Flow resistance on lower regime river beds is discussed with the data of Colorado University given by Guy et. al. The Engelund method to estimate the flow depth in an alluvial channel for a given flow discharge is modified for the lower flow regime. The hydraulic conditions to classify flat, ripple, and dune beds are given by the relationship between dimensionless bed shear stress and Reynolds number with respect to sand diameter. Moreover relationships between total and effective bed shear stresses in a dimensionless form are modified for dune bed in the Engelund diagram, and newly proposed for ripple and flat beds, which were not presented in the diagram. The accuracy of flow depth estimation for a given flow discharge with the modified diagram is much improved than without modification.