Investigating the Role of DEM Resolution and Accuracy on Flood Inundation Mapping

Topography plays an important role in the accuracy of flood inundation maps. Most current flood inundation maps are created using topographic information derived from Light Detection and Ranging (LiDAR) data. Although LiDAR data are very accurate, handling of very high resolution Digital Elevation Models (DEMs) from LiDAR can be computationally challenging and expensive in long river reaches. As a result, the DEMs from LiDAR are sometimes resampled to coarser resolutions to expedite the creation and processing of flood inundation maps. The first objective of this study is to quantify the errors arising from DEM properties such as resolution and accuracy on flood inundation maps using the principle of resampling and error analysis. The results show that water surface elevations and flood inundation area have a linear relationship with the DEM resolution and accuracy. The second objective of this study is to use the linear relationship between the flood inundation extent and the DEM resolution or accuracy to create an approach for developing more accurate flood inundation maps by modeling the spatial distribution of errors using less accurate and coarser resolution DEMs. The results show that the hydraulic modeling outputs obtained from coarser resolution DEM using this approach are comparable to the results obtained using high resolution accurate DEMs. The accuracy of flood inundation maps can be improved significantly by modeling the spatial distribution of DEM errors. Therefore, by using the approach developed in this study, it is possible to obtain more accurate flood maps from less accurate topographic data in areas where LiDAR or any other form of accurate topography information is not available.