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Open AccessArticle

A Model-Based Flood Hazard Mapping on the Southern Slope of Himalaya

1
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
CAS Center for Excellence in Tibetan Plateau Earth Sciences, CAS, Beijing 100101, China
4
Central Department of Hydrology and Meteorology, Tribhuvan University, Kirtipur, Kathmandu 44600, Nepal
5
Water and Energy Commission Secretariat, Kathmandu 44600, Nepal
6
Regional Climate Group, Department of Earth Sciences, University of Gothenburg, Box 460, S‐405 30 Gothenburg, Sweden
*
Author to whom correspondence should be addressed.
Water 2020, 12(2), 540; https://doi.org/10.3390/w12020540
Received: 18 November 2019 / Revised: 2 February 2020 / Accepted: 12 February 2020 / Published: 14 February 2020
(This article belongs to the Section Hydrology)
Originating from the southern slope of Himalaya, the Karnali River poses a high flood risk at downstream regions during the monsoon season (June to September). This paper presents comprehensive hazard mapping and risk assessments in the downstream region of the Karnali River basin for different return-period floods, with the aid of the HEC-RAS (Hydrologic Engineering Center’s River Analysis System). The assessment was conducted on a ~38 km segment of the Karnali River from Chisapani to the Nepal–India border. To perform hydrodynamic simulations, a long-term time series of instantaneous peak discharge records from the Chisapani gauging station was collected. Flooding conditions representing 2-, 5-, 10-, 50-, 100-, 200-, and 1000-year return periods (YRPs) were determined using Gumbel’s distribution. With an estimated peak discharge of up to 29,910 m3/s and the flood depths up to 23 m in the 1000-YRP, the area vulnerable to flooding in the study domain extends into regions on both the east and west banks of the Karnali River. Such flooding in agricultural land poses a high risk to food security, which directly impacts on residents’ livelihoods. Furthermore, the simulated flood in 2014 (equivalent to a 100-YRP) showed a high level of impact on physical infrastructure, affecting 51 schools, 14 health facilities, 2 bus-stops, and an airport. A total of 132 km of rural–urban roads and 22 km of highways were inundated during the flood. In summary, this study can support in future planning and decision-making for improved water resources management and development of flood control plans on the southern slope of Himalaya.
Keywords: flood frequency; hydrodynamic simulation; hazard mapping; risk assessment; Himalaya flood frequency; hydrodynamic simulation; hazard mapping; risk assessment; Himalaya
MDPI and ACS Style

Aryal, D.; Wang, L.; Adhikari, T.R.; Zhou, J.; Li, X.; Shrestha, M.; Wang, Y.; Chen, D. A Model-Based Flood Hazard Mapping on the Southern Slope of Himalaya. Water 2020, 12, 540.

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