ABSTRACT
This paper presents a new calculation method for flow over rough bed with a superimposed array of wall-mounted boulders. Since the resistance of roughness depends on the relative water depth to roughness height for the case of Large Scale Roughness (LSR), it is necessary for calculating the flow over gravel bed rivers to separate the effects of LSR from that of the Small Scale Roughness (SSR). A quasi-3D calculation method (BVC method) is developed to evaluate velocity vertical distributions around boulders without making the shallow water assumption. To evaluate additional resistance on rough bed resulted from the increment in momentum exchange due to flow around boulders, a non-equilibrium wall law is proposed and the bottom vortex layer and roughness layer equations are derived. The advantages of BVC method with the non-equilibrium wall law over the 2D and BVC method with the conventional equilibrium wall law are demonstrated through comparisons with benchmark experimental results.
