The streamflow hydrograph analysis and simulation for a study case watershed was carried out using the hydrologic engineering centre - geospatial hydrologic modelling system (HEC-GeoHMS) and the hydrologic engineering centre - hydrologic modelling system (HEC-HMS) software coupling. HEC-GeoHMS is integrated in a geographic information system (GIS) so as to develop a terrain's pre-processing tool and to generate output files which are inputted to the hydrologic model. Soil map data, land use map and digital elevation model (DEM) were used in order to delineate the physical watershed's characteristics. The runoff estimation was based on the soil conservation service curve number (SCS-CN) approach while the watershed's outflow estimation was carried out by employing SCS unit hydrograph method. The rainfall - runoff modelling is applied on a storm event which occurred on 01/10/2005 at Kastaneri watershed. The coupled hydrological models simulated runoff hydrograph for the latter storm event whilst the CN and the peak discharge values were computed equal to 69.5 and 72.8 m3/s respectively.