Application of time domain reflectometry to high suspended sediment concentration measurements: Laboratory validation and preliminary field observations in a steep mountain stream

Abstract

The dielectric constant around a sensor was measured with a time domain reflectometry (TDR) system and used to calculate the volumetric sediment concentration (SC) of stream water and deposition on a streambed. The measurements of various SCs in laboratory experiments demonstrated that the TDR system proposed in this study had an accuracy of 0.01 m³ m⁻³ for practical uses, and that the measured concentrations were not sensitive to particle size. The vertical SC distributions were measured at heights of 17–37 cm in a steep mountain stream. The resulting SCs at the various heights increased by 0.01–0.07 m³ m⁻³ at the time of peak stream discharge during an extreme storm with a return period of approximately 12 years. After extreme precipitation, the SC of the lowest probe increased rapidly from approximately 0 to 0.4 m³ m⁻³. This was followed by rapid increases in the SCs at the other heights, indicating deposition around each probe. The TDR measurement system, with its straightforward calibration procedure, effectively measured deposition and a high-concentration layer above the deposited layer even during the storm event.