Using discrete elements simulations, we investigated 2D unsteady granular flows down a rough inclined plane and overflowing a wall, for a large range of slope inclinations. We first characterized flows without any obstacle by measuring time evolution of flow depth, mean velocity and volume fraction. These unsteady flows display similar scalings as ones observed for steady and uniform flows. We then introduced a wall normal to the bottom and we measured the mean force exerted by the incoming flow. Two regimes appear, a dense and a collisional regime, depending on the slope inclination and for which the mean force strongly differs. We attempted to compare the mean force with two typical forces linked to the control flow without obstacle for both regimes. The comparison highlights an important contribution due to a stagnant zone formed in front of the obstacle, particularly in the dense regime and the transition towards a static regime.