A one-dimensional depth-averaged velocity deformation model is developed to study the characteristics of the unsteady flows in open channels. The vertical profile of the streamwise velocity is expressed in a power series, and the coefficients of the velocity are evaluated by using the unsteady equation of motion. A concise form of the friction velocity for unsteady nonuniform flow is then proposed by utilizing the coefficients of the power series. The applicability of the model is validated with experimental data, producing reasonably good agreement between the model results and the observed data. Finally, the deformation of velocity at the surface is assured by comparing velocity distribution of numerical model with the computational results from a previous model. © 2013 American Society of Civil Engineers.