Hochwasserrückhaltebecken Hölltal, Flood detention basin in Giengen an der Brenz, Germany.

The Hölltal detention basin is a water storage facility in the Brenz valley that collects and holds water during heavy rainfall to prevent flooding. It takes advantage of the natural valley formation to serve its protective purpose for downstream communities.

This water retention facility was built in 1958 to provide flood protection for residential areas in the Giengen municipality. It was designed to handle water overflow and release it gradually during heavy rainfall events.

The name comes from the field name "Hölle", meaning gorge, which covers the whole Hölltal between its two narrow points. The valley name also appears in local street names: the Hohenmemmingen shooting club has its address at Hölle 1, while the Giengen club's Schützenhaus stands at In der Höll 1 above the basin.

The basin can be reached on foot as it sits in an easily accessible valley area. It is best visited during dry periods when you can observe the structure of the facility clearly without water covering the ground.

After passing through the dam's bottom outlet, the Höllbach does not immediately reappear: because the second gorge is so narrow, it runs underground for about 270 metres to protect the properties at its end, then flows openly for roughly 170 metres before entering a canalisation of about 1 km.