Effect of bedload shape on the signal characteristics of a hybrid impact plate

Abstract

Understanding bedload dynamics is critical for insights into erosion, sedimentation, and channel evolution of river systems. Designing hydraulic structures and validating existing sediment transport models need accurate bedload data. Bedload measurement is done using direct methods involving physical samplers or indirect devices with various acoustic sensors. One widely used indirect method is the impact plate system, which houses an acoustic sensor under it to detect bedload particles. Impact plate systems have been tested under varying velocity, bed roughness and bedload grain sizes. However, the influence of bedload particle shape on the signal characteristics in impact plate systems has yet to be investigated in detail. In the present study, an impact plate system with a hybrid sensor (accelerometer and geophone) attached to the plate's underside is used to understand the role of the shape of the bedload in an experimental flume. Five different particle sizes (4 to 40 mm) are grouped into three classes based on their sphericity index (0.45-0.6, 0.6-0.75, and 0.75-0.9), creating a total of fifteen classes. Ten bedload particles from each class are manually released over the impact plate for 20 runs, and the signals are recorded. It is found that the bedload shape significantly affects the signal characteristics, and with increasing sphericity, the mean maximum amplitude of the signal increases while the centroid frequency decreases. A calibration equation is thus developed between the signal parameters and the sphericity of the bedload grains.