FLOOD MONITORING USING MULTI SOURCES DIGITAL ELEVATION MODEL IN THE LOWER NAM NGUM RIVER BASIN, LAO PDR

Name: Phonesavanh Sivanthong

ID: –

Title: FLOOD MONITORING USING MULTI SOURCES  DIGITAL ELEVATION MODEL   IN THE LOWER NAM NGUM RIVER BASIN, LAO PDR

Type: Thesis

Abstract

          The resolution and accuracy of digital elevation models (DEMs) can affect the hydraulic simulation results for simulating. However, for the Lower Nam Ngum River Basin, high quality DEM data are often not available, leaving researchers with near-global, freely available DEMs, such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) and the Shuttle Radar Topography Mission data (SRTM) for hydraulic modeling. This study explores the suitability of two freely available DEMs. Reference DEM that generate from contour maps scale 1:100,000 interval 20 m for hydraulic modeling (HEC-RAS model). Moreover, the reference DEM, ASTER GDEM resolution 30 m and SRTM DEM resolution 90 m were used as basic topographic data to simulate peak discharge propagation, as well as flood inundation area in the HEC-RAS one dimension hydraulic model. Results of the three DEMs simulation were compared to investigate the suitability DEM for flood generation modeling. Comparisons of ASTER GDEM and SRTM each with reference DEM in the flood area show the RMSE = 3.90 of ASTER GDEM, RMSE = 3.89 of SRTM DEM. However, small errors still exist in the cross sections that may influence the propagation of average peak discharge. The flood inundation obtained from the reference DEM, SRTM DEM and ASTER GDEM simulation.

          The main objective of the study was investigated the accuracy of three different sources Digital Elevation Model (DEM) after flood model outputs for the Lower Nam  Ngum River Basin and estimated the inundation area for the year 2008. The other objectives verified the model by the model calibration and validation results and prepared flood map.

          For the flood inundation simulation involves the integration of hydraulic approaches. The HEC-RAS model was successfully applied to represent the Lower Nam Ngum River Basin corresponding to different discharge. The discharge used to calibrate and validate the distributed hydraulic model cover extreme flood events in this study area.   During the first stage, calibration was performed on the data set of 2008 at A Veunkham station.  The calibration and validation procedure was performed by adjusting the Manning’s “n” coefficients parameter values and evaluating the performance both qualitatively by visually comparing the observed and simulated discharge as mention earlier. The NSE was 0.957, 0.605 and 0.904 and VB were 0.06, 0.26 and 0.06 respectively. During validation period of 2009, the NSE was 0.948, 0.592 and 0.913 and VB were 0.05, 0.27 and 0.05 respectively. The Manning’s coefficients varied 0.05 from downstream to upstream. The results of calibration and verification showed good agreement. 

          Infrequent large floods usually occur in northern of Nam Ngum River Basin in the April – October rainy season. The rainfall distribution in the region is significantly influenced by the central mountain range. The highest rainfalls are near Thalath village and the lowest near Hai Pakngum village. Flood events on the Lower Nam Ngum River Basin in August September of year 2008 are flooded parts of Vientiane capital areas.  

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