Flood Hazard Mapping in Nam Ngum River Basin

This project in Lao PDR was undertaken with an objective to develop flood hazard maps for Nam Ngum river basin for 10, 20 and 50 years return periods using satellite data, river discharge data and a hydraulic model (HEC-RAS). Six districts along the Nam Ngum river were selected covering two provinces as the study area.

      Topographic data, population data and GIS data such as river networks, provincial boundaries and village locations were collected for the study. A landuse map was prepared by classifying remote sensing data to generate the Manning’s roughness coefficients for different landuse types to input into the HEC-RAS model for flood simulation. Frequency analysis of river discharge data was done using Gumbel’s method and peak discharges for 10, 20 and 50 years flood were obtained. The corresponding flood depths and extents were obtained using the HEC-RAS model for these three return periods. Further analysis was done for the 10 year flood and it was found that 42% of the study area would be affected. Eighty five percent population of the Thourakhom district will be affected by the 10 year flood, while Keo-Oudom district will remain free from the flood. 
The project had helped in institutional knowledge and skill development in applications of remote sensing and GIS and flood modeling as two major agencies namely, Department of Meteorology and Hydrology and National Disaster Management Office (NDMO) had participated in the implementation of the project. Nam Ngum river being the lifeline of the country’s economy, therefore, flood mapping activity had helped in planning and management of the recurrent floods.