Understanding the interaction between complicated geophysical flows and barriers remains a critical challenge for hazards countermeasures in engineering design. In this study, the impact of geophysical flows on a rigid barrier is studied numerically using coupled computational fluid dynamics and discrete element method (CFDDEM). Three types of fluid: Bingham, Herschel-Bulkley, and water are chosen as the fluid phase to mix with particles in the simulation, corresponding to Case B-P, Case HB-P, Case W-P, respectively. The results of twophase simulations are then compared with initial volume controlled dry granular flow (Case P) under the same Froude condition. Two impact mechanisms, namely pileup and runup mechanisms, are recognised in flowbarrier interaction. The effects of fluid properties including viscosity and density on the impact force against the flume base and barrier and inter-particle contacts are also systematically examined. In addition, the dynamic pressure coefficient alpha is also predicted by a newly proposed analytical model, which has been validated by the data from experimental and numerical tests. Findings indicate that the new model may provide a useful reference to calculate the impact force for the design of a rigid barrier in intercepting hazardous geophysical flows.