Effects of Instrumented Bottom Tripods on Process Measurements

Bolaños, Rodolfo; Amoudry, Laurent O.; Doyle, Ken

doi:10.1175/2010jtecho816.1

Cited by 10 publications

(11 citation statements)

References 26 publications

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“…Altogether, this confirms the good predictive capability of this model in terms of hydrodynamics. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 but may also be due to some effect of the tripod on the measured turbulent stresses (e.g., Bolaños et al, 2011). Finally, the turbulent kinetic energy calculated from the ADV measurements is presented alongside the model friction velocity in panel d, as…”

Section: Numerical Experimentsmentioning

confidence: 99%

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

et al. 2014

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We investigate the dynamics of suspended sediment transport in a hypertidal estuarine channel which displays a vertically sheared exchange flow. We apply a three-dimensional process-based model coupling hydrodynamics, turbulence, and sediment transport to the Dee Estuary, in the north-west region of the UK. The numerical model is used to reproduce observations of suspended sediment and to assess physical processes responsible for the observed suspended sediment concentration patterns.The study period focuses on a calm period during which wave-current interactions can reasonably be neglected. Good agreement between model and observations has been obtained. A series of numerical experiments aims to isolate specific processes and confirm that the suspended sediment dynamics result primarily from advection of a longitudinal gradient in concentration during our study period, combined with resuspension and vertical exchange processes. Horizontal advection of sediment presents a strong semidiurnal variability, while vertical exchange processes (including time-varying settling as a proxy for flocculation) exhibit a quarter-diurnal variability. Sediment input from the river is found to have very little importance and spatial gradients in suspended concentration are generated by spatial heterogeneity in bed sediment characteristics and spatial variations in turbulence and bed shear stress.

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Section: Numerical Experimentsmentioning

confidence: 99%

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

et al. 2014

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“…Significant effort was made to deploy the instruments on a frame that would minimise frame effects on the bed, such as those described by Bolaños et al (2011). To this end, over a series of pilot studies, the SEDbed frame was developed for the present study.…”

Section: Discussionmentioning

confidence: 99%

Field deployment and evaluation of a prototype autonomous two dimensional acoustic backscatter instrument: The Bedform And Suspended Sediment Imager (BASSI)

Moate

Thorne

Cooke

2016

Continental Shelf Research

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The processes of sediment entrainment, transport and deposition over bedforms are highly dynamic and temporally and spatially variable. However, most measurements of these processes tend to be collected in a vertical line at one spatial location above the bed; one dimensional in the vertical, 1D-V. Such measurements capture the temporal signature, and, to a lesser degree, the spatial variability when bedforms migrate, and they have contributed greatly to our understanding of sediment transport processes. It is generally acknowledged, however, that such 1D-V systems provide a limited description of the spatially three dimensional processes occurring at the turbulent and intra-wave time scales. It would undoubtedly facilitate the interpretation of fundamental sediment processes above bedforms if other spatial dimensions could be simultaneously interrogated. To this end a multifrequency acoustic array has been developed to measure suspended sediments and bedforms over a horizontal transect of the bed in the vertical, providing two dimensional observations in the vertical and horizontal, 2D-HV. This new acoustic instrument, the BASSI; Bedform And Suspended Sediment Imager, has been deployed in the River Dee tidal estuary in the UK. The design of the BASSI and results from the deployment are presented and its performance assessed against more conventional instrumentation. Measurements and images of 2D-HV suspended sediments and bedforms are provided to illustrate the capability and future use of the BASSI for the investigation of sediment transport processes.3

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“…The interaction of the frame with the flow and movable seabed can result in a scour pit around the frame (Bolaños et al 2011). If substantial scouring has occurred, the angle of the seabed relative to the sonar will be decreased, affecting the estimated asymmetry and height of the bedform.…”

Section: B Scoured Seabedmentioning

confidence: 99%

“…This extrapolated value accounts for some of the overestimation in bedform wavelength and is also able to capture the sudden decrease in wavelength around 6 October 2007. Studies on the effect of frames on the seabed and flow have shown that in the presence of waves, there is increased turbulence near the frame (Bolaños et al 2011;Williams et al 2003). While the results of Bolaños et al (2011) and Williams et al (2003) indicate that the frame does not have as large of an effect on the flow and seabed in wave conditions as opposed to strong currents, it is hypothesized that this increased turbulence can result in the bedforms under the frame adjusting to a new equilibrium configuration faster than the bedforms away from the frame.…”

Section: A Wave-orbital Ripplesmentioning

confidence: 99%

“…The difference in bedform wavelength in the presence of the frame is hypothesized to be attributed to current-frame interactions. Bolaños et al (2011) found that underwater frames increase the horizontal velocity under the frame, resulting in a scour pit. Because the megaripple wavelengths are on the same order of size as the frame, it is believed this scour pit alters the bedform morphodynamics such that the wavelengths of bedforms under the frame are larger than those away from the frame.…”

Section: B Tidally Reversing Megaripplesmentioning

confidence: 99%

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A Method to Quantify Bedform Height and Asymmetry from a Low-Mounted Sidescan Sonar

Jones

Traykovski

2018

Journal of Atmospheric and Oceanic Technology

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Rotary sidescan sonars are widely used to image the seabed given their high temporal and spatial resolution. This high resolution is necessary to resolve bedform dynamics and evolution; however, sidescan sonars do not directly measure bathymetry, limiting their utility. When sidescan sonars are mounted close to the seabed, bedforms may create acoustical ''shadows'' that render previous methods that invert the backscatter intensity to estimate bathymetry and are based on the assumption of a fully insonified seabed ineffective. This is especially true in coastal regions, where bedforms are common features whose large height relative to the water depth may significantly influence the surrounding flow. A method is described that utilizes sonar shadows to estimate bedform height and asymmetry. The method accounts for the periodic structure of bedform fields and the projection of the shadows onto adjacent bedforms. It is validated with bathymetric observations of wave-orbital ripples, with wavelengths ranging from 0.3 to 0.8 m, and tidally reversing megaripples, with wavelengths from 5 to 8 m. In both cases, bathymetric-measuring sonars were deployed in addition to a rotary sidescan sonar to provide a ground truth; however, the bathymetric sonars typically measure different and smaller areas than the rotary sidescan sonar. The shadow-based method and bathymetric-measuring sonar data produce estimates of bedform height that agree by 34.0% 6 27.2% for wave-orbital ripples and 16.6% 6 14.7% for megaripples. Errors for estimates of asymmetry are 1.9% 6 2.1% for wave-orbital ripples and 11.2% 6 9.6% for megaripples.

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Effects of Instrumented Bottom Tripods on Process Measurements

Cited by 10 publications

References 26 publications

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

Field deployment and evaluation of a prototype autonomous two dimensional acoustic backscatter instrument: The Bedform And Suspended Sediment Imager (BASSI)

A Method to Quantify Bedform Height and Asymmetry from a Low-Mounted Sidescan Sonar

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