and standard deviation of these statistical variables changed with damage progression, whereas the probability distributions of the normalized variables were practically invariant. The mean and standard deviation of the damage variables are shown to be represented empirically by the mean eroded area alone. The damage variability along the breakwater was significant. Finally, an empirical formula is proposed to predict the mean eroded area in sequences of storms for these three tests.

Analysis of marine radar image spectra collected during the grand banks ERS‐1 SAR wave experiment

Abstract Remote measurements of wave spectra were made using MacLaren Plansearch's Marine Radar Wave Measuring System (Macrada©) for the duration of the ERS‐1 Grand Banks Experiment (10–27 November 1991). The system consists of a Furuno X‐band marine navigation radar and a personal computer. The system was installed and operated onboard the BIO Research vessel CSS Hudson during the experiment. The radar system provides fully directional wave spectra in real time (within minutes of image acquisition) as well as archiving of the raw images for future analysis. During each of the satellite overpasses, excellent data were collected, covering a variety of wave conditions. This paper describes the data analysis procedures and presents the results of the experiment. In addition, a sensitivity analysis is carried out to study: (1) sensitivity to the number of radar images processed on the resultant spectra, (2) effect of missing one or more images in a dataset, and (3) sensitivity to azimuth angle variation. Fina...

User‐Friendly PC‐Based Design Package for Gravity‐Type Seawalls

Designing gravity-type vertical seawalls involves repetitive design calculations in each block layer at different water levels under a variety of wave conditions. Incautious human errors that are fatal to the design may be introduced in calculations or in interpolations of design charts. In view of this, a computer-aided-design package is a real necessity. This paper presents the development of a user-friendly program in BASIC language tailored for use on microcomputers for the computer-aided design of such vertical seawalls. The program simulates the conventional manual design procedures, combining the relevant codes of practice and some heuristic rules of thumb from design experience. It automatically computes forces and moments due to surcharge and soil pressure behind the seawall together with wind-generated wave forces, and it checks for the adequacy of the seawall configuration under a variety of loading cases.

The application of Stokes' wave theory under changing sea levels in the Irish Sea

Although recent models of wave-dominated coastal systems have incorporated the Stokes wave equations, neither the flow predictions nor the shorewards limits of the theory have been adequately tested with field or laboratory experiments. Results are reported from 315 laboratory measurements of peak onshore and offshore flow speeds under a variety of wave conditions. Use of the complete data set indicates that predictions of nearbed flow velocity by Stokes' second-order theory are not accurate over the entire range of depths tested, and the importance of defining a shallow-water limit is discussed. The results suggest that the ratio of the first two harmonics of the nearbed flows is a useful criterion for constraining the depth range of the corrected wave theory. The results also indicate that flow velocity attenuates more rapidly with depth than is predicted by theory, and an empirical correction is derived. These analyses are applied to the wave-dominated seabed off the west coast of the Isle of Man in the central Irish Sea and show that the corrected theory is applicable to within 80 m of the shoreline at high water on a typical spring tidal cycle.

VALIDATION OF CROSS-SHORE TRANSPORT FORMULATIONS

Seymour and King (1982) evaluated eight models for predicting cross-shore transport using beach profile data from the Torrey Pines experiment of the Nearshore Sediment Transport Study (NSTS). None of the models showed useful skill in predicting the sense, or direction, of transport. Three more data sets were acquired under NSTS and have been used in the present work to re-evaluate the original four models as well as another six not previously tested. The three new data sets include two nominally plane West Coast beaches and a barred beach on the Atlantic coast, each under a variety of wave conditions. Six of the models evaluated claimed a capability to predict the sense of the cross-shore transport, two predicted the beach slope as a result of cross-shore movement, and two gave detail predictions of changes to the beach profile position and shape. The performance of the six models predicting direction of transport ranged from a skill factor of 0.49 (less than chance) to only 0.68. Five of the models required large changes to their calibration factor (usually based upon laboratory data) in order to have approximately the same skill in predicting erosion or accretion. One of the slope models was validated and the other gave no useful results. One of the two generalized models gave interesting results in predicting the time history of profile changes on the plane beaches for which it was developed. The other general model was not evaluated because it exhibited the lowest skill in predicting direction of transport.

A suspended sediment stratification correction for combined wave and current flows

A simple model for the near‐bottom combined wave and current flow over a moveable sediment bed is presented. The model is an extension of the Grant and Madsen (1979) combined wave and current model, with moveable bed effects on the physical bottom roughness included as by Grant and Madsen (1982). The unsteady conservation of fluid momentum and sediment mass equations, which are coupled through an eddy diffusivity closure scheme, are solved for the wave and current velocity profiles, along with the suspended sediment concentration and transport profiles. Sample runs are presented to illustrate the effect of varying wave conditions on the current, the mean sediment concentration, and the mean sediment transport. Results show that for fine to medium sands, self‐stratification of the flow can be important during storms owing to the large amount of sediment suspended by the waves and the enhanced turbulent mixing associated with the wave‐current interaction. The theory easily can be generalized for inclusion in a full Ekman layer model.

DYNAMIC STABILITY OF ROCK SLOPES AND GRAVEL BEACHES

More than 150 tests have been analyzed in order to describe the dynamically stable profiles of rock slopes and gravel beaches under wave attack. Relationships between profile parameters and boundary conditions have been established. These relationships have been used to develop a computer program. This program is able to predict the profiles of slopes with an arbitrary shape under varying wave conditions, such as those found in storm surges and during the tidal period.