Flooding is a natural disaster whose damage to human beings is higher than other natural disasters, such as drought and famine, and is a major concern in many regions of the world. Therefore, we must select appropriate and effective methods for flood management and control by understanding the hydraulic flow in the flood plains. The change in land use can cause changes in hydrological conditions, such as the frequency of floods, the base flow and the average annual discharge. As it is not possible to fully protect against the risk of flooding, it is necessary to live in floods and apply new policies on land use management and residential development on the river bank to reduce the impact of their destruction.
The knowledge of floods and the study of their behavior require sufficient data on the hydrological condition of the basin and the discharge of the river, and it is not possible to reach this objective in seasonal rivers and regions where there is no constant flow, so the implementation of hydrological models is useful for rainfall simulation. Runoff process and hydraulic models for the analysis of runoff flow in the river and its distribution. Traditional rain gauges provide a fine enough resolution for accurate runoff calculations and flood warnings. Therefore, flood modelling requires predictions of distributed models related to planning and insurance.
Recently, interest in flood analysis has been increased using powerful HEC-HMS and HEC-RAS tools to manage spatially distributed data and the distributed basin model. The use of these hydrological and hydrological parameters of the watershed can analyze the risk of flooding in my selected watershed in Sri Lanka.