A Groundwater Model for Studying the Straßberg Flood Detention Basin

We are currently designing the Straßberg flood detention basin (FDB) for Saxony-Anhalt’s dam operating agency. The FDB has a volume of approx. 2.5 million m³ and is located in the Selke Valley near Straßberg in the eastern Harz region. The roughly 270 m long and 20 m high retaining structure and the impoundment area of approx. 40 hectare are located within a fauna/flora habitat and are of importance for recreational use.

The temporary impoundment during floods that results from operation of the FDB has an impact on the water level conditions surrounding the retaining structure and on the subsurface groundwater conditions.

To minimize the impact on groundwater conditions, flow windows are provided in the ground below the retaining structure, which reduce the rise in groundwater levels during flood events by facilitating discharge and accelerate the rate at which upstream floodwater recedes. Even in flood-free periods, the hydraulic windows enable a relieving groundwater exchange in the ground beneath the retaining structure. First, a numerical groundwater model is created and calibrated on the basis of a substantiated hydrogeological model. In various scenarios, the effects of the structural interventions are quantified under different boundary conditions and the groundwater flow windows are dimensioned