Event flow hydrograph-based method for shear velocity estimation

Abstract

Due to the lack of a simple method for finding the shear velocity during flood events, most sediment resuspension or transport models either resort to complex numerical models requiring detailed input data or rely on uniform steady flow formula. Here a practical method for estimating the shear velocity of unsteady flow is presented by using the flow hydrograph and channel geometry data. Using equations for open channel flow, formulas for shear velocity are derived in terms of discharge gradient, representing the friction slope of unsteady flow in prismatic channels. Applications of the new method using published experimental data and simulated results indicate that the method is comparable with existing methods in terms of accuracy but requires less input data. This method is particularly applicable to natural floods in relatively straight reaches of lowland rivers where the non-inertia wave approximation to the Saint-Venant equations is theoretically appropriate.

Keywords:

• Friction slope
• hydrograph
• shear velocity
• unsteady flow
• wave

Acknowledgements

Support for this research by USGS and the Louisiana Water Resources Research Institute is gratefully acknowledged.