1 Bedload transport measurements with impact plate geophones in two 2 Austrian mountain streams (Fischbach and Ruetz): system 3 calibration, grain size estimation, and environmental signal pick-up 1 1 4 Dieter Rickenmann , Bruno Fritschi 5 1Swiss Federal Research Institute WSL, Birmensdorf, 8903, Switzerland 6 Correspondence to: Dieter Rickenmann (
[email protected]) 7 Abstract. 8 The Swiss plate geophone system is a bedload surrogate measuring technique that has been installed in more than 20 9 streams, primarily in the European Alps. Here we report about calibration measurements performed in two mountain streams 10 in Austria. The Fischbach and Ruetz gravel–bed streams are characterized by important runoff and bedload transport during 11 the snowmelt season. A total of 31 (Fischbach) and 21 (Ruetz) direct bedload samples were obtained during a six year 12 period. Using the number of geophone impulses and total transported bedload mass for each measurement to derive a 13 calibration function, results in a strong linear relation for the Fischbach, whereas there is only a poor linear calibration 14 relation for the Ruetz measurements. Instead, using geophone impulse rates and bedload transport rates indicates that two 15 power law relations best represent the Fischbach data, depending on transport intensity; for lower transport intensities, the 16 same power law relation is also in reasonable agreement with the Ruetz data. These results are compared with data and 17 findings from other field sites and flume studies. We further show that the observed coarsening of the grain size distribution 18 with increasing bedload flux can be qualitatively reproduced from the geophone signal, when using the impulse counts along 19 with amplitude information.