A particle counting system for calculation of bedload fluxes

Abstract

Channel bed morphology depends on bedload fluxes which are difficult to determine even in controlled laboratory conditions. Particle counting can provide time resolved bedload fluxes. Determination of particle rates by means of digital image processing is computationally expensive and the requirement for optical access is not always met. Weighing methods are limited by short dynamic ranges. To overcome these difficulties this paper presents a prototype of a particle counter device that works by detecting impacts on a sensitive surface. The accuracy of the device is validated, by means of laboratory experiments, contrasting its results against those obtained by means of digital image analysis. This device proved to be capable of measuring bedload fluxes, determining long time series of bedload transport rates, in particles per unit time, with high accuracy and with a much lower computation cost relatively to digital image processing. The device is also able to gather meaningful data in real-time, like particle arrival time-series and real-time lateral bedload distribution. The parameters involved in the detection criterion must be previously set through a heuristic procedure. However, the method itself is direct—it requires no calibration between the acquired signal and bedload transport rates. Particle counts can be transformed in bedload discharges by a simple binning process or by taking finite differences of the cumulative mass function. First and second order moments of bedload discharge are in agreement with the values obtained by direct counting. The low requirement for data storage, allowing for very large data series, the real time analysis capabilities, the low cost of such system when compared with a digital image acquisition system constitute the main advantages of the device for the study of integral scales of bedload and bedload intermittency.

Estimating Mean Bedload Transport Rates and Their Uncertainty

“…For instance, in the laboratory, it has long been common to collect the sediment transported to the flume outlet over a given time interval and weigh it to deduce a time‐averaged value of . Today, techniques based on impact plates, acoustic sensors and image processing enable high‐frequency measurements of (Geay et al., 2017; Gray et al., 2010; Mendes et al., 2016; Rickenmann et al., 2014; Singh et al., 2009; Tsakiris et al., 2014). In both cases, is defined as the particle flux through a surface.…”

Multicamera, Multimethod Measurements for Hydromorphologic Laboratory Experiments

“…At least for laboratory work, that can be performed in more controlled conditions than in the field. These drawbacks have motivated, for example, equipping sediment samplers or traps with scales or even alternative measurement techniques to achieve an automatic measurement of transport rates (e.g., [26,27]). Furthermore, movable instruments may reduce measuring frequency due to the time needed to move the probe from one location to another.…”

Image-based Lagrangian Particle Tracking in Bed-load Experiments

“…The measurement of sediment transport can be performed using a Eulerian approach that targets measurement of sediment fluxes, or a Lagrangian one that aims at measuring trajectories of individual grains as they move. Image processing offers unique possibilities for particle tracking in comparison to other Eulerian methods 6 7 . However, despite these potentialities, the application of image analysis to bed-load sediment transport suffers from some critical experimental limitations, in terms of spatial/temporal support scales for the measurement and size of data samples.…”