Flood protection area
Usually this is the topmost slat of the storage space. In the case of pure flood retention basins, the entire storage space is often designated as a flood protection area and the basins are kept completely empty during normal operation. In the case of larger dams, the storage space is often divided up for various functions ( flood protection , low water elevation , power generation , drinking water production ) and an operating plan regulates the various uses.
The flood protection area can vary over the course of the year; A larger flood protection area is often provided in the flood-typical seasons, which can also go back to zero in the case of some dams in low-flood seasons. If the flood protection area has been filled or partially filled by a flood, it must be emptied again as quickly as possible. This is done by increasing the underwater discharge accordingly. Since the flood protection area should be cleared again as quickly as possible, even this increase in the levy can be perceived as a minor flood by the people below.
Since storage volumes are expensive, the flood protection area is usually rather tight. If, despite the provision of a flood protection area, the dam overflows, the incoming flood was usually greater than the design flood originally planned. The flood relief system often starts up when several floods come in quick succession and the flood protection area has not yet been cleared again.
The “ordinary flood protection area”, also called “controllable flood protection area”, is the part of the storage space that is below the level of the overflow threshold . Even if the dam overflows via the flood relief system, it can still have a strong flood-dampening function, as the retention through the "extraordinary" or "uncontrollable flood protection area" now unfolds its effect. This means the volume above the level of the flood relief system, which is created by the height of the overflow above the overflow threshold. The difference between the total storage space and the storage space corresponds to the volume of the uncontrollable flood protection area.
- Peter Rißler: dam practice . 1st edition. R. Oldenbourg, Munich and Vienna 1998, ISBN 3-486-26428-1 .