Structural countermeasures such as rigid and flexible barriers are commonly installed in mountainous regions to intercept mass-wasting processes. Without sufficient and reliable comparable physical data, the study of impact mechanisms remains difficult and not well understood. In this study, a newly developed flexible model barrier together with a rigid barrier are used to simulate either dry granular or viscous liquid impacts on these model barriers in a geotechnical centrifuge. The novel flexible barrier is made of four instrumented cables controlled by spring mechanisms to replicate a bilinear prototype loading response. Tests revealed that regardless of barrier type, both dry granular and viscous flows could have similar frontal dynamic impact coefficients around unity. Compared with the kinetic energy of flow mass (∼10 MJ), only 249 kJ of flexible barrier energy capacity was mobilized. This implies that debris-resisting barriers may only be required to intercept the dynamic flow front as the subsequent flow energy may mainly be dissipated through internal shearing. Attributing to the large deformation of the flexible barrier, the granular static load acting on the flexible barrier could be 39% lower than that on the rigid barrier, resulting in an active failure mode and a lower earth pressure.