The hazard index map shows flood areas and intensities (water depth or specific discharge) during extreme floods for the Elbe river and waters of the 1st order in Saxony on an overview scale (1:100,000) with data from 2004. An extreme flood (EHQ) is an event that is significantly greater than HQ(100), at least the highest event observed, but generally HQ(300). The flood plains were calculated without taking into account the effect of existing flood protection facilities such as dams, dikes or polders. The intensities and extents shown represent an envelope of all possible flooding scenarios, i.e. not all of the areas shown are affected by a single event. This also applies if protective devices fail. In addition, the boundaries of the flooded areas at HQ(20) and HQ(100) are shown, also without considering the effect of flood protection facilities. Due to the various flooding and thus damage processes, a distinction was made between flat valley areas (free of bedload, mostly flooding that does not change course) and steep areas (dynamic flooding with bedload transport, erosion and expected course change). Since the depth of flooding in the steep stretches of water can only provide indirect information about the intensity and thus the risk, the flow velocity on the forelands was also determined. The product of inundation depth and flow velocity is presented as specific runoff (runoff per meter water body width) for EHQ.
