A computer-based graphical user interface for graphically controlling processing of hydrological data, comprising a display menu interface listing executable tools from the group comprising one or more of: hydrological data input, hydrological data validity checking and correction, and hydrological modeling, a GUI for selecting and arranging tools from the display menu in a graphical display area to construct a hydrological process, the selected tools each being represented by icons on the graphical display, and for establishing a connection between at least one output of a first tool and an input of a second tool said tools by graphically displaying the connection between said tools representative icon and input means for receiving user input to arrange and execute said constructed hydrological data processing process.