The grain‐scale topography of a sediment surface is a key component of a fluvial system,affecting aspects including sediment transport, flow resistance and ecology. However, itseffect is hard to quantify because of the need for grain‐scale elevation data from in situfluvial gravel surfaces which are difficult to collect. The sediment surface properties are,therefore, commonly estimated as a function of the sediment grain‐size distribution;however, because of additional factors, such as grain packing and shape,