Nearshore wave height variation in unsaturated surf

Power, Hannah E.; Hughes, Michael G.; Aagaard, Troels; Baldock, Tom E.

doi:10.1029/2009jc005758

Cited by 41 publications

(40 citation statements)

References 53 publications

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“…Thus, the results presented in section are novel in the literature and show that Q b is highly variable at all locations analyzed in the present work which covered ranges of 0.1< γ <2. Such observations are in agreement with previous studies of the cross‐shore structure of other surf zone parameters, such as γ and H (Martins et al, ; Power et al, , ) and the instantaneous wave speed ( c ) (Postacchini & Brocchini, ; Tissier et al, ).…”

Section: Discussionsupporting

confidence: 92%

“…Note that Q b values at the surf-swash boundary could be even lower if the wave height threshold value used to separate individual waves was lower (see section 3.2.1) as small wavelets being detect as unbroken waves would cause Q b to decrease. Finally, where it was captured in the data, the outer limit of the surf zone was observed to be in the range 1 < h∕H m 0∞ < 2 (0.5 < < 1) instead of the value of 2 < h∕H m 0∞ < 3 (0.3 < < 0.5) suggested by several other publications (Power et al, 2010;Ruessink et al, 1998;Thornton & Guza, 1982, 1983.…”

Section: Results Of Field Observationsmentioning

confidence: 54%

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The Fraction of Broken Waves in Natural Surf Zones

Stringari

Power

2019

JGR Oceans

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This paper presents a novel quantification of the fraction of broken waves (Q b ) in natural surf zones using data from seven microtidal, wave-dominated, sandy Australian beaches. Q b is a critical, but rarely quantified, parameter for parametric surf zone energy dissipation models, which are commonly used as coastal management tools. Here, Q b is quantified using a combination of remote sensing and in situ data. These data and machine learning techniques enable quantification of Q b for a substantial data set (>330,000 waves). The results show that Q b is a highly variable parameter with a high degree of interbeach and intrabeach variability. Such variability could be correlated to environmental parameters: tidal variations correlated with changes in Q b of up to 70% for a given local water depth (h) on a low tide terrace beach, and increased infragravity relative to sea-swell energy correlated to lower values of Q b at the surf-swash boundary. Q b also correlates well with the Australian beach morphodynamic model: For more dissipative beaches Q b increases rapidly in the outer surf zone, whereas for more reflective beaches Q b increases slowly throughout the surf zone. Finally, when comparing data to existing models, three commonly used theoretical formulations for Q b are observed to be poor predictors with errors of the order of 40%. Existing theoretical Q b models are shown to improve (revised errors of the order of 10%) if the Rayleigh probability distribution that describes the wave height is in these models is replaced by the Weibull distribution. Plain Language SummaryAn observer looking at a beach from a headland or sand dune can easily distinguish between the waves that are breaking and those that are not. Several wave models that are used as coastal management tools require the percentage of waves that are broken to describe how the wave energy changes as the waves travel across the surf zone. Despite its importance, this "fraction of broken waves" has rarely been quantified for natural beaches. In this paper, we use a combination of video cameras to image the waves and sensors that directly record the waves in the water to quantify the number of broken waves as a percentage of the total number of waves for several beaches. This allows us to accurately distinguish between broken and unbroken waves, obtaining a large field data set of what the fraction of broken waves is and how it varies between beaches. We also compared our data with three widely used models and showed that these models are poor predictors with errors of approximately 40%. We could reduce these errors to approximately 10% using our field data to better describe the probability of a given wave being broken.

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Section: Discussionsupporting

confidence: 92%

Section: Results Of Field Observationsmentioning

confidence: 54%

The Fraction of Broken Waves in Natural Surf Zones

Stringari

Power

2019

JGR Oceans

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“…Using zero crossing analysis in the inner surf and swash causes some problems because the water level varies a lot in this zone, and the method is very sensitive to the definition of the mean water level around which the zero crossings are defined. Power et al (2010) have demonstrated how the use of zero crossing analysis can lead to misinterpretation of wave heights and the shape of the waves. When using the steepness criterion however, it is possible to exclude undulations on the water surface which are caused by turbulence while still identifying all the bores.…”

Section: Discussionmentioning

confidence: 99%

Swash Zone Bed Level Changes and Sediment Entrainment at the Surf-Swash Boundary

Jensen

Aagaard

Baldock

2011

Int. Conf. Coastal. Eng.

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In the process of estimating the effect of sediment advection into the swash zone from bore collapse, a method in which buried self-logging pressure transducers are used to measure bed level changes in the swash zone, over a timeframe of several hours to inter-swash level, has been tested against bed level changes obtained from rod measurements. The test shows perfect agreement in the upper and mid swash while minor disagreement (1 cm) in the lower swash occurred. The deployment of self-logging pressure transducers has proven to be an accurate, easy and flexible method to obtain highly detailed data on water levels and bed elevations in the swash zone. Water levels derived from the pressure transducers show that swash zone characteristics vary from the upper to lower swash. Using pressure transducers in the swash zone coupled with measurements of the hydrodynamics and sediment concentrations at the outer boundary of the swash zone will improve the ability to explain the role of sediment advection from bore collapse. In relation to this, a method which consistently identify bores at the surf-swash boundary and quantifies the suspended sediment load carried by such bores prior to their collapse and run-up in the swash zone, is also presented.

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“…The assumption of the constant value of γ b across the surf zone has been questioned by several authors (Raubenheimer et al, 1996;Power et al, 2010). On the one hand, there is some evidence that it probably increases shoreward (Raubenheimer et al, 2001;Yemm, 2004).…”

Section: Evaluation Of Wave Set-upmentioning

confidence: 99%

“…Local (national) wind data sets are only reliable in the vicinity of each country (Räämet et al, 2009), and high-resolution modelled winds, optionally coupled with wind sea properties, suffer from being substantially inhomogeneous over time (Tuomi et al, 2012). Furthermore, the Gulf of Finland has a specific wind and wave regime (Pettersson et al, 2010;Soomere et al, 2008b) mainly because the strongest winds blow obliquely across this water body with respect to the topography. The biggest problem in the reconstruction of wave set-up is the mismatch in the direction of even the best modelled versions of wind fields compared with high-quality measured data (Keevallik and Soomere, 2010).…”

Section: T Soomere Et Al: Mapping Wave Set-up Near a Complex Geometmentioning

confidence: 99%

Mapping wave set-up near a complex geometric urban coastline

Soomere

Pindsoo

Bishop

et al. 2013

Nat. Hazards Earth Syst. Sci.

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Abstract. Wave induced set-up is a process that leads to increased water levels in coastal regions. When coupled with storm conditions, wave set-up -or, for brevity, set-up -can significantly increase the risk of flooding or structural damage and therefore is of particular importance when considering coastal management or issues related to the planning of nearshore infrastructures. Here, we investigate the effects of set-up in the coastal region of the Gulf of Finland in the Baltic Sea, close to Tallinn, Estonia, although the results will have wider relevance for many other areas. Due to a lack of continuous wave data we employ modelling to provide input data using a calculation scheme based on a high-resolution (470 m) spectral wave model WAM to replicate spatial patterns of wave properties based on high-quality, instrumentmeasured wind data from the neighbourhood of the study site. The results indicate that for the specific geometry of coastline under consideration, there is a variation in set-up which is strongly affected by wind direction. The maximum set-up values are up to 70-80 cm in selected locations. This is more than 50 % of the all-time maximum water level and thus may serve as a substantial source of marine hazard for several low-lying regions around the city. Wind directions during storms have changed in recent years and, with climate variability potentially increasing, these results will encourage further tests which may be used in a policy setting regarding defences or other structures in and around coastlines. In particular, with urban development now taking place in many coastal regions (including the one within this study) these results have implications for local planners. They may also be incorporated into new storm warning systems.

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Nearshore wave height variation in unsaturated surf

Cited by 41 publications

References 53 publications

The Fraction of Broken Waves in Natural Surf Zones

The Fraction of Broken Waves in Natural Surf Zones

Swash Zone Bed Level Changes and Sediment Entrainment at the Surf-Swash Boundary

Mapping wave set-up near a complex geometric urban coastline

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