BEDLOAD MEASSURMENTS USING ADCP - CONFIRMATION AND ANALYSIS

Measuring the bedload transport in fluvial environments is a difficult and labor-intensive task. The temporal and spatial variability of the bed load together with the instrument disturbance can induce stochastic and systematic uncertainties. These data are usually considered as unreliable, which complicates the further elaboration of the sediment transport behavior. Statistically valid measurements are extremely important for the evaluation of the sediment transport masses, especially in large navigable or heavily exploited rivers. Recently, many studies showed that the measurements with the bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as a promising technique in evaluating the bed load (Rennie, et al., 2002; Gaeuman & Jacobson, 2006; Latosinski, et al., 2017). The use of these non-intrusive techniques could significantly reduce the uncertainty. Firstly, they do not disturb the riverbed and are easy to deploy. Secondly, very long and frequent measurements can be easily performed. Widespread implementation of the ADCP BT bedload technique would reduce the scarcity and statistical uncertainty of bed load data. The ADCP velocity is commonly denoted as the apparent velocity. It represents a velocity calculated as the difference between the Bottom Tracking (BT) mode and the GPS velocity. Nevertheless, the bedload transport is usually characterized with near-bed turbulent conditions and the rough loose bed. Therefore, the acoustic footprint contains data from mobile and immobile particles, as well as the undulations of the bottom. The signal is noisy and contains erroneous data. This study aims to develop a methodology of using the ADCP BT Mode to measure the velocity of the bedload. The capability of two commercially available ADCPs were tested in controlled laboratory conditions (Conevski, et al., 2018). In addition, the results from two measurement campaigns are presented. The first measurement is in the Devoll River Valley, Albania, while the second campaign is in Oder River in Germany. This work offer a correlation and confirmation of a potential usage of the filtered temporally averaged ADCPs velocity and eventual application of the kinematic transport model (e.g. Kinematic Transport Theorem) in future

Evaluation of an acoustic Doppler technique for bed-load transport measurements in sand-bed Rivers

The bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as a promising technique in evaluating the bed load. Strong statistical correlations are reported between the ADCP BT velocity and the transport rate obtained by physical sampling or dune tracking; however, these relations are strictly site-specific and a local calibration is necessary. The direct physical sampling is very labor intensive and it is prone to high instrument uncertainty. The aim of this work is to develop a methodology for evaluating the bed load transport using commercial ADCPs without calibration with physical samples. Relatively long stationary measurements were performed in a sand-bed and sand gravel rivers, using three different ADCPs working at 3MHz, 1.2MHz and 0.6MHz. Simultaneously, bed load samples were collected with physical samplers, and the riverbed was closely observed with digital cameras mounted on the samplers. It is demonstrated that the kinematic transport model can yield a relatively good estimate of the transport rate by directly using filtered apparent velocity, the knowledge of the hydraulic conditions and instrument-related calibration coefficients. Additionally, the ADCP data can help in qualitative assessment of the physical sampling. Future investigation of the backscattering echo and further confirmation of the BT apparent velocity should be performed in laboratory-controlled conditions

Acoustic sampling effects on bedload quantification using acoustic Doppler current profilers

This paper provides an evaluation of a hydro-acoustic technique for efficient quantification of the bedload transport in riverine environments. Stationary bedload measurements were conducted simultaneously at different study sites, using three different acoustic Doppler current profilers (ADCP) working at four different frequencies. The raw apparent bedload velocities were de-spiked and filtered in a streamwise direction. Then, functional correlations were observed between the magnitudes of the apparent velocities and the bedload transport rates measured by the conventional bedload sampler. Each ADCP yielded different results because of the different frequency backscatter sensitivity and acoustic penetration in the active bedload layer. In addition to the frequency, other acoustic parameters such as the percentage of the filtered data, transducers width, beam opening angle, beam-grazing angle and the pulse length, contributed to the acoustic bedload sampling. The influence of these parameters is examined, and recommendations are given for the performance and limitations of each instrument

Thieme Chemistry Journals Awardees – Where Are They Now? Molybdenum(V)-Mediated Synthesis of Nonsymmetric Diaryl and Aryl Alkyl Chalcogenides

Oxidative chalcogenation reaction using molybdenum(V) reagents provides fast access to a wide range of nonsymmetric aryl sulfides and selenides. The established protocol is tolerated by a variety of labile functions, protecting groups, and aromatic heterocycles. In particular, when labile moieties are present, the use of molybdenum(V) reagents provides superior yields compared to other oxidants