By using analytic elements to model steady state, two-dimensional, Dupuit-Forchheimer groundwater flow and its contribution to surface water flow, average base flows and groundwater flows in a groundwater and surface water system can be represented. Changing boundary conditions are modeled by adding or removing streams from the groundwater flow domain according to the availability of water in the stream. This dynamic representation of boundary conditions allows for the anticipation of unknown effects due to future aquifer stresses or stream withdrawals. The model does not account for transient streamflow but significantly improves the realism of steady state surface water and groundwater interactions by simulating average base flows and limiting the infiltration rates of losing streams. When steady state groundwater flow is modeled without considering the limits of available streamflow, recharge rates or hydraulic conductivities that are estimated during model calibration can be substantially in error. The capability to model groundwater and surface water conjunctively is accomplished without substantial increases in model complexity or data requirements. ¿ American Geophysical Union 1996