The effects of 2-D roughness elements on the Reynolds stress anisotropy tensor, and of the energy dissipation rate anisotropy tensor of a turbulent channel flow are investigated using data obtained from direct numerical simulations (DNSs). The roughness elements consist of transverse square rods of size , placed on one wall of the channel only. While is kept constant ( , is the half-width of the channel), the spacing between the rods is varied from to . The results show that the variation in can dramatically change the structure of the wall region flow. The modeling of the near-wall region needs to reflect the structural changes caused by the variation in . On the basis of the Reynolds stress budgets, attention needs to be given to the turbulent energy and pressure diffusion terms while local isotropy may be a reasonable approximation for the energy dissipation rate, especially over a range of for which the drag is near its maximum.