Detection of flood-prone areas using digital elevation models

Abstract: The availability of new technologies far the measurement of surface elevation has addressed the lack of high-resolution elevation data, which has led to an increase in the attraction of automated procedures based on digital elevation models (DEMs) far hydrological applications, including the delineation of floodplains. In particular, the exposure to flooding may be delineated quite well by adopting a modified topographic index (TIm) computed from a DEM. The comparison of TI", and flood inundation maps (obtained from hydraulic simulations) shows that the portion of a basin exposed to flood inundation is generally characterized by a TIm higher than a given threshold, T (e.g., equal to 2.89 far DEMs with cell size of 20 m). This allows the development of a simple procedure far the identification of flood-prone areas that requires only two parameters far the calibration: the threshold T and the exponent of TIm ' Because the modified topographic index is sensitive to the spatial resolution of the DEM, the optimal scale of representation for the performance of the method is investigated. The procedure is tested on the Arno River Basin by using the existing documentation of flood inundations produced by the Arno River Basin Authority for calibration and validation. This approach is applied on Il subcatchments with areas ranging from 489-6,929 km2 utilizing DEMs of different resolutions with cell sizes ranging from 20-720 m. Results show that the proposed procedure may help in the delineation of flood-prone areas, especially in basins with marked topography. The method is sensitive to the DEM resolution, but a cell size of-100 m i