A major goal of current studies of Amazonian hydrology is to understand the impact of land use on streamflow. Analysis of hydrographs from four 1,000 km2 basins in Rondonia shows that there is a strong correlation between the ruggedness of topography and the hydrologic response time of the river basin. This evidence supports the idea that before one can study how deforestation in a basin influences the streamflow, it is necessary to understand the antecedent factors that control the streamflow: land cover, topography, soil hydraulic properties, climate, and channel network topology. A physically based recharge model, groundwater model (MODFLOW), and river routing model (HEC-1), were employed to generate a modeled hydrograph which was validated against known basin hydrographs. MODFLOW was chosen as the central model because field observations and measurements show that most rainfall infiltrates to the aquifer before it reaches the channel by overland flow. MODFLOW was used to explore the hydrologic influence of topography on two forested basins representing extremes of rugged and smooth topography. After validating the model, a sensitivity analysis was performed to explore the influence of varying degrees of ruggedness in the basins. Based on this understanding of the importance of topography, two other basins with moderate degrees of deforestation and topography were modeled to understand how the effect of deforestation on the soil-water balance and groundwater recharge interacts with topography in affecting response time. Finally, the results were generalized to model the impact of various deforestation scenarios on the hydrology in these basins.