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Showing papers on "Wave height published in 2001"


01 Jan 2001
TL;DR: In this paper, the authors used particle image velocimetry (PIV) and laser distance sensors (LDS) to measure the wave run-up in Gilbert Inlet.
Abstract: On July 8, 1958, an 8.3 magnitude earthquake along the Fairweather fault triggered a major subaerial rockslide into Gilbert Inlet at the head of Lituya Bay on the South coast of Alaska. The rockslide impacted the water at high speed creating a giant nonlinear wave and the highest wave run-up in recorded history. The soliton like wave ran up to an altitude of 524 m causing forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis. Total area between trimline of forest destruction on shores of Lituya Bay and high-tide shoreline covered about 10 km*. A cross-section of Gilbert Inlet was rebuilt at 1:675 scale in a two-dimensional physical laboratory model at VAW. The subaerial rockslide impact into Gilbert Inlet, wave generation, propagation and run-up on headland slope were considered in a geometrically undistorted Froude similarity model. A novel pneumatic landslide generator was used to generate a high-speed granular slide with controlled impact characteristics. State-of-the-art laser measurement techniques such as particle image velocimetry (PIV) and laser distance sensors (LDS) were applied to the decisive initial phase with rockslide impact and wave generation. PIV-measurements of wave run-up on headland slope were conducted to complement wave and run-up gage records. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and run-up. The whole process of a high speed granular slide impact may be subdivided into two main stages: a) Rockslide impact and penetration with flow separation, cavity formation and wave generation, and b) air cavity collapse with rockslide run-out and debris detrainment causing massive phase mixing. Impact stages overlap and their transition from wave generation to propagation and run-up is fluent. Formation of a large air cavity similar to an asteroid impact in the back of the rockslide is highlighted. The laboratory experiments confirm that the 1958 trimline of forest destruction on Lituya Bay shores was carved by a giant rockslide generated impulse wave. The measured wave run-up perfectly matches the trimline of forest destruction on the spur ridge at Gilbert Inlet. Back-calculation of wave height from observed trimline of forest destruction using Hall and Watts (1953) run-up formula equals measured wave height in Gilbert Inlet. PIV-measurements of wave run-up indicate that enough water ran up the headland slope to cause the flooding observed in Lituya Bay as estimated by Mader (1999) with numerical simulations of the whole Lituya Bay. ’ Research Engineer, VAW, ETH-Zentrum, CH-8092, Switzerland 2 Professor, VAW, ETH-Zentrum, CH-8092, Switzerland ’ Professor, Director of VAW, ETH-Zentrum, CH-8092, Switzerland Science of Tsunami Hazards, Vol 19, NO. 1 (2801) page 3

179 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe an experimental study of two-dimensional surface water waves propagating on a depth-varying current with a non-uniform vorticity distribution.
Abstract: This paper describes an experimental study of two-dimensional surface water waves propagating on a depth-varying current with a non-uniform vorticity distribution. The investigation is divided into two parts. The first concerns the ‘equilibrium’ conditions in which the oscillatory wave motion and the current co-exist. Measurements of the water-surface elevation, the water-particle kinematics, and the near-bed pressure fluctuations are compared to a number of wave and wave–current solutions including a nonlinear model capable of incorporating the vertical structure of the current profile. These comparisons confirm that the near-surface vorticity leads to an important modification of the dispersion equation, and thus affects the nature of the wave-induced orbital motion over the entire water depth. However, the inclusion of vorticity-dependent terms within the dispersion equation is not sufficient to define the combined wave–current flow. The present results suggest that vorticity may lead to a significant change in the water-surface profile. If a current is positively sheared, dU/dz > 0, with negative vorticity at the water surface, as would be the case in a wind-driven current, a wave propagating in the same direction as the current will experience increased crest–trough asymmetry due to the vorticity distribution. With higher and sharper wave crests there is a corresponding increase in both the maximum water-particle accelerations and the maximum horizontal water-particle velocities. These results are consistent with previous theoretical calculations involving uniform vorticity distributions (Simmen & Saffman 1985 and Teles da Silva & Peregrine 1988).The second part of the study addresses the ‘gradually varying’ problem in which there are changes in the current, the wavelength and the wave height due to the initial interaction between the wave and the current. These data show that there is a large and non-uniform change in the current profile that is dependent upon both the steepness of the waves and the vorticity distribution. Furthermore, comparisons between the measured wave height change and a number of solutions based on the conservation of wave action, confirm that the vorticity distribution plays a dominant role. In the absence of a conservation equation for wave action appropriate for nonlinear waves on a depth-varying current, an alternative approach based on the conservation of total energy flux, first proposed by Longuet-Higgins & Stewart (1960), is shown to be in good agreement with the measured data.

131 citations


Journal ArticleDOI
TL;DR: In this paper, a nonlinear solution to the classical shallow water equation, that describes the wave characteristics on the beach, is obtained analytically by using a hodograph transformation.
Abstract: This study deals with the runup of solitary waves on a uniform plane beach connected to an open ocean of constant depth. The waves are nonbreaking during the runup process. A nonlinear solution to the classical shallow water equation, that describes the wave characteristics on the beach, is obtained analytically by using a hodograph transformation. It was found that the nonlinear theory agreed well with experimental results. The maximum runup predicted by the nonlinear theory is larger than that predicted earlier and the correction is on the order of the offshore relative wave height for a given slope. This correction for nonbreaking waves on beaches decreases as the beach slope steepens.

128 citations


Journal ArticleDOI
Abstract: Remote sensing of wave breaker patterns, clearly visible as high-intensity bands in time exposure video images, has become a powerful tool to obtain large-scale (kilometers) and long-term (years) time series of nearshore sandbar position. However, intensity-based bar crest positions xi differ from directly measured positions xb by a time-varying distance Δx, which is of O(10 m) and depends on the offshore wave height H0, the water level η0, and the bathymetry itself. The effect of these parameters on Δx was investigated from simultaneous video observations and bathymetric surveys, obtained in the double-barred system at Egmond aan Zee, Netherlands, and from wave model predictions, assuming that the roller energy represents image intensity. When the wave field over a bar was predicted to be nonsaturated, xi was observed and predicted to move offshore as either η0 decreased or H0 increased. Under saturated conditions, Δx only responded to changes in η0. Additional model investigations showed that an increase in outer bar crest depth, similar to that observed during interannual bar behavior, significantly reduced the Δx variability at the outer bar and increased the Δx variability at the inner bar. Implications of our observational and model findings for studying sandbar position from video imagery are outlined.

125 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the observed setdown and setup observed for 3 months on a cross-shore transect between the shoreline and 5 m water depth on a barred beach.
Abstract: Wave-driven setdown and setup observed for 3 months on a cross-shore transect between the shoreline and 5 m water depth on a barred beach are compared with a theoretical balance between cross-shore gradients of the mean water level and the wave radiation stress. The observed setdown, the depression of the mean water level seaward of the surf zone, is predicted well when radiation stress gradients are estimated from the observations using linear theory at each location along the transect. The observed setdown also agrees with analytical predictions based on offshore wave observations and the assumption of linear, dissipationless, normally incident waves shoaling on alongshore homogeneous bathymetry. The observed setup, the superelevation of the mean water level owing to wave breaking, is predicted accurately in the outer and middle surf zone, but is increasingly underpredicted as the shoreline is approached. Similar to previous field studies, setup at a fixed cross-shore location increases with increasing offshore wave height and is sensitive to tidal fluctuations in the local water depth and to bathymetric changes. Numerical simulations and the observations suggest that setup near the shoreline depends on the bathymetry of the entire surf zone and increases with decreasing surf zone beach slope, defined as the ratio of the surf zone-averaged water depth to the surf zone width. A new empirical formula for shoreline setup on nonplanar beaches incorporates this dependence.

116 citations


Journal ArticleDOI
TL;DR: In this paper, a large-scale laboratory facility for conducting research on surf-zone sediment transport processes has been constructed at the U.S. Army Engineer Research and Development Center, where an active pumping and recirculation system comprised of 20 independent pumps and pipelines is used to control the cross-shore distribution of the mean longshore current.

77 citations


Journal ArticleDOI
TL;DR: In this article, a tsunami simulation is conducted without using these kinds of simplification, taking into account both the dynamic displacement and acoustic effects, thus simulated tsunamis are found to be remarkably larger in the wave height especially in the near-fault area where these two effects are superposed.
Abstract: In conventional tsunami-simulation techniques, simplifications have been employed by neglecting the dynamic seabed displacement resulting from fracturing of a seismic fault and considering only the static contribution. The water layer is also assumed to be incompressible, regardless of its acoustic effects. They should be reconsidered in light of the state-of-the-art technology because considerable discrepancies between numerical simulations and actual observation have been pointed out regarding, for example, arrival time and wave height. In the present study, tsunami simulation is conducted without using these kinds of simplification, taking into account both the dynamic displacement and acoustic effects. As a result, thus simulated tsunamis are found to be remarkably larger in the wave height especially in the near-fault area where these two effects are superposed. In far-field, however, tsunamis thus simulated are likely to show little difference in the wave height, but show considerable difference in the arrival time. In addition, the present dynamic analysis is capable of simulating the water wave induced by the Rayleigh wave propagated along the seabed.

75 citations


Journal ArticleDOI
TL;DR: In this paper, the nearshore velocity field in the wind-wave frequency band was estimated from acoustic Doppler, acoustic travel time, and electromagnetic current meters, and the results showed that the relationship between pressure and velocity fluctuations increased with increasing ratio of wave height to water depth.
Abstract: Statistics of the nearshore velocity field in the wind‐wave frequency band estimated from acoustic Doppler, acoustic travel time, and electromagnetic current meters are similar. Specifically, current meters deployed 25‐ 100 cm above the seafloor in 75‐275-cm water depth in conditions that ranged from small-amplitude unbroken waves to bores in the inner surf zone produced similar estimates of cross-shore velocity spectra, total horizontal and vertical velocity variance, mean currents, mean wave direction, directional spread, and cross-shore velocity skewness and asymmetry. Estimates of seafloor location made with the acoustic Doppler sensors and collocated sonar altimeters differed by less than 5 cm. Deviations from linear theory in the observed relationship between pressure and velocity fluctuations increased with increasing ratio of wave height to water depth. The observed covariance between horizontal and vertical orbital velocities also increased with increasing height to depth ratio, consistent with a vertical flux of cross-shore momentum associated with wave dissipation in the surf zone.

61 citations


Journal ArticleDOI
TL;DR: In this article, the effects of sloshing are computed in the time domain using Newmark's time integration scheme, and the experimental results are compared with those obtained from the present theoretical analysis, and good agreements are observed.
Abstract: This paper is concerned with the experimental studies on the sloshing response of liquid-filled containers. A three-dimensional finite element analysis is carried out for the numerical simulation of this problem. The effects of sloshing are computed in the time domain using Newmark's time integration scheme. A simple experimental setup is designed and fabricated in-house to conduct experiments for measuring some of the basic parameters of sloshing. A sensor device is especially developed to record the free-surface wave heights. Each wave height sensor is a capacitance probe that detects the change in level of liquid (water) precisely with no time lag. The sensors are used in conjunction with a signal-processing unit in which the capacitance values are transduced to a voltage signal between 0 V and 10 V. These wave height sensors simultaneously record the slosh wave height near the periphery of the container wall from 16 predetermined locations to give the free-surface profiles of liquid at desired time steps. The experimental results are compared with those obtained from the present theoretical analysis, and good agreements are observed.

58 citations


Journal ArticleDOI
TL;DR: In this article, the applicability and implications of Bagnold's sediment transport model to nearshore profile modeling are discussed. But the authors focus on the morphologic implications of both the strengths and weaknesses of Baddour's model, isolating the transport terms that are well predicted (i.e., mean flow terms) from those that are not well predicted, i.e. transport due to correlations between flow and sediment load.
Abstract: This paper builds on the now classical discussions by Bowen [1980] and Bailard [1981] on the applicability and implications of Bagnold's [1963] sediment transport model to nearshore profile modeling. We focus on the morphologic implications of both the strengths and weaknesses of Bagnold's model, isolating the transport terms that are well predicted (i.e., mean flow terms) from those that are not well predicted (i.e., transport due to correlations between flow and sediment load). We factor Bagnold's model into a dimensional transport magnitude and a nondimensional term. The nondimensional term describes the relative importance of transport due to undertow, gravity, and correlations between flow and sediment load. The transport magnitude largely determines the response time of nearshore profiles. For typical nearshore environments this response time was estimated to vary as a function of incident rms wave height (Hrms) from ∼500 years (Hrms ∼ 0.5 m) to 2 years (Hrms ∼ 3 m). The relative importance of competing transport mechanisms is shown to depend strongly on the relative wave height (defined as the ratio of the rms wave height to the local depth). Simplified nearshore transport parameterizations that are a function of this variable were derived and were interrogated for the existence and form of equilibrium profiles. Several differences from previously computed equilibrium profiles were noted. First, because the relative wave height saturates in natural surf zones, equilibrium profiles converge to a relatively flat profile near the shoreline. Second, under some situations a seaward sloping equilibrium profile may not exist. Third, the long response times combined with unknown stability of an equilibrium profile make it difficult to assess the physical connection between theoretical equilibrium profiles and profiles observed in nature.

57 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a set of marine radar image sequences and applied this linear approximation, using a 3-D FFT analysis of 88 sets of image sequences spaced half an hour apart.
Abstract: The phenomenon of ocean wave-shoaling, and the associated reduction of ocean wave phase speed with decreased water depth, provides useful information for inferring water depth D (bathymetry) in coastal environments. One strategy for relating D to phase speed C and wave-vector K of long wavelength ocean waves involves using the one-dimensional (1-D) linear (gravity wave) dispersion relationship C/sup 2/=g*tanh(KD)/K. In principle, this approach has limitations because the approach is based on a WKB approximation, so it cannot be applied when D varies appreciably over the wavelength of a shoaling wave. Also, the approach is restricted to waves that have small wave height. The author uses a set of marine radar image sequences and applies this linear approximation, using a 3-D FFT analysis of 88 sets of image sequences spaced half an hour apart. The author inverts the dispersion relation to solve for D. Depths between 3.6 and 5.8 m were tested, for root mean square (RMS) wave heights offshore between 8 and 3 m. The author shows that for low to moderate wave heights, the approach does generally retrieve the correct depth in water depths of 5 m and greater for moderate wave RMS heights. However, an increase in the RMS wave height from 1 m to 3.5 m produced a much poorer depth estimate, proving the need for an application of a nonlinear wave model to the problem. The errors also increase with shallower depths as expected, as the error dependence on depth and wave height is determined.

Journal ArticleDOI
TL;DR: In this paper, the influence of wave reflection and energy dissipation by breaking and by porous flow induced by a permeable submerged structure on second-order mean quantities such as mass flux, energy flux, radiation stress, and mean water level is analyzed.
Abstract: The influence of wave reflection and energy dissipation by breaking and by porous flow induced by a permeable submerged structure on second-order mean quantities such as mass flux, energy flux, radiation stress, and mean water level is analyzed. For this purpose, analytical expressions for those mean quantities in terms of the shape functions are obtained. The dependence of those quantities on the incident wave characteristics, structure geometry, and permeable material characteristics is modeled, extending the writers' previous work including wave breaking. Two models for regular waves are presented: a 2D model to be applied to submerged trapezoidal breakwaters and a 3D model for submerged permeable rectangular breakwaters. Both models are able to reproduce experimental wave height transformation as well as mean water level variations along the wave flume with reasonable accuracy. Results give useful information for engineering applications of wave height evolution and set-up and set-down evolution in th...

Book ChapterDOI
01 Jan 2001
TL;DR: In this paper, a three-dimensional, shallow-water numerical model for a viscous landslide with full slide-wave interaction (Kulikov et al., 1996; Fine et al, 1998) was used to simulate the November 3, 1994 tsunami in Skagway, Alaska generated by collapse of the PARN Dock.
Abstract: A three-dimensional, shallow-water numerical model for a viscous landslide with full slide-wave interaction (Kulikov et al; 1996; Fine et al, 1998) has been modified to include the subaerial component of the landslide The model is used to simulate the November 3, 1994 tsunami in Skagway, Alaska generated by collapse of the PARN Dock Results show that the dock slide moved down the steep (30–35°) slope of Taiya Inlet and was guided along the trough at the base of the slope, consistent with geomorphological findings The leading tsunami wave, propagating in front of the advancing slide, impacted the Alaska State Ferry Terminal and the NOAA tide gauge site as a positive wave (crest), consistent with the tide gauge record and with the results of laboratory modelling by Raichlen et al (1996) Computed wave heights for the PARN Dock failure (13 m at the Ferry Terminal, 77 m at the tide gauge site, and 13 in the Small Boat Harbor) agree closely with the tide gauge record and eyewitness accounts The computed 30 min period for the fundamental long-wave mode for Skagway Harbor is nearly identical to the observed period Estimates of the Q-factor (Q≈24) are comparable to observed values (Q≈21), suggesting significant tsunami energy retention in the harbour Energy loss appears to be through radiation damping rather than from frictional effects A detailed examination of the slide motion and associated tsunami waves in the vicinity of the PARN Dock reveals that, in the first few seconds, a “wall of water” would have formed opposite the dock and that the floating Ferry Terminal would have been impacted 15 to 20 s after onset of the event, consistent with eyewitness accounts The floating debris observed at the still-standing northern portion of the dock was apparently carried alongshore by a secondary wave crest originating near the collapsed southern part of the dock

Proceedings ArticleDOI
TL;DR: In this article, the effect of wave period and spectral shape on wave transmission over low-crested structures has been investigated, and the effect on the total wave climate is discussed.

Journal ArticleDOI
TL;DR: In this paper, a method is described in which range is calculated from the angle subtended between the horizon and the waterline of the object measured from single video or photographic images taken at a known elevation.
Abstract: Summary 1 Estimating range to objects at sea by eye is notoriously difficult yet there are many occasions in management and research when accurate measures of range are required. 2 A new method is described in which range is calculated from the angle subtended between the horizon and the waterline of the object measured from single video or photographic images taken at a known elevation. Possible errors are explored and practical analysis methods outlined. Images can be collected and analysis performed using relatively inexpensive standard equipment. 3 In offshore waters, uncertainty in the height of the camera and target object due to the effects of waves and swell are likely to be the most significant sources of error. The effects of errors in camera height on ranges calculated using this method are approximately proportional to the ratio of the height error to camera height. Simulations indicate that wave- and swell-induced errors in the height of both object and camera will lead to range estimates with a standard deviation (SD) of 0·5 × (error due to wave height)/(camera height). 4 Three trials were conducted in which ranges (out to 2000 m) measured using this method were compared with those determined using alternative methods (laser range-finding binoculars or non-differential global positioning system). Mean percentage discrepancies in range measurements between the two methods varied from 6·4% to 2·6%, while the SD of discrepancies in trials varied between 6·5% and 4·3%. The independent range measuring methods used here were not without error, however, and it is suggested that a mean absolute error of > 2% is an appropriate figure for the video method. 5 Field tests indicated that the necessary photos or video sequences could be collected from most types of cetaceans in the field. A variety of applications for the method during activities such as line transect surveys, mitigation monitoring and behavioural studies are suggested and discussed.

Journal ArticleDOI
TL;DR: Li et al. as mentioned in this paper recast the extended refraction-diffraction equation into a time-dependent parabolic equation to account for a rapidly varying topography and wave energy dissipation in the surf zone.

Journal ArticleDOI
TL;DR: The first offshore reef developed to amalgamate world-class surfing, public amenity and coastal protection is described in this paper, where the shape that met the design criteria, for both the surfing and shoreline protection characteristics, was found to be a submerged double-sided headland.
Abstract: The first offshore reef developed to amalgamate world-class surfing, public amenity and coastal protection is described. The reef is at Narrowneck Beach on the Gold Coast, Australia, a long, sandy coast experiencing large cyclone waves and high net longshore transport. The reef design was based on bathymetric and wave breaking studies of world-class surfing breaks and numerical model predictions. A broad range of different shapes was numerically tested using refraction, Boussinesq refraction/diffraction and sediment transport models. The shape that met the design criteria, for both the surfing and shoreline protection characteristics, was found to be a submerged double-sided headland. The designed reef is 400 m long and extends from the natural 2 m isobath to a toe in 10.4 m depth, with the crest at 0.4 m below the Lowest Astronomical Tide. The shape allowed both 'left' and 'right' surfing waves to be included. Peel angles are rarely less than 40? (in predominant small waves) and seabed gradients of up to 1:12 produce steep plunging wave faces, making the surfing wave 'fast' and 'hollow'. In small swell, a large, focussing underwater segment will more than double the deep water wave height at the breakpoint. A slower 100 m long segment at the shoreward end is designed for surfing beginners and casual tourists. Because the adjacent beaches experience close-out conditions in big swells, a paddling channel has been placed at the offshore tip of the reef to give surfers access during large swell. A lagoon shoreward of the reef provides sheltered paddling and, at low tide, sheltered swimming for beach-goers. Wave interference patterns inshore of the reef are expected to provide challenging 'wedgey' waves for body boarders, while the offshore placement of the reef provides ideal wave jumping conditions for the sailboarder.

Journal ArticleDOI
TL;DR: An airborne single pass across-track interferometric synthetic aperture radar (InSAR) is used to image ocean waves, and a theoretical model explaining the imaging mechanisms is developed, and simulations of the interferogram as well as the conventional SAR intensity image are presented.
Abstract: An airborne single pass across-track interferometric synthetic aperture radar (InSAR) is used to image ocean waves. A theoretical model explaining the imaging mechanisms is developed, and simulations of the interferogram as well as the conventional SAR intensity image are presented for given ocean wave spectra. Distortions of digital elevation models (DEM) derived from InSAR data are explained by the motion of the sea surface. A Monte Carlo method based on forward simulations is used to estimate variance spectra of the distorted elevation models. It is shown that a straightforward estimation of wave height using the distorted InSAR elevation model is in good agreement with true wave height for low amplitude swell with about 10% error depending on propagation direction and coherence time. However, severe underestimation of wave height is found for wind seas propagating in flight direction. Forward simulations show that the distorted InSAR DEM is less dependent an the model chosen for the real aperture radar mechanism than conventional SAR images. Data acquired during an experiment over the North Sea by a high precision InSAR system are compared with simulations.

Journal ArticleDOI
01 Apr 2001
TL;DR: In this paper, the authors investigated the hydrodynamics of megatidal beaches outside the surf zone and found that strong longshore currents with velocities up to 0.5m−s −1 were observed on the Cotentin coast of the Cherbourg Peninsula in Normandy.
Abstract: Several experiments aimed at characterising the hydrodynamics of megatidal beaches outside the surf zone were carried out between 1990 and 1994 on the Cotentin coast of the Cherbourg Peninsula in Normandy. The database was established from the records of several electromagnetic current meters and pressure sensors and from field surveys. The mean spring tidal range on these beaches varies between 9.3 and 11.4 m. The results show the prevalence of strong longshore currents, with velocities up to 0.5 m s −1 , on the low- and mid-tidal beach zones. Mostly oriented northward, these currents reflect both a progressive tidal wave and a strong longshore gradient in water level between the Channel Islands embayment and the English Channel. While varying largely during a typical tidal cycle, these longshore velocities are maximum at high tide, reflecting the progressive nature of the tides. This high-tide maximum velocity increases by a factor of 1.5 between the mean tide and mean spring tide, and between the mid- and low-tidal zones due to bed friction effects. Cross-shore velocities are generally weak ( −1 ), but sometimes stronger in smaller water depths. In the low-tidal zone, they are commonly oriented onshore at the beginning of the rising tide and offshore during the falling tide. This circulation results from a west–east cross-shore gradient in water level that is particularly important around the mean water level. Towards high tides, weak offshore steady flows were observed in the presence of waves. Site-specific relationships were defined in order to characterise the modulation of significant wave height by sea level fluctuations both on the shoreface and in the intertidal zone. The water depth variability during the tidal cycle induces fluctuations in the dissipation by bottom friction, resulting in wave height changes. The influence of tidal currents on the wave height proved to be very small in this context. The tidal fluctuations also influence the instantaneous near-bed currents induced by simultaneous action of non-breaking waves and the tides. During stormy conditions, wave-induced gravity orbital motions dominate the steady flows in the mid-tidal zone, outside the surf zone. At this location, the shallow water friction effect results in weak steady longshore currents, and low water depths explain strong orbital motions. The opposite conditions prevail in the low-tidal zone, where the steady tidal currents are stronger than gravity orbital velocities during a few hours around high tide. Outside this period, with the decrease in water depth and in steady current intensity due to friction effects, the tidal and gravity wave-induced currents have comparable intensities. In both the low- and mid-tidal zones, infragravity motions are weak outside the surf zone. The foregoing results show that outside the surf zone, these megatidal beaches are characterised by wave-dominated mid-tidal zones and tide-dominated low-tidal zones during spring tides. We suggest the term “mixed wave-tide-dominated” for these beaches with very large tidal ranges.

Proceedings ArticleDOI
23 Mar 2001
TL;DR: Tanaka et al. as discussed by the authors analyzed the relationship between wave set-up height and deep water wave height, which shows a slight difference from a previous expression for wave setup at the shoreline on a sloping beach.
Abstract: Field observation data of water level at three river mouths are collected and analyzed in order to find quantitative relationship between wave set-up height at a river entrance and wave characteristics. At a relatively bigger river mouth which is protected by two jetties, wave set-up cannot be observed in the river entrance, whereas at smaller river mouths, distinct water leve l rise above tidal elevation can be observed during the period high waves. An empirical expression is obtained for the relationship between wave set-up height and deep water wave height, which shows slight difference from a previous expression for wave set-up at the shoreline on a sloping beach. Introduction There have been a lot of observations of wave set-up caused by breaking waves, though, most of them have been limited to laboratory flume experiments ( e.g., Bowen et al., 1968; Battjes and Janssen, 1978 ). The reason of the scarcity of field observations might be its considerable difficulty in the surf zone, especially during high waves. In recent years, several field observations have been reported on wave set-up height in a river entrance ( Hanslow and Nielsen, 1992 ; Hanslow et al., 1996 ; Santoso et al., 1998 ; Tanaka and Shuto, 1992 ). Among these, Hanslow and Nielsen (1992) obtained very little set-up in a river entrance in Australia, whereas Tanaka and Shuto (1992) found that the wave set-up height measured at the Nanakita River mouth attained to 10-20% of the deep water wave height. The difference 1 Professor, Department of Civil Engineering, Tohoku University, 06 Aoba, Sendai 980-8579, Japan. Phone & Fax:(+81)-22-217-7451, e-mail: tanaka@ tsunami2.civil.tohoku.ac.jp 2 Professor, Department of Civil Engineering, Nihon University, Nakagawara, Tokusada, Tamura-machi, Koriyama 963-8642, Japan. 3 Civil Engineer, Construction Department, OBAYASHI Co. Ltd., 2-15-2 Kounan, Minato-ku, Tokyo 108-8502, Japan. between the results from these groups indicates that the occurrence of wave set-up has distinct dependence on the geometry of river entrance. In the present study, the measurement and analysis of wave set-up height is carried out at three river mouths with different geometry in Japan and the height is formulated in terms of the deep water wave quantities. Study Area and Data Collection Measured time-variations of water level at three river mouths ( see Table 1 and Figure 1 ) are collected and analyzed. Rivers in Japan are classified into class A and B according their dimensions and its importance. The former are governed by the national government, whereas the latter by prefectural government. The Natori River in Table 1 belongs to the former category and, subsequently, has larger catchment area as compared with other two rivers investigated in the present study. There are two jetties at the river entrance as depicted in Figure 1 to protect sediment intrusion into the mouth by waves. The water level variation in the mouth is measured every one hour by the Sendai Construction Office, Ministry of Construction. More detail of the study area can be found elsewhere ( Tanaka et al., 1996 ; Tanaka et al., 1997 ). On the other hand, the Nanakita River is classified into class B river as shown in Table 1. It is located about 9km north to the Natori River as seen Figure 1 and there is a jetty on the left-hand side of the mouth which limits the northward migration of the mouth, while the movement towards to the south is not limited. A comprehensive investigation on river mouth topography change has already been made one of the authors ( Tanaka et al., 1996 ; Tanaka and Ito, 1996 ). The water level variation in the river entrance is measured by means of an automatic water level gauge shown in Photo 1 every 5 minutes. The Natsui River is also rank B river, though, its has about three times larger catchment area as compared with the Nanakita River as seen in Table 1. Another distinct difference from other river mouths in Table 1 is the absence of a jetty at the river mouth. A water level gauge has already been installed at Suga and Yokokawa Stations in Figure 1 by the Fukushima Prefectural Government and the data has been being obtained every three hours. Table 1 Characteristics of study area. class catchment area (km) length of river (km) number of jetties Natori River A 984 55 two Nanakita River B 229 45 one Natsui River B 749 67 none Figure 1 Location map of observation sites. Photo 1 Measuring station of water level at the Nanakita River mouth. JAPAN SENDAI .. IWAKI

Journal ArticleDOI
TL;DR: In this paper, a method is presented by which the wave wake generated by a ship may be repeatedly calculated very rapidly, based on linear thin-ship theory, using the idea of elemental tent functions as building blocks to represent the hull, which have previously been applied in the context of resistance minimization.
Abstract: A method is presented by which the wave wake generated by a ship may be repeatedly calculated very rapidly. The method is based on linear thin-ship theory, using the idea of elemental tent functions as building blocks to represent the hull, which have previously been applied in the context of resistance minimization. This approach allows much of the calculation to be carried out in advance, with the results stored in a database. Issues of convergence, accuracy, and storage strategy are discussed. In order to demonstrate the application of the approach to preliminary design optimization, an illustrative study is carried out in which hull forms for monohull and catamaran vessels are optimized in the sense of minimizing the maximal wave height along a series of longitudinal cuts. The effect of the transverse location of the cuts on the resulting hull forms is found to be quite substantial, especially for the catamarans; the performance of the vessels optimized to reduce wave height at one transverse location may be quite suboptimal at another location, illustrating the difficulty of choosing an appropriate specification for low-wash vessels.

DOI
01 Jan 2001
TL;DR: In this paper, properties of the saturated wave field in the neighbourhood of possible sites of the Saaremaa deep harbor during typical (about 15 m/s) and extreme (about 25 m/S) storms, forced by steady winds, were analysed on the basis of the wave model WAM.
Abstract: Properties of the saturated wave field in the neighbourhood of possible sites of the Saaremaa deep harbour during typical (about 15 m/s) and extreme (about 25 m/s) storms, forced by steady winds, are analysed on the basis of the wave model WAM. The toughest wave regime is at Undva (Uudepanga Bay, probability of occurrence of waves exceeding 3 m is 1%), slightly better at Suuriku-Kuriku (0.6%) and the mildest at Vaigu (0.13%). Directional distribution of wave heights in typical and extreme storms is highly anisotropic. The highest waves correspond to NNW storms. Remarkable wave height anomalies may occur in the neighbourhood of the harbour sites. The anomalies emerge only during very strong storms and may serve as a major navigation danger.

01 Jan 2001
TL;DR: An online oceanographic and meteorological observing system has been developed and is being implemented off the Louisiana coast to provide critical information during offshore emergencies including oil spills as mentioned in this paper, which is called WAVCIS (WAVe Current Information System).
Abstract: An online oceanographic and meteorological observing system has been developed and is being implemented off the Louisiana coast to provide critical information during offshore emergencies including oil spills. The program, WAVCIS (WAVe Current Information System), provides wave information (sea state) including wave height, period, direction of propagation, water level, surge, water column velocity profiles, and meteorological conditions on a near real time basis. Information of this sort does not exist for an area approximating 135,000 km 2 off Louisiana’s coast. WAVCIS involves offshore deployment of instrumentation around the entire state in order to provide near real time data describing sea state, current velocity and meteorological conditions. Information from each station is transmitted via cellular satellite telephone to a base station at Louisiana State University where it undergoes quality control, post-processing and archiving in an online database. The information is then made available on the World Wide Web and is accessible to computers with an Internet connection and web browser. Various data displays are available for the near real time information, as well as a specified time history for archived data

Journal ArticleDOI
TL;DR: In this paper, the steady-state spectral wave model is described and evaluated with directional wave data measured during two storms at Ponce de Leon Inlet, on the Atlantic coast of Florida.
Abstract: Coastal inlets pose challenges of complex bathymetry, wave-current interaction, and influences of natural and artificial barriers for prediction of wave transformation with numerical wave models. The steady-state spectral WAVE model is described and evaluated with directional wave data measured during two storms (5.4 m and 2.4 m peak wave height) at Ponce de Leon Inlet, on the Atlantic coast of Florida. Model simulations of the two storms agreed well with measurements (within measurement uncertainty) except when incident waves were strongly nonlinear. Wave-current interaction was found to be a small influence compared to refraction by changing water depth.

Proceedings ArticleDOI
23 Mar 2001
TL;DR: In this article, two years of daily time exposure video images were analyzed to examine the effect of incident wave conditions on the spacing and persistence of rip channels along a swell dominated, microtidal beach (Palm Beach, Sydney, Australia).
Abstract: Two years of daily time exposure video images were analysed to examine the effect of incident wave conditions on the spacing and persistence of rip channels along a swell dominated, microtidal beach (Palm Beach, Sydney, Australia). The results indicated that rip channels do not have any preferred locations along the beach. Rip spacing did not increase or decrease with likewise variations in wave height. Once formed, rip channels migrated longshore under obliquely incident waves, while they were fixed in location under normal wave incidence. Gradients in longshore sediment transport caused by longshore currents due to obliquely incident waves appear to govern longshore migration of rip channels. A two-dimensional depth averaged hydrodynamic model (2DBEACH) was applied to idealised bathymetry to examine processes governing rip strength. The model results indicated that both rip velocity and transport increased with increasing wave height. Rip velocity also increased with falling tide levels, while rip transport initially increased and then decreased with falling tide levels. Centre for Natural Resources, Dept. of Land & Water Conservation, PO Box 2185, Dangar, NSW 2309, Australia. Phone: +61 2 4960 5033; E-mail: rranasinghe@dlwc.nsw.gov.au 2 School of Geography & Oceanography, Australian Defence Force Academy, Canberra, ACT 2600, Australia. E-mail: Graham.Symonds@adfa.edu.au 3 Department of Earth Sciences, University of Waikato, PB 3105, Hamilton, New Zealand. Email: kblack@ mailserv.waikato.ac.nz 4 College of Atmospheric and Oceanic Sciences, Oregon State University, 104 Ocean admin building, Corvallis, Oregon 97331-5503, USA. E-mail: holman@oce.orst.edu

Journal ArticleDOI
TL;DR: In this paper, the runup heights of random waves on a small diameter circular pier installed on a uniform slope bottom were investigated by laboratory experiments under various conditions of waves, bottom slopes, and installed water depths of the pier.
Abstract: This study investigates runup heights of random waves on a small diameter circular pier installed on a uniform slope bottom, by laboratory experiments under various conditions of waves, bottom slopes, and installed water depths of the pier. The main purpose of the study is to propose a prediction formula for the 2% excess runup height on a pier. The formula is expressed by the exponential function. The correlation coefficient between the predictions and observations is 0.98. Since the maximum and one-third maximum runup heights are found to be related linearly to the 2% excess runup height, those are estimated through the prediction formula. By employing the prediction formula, one can also estimate the water depth where the runup on a pier becomes maximum.

Journal ArticleDOI
TL;DR: Wave development was studied at six sites along a transect across Manukau Harbour, New Zealand, which is a large intertidal estuary with a tidal range of up to 4 m.
Abstract: Locally generated wind‐waves in estuaries play an important role in the sediment dynamics and the transport of biota. Wave growth in estuaries is complicated by tidally varying depth, fetch, and currents. Wave development was studied at six sites along a transect across Manukau Harbour, New Zealand, which is a large intertidal estuary with a tidal range of up to 4 m. Three meteorological masts were also deployed across the measurement transect to measure wave forcing by the wind. A spatial variation in wind speed by up to a factor of 2 was observed which has a significant effect on wave development at short fetches. The wind variation can be explained by the extreme change in surface roughness at the upwind land‐water boundary. The tidally varying depth results in non‐stationary wave development. At the long fetch sites wave development is dictated by the tidally varying depth with peak frequencies continuing to decrease after high water, whereas wave height is attenuated by bottom friction. The ...

Journal ArticleDOI
TL;DR: In this article, an efficient numerical model based on the time-dependent mild-slope equation is presented for the estimation of wave deformation across the surf zone, which incorporates an approximate nonlinear shoaling formula and an energy dissipation factor due to wave breaking to improve the accuracy of the calculation of wave height deformation prior to the wave breaking.

Journal ArticleDOI
TL;DR: In this article, the three-dimensional wave number-frequency spectra were derived from the sequences of captured images using an analysis method developed by Young et al. [J. Geophys. Res. 90(C1) (1985) 1049].

Journal ArticleDOI
TL;DR: In this article, a two-phase numerical model was described and tested for some simple cases under wave conditions, and the authors applied that numerical model to simulate the interfacial waves and oil free-surface waves under a number of key hydrodynamic conditions.
Abstract: In the first of these companion papers, a two-phase numerical model was described and tested for some simple cases under wave conditions. This paper applies that numerical model to simulate the interfacial waves and oil free-surface waves under a number of key hydrodynamic conditions. The characteristics of oil-water interfacial waves and free-surface waves are discussed. Effects of currents and waves on the interfacial waves (interfacial elevation, oil-water relative velocity, and interfacial velocity components) are investigated. The variation of the oil thickness under current and wave conditions is also discussed. The computational results indicate that an increase in the incoming wave height and period may (1) cause instability of the oil-water interfacial waves near the front of the oil slick and this may promote entrainment failure; (2) increase the interfacial waves and free-surface waves at the boom; (3) lower the trough of the oil-water interface at the boom and thus promote drainage failure if the oil thickness exceeds the boom draft; and (4) decrease the freeboard of the boom and thus encourage oversplashing failure.