This study aims to build flood hazard map for a lowland area in Danang city, Vietnam based on topographical data, land-cover and flood inundation map. ALOS PALSAR imageries with respect to the time before and during flood event in 2007 were used to characterize flood inundation. In addition, topographical data was developed via 5m resolution DEM generated by a bi-cubic spline algorithm that implemented in BS-Horizon program (Nonogaki et al., 2012). This high resolution DEM was used to enhance the accuracy of flood map as well as determine the geomorphological features of the study area and the relations on flood hazards. Land-cover map in 2007 extracted from Landsat TM data was also applied for the landform classification process. The flood hazard map was generated based on the probability of submergence of each landform unit.
The changes in land-cover as well as topography have significant effect on flood hazard. In this study, optical Rapid Eye remote sensed data in 2014 was used to extract land-cover by the time and the land-cover change from 2007 to 2014. The estimated landform and potential flood hazard map in 2014 was built based on the updated land-cover. The result was compared with field survey flood pillar data, flood map in the past, land-cover change and flood scenario given by Danang City government to assess the accuracy. This research has also proposed some flood prevention plans for this alluvial lowland area.
Landforms units derived rule-based classification of land cover map, 5m resolution DEM data and flood inundation map not only facilitates the understanding of the nature of flood but also in flood risk zoning. The methodology developed in this study would be useful in low relief areas in Vietnam and other parts of the world. |