This contribution considers the methods available to hydrologists to simulate flow routing and inundation in natural channels. Whilst the fluid dynamics of free surface flow in rivers and over floodplains may be complex, the methods available to treat such problems range widely in complexity from simple empirical models to full solutions of three‐dimensional Navier–Stokes equations with sophisticated representations of flow turbulence. These methods are reviewed in detail, followed by a consideration of their requirements for topography, friction, initial condition, boundary condition, and validation data. In particular, the contribution discusses how these needs are being met increasingly using remote sensing techniques. Lastly, the contribution considers techniques to evaluate uncertainties in flow modeling.