Continuous monitoring of bedload transport in a laboratory flume using an impact sensor

Bedload transport rate in gravel-bed rivers shows large non-Gaussian fluctuations, even under steady flow conditions. The development of high-resolution measurement techniques during the last two decades creates research opportunities to study the intermittent character of bedload transport and the significance of its fluctuations. In this paper, we investigate the use of an impact plate as an alternative to video-based technology for laboratory applications. The objective is to develop a simple and robust technology that can be run continuously over long periods of time. The impact plate is mounted vertically at the flume outlet. This is a novel non-intrusive configuration, which reduces the uncertainties in the particle transport rate measurement compared to the classical configuration: in that configuration, the impact plate is indeed parallel to the bed and the vibrations recorded by the sensor depend a great deal on the features of particle motion (e.g., the mode of transport, the angle of impact and the particle velocity). In our experiments, we focused on two key variables: the number of moving particles and the bedload transport rate. We measured these variables using the vertical plate sensor and image processing in different flume experiments. We found that the impact plate and the camera reached the same level of accuracy. The vertical impact plate can therefore be an efficient measurement technique, which requires reduced costs and computational resources.