The study aims to quantify the gravel and vegetation induced roughness effects on flows and mixings in open-channels using experimental and numerical methods. Firstly, a Double Averaged Navier-Stokes equation (DANS) model has been developed for depth-limited open-channel flows over gravels. Secondly, laboratory measurements of the velocity profiles and flow resistances of depth-limited open-channel flows over fixed gravel patches (GPs) under different bed slopes and flow rates were carried out. Finally, the hydrodynamics of flows over a finite length flexible vegetation patch (VP) was investigated in the laboratory.