Video Depth Inversion at a Microtidal Site Exposed to Prevailing Low-energy Short-period Waves and Episodic Severe Storms

Bouvier, Clément; Balouin, Yann; Castelle, Bruno; Valentini, Nico

doi:10.2112/si95-199.1

Cited by 3 publications

(7 citation statements)

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“…In addition, non-linear effects affect the estimation of the bathymetry in the outer and inner surf zone as the depth range decreases at low tide. Surprisingly, large waves (H s > 2 m) do not appear to significantly reduce cBathy estimations in the sampled area as opposed to the results of Bouvier et al [42]. Nevertheless, it is important to note that this quality assessment is based only on the total number of individual depth outputs within the grid, whose performance at the end is given by the same cBathy algorithm.…”

Section: Cbathy Error Assessmentmentioning

confidence: 79%

“…Following the approach proposed by Bouvier et al [42], a quality assessment was computed for each of the non-filtered cBathy-derived bathymetries ĥ(x m , y m ) by counting the number of points for which the cBathy algorithm returns a physical value (skill higher than 0.5 with associated depth errors lower than 1 m). The quality assessment (Qual) of video-derived bathymetries was assessed in percentage terms in relation to the total number of grid points inside the camera viewfield delimited by values below the zero-elevation contour line.…”

Section: Cbathy Error Assessmentmentioning

confidence: 99%

“…The cBathy algorithm, developed by Holman et al [19], is a spectral depth inversion method that is nowadays the most popular algorithm to obtain two-dimensional bathymetries from video stations [6,25,[32][33][34][35][36][37][38][39][40][41][42][43][44]. cBathy is based on the linear wave dispersion relationship, and therefore, its validity is inherently bounded to the increasing degree of wave non-linearity (finite amplitude effects) as waves approach the shore, leading to larger propagation speeds for higher waves [45,46].…”

Section: Introductionmentioning

confidence: 99%

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Video-Based Nearshore Bathymetric Inversion on a Geologically Constrained Mesotidal Beach during Storm Events

et al. 2022

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Although geologically constrained sandy beaches are ubiquitous along wave-exposed coasts, there is still a limited understanding of their morphological response, particularly under storm conditions, which is mainly due to a critical lack of nearshore bathymetry observations. This paper examines the potential to derive bathymetries from video imagery under challenging wave conditions in order to investigate headland control on morphological beach response. For this purpose, a video-based linear depth inversion algorithm is applied to three consecutive weeks of frames collected during daylight hours from a single fixed camera located at La Petite Chambre d’Amour beach (Anglet, SW France). Video-derived bathymetries are compared against in situ topo-bathymetric surveys carried out at the beginning and end of the field experiment in order to assess the performance of the bathymetric estimates. The results show that the rates of accretion/erosion within the surf zone are strongly influenced by the headland, whereas the beach morphological response can be classified into three main regimes depending on the angle of wave incidence θp: (1) under deflection configuration (θp>0°), the alongshore sediment transport was trapped at the updrift side of the headland, promoting sand accretion. (2) Under shadowed configuration (θp<0°), the interruption of the longshore current drove a deficit of sand supply at the downdrift side of the headland, leading to an overall erosion in the surf zone. (3) Under shore-normal configuration (θp=0°), rip channels developed, and up-state beach transition was observed. A comparison between video-derived bathymetries and surveys shows an overall root mean square error (RMSE) around 0.49 to 0.57 m with a bias ranging between −0.36 and −0.29 m. The results show that video-derived bathymetries can provide new insight into the morphological change driven by storm events. The combination of such inferred bathymetry with video-derived surface current data is discussed, showing great potential to address the coupled morphodynamics system under time-varying wave conditions.

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Section: Cbathy Error Assessmentmentioning

confidence: 79%

Section: Cbathy Error Assessmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Video-Based Nearshore Bathymetric Inversion on a Geologically Constrained Mesotidal Beach during Storm Events

et al. 2022

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“…In Lido of Sète, the SPAW event observations consist of a 3-month (October -December 2018) data set of daily rectified time-exposure images and 17 min pixel time series data (Holman et al, 2013) with the corresponding offshore wave and tide measurements. From the images we detected sandbar and shoreline positions (Bouvier et al, 2017) and applied the cBathy depth inversion algorithm (Holman et al, 2013 ;Bouvier et al, 2020) to quantify the subtidal morphology, including that of the SPAW, during the study period. Subsequently, these bathymetries and the offshore hydrodynamic data were used to initialize a process-based morphodynamic model.…”

Section: Methodsmentioning

confidence: 99%

Observation and Modelling of Shoreward Propagating Accretionary Waves (Spaws) on Microtidal Beaches

Bouvier¹,

Korteling²,

Price³

et al. 2020

Int. Conf. Coastal. Eng.

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At straight sandy coasts, wave-induced processes often lead to intriguing alongshore-variable morphology on spatial scales from 10s - 1000s of meters. Observations have shown that the horns of crescentic bars may separate from the bar during storms and subsequently migrate onshore towards the beach during calmer periods as a spatially coherent structure, termed Shoreward Propagating Accretionary Wave, or SPAW. Here, we aim to (1) quantify the morphological evolution of a SPAW and (2) unravel the physical processes underlying its onshore migration and spatial coherence. To do so, we studied onshore migration of a SPAW using a process-based morphodynamic model.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5P22G_S0FJM

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“…Shemdin et al [11] obtained wave direction from images captured by optical sensors installed on an oceanographic offshore tower, using image processing and spectral analysis techniques. Optical sensors had also been exploited to estimate sea current direction and speed [12], shoreline position [13,14], run-up levels [15], bathymetric data [16], for bathymetry inversion [17,18], and beach resilience evaluation [19].…”

Section: Introductionmentioning

confidence: 99%

A Sterescopic System to Measure Water Waves in Laboratories

et al. 2020

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A new system for estimating the synthetic parameters of sea states during physical investigations has been implemented. The technique proposed herein is based on stereographic analysis of digital images acquired with optical sensors. A series of ad hoc floating markers has been made and properly moored to the bottom of a large wave tank to estimate the synthetic parameters of generated waves. The implemented acquisition system and the proposed algorithm provide automatic recognition of all markers by a pair of optical sensors that synchronously captures their instantaneous location and tracks their movements over time. After transformation from the image to the real-world coordinates, water surface elevation time series have been obtained. Several experimental tests have been carried out to assess the feasibility and reliability of the proposed approach. The estimated wave synthetic parameters have been then compared with those obtained by employing standard resistive probes. The deviation were found to be equal to ~6% for the significant wave height and 1% for peak, mean, and significant wave periods.

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Video Depth Inversion at a Microtidal Site Exposed to Prevailing Low-energy Short-period Waves and Episodic Severe Storms

Cited by 3 publications

References 0 publications

Video-Based Nearshore Bathymetric Inversion on a Geologically Constrained Mesotidal Beach during Storm Events

Video-Based Nearshore Bathymetric Inversion on a Geologically Constrained Mesotidal Beach during Storm Events

Observation and Modelling of Shoreward Propagating Accretionary Waves (Spaws) on Microtidal Beaches

A Sterescopic System to Measure Water Waves in Laboratories

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