Developing a method to include flood defenses explicitly in flood hazard maps based on limited available information

Abstract

Flooding is one of the most damaging natural disasters worldwide, and presents a signi_cant risk for a large amount of the global population. For the development of ood disaster management strategies, policy makers make use of ood hazard maps to inform investment strategies to reduce risk. In many current ood hazard mapping methods, the role of embankments is either implicit or completely unaccounted for. However, these defense systems can play a key role in both the _nal extent of the inundation as well as in the development of the inundation. Limitations in available data are often the reason for the lack of explicit implementation of embankments. The goal of this study is the development of a method that can explicitly include the e_ects of ood defenses in a ood hazard map based on limited available data. Next, this has been tested for a low-lying riverine area and the Tisa river basin in Serbia was selected as a case study area for this purpose. First, an idealized approach has been followed to better understand the model behavior using settings resembling this river. Finally, the method has been applied with a more realistic river schematization.
To develop a method for a more explicit inclusion of ood defenses, an understanding of the di_erent current approaches has been generated based on a literature review. On the scale of global ood maps, the failure probabilities of ood defenses are not used. Only with post-processing, certain areas are considered protected by removing inundation from the maps. Many studies of ood hazard mapping use the so-called bathtub approximation. Hereby is assumed that the complete oodplain will ood and that the inundation depth is found by extrapolating the water surface level outside of the embankments to the area inside of the embankments. The inuences of the ood defenses on the inundation are not included. Regional ood hazard maps are still made without ood defenses in many cases. While the improved resolution allows for more detailed maps, the lack of available data still limits the implementation of ood defenses. Flood mapping methods exist that include failure probabilities for ood defenses but these require large amounts of data that is not available everywhere.
An idealized model based on the Tisa river characteristics is used to test a ood mapping method which includes explicitly the presence and potential failure of embankments. Based upon data on the river geometry, hydraulics as well as land-use in the oodplains, a model schematization has been set up with the SOBEK software. The embankments were simpli_ed to a crown height for the purpose of overow and an estimated failure probability. The breaching of the levee is simulated according to the Verheij-vdKnaap breach growth model. The estimation of the failure probabilities was based on historical failure rates of a comparable ood defense system along the Elbe River. The levees were schematized into segments based on the maximum breach width of the breaching model…