Flood Assessment Using Hydrodynamic HEC-RAS Modelling

Introduction

A Flood is a natural calamity that occurs due to excessive rainfall. When the discharge rises to the point that the banks can no longer hold the water, it overtops its banks and floods the surrounding areas, impacting the lives of the people residing in the vicinity of the river. This process in which the water overtops the banks of the river causes riverine flooding (Eccles & Hamilton, 2019). It is the most common, hazardous and widespread natural calamity that disrupts the normal life of mankind. Some of its hazardous effects include damage of crops, loss of livestock, and worsening of health and hygiene conditions owing to waterborne ailments. It also hinders the economic growth and development of a country as a huge amount of funding goes into post-relief operations. According to a survey conducted by UNICEF (United Nations Children's Fund), India is the second most flood affected country in the world after Bangladesh. It is not possible to prevent such events, but with the help of engineering techniques, their effect can be minimized.

Due to the unpredictable behaviour of the rivers during floods, computer modelling is the most efficient and economical tool to simulate the flows. It involves the minimum cost to study and replicate the behaviour of the channels and natural streams. Flood mapping is usually done by hydraulic mathematical models. These models can be very useful in determining the water levels and flood prone areas. Hydraulic modelling is a powerful tool in planning infrastructure development as it gives a complete conceptual representation of the actual problem area (Monte et al., 2016). Hydrodynamic models with the integration of GIS is the most suited way to develop flood model and assessment of flooding in the local areas (Ullah et al., 2016). HEC-RAS (Hydrologic Engineering Centre River Analysis System) is a powerful tool for dealing with such issues. It is well developed and the models created by the software are quite realistic. It is very easy to use and has found wide acceptance in the hydraulic community (Ahmad et al., 2016).

HEC-RAS was developed by the U.S. Army Corps of Engineers to manage rivers, canals, and other public works under water resource engineering. It was developed in 1995 and since then, it had a wide acceptance and popularity. It is easy to use very handy software with geospatial capabilities. HEC-RAS has a broad range of data entry capabilities. HEC-RAS Version 5 now offers geospatial functionality for obtaining river geometry data, which was previously done with the HEC-GeoRAS module in ARC-GIS, but now HEC-RAS can perform these functions very easily. The hydraulic modelling approach has become more practical as a result of the introduction of geospatial approaches, and it saves a lot of time on pre-processing operations.

This aim of this research work is to indicate the applicability of HEC-RAS in one dimensional flood modelling in balaghat district. The steady flow condition has been utilised to simulate the model on the Chandan River. The output of the model was obtained in context of water depth. The results were also validated by performing error analysis to acquire the accuracy and precision of the HEC-RAS model. The study can be helpful for the local government to plan flood control and management plan for the study area.