Are open-source hydrodynamic models efficient in quantifying flood risks over mountainous terrains? An exhaustive analysis over the Hindu-Kush-Himalayan region

Trashi Namgyal; Dev Anand Thakur; Rishi D S; Mohit Prakash Mohanty

doi:10.1016/j.scitotenv.2023.165357

Are open-source hydrodynamic models efficient in quantifying flood risks over mountainous terrains? An exhaustive analysis over the Hindu-Kush-Himalayan region

Sci Total Environ. 2023 Nov 1:897:165357. doi: 10.1016/j.scitotenv.2023.165357. Epub 2023 Jul 6.

Authors

Trashi Namgyal¹, Dev Anand Thakur², Rishi D S³, Mohit Prakash Mohanty⁴

Affiliations

¹ Department of Water Resources Development and Management, Indian Institute of Technology Roorkee, Roorkee 247667, India; National Centre for Hydrology and Meteorology, Royal Government of Bhutan, Bhutan.
² Department of Water Resources Development and Management, Indian Institute of Technology Roorkee, Roorkee 247667, India.
³ TUFLOW India - SRA Consultants, Telangana 500080, India.
⁴ Department of Water Resources Development and Management, Indian Institute of Technology Roorkee, Roorkee 247667, India. Electronic address: mohit.mohanty@wr.iitr.ac.in.

PMID: 37419355
DOI: 10.1016/j.scitotenv.2023.165357

Abstract

The Hindu-Kush-Himalaya is abode to numerous severely flood-prone mountainous stretches that distress vulnerable communities and cause massive destruction to physical entities such as hydropower projects. Adopting commercial flood models for replicating the dynamics of flood wave propagation over such regions is a major constraint due to the financial economics threaded to flood management. For the first instance, the present study attempts to investigate whether advanced open-source models are skillful in quantifying flood hazards and population exposure over mountainous terrains. While doing so, the performance of 1D-2D coupled HEC-RAS v6.3 (the most recent version developed by the U.S. Army Corps of Engineers) is reconnoitred for the first time in flood management literature. The most flood-prone region in Bhutan, the Chamkhar Chhu River Basin, housing large groups of communities and airports near its floodplains, is considered. HEC-RAS v6.3 setups are corroborated by comparing them with 2010 flood imagery derived from MODIS through performance metrics. The results indicate a sizable portion of the central part of the basin experiences very-high flood hazards with depth and velocities exceeding 3 m, and 1.6 m/s, respectively, during 50, 100, and 200-year return periods of floods. To affirm HEC-RAS, the flood hazards are compared with TUFLOW at 1D and 1D-2D coupled levels. The hydrological similarity within the channel is reflected at river cross-sections (NSE and KGE > 0.98), while overland inundation and hazard statistics differ, however, very less significant (<10 %). Later, flood hazards extracted from HEC-RAS are fused with the World-Pop population to estimate the degree of population exposure. The study ascertains that HEC-RAS v6.3 is an efficacious option for flood risk mapping over geographically arduous regions and can be preferred in resource-constrained environments ensuring a minimal degree of anomaly.

Keywords: Bhutan; Flood risk; HEC-RAS v6.3; MODIS; Population exposure; TUFLOW.