A type of flood occurs in rivers when the flow exceeds the capacity of the fluvial canal, particularly when it is bent or tilted in a stream. Floods often cause damage to homes and businesses if they are in the natural flood plains of rivers. Flooding in river basins can be eliminated far from rivers and other water areas, but people have usually lived and worked in rivers because the land is generally flat and fertile and because rivers facilitate movement and access to trade and industry. In my study area is limited around analysis of river basin flooding.Study area: Kelani river basin around Kaduwela area was selected as the study area for this research. Kaduwela is the one of most populated and industrial area in Gampaha district.
Data collection: In HEC HMS modelling, it needs to find the number of catchments and area of each catchments in my study area. So Arc GIS software can use to find those parameters by using DEM (Digital Elevation Modelling) file which can collect from Survey Department of Sri Lanka. Also rainfall data can be collected from rain gauge stations which are situated in catchments of my study area and cross-section details of Kelani river can be collected from Irrigation Department of Sri Lanka.