Non-linearity and spatial resolution in a cellular automaton model of a small upland basin

The continuing development of computational fluid dynamics is allowing the high resolution study of hydraulic and sediment transport processes but, du e to computational complexities, these are rarely applied to areas larger t han a reach. Existing approaches, based upon linked cross sections, can giv e a quasi two-dimensional view, effectively simulating sediment transport f or a single river reach. However, a basin represents a whole discrete dynam ic system within which channel, floodplain and slope processes operate over a wide range of space and time scales. Here, a cellular automaton (CA) app roach has been used to overcome some of these difficulties, in which the la ndscape is represented as a series of fixed size cells. For every model ite ration, each cell acts only in relation to the influence of its immediate n eighbours in accordance with appropriate rules. The model presented here takes approximations of existing how and sediment transport equations, and integrates them, together with slope and floodplai n approximations, within a cellular automaton framework. This method has be en applied to the basin of Cam Gill Beck (4.2 km(2)) above Starbotton, uppe r Wharfedale, a tributary of the River Wharfe, North Yorkshire, UK. This approach provides, for the first time, a workable model of the whole b asin at a 1 m resolution. Preliminary results show the evolution of bars, b raids, terraces and alluvial fans which are similar to those observed in th e field, and examples of large and small scale non-linear behaviour which m ay have considerable implications for future models.