Distributed parameter samples was merged with the often-used goal of maximizing sample spread. The evaluation of this strategy with benchmark strategies indicated that it was more than an order of magnitude computationally faster for high dimensional models and that it also somewhat improves parameter screening. The last objective was aimed at the evaluation of the routing and pollutant attenuation module of the Watershed Assessment Model (WAM). GSA/UA showed that WAM was most sensitive to empirical/conceptual parameters, indicating their importance in the model calibration/validation process and the need for monitoring efforts to verify the selection of these parameters. As the first formal evaluation of WAM by GSA/UA, the results obtained in this work are a valuable contribution to the application of WAM to addressing water quality issues in the state of Florida.