Observation of vertical profiles of suspended sediment using TDR at a mountain stream

Abstract

We applied TDR (time domain reflectometry) to monitor vertical profile of suspended sediment in a mountain river. Sediment concentrations of stream water were calculated using observed dielectric constants of the turbid water. The TDR system contained five coil-type probes installed at the heights of 0.03-0.23 m from the bed. Because bare land occupied 39% of the study catchment, high sediment concentrations greater than 0.01 were measured during rainfall events at the outlet of the catchment. Sediment concentrations of collected samples were generally lower than those measured by TDR, suggesting that the TDR method targeted various sizes of suspended sediment. The TDR system could measure vertical profiles of sediment concentration during a heavy rainfall event from October 22 to October 23, 2017. The concentration profiles were well fitted by the Rouse equation with the measured concentrations at the 0.03 m height as the near-bed concentration. Thus, averaged concentrations as well as discharge of suspended sediment were able to be estimated using the measured concentrations at the 0.03 m height during the heavy rainfall event.