The management of urban channel systems constitutes an important problem in most developing cities of the world. In this study, a deterministic approach was followed to obtain water-diversion function through development of a numerical model that includes main hydrological elements such as stream flow, groundwater flow with stream-aquifer interaction, and evapotranspiration. An application to the city of Eskisehir (Turkey) is presented. The city has an extending channel network lying on an alluvium plain. In developing the new diversion function, three main criteria were taken into consideration: (1) the conservation of ecosystem; (2) flood prevention; and (3) aquifer replenishment. As the aquifer is the main water resource in the basin, a total of 96 boreholes were drilled in the framework of two projects. From these borehole data, stratigraphy and the piezometric head distribution were obtained. The basin was modeled using MODFLOW under Ground-water Modeling System (GMS) software. For calibration of hydraulic conductivities, the parameter estimation model was used. Through steady-state analysis, flood-prone areas were determined. Transient simulations were performed over a period of 650 days covering both low and high flows. A computer code following an iterative procedure was written in order to integrate the diversion function into MODFLOW. Simulation results demonstrated that the proposed function was successful in satisfying all three criteria. (C) 2016 American Society of Civil Engineers.