This study developed a set of techniques to assist the decision-making process in agricultural watershed management As local governments develop water reservoirs for water storage and use, there is need to accurately forecast not only the amounts of runoff going into reservoirs, but also the patterns and potential quantities of peak flow. Major components of the study involved the acctirate modeling of the hydrology of an agricultural watershed, the enhancement of the presentation of simulated hydrology results to decision makers, and the exploration of alternative management options in an agricultural watershed. The objectives of this study were to: (1) evaluate the performance of a distributed-parameter hydrologic model to simulate daily runoff of an agricultural watershed, (2) visualize the simulation results generated by the model from observed data, and (3) use the visualization procedvires developed to examine scenarios of impacts of alternative land management practices on the streamflow from an agricultural watershed. Geographic information systems (GIS) techniques were used to prepare input data for the Precipitation and Runoff Modeling System (PRMS) to simulate surface hydrology of an agricultural watershed. Results from the simulation were then used as input for a dynamic visualization process. The visualization procedures developed in this study assisted in the examination of different scenarios of streamflow resulting from alternative land management practices. New procedures were developed for the evaluation, application and visualization of results of a widely used hydrologic modeling system. 1 CHAPTER 1 GENERAL INTRODUCTION Overview Accurate prediction of streamflow and surface runoff in complex watersheds and drainage basins is becoming urgently necessary. This is because of the potential for flood damage and the increasing concern about the adverse effects of non-point source pollution on surface water quality. This study evaluated the perfomiiance of a precipitation and runoff model in an agricultural watershed, developed procedures to visualize simulation results from the model, and visualized results of simulations of different land management scenarios. Thus, a distributed-parameter hydrologic modeling system was used to simulate surface runoff from a watershed in east central Iowa. A geographic information system (GIS) was used in input data preparation. The results from the simulation model were then used as input to a visualization process. The visualization process developed in this research was used to display simulated streamflow resulting from different land management practices. Through visualization of modeling results, decision-makers can obtain improved understanding of phenomena and, hopefully, make more informed management decisions. Watershed Hydrologic Modeling The computer modeling component of the research focused on the Precipitation Runoff Modeling System (PRMS) developed by Leavesley et a/.(1983). Previous studies that used PRMS have been confined mainly to watersheds und...