Real-time coastal flood hazard assessment using DEM-based hydrogeomorphic classifiers

Abstract

Abstract. In the last decade, DEM-based classifiers based on height above nearest drainage (HAND) have been widely used for rapid flood hazard assessment, demonstrating satisfactory performance for inland floods. The main limitation is the high sensitivity of HAND to the topography, which degrades the accuracy of these methods in flat coastal regions. In addition, these methods are mostly used for a given return period and generate static hazard maps for past flood events. To cope with these two limitations, here we modify HAND, propose a composite hydrogeomorphic index, and develop hydrogeomorphic threshold operative curves for rapid real-time flood hazard assessment in coastal areas. We select the Savannah River delta as a test bed, calibrate the proposed hydrogeomorphic index on Hurricane Matthew, and validate the performance of the developed operative curves for Hurricane Irma. The hydrogeomorphic index is proposed as the multiplication of two normalized geomorphic features, HAND and distance to the nearest drainage. The calibration procedure tests different combinations of the weights of these two features and determines the most appropriate index for flood hazard mapping. Reference maps generated by a well-calibrated hydrodynamic model, the Delft3D FM model, are developed for different water level return periods. For each specific return period, a threshold of the proposed hydrogeomorphic index that provides the maximum fit with the relevant reference map is determined. The collection of hydrogeomorphic thresholds developed for different return periods is used to generate the operative curves. Validation results demonstrate that the total cells misclassified by the proposed hydrogeomorphic threshold operative curves (summation of overprediction and underprediction) are less than 20 % of the total area. The satisfactory accuracy of the validation results indicates the high efficiency of our proposed methodology for fast and reliable estimation of hazard areas for an upcoming coastal flood event, which can be beneficial for emergency responders and flood risk managers.

Assessing potential coastal flood exposure along the Port-Bouët Bay in Côte d’Ivoire using the enhanced bathtub model

“…In the case of the current research, only flood extent was considered in the exposure analysis though both flood depth and extent were provided as outputs from the eBTM. This consideration is consistent with several studies recently carried out in the field of flood management (Dandapat & Panda 2018, Hadipour et al 2020, Jafarzadegan et al 2022, Stephens et al 2017. In this study, the omission of flood depth was based on two main factors: the unreliability of the flood depth outputs, which were not validated, and the resolution of the DEM used in the analysis, potentially affecting flood depth accuracy.…”

Comparison of estimated flood exposure and consequences generated by different event-based inland flood inundation maps

“…In fact, Bass and Bedient (2018) have already developed such a surrogate modeling approach to create a FIM within our study area that loosely couples inland and coastal models, forcing both with a full range of potential tropical-cyclone characteristics. Recently, Jafarzadegan et al (2022) demonstrated a new methodology for replicating high-fidelity hydrodynamic model output by using a revised version of the HAND methodology that accounts for the height above and distance to the nearest drainage feature and is computationally efficient enough for FIM construction during flood events. This revised HAND methodology could function as a form of surrogate modeling for timely FIM creation.…”

“…Thus, steady-state hydraulic models, such as HAND and AutoRoute, tend to have limited effectiveness in providing FIMs during compound coastal floods in coastal watersheds. However, nonoperational alternative HAND approaches for coastal flooding in low-lying areas exist (Jafarzadegan et al, 2022).…”

Raspberry Pi Reflector (RPR): A Low‐Cost Water‐Level Monitoring System Based on GNSS Interferometric Reflectometry

“…For coastal flood hazard assessment, hydrodynamic models should be calibrated and validated against observed water level at river gauges. For example, Jafarzadegan et al (2022) proposed using a digital elevation model based approach for the rapid real-time assessment of flood hazard in coastal areas. A two-dimensional hydrodynamic model is first calibrated based on observed water levels at USGS gauges and then the calibrated model is used to generate a flood inundation map for further analysis.…”