Measurements and analysis of natural debris flow impacts in the Gadria Creek

Debris flows-mixtures of water, sediment including boulders up to several meters in diameter—pose significant hazards in steep mountainous regions. For engineering design of mitigation measures, it is needed to constrain potential impact forces from measurements at the full scale. This study investigates the dynamics and impact forces of natural debris flows using in-situ measurements from three events at Gadria Creek, Italy. The monitoring station, positioned mid-channel, is equipped with 14 load cells, two ultrasonic sensors, a Pulse-Doppler radar, and two video cameras, capturing high-resolution data on flow height, velocity, and impact forces. Results show that maximum impact forces occur in the upper half of the flow, with primary surges generating total bulk forces up to 6.2 × 10 5 N. Single boulder impacts, characterized by brief intense forces, were distinguished from bulk pressure effects using wavelet denoising and statistical binning. We evaluated existing impact models (hydrostatic, hydrodynamic, and Froude-dependent) against the measured data. While some models provide satisfactory estimates, others show substantial deviations, highlighting the need for refinement to account for flow heterogeneity, particle size distribution, and dynamic interactions. These findings advance understanding of debris flow impact behavior and inform mitigation structure design.