Evaluation of continuously recorded fractional bedload transport rates in Swiss mountain streams

Abstract

In mountainous regions, the dynamics of bedload transport can vary considerably, including significant changes over brief periods, thus also posing a substantial challenge for bedload transport measurement and prediction. Indirect monitoring systems like the Swiss Plate Geophone (SPG) have led to a significant advancement in our capacity to continuously monitor bedload processes (Rickenmann, 2017). Based on recording important parts of the raw measuring signal of the SPG system, we have developed a procedure to determine fractional bedload transport rates (Wyss et al., 2016; Nicollier et al., 2022). For this, each sediment collision (for particles larger than 9.5mm) is recorded with the SPG system as a discrete «packet», capturing raw signal information such as collision start and end times, raw and envelope amplitude, squared integral, and centroid frequency of the raw signal. This research undertakes a detailed analysis of continuously recorded packet data from the SPG for several mountain streams in Switzerland. It aims to quantify fractional bedload transport rates and grain size distribution across various periods. To check the plausibility of the calculated fractional transport rates, we aggregated the data based on the packet analysis and compared it to the so-called «impulse-based» conversion of the SPG signal into total transport rates (independent of grain size classes). The objective of this study is to enhance the understanding of how grain size distribution of the bedload alters with changing discharge and bedload transport conditions, by considering different channel characteristics and evaluation periods.