A new equation is proposed for the design of armor units on protected river banks under the combined action of ship-induced waves and river flow. Existing observed field and experimental data in the literature have been examined and a valuable database has been developed. Different conditions, including the river water depth, flow velocity, river bank slope, Froude number, wave height, wave period, and wave obliquity have been considered. Results from an empirical equation (Bhowmik, 1978) that only considers the maximum wave height and river bank slope have been compared with the results calculated by the newly developed equation. Calculated results have also been verified against field data. Results show that not only the maximum wave height and river bank slope but also the water depth, flow velocity, wave length, wave obliquity, and wave period are important parameters for predicting the mean diameter of the armor units, highlighting the multivariate behavior of protecting the river bank in the presence of ship-induced waves and river flow velocity.