Sensitive analysis of roughness coefficient estimation using velocity data

Abstract

    An accurate estimation of Manning's roughness coefficient n is of vital importance in any hydraulic study including open channel flows. In many rivers, the velocities at two-tenths and eight-tenths of the depth at stations across the stream are available to estimate Manning's roughness n based on a logarithmic velocity distribution. This paper re-investigates the method of the two-point velocity method and a sensitive analysis is theoretically carried out and verified with experiment data. The results show that velocity data can be used to estimate n for fully rough-turbulent wide channels. The results also indicate that the errors in the estimated n are very sensitive to the errors in x (the ratio of velocity at two-tenths the depth to that at eight-tenths the depth). The theoretical and experimental work shows that the smoother and deeper a stream, the more sensitive the relative error in estimated n is to the relative error in x.