The shear stress values reported in the cross section output table are cross- section averages. You can check this by computing the shear stress (τ=γ∙d∙S); where γ is the specific weight of water, the average depth (d) is the flow area divided by the top width, and the slope is the computed local energy grade line slope. You should be able to verify this computation from the RAS standard output table which contains the values for these variables.