Flood Risk Assessment of the Ladara River, Chitwan, Nepal Using Hydrodynamic Model (HEC-RAS)

Manash Osti; Surath Ghimire; Rijan Bhakta Kayastha

Manash Osti Environmental Specialist, Special Economic Zone Authority Nepal, Tripureshwor, Kathmandu, Nepal
Surath Ghimire Research Assistant, Webster University, St. Louis, USA
Rijan Bhakta Kayastha Professor, Department of Environmental Science and Engineering, Kathmandu University, Dhulikhel, Nepal

Abstract

Objective: This study aims to assess flood risks in the Ladara River watershed in Chitwan, Nepal, utilising hydrodynamic modelling to estimate flood extent and depth across different return periods.
Methods: The study employs HEC RAS software to model flood scenarios and analyse the peak discharge of the Ladara River for 2, 10, 20, 50, and 100-year return periods. Peak discharge estimates are derived using the WECS/DHM method and Modified Dicken’s method, with comparisons made to the Sharma and Adhikari (2004) method.
Results: Findings indicate that the Ladara River watershed is susceptible to flooding, with significant inundation areas identified for various return periods. Vulnerability varies by land use, with agricultural lands and settlements facing the highest flood risks. The peak discharge estimates
from the Sharma and Adhikari method were found to be greater than
those from the other methods. Vulnerability varies by land use, with agricultural lands and settlements facing the highest flood risks.
Limitations: The accuracy of the flood risk assessment is constrained by the absence of a hydrological station in the river and the inadequate resolution of available data.
Conclusion: Flood hazard maps are identified as critical tools for public awareness, although they cannot prevent floods. The study advocates for further research to acquire high-resolution data to enhance flood risk assessments and inform effective flood management strategies.