Continuous Monitoring of Bed-Load Transport in a Laboratory Flume Using an Impact Sensor

Bed-load 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 bed-load transport and the significance of its fluctuations. In this paper, the use of an impact plate as an alternative to video-based technology for laboratory applications is investigated. The objective is to develop a simple and robust technology that can be run continuously over several hours. The impact plate is mounted vertically at the flume outlet. This is a novel nonintrusive configuration, which reduces the uncertainties in the particle transport rate measurement compared with 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). Two key variables were monitored in different flume experiments: the number of moving particles and the bed-load transport rate. They were measured using the vertical plate sensor and image processing. The impact plate and the camera were found to reach the same level of accuracy. The vertical impact plate can therefore be an efficient measurement technique, which requires reduced costs and computational resources.