1. A method of predicting output/state variables in a groundwater/surface water system, comprising the steps of (a) providing and training a neural network with hydrologic and control data for a groundwater/surface water system, and (b) operating the trained neural network to predict output/state variables in the groundwater/surface water system, the output variables comprising one or more of the following: surface water elevations, surface water flow rates, groundwater heads and elevations, groundwater gradients, groundwater velocities, and chemical concentrations.