An integrated decision support system (DSS) that aids the operation of a tank (small-scale reservoir) irrigation system in south India is described. The DSS includes data subsystem, a model subsystem, a knowledge base, and a user interface. The knowledge base of the DSS was developed from the knowledge derived from field experts as well as from the results of an optimization model. The DSS was evaluated to assess its decision-making capability using five years of data. Shortages in irrigation water supply simulated from the DSS were less than those occurring in the actual operation practiced by water authorities. The forecasts of system variables, namely, inflow and evapotranspiration were found to be adequate for real-time operation of the tank system. ©ASCE,.