Recent wave speed‐discharge investigations carded out on six Australian river reaches show consistent variations of wave speed with discharge and provide new knowledge in this area with applications in both flood routing and runoff routing. A model developed to define the wave speed‐discharge relation is described. The model is based on concepts of the physical factors affecting the wave speed‐discharge haracteristics of natural channels. It provides for overbank discharge as well as main channel flow. The applicability of the model is demonstrated using data from the six reaches.