Changes In Wave Characteristics Research Articles

Impact of sea level changes on future wave conditions along the coasts of western Europe

Abstract. Wind waves and swells are major drivers of coastal environment changes and coastal hazards such as coastal flooding and erosion. Wave characteristics are sensitive to changes in water depth in shallow and intermediate waters. However, wave models used for historical simulations and projections typically do not account for sea level changes whether from tides, storm surges, or long-term sea level rise. In this study, the sensitivity of projected changes in wave characteristics to the sea level changes is investigated along the Atlantic European coastline. For this purpose, a global wave model is dynamically downscaled over the northeastern Atlantic for the 1970–2100 period under the SSP5–8.5 climate change scenario. Twin experiments are performed with or without the inclusion of hourly sea level variations from regional 3D ocean simulations in the regional wave model. The largest impact of sea level changes on waves is located on the wide continental shelf where shallow-water dynamics prevail, especially in macro-tidal areas. For instance, in the Bay of Mont-Saint-Michel in France, due to an average tidal range of 10 m, extreme historical wave heights were found to be up to 1 m higher (+30 %) when sea level variations are included. At the end of the 21st century, extreme significant wave heights are larger by up to +40 % (+60 cm), mainly due to the effect of tides and mean sea level rise. The estimates provided in this study only partially represent the processes responsible for the sea-level–wave non-linear interactions due to model limitations in terms of resolution and the processes included.

Evaluation of Longshore Drift on the East Coast of Maengbang Beach (Gangwon, Korea) through Wave and Depth Changes

Kim, G.-S.; Ryu, H.-S., and Kim, S.-H., 2021. Evaluation of longshore drift on the east coast of Maengbang Beach (Gangwon, Korea) through wave and depth changes. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 499–503. Coconut Creek (Florida), ISSN 0749-0208. Numerical simulation of the sediment by the Delft3d model was conducted to examine the changes in the longshore drift transport caused by long-term wave changes at Maengbang Beach. Representative waves were identified with input reduction tools using NOAA NCEP wave data of about 40 years (i.e., January 1979 to May 2019). To verify the adequacy of the model, simulated wave and depth changes were compared with corresponding observed data for about 23-month period (from March 2017). Error analysis showed a bias of 0.05 and root mean square error of 0.23, indicating that the model results were satisfactory. Further, the observed and the simulated values of change in depth were similar. To examine the effects of long-term changes in wave characteristics, the NOAA wave data were classified into representative wave grades, and the annual trends of the representative waves were analyzed. After assessing the weight of each wave class considering the projected wave environment for year 2100, the amounts of sedimentation, deposition, and longshore drift transport were assessed for the same period. Sedimentation pattern would not change significantly compared to the current state, and the amount of the local longshore drift will likely decrease. While a local increase in the Longshore drift transport may occur, the overall drift and the amount of sediment movement are likely to remain at current levels. Regarding the coastal longshore drift under climate change, the study considered the average sea level rise as per scenarios RCP 2.6, RCP 6.0, and RCP 8.5 (IPCC, 2013). The net amount of sediment movement and its variability are projected to increase with the rise in sea level for most areas. Regarding the amount of sediment movement, local movement at the center of the coast will likely decrease compared to the present state, and, consequently, waves would have a greater impact on the edge due to sea level rise.

Evaluation of Coastal Sediment budget on Bongpo Beach by Structure installation

The coastal areas of South Korea are experiencing changes in erosion and sedimentation due to the irregular movements of silt and sediment in rivers and coasts. Erosion is particularly significant on the east coast due to changes in wave characteristics caused by the construction of artificial structures. Coastal erosion can be mitigated by evaluating coastal sediment budget based on long-term changes in wave characteristics and climate and by establishing a clear coastal management system accordingly. We investigated the changes in the movement of sand by waves, by performing an experiment to estimate the amount of sediment movement for Bongpo Beach that has been categorized as “severe” in the coastal erosion status data of the Ministry of Oceans and Fisheries(Ministry of Oceans and Fisheries, 2019). 54 representative waves were generated with input reduction tools. Each representative wave was used as input data for the Delft3d flow model and the SWAN wave model. And the final sedimentation results were calculated by considering the ratio corresponding to each representative wave. Finally, the four submerged breakwater and the one groin, which are currently installed in front of Bongpo, were simulated to analyze the changes in sedimentation before and after the structure.

О возможных причинах возникновения экстремально высоких волн в Балтийском море

Possible causes of extremely high waves in the Baltic Sea / Pohil A.E. // Hydrometeorological Research and Forecasting, 2020, no. 3 (377), pp. 58-70. The atmospheric conditions accompanying the occurrence of extremely high waves in the Baltic Sea (in particular, at the entrance to the Gulf of Bothnia) in 2004 and 2017 are analyzed. Changes in wave characteristics with a sharp decrease in the sea depth are considered. It is shown that the mechanisms like interference, when two wave systems overlap when rounding the island of Gotland, a superposition of a direct wave and a wave reflected from the steep slope at the entrance to the Gulf of Bothnia could contribute to the occurrence of extreme waves. Keywords: Baltic Sea, extreme waves, satellite data, water vapor fields Fig. 8. Ref. 19.

Change in wave characteristics during the transition from gravitational to shear flow of gas-sheared liquid films

The evolution of thin liquid films sheared by a co-current gas flow in a vertical cylindrical channel with an internal diameter of 11.7 mm was studied using a high-speed implementation of the laser-induced fluorescence method. The main purpose of the work was to study the characteristics of the waves during the transition from the gravitational to the shear flow regime. The effect of gas velocity, liquid Reynolds number, and liquid viscosity on wave characteristics has been studied.

Effect of Sea Level Rise and Offshore Wave Height Change on Nearshore Waves and Coastal Structures

In 1994, Townend proposed a method to calculate the relative changes in various wave characteristics and structure-related parameters due to sea level rise for regular waves. The method was extended to irregular waves by Cheon and Suh in 2016. In this study, this method is further extended to include the effect of future change in offshore wave height and the sea level rise. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height in nearshore area are presented as functions of the relative changes in water depth and offshore wave height. The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise and offshore wave height change on coastal structures by calculating the relative changes in wave run-up height, overtopping discharge, crest freeboard, and armor weight of the structures. The relative changes in wave characteristics and structure-related parameters are all expressed as a function of the relative water depth for various combinations of the relative changes in water depth and offshore wave height.

Cross-Correlation of Station-to-Station Free Surface Elevation Time Series for Breaking Water Waves

Free surface elevation time series of breaking water waves were measured in a laboratory flume. This was done in order to analyze changes in wave characteristics as the waves propagated from deep water to the shore. A pair of parallel- wire capacitive wave gages was used to simultaneously measure free surface elevations at different positions along the flume. One gage was kept fixed near the wave generator to provide a reference while the other was moved in steps of 0.1 m in the vicinity of the break point. Data from these two wave gages measured at the same time constitute station-to-station free surface elevation time series. Fast Fourier Transform (FFT) based cross-correlation techniques were employed to determine the time lag between each pair of the time series. The time lag was used to compute the phase shift between the reference wave gage and that at various points along the flume. Phase differences between two points spaced 0.1 m apart were used to calculate local mean wave phase velocity for a point that lies in the middle. Results show that moving from deep water to shallow water, the measured mean phase velocity decreases almost linearly from about 1.75 m/s to about 1.50 m/s at the break point. Just after the break point, wave phase velocity abruptly increases to a maximum value of 1.87 m/s observed at a position 30 cm downstream of the break point. Thereafter, the phase velocity decreases, reaching a minimum of about 1.30 m/s.

Sea-level rise induced amplification of coastal protection design heights

Coastal protection design heights typically consider the superimposed effects of tides, surges, waves, and relative sea-level rise (SLR), neglecting non-linear feedbacks between these forcing factors. Here, we use hydrodynamic modelling and multivariate statistics to show that shallow coastal areas are extremely sensitive to changing non-linear interactions between individual components caused by SLR. As sea-level increases, the depth-limitation of waves relaxes, resulting in waves with larger periods, greater amplitudes, and higher run-up; moreover, depth and frictional changes affect tide, surge, and wave characteristics, altering the relative importance of other risk factors. Consequently, sea-level driven changes in wave characteristics, and to a lesser extent, tides, amplify the resulting design heights by an average of 48–56%, relative to design changes caused by SLR alone. Since many of the world’s most vulnerable coastlines are impacted by depth-limited waves, our results suggest that the overall influence of SLR may be greatly underestimated in many regions.

Effect of sea level rise on nearshore significant waves and coastal structures

In this paper, the method to assess the impact of sea level rise under regular waves, as proposed by Townend (1994), is extended to irregular waves in order to estimate the changes in nearshore significant waves and the parameters related to hydraulic performance and stability of inclined coastal structures. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height for significant waves are presented as functions of the relative change in water depth. The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise on coastal structures by calculating the relative changes in wave run-up height, overtopping discharge, crest freeboard, and armor weight of the structures. The relative changes in wave characteristics are expressed as functions of relative water depth and deepwater wave angle or wave steepness. The relative changes in the structure-related parameters are expressed as functions of the relative change in wave height and the wave height and crest freeboard before the sea level rise.

Wave transformation on a coral reef rubble platform.

Harris, D.L. and Vila-Concejo, A., 2013. Wave transformation on a coral reef rubble platformWave transformation across coral reef platforms is the primary process affecting changes in coral reef geomorphology. Transformation regulates the amount of wave energy entering reef systems, however there have been relatively few hydrodynamic assessments conducted on coral reefs when compared to siliciclastic environments with the effects of common geomorphic features like rubble platforms on wave transformation never specifically examined. This study focuses on the changes in wave characteristics across a rubble platform in a high energy environment (One Tree Reef, southern Great Barrier Reef). Wave conditions were measured at five locations over two days along a cross-reef transect from the reef rim to lagoon. Most of the wave energy was dissipated during wave breaking with energy attenuation due to bottom friction a secondary process. Wave energy attenuation was between 60–99% of the offshore wave conditions only during high tide would wave propagation across the reef platform be capable of affecting reef geomorphology. The wave spectrum also changed with the shorter period gravity wave energy (3 – 20 s) almost completely expending during transformation while longer period infragravity waves (20 – 300 s) were capable of propagating across the reef platform. Wave heights were depth limited and primarily controlled by water depth which suggests that water depth over the reef platform and subsequently elevation of the reef platform above mean sea level govern the amount of wave energy transferred across into reef systems, with most of the gravity wave energy removed during propagation over coral rubble platforms.

Sorted bed forms as self-organized patterns: 2. Complex forcing scenarios

[1] We employ a numerical model to study the development of sorted bed forms under a variety of hydrodynamic and sedimentary conditions. Results indicate that increased variability in wave height decreases the growth rate of the features and can potentially give rise to complicated, a priori unpredictable, behavior. This happens because the system responds to a change in wave characteristics by attempting to self-organize into a patterned seabed of different geometry and spacing. The new wavelength might not have enough time to emerge before a new change in wave characteristics occurs, leading to less regular seabed configurations. The new seabed configuration is also highly dependent on the preexisting morphology, which further limits the possibility of predicting future behavior. For the same reasons, variability in the mean current magnitude and direction slows down the growth of features and causes patterns to develop that differ from classical sorted bed forms. Spatial variability in grain size distribution and different types of net sediment aggradation/degradation can also result in the development of sorted bed forms characterized by a less regular shape. Numerical simulations qualitatively agree with observed geometry (spacing and height) of sorted bed forms. Also in agreement with observations is that at shallower depths, sorted bed forms are more likely to be affected by changes in the forcing conditions, which might also explain why, in shallow waters, sorted bed forms are described as ephemeral features. Finally, simulations indicate that the different sorted bed form shapes and patterns observed in the field might not necessarily be related to diverse physical mechanisms. Instead, variations in sorted bed form characteristics may result from variations in local hydrodynamic and/or sedimentary conditions.

The influence of time-dependent wind on gravity-wave propagation in the middle atmosphere

Abstract. Ray-tracing techniques are used to computationally investigate the propagation of gravity waves through the middle atmosphere, as characterized by the vertically varying CIRA-86 wind and temperature models, plus a tidal wind model that varies temporally as well as vertically. For the wave parameters studied here, the background wind variation has a much stronger influence on the ray path and changes in wave characteristics than does the temperature variation. The temporal variation of the tidal component of the wind changes the observed frequency, sometimes substantially, while leaving the intrinsic frequency unaltered. It also renders temporary any critical levels that occur in the tidal region. Different starting times for the rays relative to the tidal phase provide different propagation environments, so that the temporary critical levels appear at different heights. The lateral component of the tidal wind is shown to advect propagating wave packets; the maximum lateral displacement of a packet varies inversely with its vertical group velocity. Time-dependent effects are more pronounced in local winter than in summer.

Small‐scale plasma, magnetic, and neutral density fluctuations in the nightside Venus ionosphere

Pioneer Venus orbiter measurements have shown that coherent small‐scale waves exist in the electron density, the electron temperature, and the magnetic field in the lower ionosphere of Venus just downstream of the solar terminator (Brace et al., 1983). The waves become less regular and less coherent at larger solar zenith angles, and Brace et al. suggested that these structures may have evolved from the terminator waves as they are convected into the nightside ionosphere, driven by the day‐to‐night plasma pressure gradient. In this paper we describe the changes in wave characteristics with solar zenith angle and show that the neutral gas also has related wave characteristics, probably because of atmospheric gravity waves. The plasma pressure exceeds the magnetic pressure in the nightside ionosphere at these altitudes, and thus the magnetic field is carried along and controlled by the turbulent motion of the plasma, but the wavelike nature of the thermosphere may also be coupled to the plasma and magnetic structure. We show that there is a significant coherence between the ionosphere, thermosphere, and magnetic parameters at altitudes below about 185 km, a coherence which weakens in the antisolar region. The electron temperature and density are approximately 180° out of phase and consistently exhibit the highest correlation of any pair of variables. Waves in the electron and neutral densities are moderately correlated on most orbits, but with a phase difference that varies within each orbit. The average electron temperature is higher when the average magnetic field is more horizontal; however, the correlation between temperature and dip angle does not extend to individual wave structures observed within a satellite pass, particularly in the antisolar region. The importance of fluctuations in the magnetic dip angle is that they inhibit vertical conduction and produce a small effective dip angle which reduces the heat flux necessary to maintain the observed temperatures.

Hydromagnetic field line resonances and modulation of particle precipitation

Hydromagnetic wave and modulated particle precipitation data are reported from conjugate areas near the particledrift shell L ∼ 4. A modulation of electrons precipitating from the magnetosphere is observed in the conjugate regions when the accompanying hydromagnetic wave period is ~ 90 s and the wave polarization is linear. When the wave period changes abruptly to ~ 30 s and the polarizations at the observing stations are no longer linear, the modulation of the precipitating electrons is no longer observed. The change in hydromagnetic wave characteristics does not appear to be related to interplanetary plasma and magnetic field conditions. Rather, it is proposed to arise from a change in the wave generation mechanism from an internal magnetospheric source near the inner edge of the plasmapause (lower frequency) to an externally driven source outside the magnetosphere (higher frequency). This observation of a change in the wave characteristics (frequency and polarization) associated with modulated electron precipitation appears to be related to two previous examples wherein modulated electron precipitation was reported to be closely associated with the existence of a wave resonance region near the observing site.

WAVE SHOALING OF FINITE AMPLITUDE WAVES

Wave shoaling is calculated, based on finite amplitude wave theories on a uniform depth which were extended by the authors using the Stokes second definition for wave celerity. Change of wave characteristics with decrease in water depth is discussed from numerical computation, and difference in shoaling characteristics is considered in comparison with results obtained from usual wave theories by the first definition. Theoretical results are compared with preliminary experimental ones on the wave transformation in shoaling water conducted by the experimental facilities satisfying the physical conditions corresponding to the definition for wave celerity as well as possible, and the validity of each theory for practical purposes is investigated.

Wave Characteristics with Restricted Fetch: Case Study of Lake Okeechobee: ABSTRACT

In the design of earth work constructions along rivers and lakes, it is important to know the relations between wind and the waves. Such observations are a first stage in a complete investigation of wave effects on beaches and earth structures of different shapes and materials. The generally used form of these relations deals with deepwater conditions, where the fetch is unlimited. Such relations cannot be applied to small lakes and protected bays. The earliest work in this field was that of Johnson on Clear Lake, California. He concluded that wind duration but not fetch was the controlling factor in any kind of change in wave characteristics. Later, on the basis of the study of Abbots Lagoon, California, Johnson showed that the dimensionless term gf/u2 is useful in estimating wave conditions within certain limits. Burling compared the wave data from Staines reservoir with the data End_Page 2210------------------------------ of Johnson, Bretschneider, and Sverdrup and Munk. Whereas the curves are of the same form, there is a great amount of discrepancy. Burling's line is 15-25 percent below the other lines. Data from Lake Okeechobee, Florida, indicate that there is a transitional region between deep water and shallow water, where the wave height is affected by combinations of wavelength and depth of water. The data from Lake Okeechobee align closely with Burling's results. However, Burling's observations were from a reservoir where the maximum fetch was about one km. In Okeechobee the fetch ranges up to 60 km. The Okeechobee study reveals that the proper method to define shallow-water waves should include fetch and wind velocities as well as the depth of water. The wave heights are lower than expected for lower wind velocities and higher than expected for higher wind velocities in shallow water, with limited fetch. End_of_Article - Last_Page 2211------------

TRANSFORMATION OF WAVES PASSING A SUBMERGED BAR

This study investigates the transformation of nonbreaking waves that pass over a submerged longshore bar. An envelope for the occurrence of ^ transformation of nonbreaking waves is established and compared with existing information. Power spectral analyses are made of both the incident and transformed waves to determine quantitatively the change in wave characteristics. The conclusion is made that the transformation process is a nonlinear phenomenon occurring over the bar, but, in the deeper water in the lee of the bar, a combination of linear wave forms results.