Simulated annealing (SA) was integrated with groundwater simulation model, the ModFlow, to determine the best zonation of hydrogeological parameters and pumping rates for the ChouShui Creek Alluvial Fan in Taiwan. Observation wells have been installed in the Alluvial Fan, and hydrogeological parameters have been surveyed for these wells. However, the spatial distribution of parameters and pumping rates are still not well known. Thus, methods to determine the spatial distribution are required. There are three major categories to determine parameters for grids in groundwater simulation, including (1) assignment based on geology, (2) interpolation such as the Kriging algorithm, (3) geometric zonation such as the Thiessen Method. This study proposes a new procedure that pumping rates and initial geometric zonations of paramenters are optimized by SA. There are two zonations and pumping rates to be optimized in this study. The procedure includes three steps, which each step applies SA to find one of the zonations or pumping rates, while the other two are fixed. The procedure was applied to the ChouShui Creek Alluvial Fan. The simulation results indicate that the procedure provides reasonable approach. However, there is still room for improvement. Copyright ASCE 2004.