The purpose of this study is to apply various techniques and models for catchment delineation, and developing methods to calculate a Curve Number values for the Kalaya river basin located in Northern Morocco, by implementing GIS software (ArcGIS, HEC-GeoHMS), Erdas Imagine and hydrologic modeling (HEC-HMS), in which the estimation of the direct runoff under the scenario with precipitation of 80 mm during the storm event that have occurred between 23 and 24 December 2009. In particular, SCS-CN (Soil Conservation Curve Number) is a model through which the estimation of the direct runoff can be achieved. This method includes several important properties of the watershed such as Hydrological Soil Groups and land use, which will be input for the HEC-HMS model.