The most common type of submarine fan is created by the passage of a succession of depositional turbidity currents. It is thus of interest to note that even in this essentially depositional environment the fan surface is often intensely channelized. Here a two-dimensional numerical model describing the formation of a submarine fan by a spreading turbidity current is presented. Layer-averaged governing equations describing the turbidity current are presented and solved numerically in conjunction with the Exner equation of bed sediment continuity. The formulation describes fan evolution from an initially flat surface. The bed is allowed to evolve in response to the exchange of sediment with the turbidity current by means of simultaneous erosion and deposition of suspended sediment. The upstream boundary condition is chosen so as to approximate a submarine canyon debouching upon the fan. Under some but not all conditions the early stage of the depositional process is accompanied by the formation of incipient natural levees that act to partially channelize the flow, indicating the formation of a channel-levee system. Dimensionless parameters are used to describe conditions for optimal channelization. The model can explain some of the basic mechanisms that account for the persistent tendency for channelization of the fan surface under a wide range of conditions. ¿ 1998 American Geophysical Union