Effect of Channel Bed Roughness on the Mode of Bedload Transport and Signal Response of Impact Plate with an Accelerometer

Studying bedload transport is essential for analysing erosion and deposition processes in the channels and designing hydraulic structures. Impact plate systems are indirect devices deployed to measure bedload consisting of a metal plate. When the bedload sediments strike the plate, they create vibrations which are recorded as signals by an acoustic sensor attached to the plate. The signal acquired is then processed to find the bedload properties. Flow velocity and mode of bedload transport can affect the signal. The effect of velocity on the impact plate signals is well documented in the literature. However, the role of channel bed roughness which hugely influences the mode of transportation of bedload, is yet to be studied in detail. This study investigates the effect of channel roughness on the mode of bedload transport and the signal registered in an impact plate in a laboratory flume. The impact plate is placed at the downstream end such that the top plate of the box is aligned with the bed of the flume. An accelerometer sensor is attached to the underside of the plate to record the vibrations. The bed of the flume 2.5m upstream of the impact plate is composed of a replaceable “rough” section. Four different tests are conducted considering four separate rough sections (smooth, 2mm, 5mm, and 10 mm). The bedload particles are sorted into five classes based on their size, from 2.36mm to 20mm. In each test, the particles from a particular grain size class are manually released 5m upstream of the impact plate. The signal generated from the bedload strike is used to develop a calibration equation relating to bedload size and channel roughness. A digital camera is used to capture the bedload movement over the plate to link the mode of bedload transport with the signal.