The effect of porosity in a row of barriers on mitigation of flow dynamics and barrier interaction: Water floods and viscoplastic debris flows in a complex terrain

Floods, whether water-dominated or viscoplastic debris, pose significant risks to communities and infrastructure in steep terrains. Protective barriers are commonly implemented to reduce flow velocities, limit run-out distances, and mitigate impact forces; however, the influence of barrier porosity on downstream loading remains insufficiently quantified. This study employs three-dimensional computational fluid dynamics (CFD) simulations over the real topography of Hobart, Tasmania, to examine porosity-controlled barrier performance in dam-break scenarios. Porosity is varied from ϕ=0.3 to 0.9 by changing the number of barriers within a fixed reference volume, while the geometry of each barrier is held constant. Two flow types are analyzed: Newtonian water floods and non-Newtonian viscoplastic debris flows with finite yield stress. Key hydrodynamic indicators including velocity fields and pressure and shear forces on both the end wall and barriers are evaluated. For water floods, end wall pressure reductions relative to the barrier-free case (ϕ=1) range from negligible at ϕ=0.3 to approximately 25% at ϕ=0.5. End-wall shear forces decrease by 59%–61% at low porosities (ϕ=0.3–0.4). Barrier pressure and shear forces peak at ϕ=0.8, whereas lower porosities reduce barrier loading by 32%–74%. For debris flows, low-porosity configurations (ϕ=0.3) reduce end wall pressure by 92% and shear by 37%, while intermediate porosities (ϕ=0.6–0.7) minimize barrier forces. End-wall shear force displays a non-monotonic variation with porosity in debris flows, with local maxima at ϕ=0.6–0.8.