This study focuses on the estimation and management of flood risk in the drainage basin of Paratrechos or Peritsi stream in Naxos Island, through the study of geomorphological characteristics, geology, land use and topography.

The catchment area of Paratrechos or Peritsi stream is approximately 54 km. High morphological relief characterizes the mountainous areas and lowland areas present mild relief. The average elevation reaches 245 m, while the average slope of the basin is 21%. The stream is known to have caused severe problems following intense rainfall, with landslides in the mountainous areas and subsidence in large parts of the road network, and with intense flooding events in the wider area of Chora of Naxos. Several floods have been recorded for Paratrechos or Peritsi stream, with the most recent at the end of March 1998, beginning of January 1999 and 18th February 2003. The aim of this study is the investigation of the relationship rain-runoff through Unitary Hydrographs, in order

to estimate and evaluate the flood potential of the hydrologic basin. In order to obtain accurate results, the hydrologic basin was divided into sub-basins, based on the class of each stream, and the characteristics of each sub-basin were studied. For the optimum application of the Clark method, the data were enriched with field measurements, through the installation of a water level recorder and a meteorological station. The results from the field measurements were used to confirm the results of the method. Through this method, the maximum flow at the mouth of each sub-basin and the concentration time were

calculated. Maps of flood risk were developed, with the use of ArcGis 9.3 software, presenting the characteristics of the flood risk locations in the study area. Furthermore, Instantaneous Unitary Hydrographs were produced for each sub-basin, in order to study and compare the relationship of rain-runoff and determine the causes of the risk. The identification of these areas and the application of the method were accomplished through the study and use of contours, elevation and trigonometric points, watersheds, land use, hydrographic network, soil characteristics, geological characteristics and flood picks.