6. Subsurface Flow and Sulfate Dissolution Response to the Construction and Restoration of the River Weir in Hessigheim, Germany

The construction of the combined ship lock weir in Hessigheim, Germany, created a river stage difference of more than 6 m and intensified subsequently the surface–subsurface water exchange and modified the natural subsurface flow field. In the sulfate-bearing hydrogeological setting, increased infiltration and intensified subsurface flow triggered related dissolution processes. Soon after construction, the structure started suffering from subsidence due to progressive leaching and demanded extensive grouting. In the course of approximately 25 years, groundwater heads and subsurface sulfate concentrations responded distinctively to grouting campaigns. The analysis confirms that as a result of its high solubility and altered hydrogeological conditions, gypsum karst develops on a human rather than on a geological time scale. Grouting measures considerably slowed down these processes, however, at the cost of subsurface flow field variations which will ultimately transfer the zone of enhanced dissolution.