Towards systematic measurements of velocity profiles and sediment concentration in a wide range of laboratory debris-flow mixtures

Debris-flow dynamics are governed by the internal deformation of sediment–water mixtures. Due to the destructive potential of natural debris flows, constitutive models predicting flow velocity, impact forces, erosion, and deposition are desired. While simplified sediment–water flows are well understood, existing debris-flow models typically rely on constitutive assumptions for internal friction, sediment concentration, and solid–fluid interaction. Systematic experiments exploring the effects of grain-size distribution and fine material content on internal deformation and flow resistance are essential to better constrain and improve these models.

In this work we introduce a novel methodological setup to measure vertical velocity profiles within steady shallow (~15 cm) flows of sediment–water mixtures in a ~2.5 m diameter rotating drum. Measurements are performed in the central, most uniform flow region using an array of paired-conductivity sensors of varying geometry. Velocities are obtained via established cross-correlation methods of adjacent signals. Spectral properties of the conductivity signals are also explored as a potential complementary source of velocity information.

A low-cost capacitance probe is being developed to enable non-intrusive estimation of sediment concentration during flow. Proof-of-concept tests in air demonstrate feasibility, and further testing in water is planned to realize its use in ongoing experiments. Upcoming work will systematically investigate how grain-size distribution, particularly the fine material content and the uniformity of the coarse fraction, influence internal deformation, pore-fluid pressure, and bulk flow resistance.