Design flood
The design flood ( BHW ) is an assumed flood event which is used for the structural dimensioning ( dimensioning ) of a flood protection system ( e.g. dyke , flood relief system ) or another (water) structural system.
The design flood is defined by the probability with which it can occur or by the time periods in which it is to be expected once (e.g. annually or every 10, 200, 5000 ... years).
Typically by extrapolating time series of precipitation or runoff measurements and taking into account all relevant influences of the catchment area with its precipitation and runoff properties, a certain design flood inflow is assumed to which the system would be exposed if such a design flood event occurred.
Standardization according to DIN
The DIN 19700 , which deals with the safety of dams , sees u. a. the flood design cases 1 and 2 before:
- In case of flood assessment 1, the dam must withstand the flood event in terms of structural safety, suitability for use and durability without restriction
- In flood design case 2, the dam must withstand the flood event in terms of structural safety and without global failure (dam break)
The design floods are defined for dams of different sizes as shown in the following table.
| Flood design case | Systems> 1 million m³ | Systems> 50,000 m³ and ≤ 1 million m³ | Systems ≤ 50,000 m³ |
|---|---|---|---|
| 1 | every 1000 a | every 500 a | every 200 a |
| 2 | every 10,000 a | every 5000 a | every 1000 a |
Examples
The Bundestag resolution 17/14112 of June 25, 2013 states (p. 5):
“Against the background of the extreme Elbe floods in 2002, 2006, 2011 and above all in 2013, flood protection is of outstanding importance for the people in the Elbe catchment area. Based on this experience, the so-called design flood along the Elbe has meanwhile increased from a design flow rate of 4000 m³ / s to 4545 m³ / s. However, there has not yet been a uniform recommendation involving the federal states. There are also different dyke heights in the individual federal states. Flood protection must therefore be included in the overall Elbe concept according to cross-border uniform standards. Instead of the previous way of thinking and acting in sections, characterized by the sectoral perspectives and limits of responsibility, we need the development of an overall strategy. "