Laboratory flume experiments with the Swiss plate geophone bed load monitoring system: 2. Application to field sites with direct bed load samples

Abstract

The Swiss plate geophone is a bed load surrogate monitoring system that had been calibrated in several gravel bed streams through field calibration measurements. Field calibration measurements are generally expensive and time consuming, therefore we investigated the possibility to replace it by a flume-based calibration approach. We applied impulse-diameter relations for the Swiss plate geophone obtained from systematic flume experiments to field calibration measurements in four different gravel bed streams. The flume-based relations were successfully validated with direct bed load samples from field measurements, by estimating the number of impulses based on observed bed load masses per grain-size class. We estimated bed load transport mass by developing flume-based and stream-dependent calibration procedures for the Swiss plate geophone system using an additional empirical function. The estimated masses are on average in the range of ±90% of measured bed load masses in the field, but the accuracy is generally improved for larger transported bed load masses. We discuss the limitations of the presented flume-based calibration approach.