Laboratory Calibration of Impact Plates for Measuring Gravel Bed Load Size and Mass

Abstract

Continuous monitoring of gravel transport in rivers is necessary for understanding the effect of dam removal on river systems. Impact plates, such as those deployed on the Elwha River in the state of Washington, are a promising technique; however, relating the data generated by the plates to sediment load is difficult. In order to refine methods described in a recent study, coarse bed load transport was measured in a laboratory channel and compared to the output from two accelerometer-equipped impact plates that were full-scale replicas of 72 plates deployed in the Elwha River. Relations were developed for converting the signal amplitude generated by particles impacting the plates to particle mass. Mean discrepancy ratios indicate that estimates of coarse bed load transport were within 25% of the measured values if one outlier from the experiments was removed. Methods to transfer these relations to field locations are also discussed.