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Flood Hazard Assessment in Dhobi-Khola Watershed (Kathmandu, Nepal) using Hydrological Model

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Author Affiliations

  • 1Golden Gate International College, Battisputali, Kathmandu, Nepal
  • 2Central Department of Hydrology and Meteorology, Tribhuvan University, Kirtipur, Nepal
  • 3Golden Gate International College, Battisputali, Kathmandu, Nepal
  • 4Genesis Consultants Pvt. Ltd, Lalitpur, Nepal

Int. Res. J. Environment Sci., Volume 5, Issue (11), Pages 21-33, November,22 (2016)

Abstract

Flood, one of the main hazards in Nepal, requires an effective modelling to mitigate their impacts. Flood inundation models provide anestimation of flood extents and depths that are used in the preparation of hazard maps. Streams, like Dhobi-Khola in Kathmandu, with potential flood risks to infrastructures and settlements, are not studied to a level to predict and mitigate the flood hazards. This study assesses the flood vulnerable sites of Dhobi-Khola watershed and delineate theflood prone areas using hydrological HEC-HMS model and GIS application.The model was calibrated and validated in Bagmati River with discharge data of Gaurighat and rainfall data of Sundarijal stations. The model was then transposed to Dhobi-Khola watershed using hydrological data of Budhanilkantha station. The Slope-Area method of discharge measurementwas used to validate the model outputs in Dhobi-Khola using the field survey data. Final model outputswere used to predict the floods for different return periods using HEC-RAS model together with HEC-GeoRAS to generate flood inundation maps. Results indicate that the maximum flood depth can reach up to 5.24 m in 100 year return period (YRP) in Dhobi-Khola watershed. One site is inundated during the flood of 5 YRP and three sites in 10 to 20 YRPs. A total of five and seven sites is inundated during flood of 50 and 100 YRP, respectively. Vulnerabilityassessment showed two sites are very highly vulnerable and a site in low flood vulnerable due to low levee height, putting several households in the riverbanks and surrounding at the highest risk.

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