SENSITIVITY OF A BASIN EVOLUTION MODEL TO THE NATURE OF RUNOFF PRODUCTION AND TO INITIAL CONDITIONS

This work investigates the effects of modifying the runoff production mechanism used in the Willgoose-Bras-Rodiguez-Iturbe basin evolution model from Hortonian to subsurface saturation. The modified model also simulates basins that reproduce well common geomorphological statistics. This result confirms the ability of the model to adapt to different hydrological environments. The most important difference between the original and the modified model appears in the evolution of the hypsometric curve, particularly in the transition between saturated and unsaturated nodes. The role of mass movement due to diffusive processes (such as rain splash and rock slides) is more significant in the modified model due to decreased role of wash in unsaturated regions. A measure is developed to quantify the sensitivity of the model to initial conditions. Evolutions were found to separate in time following a power law, explaining the apparent randomness present in catchments simulated with only slight perturbations in their initial conditions. This apparent randomness is the result of the weakly chaotic features of the model.