Estimating Flood Characteristics Using Geomorphologic Flood Index with Regards to Rainfall Intensity-Duration-Frequency-Area Curves and CADDIES-2D Model in Three Iranian Basins

Abstract

There is not enough data and computational power for conventional flood mapping methods in many parts of the world, thus fast and low-data-demanding methods are very useful in facing the disaster. This paper presents an innovative procedure for estimating flood extent and depth using only DEM SRTM 30 m and the Geomorphic Flood Index (GFI). The Geomorphologic Flood Assessment (GFA) tool which is the corresponding application of the GFI in QGIS is implemented to achieved the results in three basins in Iran. Moreover, the novel concept of Intensity-Duration-Frequency-Area (IDFA) curves is introduced to modify the GFI model by imposing a constraint on the maximum hydrologically contributing area of a basin. The GFA model implements the linear binary classification algorithm to classify a watershed into flooded and non-flooded areas using an optimized GFI threshold that minimizes the errors with a standard flood map of a small region in the study area. The standard hydraulic model envisaged for this study is the Cellular Automata Dual-DraInagE Simulation (CADDIES) 2D model which employs simple transition rules and a weight-based system rather than complex shallow water equations allowing fast flood modelling for large-scale problems. The results revealed that the floodplains generated by the GFI has a good agreement with the standard maps, especially in the fluvial rivers. However, the performance of the GFI decreases in the less steep and alluvial rivers. With some overestimation, the GFI model is also able to capture the general trend of water depth variations in comparison with the CADDIES-2D flood depth map. The modifications made in the GFI model, to confine the maximum precipitable area through implementing the IDFAs, improved the classification of flooded area and estimation of water depth in all study areas. Finally, the calibrated GFI thresholds were used to achieve the complete 100-year floodplain maps of the study areas.

Using geomorphologic indicators in preparation for flood zoning and flood risk maps in the Kashafroud basin, Iran

“…Based on Equation (1), a normalized GFI value is a coefficient between 1 and −1 (−1 ≤τ ≤1), and it is called the threshold value (Faridani et al, 2020). An optimal threshold is obtained for flood zoning with the return periods for each basin.…”

“…R FP is indicative of the pixel rate that indicates flood zone, but pixels with flood zone should not be included based on the standard flood map (Faridani et al, 2020). R TP indicates the rate of pixels that have flooded and have been flooded zones based on validation using a standard flood map (Faridani et al, 2020). Considering the R FP and R TP values, it can be said that the model used in the Kashafroud basin has been a good performance for flood zoning.…”

“…In this regard, geomorphic flood area (GFA) is a tool that is based on the GI method to provide flood zoning and flood risk maps. Previous studies showed that using the GFA tool provides acceptable results for flood zoning (Albano et al, 2020;Faridani et al, 2020).…”

“…The calculation method of this coefficient has been described in the study of Samla et al in more detail . Figure 3 shows the false positives and false negatives values for a study (Faridani et al, 2020). As shown in Figure 3, there are cells in the training area using the model that have floods based on the standard flood map but do not have floods based on the model results.…”

Modified geomorphic flood index (GFI) method on backwater problem in tidal tropical river for rapid flood assessment

“…Therefore, identification of flood-prone areas is a critical issue that is becoming increasingly important in every region [5]. Fast and low-data-demand methods can be very useful for identifying flood-prone areas [6]. This approach may help in performing and updating risk assessments and management by considering temporal and spatial changes in hazards, exposure, and vulnerability [7].…”