Total storage space
The total storage space is the volume of the accumulated water in a dam at the highest storage destination . He goes beyond the storage space with full back (to the level of the overflow threshold ) out and additionally includes nor the amounts of water that in addition the design flood flow are held in the dam. The dam then reaches the " highest storage target " and overflows a certain amount at the flood relief (HWE). The total stowage space thus includes, in addition to the stowage content up to the overflow threshold, the additional stowage space, which is determined by the extent of the overflow heightis used above the overflow threshold. This additional storage space is also called uncontrollable flood protection area , as there is no control here. The damping and delaying of the flood created by the uncontrollable flood protection area is called retention .
The design water inflow is the largest inflow or outflow for which a dam is designed. As a rule, a flood is assumed which arithmetically only occurs once every 1,000-10,000 years. Since there are hardly any measured values for such rare floods, this is calculated by means of a hydrological probability calculation based on the floods measured over a number of decades. As a result, the water level, namely the highest storage target that is achieved, and the total storage space are only theoretical values that depend on the calculation assumptions made.
The flood discharge (overflow) must be dimensioned for this drain in such a way that it can drain away without damage. The upper edge of the barrier structure ( dam , dam ) must be so high that there is still enough freeboard even when the entire storage space is used. As a rule, the wave run-up must also be taken into account.
In the case of dams in Germany, the total storage space is one of the deciding factors for the classification according to DIN 19700 in dam class 1 or 2. The other criterion is the height of the barrier structure above the foundation base .