315 THE USE OF HEC-RAS MODELLING IN FLOOD RISK ANALYSIS IOSUB MARINA 1 , MINEA I. 1 , HAPCIUC OANA 1 , ROMANESCU GH. 1 ABSTRACT. – The use of HEC-RAS modelling in flood risk analysis. The fact that, in the Ozana drainage basin, most of the people have built their homes in the river valley, determines that a study focused on identifying the areas exposed to hydrological risk is vital, mostly in the development decisions for villages and in the creation of management plans for emergency situations. This study analyses the mapping methodology of the flood prone areas in the middle and lower sector of the Pluton river, which is a tributary of Ozana river, in its upper sector. In order to correctly draw the flood risk maps, the HEC-RAS method has been used, together with the HEC-GeoRAS extension, in ArcGIS. The results that have been obtained, correlate with the field situation in a very high proportion: for a 1% occurance flood, almost 123 households have been damaged, and according to the simulation, a number of 147 buildings have been damaged, therefore other probabilities (that overcome the 1% situation) can be used for similar simulations. Keywords: HEC-RAS, risk, flood, flood band, Ozana 1. INTRODUCTION At present, GIS modelling for floods or delimiting some flood prone areas is very advanced, and numerous mathematical methods for calculating the extent of a river (according to its flow rate, the water infiltration rate into the soil, land use etc) have been developed. These mathematical models have been integrated into GIS software, whose purpose is to create a model that would replicate the shape of the landscape as precise, as possible (Edsel et al. 2011). The flood risk maps have a clear purpose of identifying vulnerable areas and the population that is exposed in a certain region; they represent a useful tool during General Urban Plan creation, and intend to be used in the interdiction of constructing houses in the affected areas and creating management plans for emergency situations, as close as possible to the probabilities of certain events of this type (Iosub et al, 2014). The existing hydrological models are numerous. In 1991, there were 65 known hydrological models, and during the years, this number has risen, but attention has been directed only to the most important. (Edsel et al. 2011). Therefore, in 1995, Singh counted and considered 26 to be the most used, on the planet (Singh et al. 2006). In 1998, The Subcommittee on Hydrology of the Interagency Advisory Committee on Water Data has indexed models created and used by state institutions in the USA, which were synthesised by Wurbs, in 7 cathegories (Wurbs, 1998). In 2002, Singh and Fevert published two books, inside 1 "Alexandru Ioan Cuza" University, Faculty of Geography, Carol I, no. 20, 700505 Iaşi, Romania E-mail: iosub.marina@gmail.com