In the Erlenbach stream, a pre‐alpine steep channel in Switzerland, sediment transport has been monitored for more than 25 years. Near the confluence with the main valley river, stream flow is monitored and sediment is collected in a retention basin with a capacity of about 2000 m3. The basin is surveyed at regular intervals and after large flood events. In addition, sediment transport has been continuously monitored with piezoelectric bedload impact and geophone sensors since 1986. In 2008–2009, the measuring system in the Erlenbach stream was enhanced by installing an automatic system to obtain bedload samples. Movable metal baskets are mounted on a rail at the downstream wall of the large check dam above the retention basin, and they can be moved automatically into the flow to take bedload transport samples. The wire mesh of the baskets has a spacing of 10 mm to sample all sediment particles coarser than this size (which is about the limiting grain size detected by the geophones). The upgraded measuring system permits to obtain bedload samples over short sampling periods and to measure the grain size distribution of the transported material and its variation over time and with discharge. The analysis of calibration relationships for the geophone measuring system confirms findings from very similar measurements which were performed until 1999 with piezoelectric bedload impact sensors; there is a linear relationship between impulse counts and bedload mass passing over the sensors. Findings from flume experiments are used to discuss the most important factors which affect the calibration of the geophone signal. The bedload transport rates as measured by the moving baskets are among the highest measured in natural streams, with values of the order of several kilograms per meter per second. Copyright © 2012 John Wiley & Sons, Ltd.

Indirect bedload transport measurements have been made with the Swiss plate geophone system in five gravel‐bed mountain streams. These geophone sensors record the motion of bedload particles transported over a steel plate mounted flush with the channel bed. To calibrate the geophone system, direct bedload transport measurements were undertaken simultaneously. At the Erlenbach in Switzerland, a moving‐basket sampler was used. At the Fischbach and Ruetz streams in Austria, a Helley–Smith type bedload sampler provided the calibration measurements. A Bunte‐type bedload trap was used at the Rofenache stream in Austria. At the Nahal Eshtemoa in Israel, Reid‐type slot bedload samplers were used. To characterize the response of the geophone signal to bedload particles impacting on the plate, geophone summary values were calculated from the raw signal and stored at one second intervals. The number of impulses, i.e. the number of peaks above a pre‐defined threshold value of the geophone output signal, correlated well with field measured gravel transport loads and was found to be a robust parameter. The relations of impulses to gravel transport loads were generally near‐linear, but the steepness of the calibration relations differed from site to site. By comparing the calibration measurements from the different field sites and utilizing insights gained during preliminary flume experiments, it has been possible to identify the main factors that are responsible for site specific differences in the calibration coefficient. The analysis of these calibration measurements indicates that the geophone signal also contains some information about the grain size distribution of bedload. Copyright © 2013 John Wiley & Sons, Ltd.

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We performed systematic flume experiments using natural bed load particles to quantify the effect of different parameters on the signal registered by the Swiss plate geophone, a bed load surrogate monitoring system. It was observed that the number of impulses computed from the raw signal clearly depends on bed particle size, mean flow velocity, bed roughness, and to a minor extent on particle shape. The centroid frequency of the signal resulting from the collision of a bed load particle against the geophone plate was found to be inversely related to particle size but to be less sensitive to variations in mean flow velocity and bed roughness than the signal amplitude, which is also related to particle size. Combining frequency and amplitude information resulted in a more robust identification of the transported particles size over a wide range of sizes than using amplitude information alone.

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.