Application of TDRiTime Domain Reflectometryjto measurements of surface height
and porosity of sediment below water surface

Shusuke MIYATA and Masaharu FUJITA

Toward a novel approach of bedload monitoring in mountainous streams, this study aimed to examine measurements of height and porosity of sediment layer below water surface by applying TDR (Time Domain Reflectometry). A column experiment was conducted to validate accuracies of estimated sediment height and porosity using a commercial probe(0.3m in length) and a simple probe consisted of a PCV pipe and stainless steel wires (0.9mm in diameter and1.0m in length) and two sets of experimental sand with different grain size distributions. The probes were inserted into a container filled with water. TDR waveforms were then measured during supply of the sand until the probes were totally covered by sediment layer. The waveforms were analyzed and used for calculating height and porosity of sediment layer. Our results indicate that height of sediment layer is estimated better by analyzing a part of waveform corresponding with the probe in the water layer rather than waveform corresponding with the entire probe. Calculated sediment heights agreed well with measured heights for both experimental sands. Small oscillations of TDR waveforms obtained by the simple probe may affect overestimates of porosity. In contrast, calculated porosity by the commercial probe agreed well with measured porosity. A monitoring system with TDR probes scattered in a sand pocket or upstream of a check dam will enable us to investigate temporal change of bedload transport in mountainous streams.