Karlovassi basin area has been studied for long period by the team from University of Athens. This area suffers from frequent floods which frequency even raised after large area of forests in Kerketeas Mountain area was burned down in year 2000. In recent period the area has been studied from the point of view of flood risk. High volume of data was collected and processed as an input to the flood risk model. The model was built using Arc Hydro toolset in ArcGIS environment (Maidment, 2002). Based on this model a GIS based flood risk map was created. In order to get more detail description of rainfall-runoff process a decision has been made to apply hydrologic model which works with more detail description of runoff process. For these purposes fully HEC-1 model (Hydrologic Engineering Center, 1998) was chosen. HEC-1 describes runoff process with semi-distributed approach. Results for modeling of precipitation event from November 2001 are presented here.