Cellular models in geomorphology can be defined as representing the modelled landscape with a grid of cells, over which the development of the landscape is determined by the interactions between cells (for example, fluxes of water and sediment) using rules based on simplifications of the governing physics. In fluvial geomorphology, cellular models use simplified or ‘relaxed’ versions of the complex flow equations (Coulthard et al. (2007) Geomorph. 90, 3–4; see also Nicholas (2005) ESPL 30, 5).