The paper introduces some GIS-modeling theoretical basics and applied software implementation through author’s software for processing, analysis and visualization of the extreme channel discharges upon spring floods and shortly discusses model peculiarities for summer rainfall. The following definitions have been discussed: “a distributed hydrological model”, “and extreme channel discharge from spring flood”, “the extreme channel discharge from summer rainfall”, “the distributed hydrological modeling GIS-module interface”. The procedures of the watershed hydrological regime distributed modeling have been described in details, as well as the original software user’s interface for the GIS-module elaborated.