Deriving flash floods in the case of simulated precipitations. The present study sets to determine the historical flash-floods on the Petriş watershed making use of the implemented mathematical models in a Hydrological Modeling System. In order to simulate the 1%, 2% and 10% exceedance probability flash-floods, the Intensity-Frequency-Duration (IDF) curves have been built on the basis of 22 years of precipitation records (1988-2009). They serve as input data together with the hydrological parameters identified by the means of a Geographic Information Systems. The results, computed mainly on the basis of the Soil Conservation Service (SCS) method, consist of hyetographs and hydrographs at the outlet of the main watershed, as well as to that of the ungauged tributaries of the Petriş River.