Elbe flood - return period and historical classification

On April 4, 2006 (7:00 am), the water level at the Dresden gauge reached the value of 749 cm. This corresponds to a runoff of 2591 m³/s. The time series of the yearly maximum runoff at the Dresden gauge between 1853 and 2006 (Fig. 1) shows that a this value has not been reached since April 10, 1941, except of the flood in August, 2002. At that time, the runoff equaled 2650 m³/s. In comparison, the flood of July, 1954, led to a runoff of 2300 m³/s, while in August, 2002, 4580 m³/s were reached.

Figure 1: Time series of the yearly maximum runoff at the Dresden gauge between 1853 and 2003. Shown in red: Runoff on April 4, 2006 (7:00 am).

The series shown in (Fig. 1) was used in a statistical analysis in order to estimate the return period of the currently ongoing event. Like it is shown in (Fig. 2), a return period of approx. 10 years is the result. This means that an event of that size occurs once within 10 years according to the long-term statistical mean. Statistical analyses of this kind highly depend on the time series they rely on: Based on a shorter series of data from 1931 to 2003, the return period of the current event would be estimated to be 20 years. As it can be seen clearly in (Fig. 1), a runoff of 2500 m³/s was exceeded considerably more often before 1941 than afterwards. Between 1853 and 2003, a value of 2500 m³/s was exceeded 21 times, but only 3 times from 1931 to 2003. Hence, a higher return period for the current event results from the shorter data series.

Figure 2: Flood probability graph for Dresden gauge based on the yearly maximum runoff series from 1853 to 2003. To the yearly maximum runoff values, different distribution functions were fitted (G: Gumbel distribution, LN2, LN3: log-normal distribution with 2 and 3 parameters, W2: Weibull distribution, GEV: common extreme values distribution, GL: generalized logistic distribution, PE3: Pearson-III distribution). In this graph, the return period of a certain runoff value can be read.

Definitions of the terms water level, return period and others can be found ont the pages of our Flood glossary.

 Back