Assessment of inundation risk in urban floods using HEC RAS 2D

Flood is the most common natural disaster upsetting the highest population of the world. In recent times, severe floods in urban areas are occurring more frequently owing to uncontrolled urbanization and climate change and it will continue to grow in upcoming years. Prevention of such events is not possible but with advancement of technology, flood-vulnerable areas can be identified through 2-D modeling of critical rainfall events. The difficulty associated with urban floods is unpredictable flow conditions in urban environment due to rapid alterations in topography and unavailability of extensive raw dataset. Thus, modeling of urban floods becomes a complex process. A vast number of numerical models have evolved over the past few years which are capable of flood mapping; most of them are commercial, rigorous and need extensive dataset to generate precise results. This paper presents a simple sophisticated approach to analyze extreme rainfall events based on past critical events and synthetic hyetographs developed from IDF curves for a part of Hyderabad, India. HEC-RAS, a freely available 2-D hydraulic model with integration to GIS is used to generate depth of flood inundation over underlying terrain and risk maps of flood inundation are developed for different rainfall scenarios. The model results identify 17% of total area is liable to floods out of which 9% area indicates high risk, 52% area shows medium risk and remaining 35% area falls under low risk of flooding.