Gravity currents flows in general and powder snow avalanches in particular are dense flows occurring on horizontal but also mild or steep slopes. They occur on smooth boundary (open slope) but also in interaction with obstacles of multiple types (trees, rocks, avalanche protection structures). In this context, an experimental study has been led. Finite size volumes of dense fluid have been released in a flume in horizontal configurations up to an inclination of \(30^\circ \) . Front position evolution with time together with typical flow depth have been measured by video recording and image processing. Flow regimes without obstacles (acceleration, slumping, buoyancy versus inertia regimes) have been studied and compared favourably with previous existing results. Obstacles made out of long thin elements but also square blocks of different heights have been organized in aligned or staggered configurations. The implication of their presence in the flume on the dense flows behaviors (front velocity and typical flow depth) has been investigated. In the vast majority of cases, the front velocity of the flow is reduced down to \(50\%\) from the non-obstructed case. There is also an influence on the flow depth, either increasing or decreasing it, depending on the blocks height and organization. Obstacles have been shown to be more effective at reducing the flow speed on horizontal or mild slopes than on steep slopes. Long thin elements are very efficient in slowing down the flows. This is all the more noticeable as their obstacle to void volume is an order of magnitude lower than the one of the square blocks. Connections with powder snow avalanches observations or mitigating implications have been proposed in the case of interaction with trees and organized buildings.
