“…(1)- (4) the subscript t denotes differentiation with respect to time, d is still the water depth, U is the horizontal velocity vector U = (U, V ) with U and V being the depth-averaged horizontal velocities along the x and y directions, respectively; ζ is the surface elevation, h the total depth (h = d + ζ ), g is the gravitational acceleration, τ b = (τ bx , τ by ) is the bottom friction term (shear stress components approximated by the use of the quadratic law according to Ribberink (1998), δ is the roller thickness (determined geometrically according to Schäffer et al, 1993). E is the eddy viscosity term (according to Chen et al, 2000), and u o is the bottom velocity vector u o = (u o , v o ) with u o and v o being the instantaneous bottom velocities along the x and y directions respectively.…”