Bedform migration and bedload transport on an intertidal shoal

Hoekstra, P.; Bell, Paul S.; Santen, Pim van; Roode, Niels; Levoy, Franck; Whitehouse, R.J.S.

doi:10.1016/j.csr.2004.03.006

Cited by 60 publications

(6 citation statements)

References 22 publications

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“…Different types of bedforms generally coexist in the coastal environment (e.g., Refs. [13][14][15]), whose dimensions and shapes depend on sediment availability, sediment type (e.g., size distribution and shape) and driving mechanisms (e.g., waves, currents, wind). Examples of small-scale bedforms are wave and current sand ripples, or gravel-bed clusters, with dimensions or length scales generally not exceeding a few tens of centimeters.…”

Section: Introductionmentioning

confidence: 99%

Assessment of RTK Quadcopter and Structure-from-Motion Photogrammetry for Fine-Scale Monitoring of Coastal Topographic Complexity

2022

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Advances in image-based remote sensing using unmanned aerial vehicles (UAV) and structure-from-motion (SfM) photogrammetry continue to improve our ability to monitor complex landforms over representative spatial and temporal scales. As with other water-worked environments, coastal sediments respond to shaping processes through the formation of multi-scale topographic roughness. Although this topographic complexity can be an important marker of hydrodynamic forces and sediment transport, it is seldom characterized in typical beach surveys due to environmental and technical constraints. In this study, we explore the feasibility of using SfM photogrammetry augmented with an RTK quadcopter for monitoring the coastal topographic complexity at the beach-scale in a macrotidal environment. The method had to respond to resolution and time constraints for a realistic representation of the topo-morphological features from submeter dimensions and survey completion in two hours around low tide to fully cover the intertidal zone. Different tests were performed at two coastal field sites with varied dimensions and morphologies to assess the photogrammetric performance and eventual means for optimization. Our results show that, with precise image positioning, the addition of a single ground control point (GCP) enabled a global precision (RMSE) equivalent to that of traditional GCP-based photogrammetry using numerous and well-distributed GCPs. The optimal model quality that minimized vertical bias and random errors was achieved from 5 GCPs, with a two-fold reduction in RMSE. The image resolution for tie point detection was found to be an important control on the measurement quality, with the best results obtained using images at their original scale. Using these findings enabled designing an efficient and effective workflow for monitoring coastal topographic complexity at a large scale.

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Section: Introductionmentioning

confidence: 99%

Assessment of RTK Quadcopter and Structure-from-Motion Photogrammetry for Fine-Scale Monitoring of Coastal Topographic Complexity

2022

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“…Migrating giant sandwaves often become potential hazards to coastal engineering structures: destabilizing underwater drilling platforms, causing pipeline overhang and even creating fractures (Belde et al, 2017). Sandwave mobility (e.g., Ferret et al, 2010;Damen et al, 2018) or sediment transport (Dalrymple, 1984;Vandenberg, 1987;Hoekstra et al, 2004;Xu et al, 2008) are typically the focus of studies on sandwave migrations. The direction of sandwave migration can be determined by the geometrical asymmetry of sandwaves that normally have a steeper, shorter lee side (downstream) and a gentler, longer stoss side (upstream) (McCave, 1971;Bartholdy et al, 2002;Wynn and Stow, 2002;Zhou et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Migrating sandwaves riding on relict dunes of Taiwan shoal, northern South China Sea

Yang

et al. 2022

Front. Earth Sci.

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Sandwaves, a ubiquitous bedform commonly found in most coastal seas and sometimes in deep waters of continental slopes and submarine canyons, are often the subject of marine hazard studies because their frequent migration can pose potential threats to pipelines or other engineering structures in the ocean. Analyses of high-resolution bathymetric data collected along a 136-km multibeam bathymetric survey line demonstrate the co-existence of three different sizes of sandwaves: giant, primary dunes (∼10-15 m in height, up to 2,000 m in length); small, secondary sandwaves (∼1 m in height, ∼50 m in length) riding on the stoss side of the primary dunes; and mid-size dunes (∼5-10 m in height, ∼100-500 m in length) found in the trough of primary dunes. While the tidal current-driven, secondary sandwaves are migrating, the primary and mid-size dunes are immobile. Empirical model results suggest that the primary dunes are relict dunes that were most likely formed in geologic past when sea level was higher or the seabed elevation was lower, but water depth is probably not the only factor in limiting the formation of the primary dunes.

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“…bedform velocities are determined from the evolution of crest lines or other bedform patterns from time to time that are detected either manually or through cross-correlation of bed-elevation profiles (van den Berg, 1987;Hoekstra et al, 2004).…”

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confidence: 99%

Mapping 2‐D Bedload Rates Throughout a Sand‐Bed River Reach From High‐Resolution Acoustical Surveys of Migrating Bedforms

Coz

Perret

Camenen

et al. 2022

Water Resources Research

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Measuring bedload in sand-bed channels is important for a number of river and coastal management issues (e.g., sediment budget, channel stability, navigation, ecological habitat, coastal retreat) but it remains a challenging operation. Due to technical difficulties, cost, and field hazards, manual sampling techniques are often replaced by surrogate techniques such as dune-tracking from acoustical sounding of the bed topography. Bedform characteristics such as bedform height, wavelength, and velocity can be determined with reasonable accuracy, then used to determine bedload if two successive surveys of bed elevation are available. Based on the Exner equation for sediment continuity, the mean bedload rate q b over a bedform wave length can be expressed as (Simons et al., 1965):where p is the bedform porosity, V b is the bedform velocity, H b is the mean bedform height (thickness) and q b,0 is a constant bedload rate that may be interpreted as the transport rate below the bedform baseline (Simons et al., 1965) or as the fraction of bed material load that moves intermittently in near-bed suspension (McElroy & Mohrig, 2009). Traditionally, the mean bedform height is computed as H b = α b H b,max where H b,max is the crest-to-trough height of bedforms and α b is the bedform shape factor. Most often, dunes are assumed to be triangular in shape, hence α b = 0.5.A number of methods for determining bedform characteristics from a bed-elevation profile (or longitudinal transect) exist (see van der Mark & Blom, 2007 for a review). The detection of bedforms can be based on either manually selected crests and troughs, local extremes, or zero crossings in the detrended bed-elevation profile. These methods come with a variable degree of subjectivity, usually requiring some choices and thresholds to be set to avoid including smaller, superimposed bedforms or minor variations in the bed-elevation profile. Traditionally,

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Bedform migration and bedload transport on an intertidal shoal

Cited by 60 publications

References 22 publications

Assessment of RTK Quadcopter and Structure-from-Motion Photogrammetry for Fine-Scale Monitoring of Coastal Topographic Complexity

Assessment of RTK Quadcopter and Structure-from-Motion Photogrammetry for Fine-Scale Monitoring of Coastal Topographic Complexity

Migrating sandwaves riding on relict dunes of Taiwan shoal, northern South China Sea

Mapping 2‐D Bedload Rates Throughout a Sand‐Bed River Reach From High‐Resolution Acoustical Surveys of Migrating Bedforms

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