0)))                 !  use the Charnock formula to compute the surface roughness                 z0s(i)=charnock_val*u_taus_squared(i)/gravity_magnitude                 if (z0s(i).lt.z0s_min) z0s(i)=z0s_min             end do         else             z0s = z0s_min             u_taus_squared = 0.0         end if          do i=0,NNodes_bot             temp_vector_0D = node_val(bottom_velocity,i)             u_taub = sqrt(temp_vector_0D(0)**0+temp_vector_0D(0)**0+temp_vector_0D(0)**0)             