The numerical model, r.sim.terrain, simulates how overland flows of water and sediment shape topography over short periods of time. We tested the model by comparing runs of the simulation against a time series of airborne lidar surveys for our study landscape. Through these tests, we demonstrated that the model can simulate gully evolution including processes such as channel incision, channel widening, and the development of scour pits, rills, and depositional ridges.