[1] This study focuses on development and application of a new modeling approach for a comprehensive flood hazard assessment along protected river reaches considering dike failures. The proposed Inundation Hazard Assessment Model (IHAM) represents a hybrid probabilistic-deterministic model. It comprises three models that are coupled in a dynamic way: (1) 1D unsteady hydrodynamic model for river channel and floodplain between dikes; (2) probabilistic dike breach model which determines possible dike breach locations, breach widths and breach outflow discharges; and (3) 2D raster-based inundation model for the dike-protected floodplain areas. Due to the unsteady nature of the 1D and 2D models and runtime coupling, the interdependence between the hydraulic loads on dikes at various locations along the reach is explicitly considered. This ensures a more realistic representation of the fluvial system dynamics under extreme conditions compared to the steady approaches. The probabilistic dike breach model describes dike failures due to three failure mechanisms: overtopping, piping and slope instability caused by seepage flow through the dike core (micro-instability). The 2D storage cell model computes various flood intensity indicators such as water depth, flow velocity, and inundation duration. IHAM is embedded in a Monte Carlo simulation in order to account for the natural variability of the input hydrograph form and the randomness of dike failures. Besides binary (wet/dry) inundation patterns, IHAM generates new probabilistic flood hazard maps for each intensity indicator and the associated uncertainty bounds. Furthermore, the novel probabilistic dike hazard maps indicate the failure probability of dikes for each considered breach mechanism.Citation: Vorogushyn, S., B. Merz, K.-E. Lindenschmidt, and H. Apel (2010), A new methodology for flood hazard assessment considering dike breaches, Water Resour. Res., 46, W08541,

Abstract. Flood detention areas serve the primary purpose of controlled water storage during large flood events in order to decrease the flood risk downstream along the river. These areas are often used for agricultural production. While various damage estimation methods exist for urban areas, there are only a few, most often simpler approaches for loss estimation in rural areas. The loss assessment can provide an estimate of the financial provisions required for the farmers' compensation (e.g., in the context of cost-benefit analyses of detention measures). Flood risk is a combination of potential damage and probability of flooding. Losses in agricultural areas exhibit a strong seasonal pattern, and the flooding probability also has a seasonal variation. In the present study, flood risk is assessed for a planned detention area alongside the Elbe River in Germany based on two loss and probability estimation approaches of different time frames, namely a monthly and an annual approach. The results show that the overall potential damage in the proposed detention area amounts to approximately 40 000 € a−1, with approximately equal losses for each of the main land uses, agriculture and road infrastructure. A sensitivity analysis showed that the probability of flooding (i.e., the frequency of operation of the detention area) has the largest impact on the overall flood risk.

Abstract. Analyses of discharge series, precipitation fields and flood producing atmospheric circulation patterns reveal that two governing flood regimes exist in the Mulde catchment in south-eastern Germany: frequent floods during the winter and less frequent but sometimes extreme floods during the summer. Differences in the statistical parameters of the discharge data can be found within the catchment from west to east. The discharges are compared to a number of landscape parameters that influence the discharge in the subcatchments. Triggering circulation patterns were assigned to all events of the annual maximum discharge series in order to evaluate which circulation patterns are likely to produce large floods. It can be shown that the cyclone Vb-weather regime (TM, TRM) generates the most extreme flood events in the Mulde catchment, whereas westerly winds produce frequently small floods. The Vb-weather pattern is a very slowly moving low pressure field over the Gulf of Genoa, which can bring large amounts of rainfall to the study area. It could also be shown that even with the two flood regimes estimates with the annual maximum series provide a safer flood protection with a larger safety margin than using summer maximum discharge series for extreme summer floods only. In view of climate change it is necessary to integrate knowledge about catchment characteristics, the prevailing flood regime or the trends of weather patterns in the estimation of extreme events.

Analyses of discharge series, precipitation fields and flood producing atmospheric circulation patterns reveal that two governing flood regimes exist in the Mulde catchment in south-eastern Germany: frequent floods during the winter and less frequent but sometimes extreme floods during the summer. Differences in the statistical parameters of the discharge data can be found within the catchment from west to east. The discharges are compared to a number of landscape parameters that influence the discharge in the subcatchments. Triggering circulation patterns were assigned to all events of the annual maximum discharge series in order to evaluate which circulation patterns are likely to produce large floods. It can be shown that the cyclone Vb-weather regime (TM, TRM) generates the most extreme flood events in the Mulde catchment, whereas westerly winds produce frequently small floods. The Vb-weather pattern is a very slowly moving low pressure field over the Gulf of Genoa, which can bring large amounts of rainfall to the study area. It could also be shown that even with the two flood regimes estimates with the annual maximum series provide a safer flood protection with a larger safety margin than using summer maximum discharge series for extreme summer floods only. In view of climate change it is necessary to integrate knowledge about catchment characteristics, the prevailing flood regime or the trends of weather patterns in the estimation of extreme events.

No abstract