Pulse Coherent Doppler Profiler Measurement of Bedload Transport

Abstract

Prior studies demonstrate that bottom velocity measurements from Doppler sonar systems are proportional to bedload transport rates. These observations suggest that acousticallybased systems offer a capability for rapid sampling of bedload transport processes. Before these measurements can be fully utilised, validation and understanding of the sampling mechanism are essential. We explore the measurement mechanism through a series of laboratory trials with a field instrument, the MFDop. The MFDop system is a multifrequency (1.2 -2.2 MHz), bistatic Doppler sonar that provides 3-component ensembleaveraged velocity profiles over a ∼30 cm depth interval with up to 1 mm resolution at a rate of 50 profiles/sec. Tests of the MFDop system were carried out in the main flume in field-scale conditions at the St. Anthony Falls Laboratory (SAFL) using 1 m s −1 mean flows over a mobile bed of sand with median grain size d 50 = 0.4 mm. We find agreement between MFDop transport measurements and measurements based on bedform migration rates, and sediment traps built into the SAFL flume. Predictions using the Meyer-Peter and Müller [1948] empirical equation closely match our observations while in contrast, predictions using the Nielsen [1992] equation are a factor of two higher.

Remote sensing of laboratory rivers

“…Although they are conveniently small, experiments are not limited to grain‐scale or reach‐scale problems. A wide array of modelling approaches allows us to investigate the evolution of entire landforms with analogue modelling (Paola et al., 2009), or to monitor bedload transport or vegetation interactions using 1:1 scaled experiments (Wilcock et al., 2008; Zedel et al., 2021). Small‐scale and analogue models have the advantage of allowing us to compress geological time, in order to observe the effects of processes that operate over durations much longer than human lifetimes (Paola et al., 2009).…”