Morphology of the Kosi megafan channels

Abstract. We study the morphology of streams flowing on the alluvial megafan of the Kosi River in north Bihar, India. All streams develop on a uniform sandy sediment and under a similar climate, allowing for statistically significant comparisons. Our data set includes both channels from the braid of the Kosi River and channels from isolated single-thread rivers. Using an Acoustic Doppler Current Profiler, we measure the width, depth and water discharge of the channels. Their average slope is also acquired with a kinematic GPS. These morphological characteristics are strongly correlated with the discharge. However, rescaling the data according to the threshold channel theory removes most of this dependency. The rescaled data suggest that the threads of the Kosi River braid are morphologically similar to isolated channels.

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Acoustic and optical methods to infer water transparency at Time Series Station Spiekeroog, Wadden Sea

Ocean Science ◽

10.5194/os-12-1155-2016 ◽

2016 ◽

Vol 12 (6) ◽

pp. 1155-1163 ◽

Cited By ~ 3

Author(s):

Anne-Christin Schulz ◽

Thomas H. Badewien ◽

Shungudzemwoyo P. Garaba ◽

Oliver Zielinski

Keyword(s):

Time Series ◽

Wadden Sea ◽

Acoustic Doppler Current Profiler ◽

Water Transparency ◽

Optical Observations ◽

Optical Methods ◽

Acoustic Measurements ◽

Data Set ◽

Backscatter Signal ◽

Current Profiler

Abstract. Water transparency is a primary indicator of optical water quality that is driven by suspended particulate and dissolved material. A data set from the operational Time Series Station Spiekeroog located at a tidal inlet of the Wadden Sea was used to perform (i) an inter-comparison of observations related to water transparency, (ii) correlation tests among these measured parameters, and (iii) to explore the utility of both acoustic and optical tools in monitoring water transparency. An Acoustic Doppler Current Profiler was used to derive the backscatter signal in the water column. Optical observations were collected using above-water hyperspectral radiometers and a submerged turbidity metre. Bio-fouling on the turbidity sensors optical windows resulted in measurement drift and abnormal values during quality control steps. We observed significant correlations between turbidity collected by the submerged metre and that derived from above-water radiometer observations. Turbidity from these sensors was also associated with the backscatter signal derived from the acoustic measurements. These findings suggest that both optical and acoustic measurements can be reasonable proxies of water transparency with the potential to mitigate gaps and increase data quality in long-time observation of marine environments.

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Krill diel vertical migration fine dynamics, nocturnal overturns, and their roles for aggregation in stratified flows

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f07-179 ◽

2008 ◽

Vol 65 (4) ◽

pp. 574-587 ◽

Cited By ~ 30

Author(s):

M Sourisseau ◽

Y Simard ◽

F J Saucier

Keyword(s):

Water Column ◽

Vertical Migration ◽

Acoustic Doppler Current Profiler ◽

Day Length ◽

Data Set ◽

Vertical Movements ◽

Lawrence Estuary ◽

Diel Vertical Migrations ◽

Current Profiler ◽

Feeding Bout

A set of high-resolution observations on short-term dynamics of krill diel vertical migrations (DVM) in the St. Lawrence Estuary are presented here, including vertical mass transfer measurements from multifrequency echo sounding coupled with stratified net sampling and tracers of individual vertical movements from stomach pigments over a 72 h period. The data set is supplemented by vertical migration speeds and biomass diel patterns from ADCP (acoustic Doppler current profiler) time series lasting up to 3 months. All krill always rapidly migrated to the surface in synchrony at sunset. Soon after the ascent, fed krill started to swim downward. A scattering layer was then formed at their daytime depth with sometimes a significant backscatter at intermediate depths, especially around midnight. A reorganisation in the upper water column then occurs, likely for a predawn feeding bout. At dawn, the krill mass still feeding in upper water column synchronously swam downward to their daytime depth. This nocturnal asynchronous vertical behaviour, conforming to the DVM hunger-satiation hypothesis, repeated between August and October in two different years, the DVM timing being determined by day length.

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Morphology of the Kosi megafan channels

Earth Surface Dynamics ◽

10.5194/esurf-3-321-2015 ◽

2015 ◽

Vol 3 (3) ◽

pp. 321-331 ◽

Cited By ~ 8

Author(s):

K. Gaurav ◽

F. Métivier ◽

O. Devauchelle ◽

R. Sinha ◽

H. Chauvet ◽

...

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Aspect Ratio ◽

Water Discharge ◽

Sandy Sediment ◽

Data Set ◽

Threshold Theory ◽

Large Dispersion ◽

Depth Water

Abstract. We report on a new set of measurements on the morphology of braided and meandering threads of the Kosi megafan, North Bihar, India. All threads develop on a uniform sandy sediment and under a similar climate. The data set is composed of the width, depth, water discharge and grain size of 51 threads. Downstream slopes and sinuosity are also available. Using this data set, we show that braided and meandering threads share common hydraulic geometries. We then use the threshold theory to explain why the aspect ratio of threads is almost naturally detrended, and rescale the data according to this theory. As expected, the rescaled dimensions of braided and meandering threads are weakly correlated to water discharge. We propose that the large dispersion observed, which is common to meandering and braided threads, is the signature of sediment transport, vegetation or cohesion effects.

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Multi-year high-frequency physical and environmental observations at the Guadiana Estuary

Earth System Science Data ◽

10.5194/essd-7-299-2015 ◽

2015 ◽

Vol 7 (2) ◽

pp. 299-309 ◽

Cited By ~ 12

Author(s):

E. Garel ◽

Ó. Ferreira

Keyword(s):

High Frequency ◽

Time Series Data ◽

Acoustic Doppler Current Profiler ◽

Time Frame ◽

Series Data ◽

Data Set ◽

Discharge Data ◽

Current Profiler ◽

Machine Readable ◽

Guadiana Estuary

Abstract. High-frequency data collected continuously over a multi-year time frame are required for investigating the various agents that drive ecological and hydrodynamic processes in estuaries. Here, we present water quality and current in situ observations from a fixed monitoring station operating from 2008 to 2014 in the lower Guadiana Estuary, southern Portugal (37°11.30' N, 7°24.67' W). The data were recorded by a multi-parametric probe providing hourly records (temperature, salinity, chlorophyll, dissolved oxygen, turbidity, and pH) at a water depth of ~ 1 m, and by a bottom-mounted acoustic Doppler current profiler measuring the pressure, near-bottom temperature, and flow velocity through the water column every 15 min. The time series data, in particular the probe ones, present substantial gaps arising from equipment failure and maintenance, which are ineluctable with this type of observation in harsh environments. However, prolonged (months-long) periods of multi-parametric observations during contrasted external forcing conditions are available. The raw data are reported together with flags indicating the quality status of each record. River discharge data from two hydrographic stations located near the estuary head are also provided to support data analysis and interpretation. The data set is publicly available in machine-readable format at PANGAEA (doi:10.1594/PANGAEA.845750).

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