Digital elevation models for high-resolution base flood elevation mapping in a densely populated city

Base flood elevation (BFE) and design flood elevation (DFE) are essential references for building floodproofing. Previous BFE and DFE mapping methods were mainly applied to inland rivers and coastal areas, and few studies mentioned the mapping method of densely populated cities. This study proposes a high-resolution BFE and DFE mapping in the densely populated city of Tainan in Taiwan using the SOBEK model and hydraulic digital elevation model. DEM 1 was a 20-m resolution DEM without the building block (BB) method. DEMs 2 and 3 were 1-m resolution DEMs without and with the BB method, respectively. Compared to the observed flooding depths from the water level gauge, the simulation results with DEMs 1 and 2 were closer to the actual situation than that with DEM 3, as DEMs 1 and 2 could represent the water storage effect in buildings. Because buildings in a high building density area (HBDA) had adopted dry floodproofing, the water level rose when the subcritical flow flowed by the buildings. From a risk management perspective, BFE and DFE mapping should adopt DEM 3. The water levels rise effect on buildings was less pronounced in a low building density area (LBDA). DEM 1 could be used for BFE and DFE mapping to save computing power. Generally, a city can be divided into different areas according to building densities. The high-resolution DEM with BB method should be used for HBDA. LBDA should use a low-resolution DEM without the BB method, which can account for model computation efficiency and flood risk management.