At this time extraordinary floods are common to many parts of our country causing a lot of losses such agricultural land and grazing land for long period of time. Temie watershed is been one among such place that has affected by flash flooding from rainfall in particular of Temie river which is located at the Right side of the river is mountainous and the left side flat terrain. This study is aimed to identify flood causative factors, peak flood estimation, delineate inundation areas that can be affected by unexpected floods. This thesis accomplished adopting application software’s like Google earth, Arc viewGIS, HEC-GeoHMS, HEC-HMS, HEC-GeoRAS and HEC-RAS models. The data used for this thesis is DEM, Land use/land cover map, soil map, soil texture to generate the curve number grid and rainfall and discharge type to determine peak flood in certain return period. Topographic data for the expected flooded area has been obtained from actual field survey data and from Google earth and TIN of the Study Area was created. The modelling process was towards performing steady flow calculations in the intent of routing the river outflow downstream of Temie watershed from the upstream up to the downstream boundary which is 13km from the outlet point .probable maximum precipitation was determined by Gumble’s extreme value type in different return period 20, 50,100, 500 and 1000 years and the corresponding results are 95.81, 104.5, 111.3, 128.04 and 134.8mm respectively. The flood magnitude is estimated for 20, 50,100,500 and 1000-years return period peak flood discharge using Computer program HEC-HMS Model.The corresponding values are 50.8, 63.5, 70.8, 86.2 and 94m3/s peak discharge is used for further analysis which is inundation mapping. These flood inundated crop lands having area of 346.7, 352.2, 357.8, 363.0 and 371.03hectares respectively. These corresponded to losses of 9309.4, 9457.4, 9606.1, 9745.5 and 9962.2 quintals of crop respectively. Therefore, the affected areas to be free of any agricultural activities, infrastructure development, investment and residence of people in order to avoid the risk of flooding in the area especially closer to the downstream of River.