Abstract
Abstract. The Swiss plate geophone system is a bedload surrogate measuring technique that has been installed in more than 20 streams, primarily in the European Alps. Here we report about calibration measurements performed in two mountain streams in Austria. The Fischbach and Ruetz gravel-bed streams are characterized by important runoff and bedload transport during the snowmelt season. A total of 31 (Fischbach) and 21 (Ruetz) direct bedload samples were obtained during a 6-year period. Using the number of geophone impulses and total transported bedload mass for each measurement to derive a calibration function results in a strong linear relation for the Fischbach, whereas there is only a poor linear calibration relation for the Ruetz measurements. Instead, using geophone impulse rates and bedload transport rates indicates that two power law relations best represent the Fischbach data, depending on transport intensity; for lower transport intensities, the same power law relation is also in reasonable agreement with the Ruetz data. These results are compared with data and findings from other field sites and flume studies. We further show that the observed coarsening of the grain size distribution with increasing bedload flux can be qualitatively reproduced from the geophone signal, when using the impulse counts along with amplitude information. Finally, we discuss implausible geophone impulse counts that were recorded during periods with smaller discharges without any bedload transport, and that are likely caused by vehicle movement very near to the measuring sites.
Highlights
In the past decade or so, an increasing number of studies have been undertaken on bedload surrogate acoustic measuring techniques which were tested both in flume experiments and in field settings
In this study we report on calibration measurements of the Swiss plate geophone (SPG) system in two mountain streams in Austria
The objectives of this paper are (i) to present and discuss different ways of analysing the geophone calibration measurements, in comparison with data and findings from other field sites and flume studies, (ii) to show that the observed coarsening of the grain size distribution with increasing bedload flux can be qualitatively reproduced from the geophone signal, and (iii) to discuss implausible geophone impulse counts that were recorded during periods with small discharge and without any bedload transport, and that are probably associated with close-by vehicle movement
Summary
In the past decade or so, an increasing number of studies have been undertaken on bedload surrogate acoustic measuring techniques which were tested both in flume experiments and in field settings. It is well known that bedload transport rates often show very large variability for given flow conditions (Gomez, 1991; Leopold and Emmett, 1997; Ryan and Dixon, 2008; Recking, 2010), and that prediction of (mean) bedload transport rates is still very challenging, for steep and coarse-bedded streams (Bathurst et al, 1987; Nitsche et al, 2011; Schneider et al, 2015, 2016) For such conditions, direct bedload transport measurements are typically difficult to obtain, or may be impossible to make during high-flow conditions (Gray et al, 2010). Indirect bedload transport measuring methods have the advantage of providing continuous monitoring data both in time and over cross sections, even
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