Calibration of Acoustic Doppler Current Profiler Apparent Bedload Velocity to Bedload Transport Rate

Abstract. Despite the inherent difficulties to quantify its value, bedload transport is essential to understand fluvial systems. In this study, we assessed different indirect bedload measurement techniques with a reference direct bedload measurement in a section of a large sandy-gravel bed river. Acoustic Doppler Current Profiler (aDcp), Dune Tracking Method (DTM) and hydrophone measurement techniques were used to determine bedload transport rates using calibration with the reference method or using empirical formula. Results show that the hydrophone is the most efficient and accurate method to determine bedload flux in the Loire River. Even though parameters controlling self-generated noise of sediments still need to better understood, the calibration determined in this study allows a good approximation of bedload transport rates. Moreover, aDcp and hydrophone measurement techniques are both able to continuously measure bedload transport associated to bedform migration.

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Calculated Potential Bedload Versus Real Transported Sands along the Guadiana River Estuary (Spain–Portugal)

Journal of Marine Science and Engineering ◽

10.3390/jmse7110393 ◽

2019 ◽

Vol 7 (11) ◽

pp. 393

Author(s):

Juan A. Morales ◽

Claudio Lozano ◽

Mouncef Sedrati

Keyword(s):

Bottom Water ◽

River Estuary ◽

Acoustic Doppler Current Profiler ◽

Bedload Transport ◽

Cohesive Sediments ◽

Coastal System ◽

Deep Channel ◽

Current Profiler ◽

Comparison Of The Results ◽

Guadiana Estuary

The Guadiana estuary is a coastal system located in the southwest of the Iberian Peninsula and is the natural border between Portugal and Spain. It is a rock-bounded estuary which extends along more than 40 km and is characterized by a semidiurnal mesotidal regime. This paper represents an approach to the bedload transport across two flow sections located in the fluvial and marine domains. In the fluvial profile, the most frequent bedform is the plane bed. In the marine area the bed of the deep channel is composed of well-sorted sand, while a lateral bar displays partially cohesive sediments with dominant fine sands in a matrix of clayey silts. Data were acquired during spring and neap tides. Near-bottom water velocities were registered by an acoustic Doppler current profiler (ADCP). Density and bed rugosity were determined in sediment samples. These data were employed using Bagnold’s equation (1963) to quantify the potential bedload (Qb). Further, real bedload values (Sb) were obtained by using Poliakoff traps. The comparison of the results of Qb under both ebb and flood conditions demonstrated a clear river-to-sea net transport in both sectors. The values of Sb were lower than those of Qb in every condition. The sand input across the fluvial estuary cannot supply the potential bedload in the lower domain of the channel, thereby causing a deficit that explains this lack of agreement between potential and real transport.

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