Godavari river catchments get flooded frequently when there is heavy rainfall and cause adverse effects to the people and property. So, flood forecasting should be done for flood warning and flood protection. The study presents a straightforward approach for processing output of Arc GIS and HEC RAS hydraulic model, to enable one and two-dimensional modelling and floodplain mapping in Arc GIS. The methodology is applied to Nanded reach of Godavari river, located in Maharashtra. From the digital elevation model of the study area, the river cross section details are extracted using Arc GIS. The cross-section details, Manning’s value and observed 35-year flow data of Purna station (upstream cross section) are the input for the HEC RAS and unsteady flow simulation have been done. The output from the simulation is water surface elevation. These results were exported to Arc GIS and floodplain modelling have been done. The validation have been done by comparing the observed and simulated water surface elevation of downstream cross section (Yelli). Two-dimensional modelling is also done using HEC RAS. Using observed flow data of Purna station, expected flood have been forecasted using Gumbel’s Distribution Method for 2,5,10,25,50,100-year return periods. Using these data, the steady flow analysis was done and the output was exported to Arc GIS and flood inundation mapping have been done for each return periods.