This paper tackles a practical problem in flood routing, the estimation of the speed of propagation of the flood wave. It is well known that this propagation speed varies with the discharge in quite a complex manner for natural rivers. The principal innovative step in this paper is the identification of a relatively simple conceptual model of river geometry to obtain two methods for generating realistic wave speeds from a standard river cross-section survey. These are verified against data from two rivers in the UK, showing good agreement with wave speeds deduced from long-term flow records. This work is expected to be of particular value in building forecasting models of ungauged or partially gauged river systems, as it removes the need for long concurrent records to estimate wave speeds.