New concepts and integrated investigations methods for karst in urban environments

Prof. Dr. P. Huggenberger, Dr. J. Epting

While the characterization and modeling of flow in heterogeneous and fractured media has been investigated intensively, there are no well-developed long-term hydrogeological research sites for gypsum karst. Conducted research focuses on an integrated approach, comprising the combination of multiple hydrometrical and geophysical data with high-resolution numerical groundwater modeling and model simulations of karstification. Existing theories describe the evolution of karst systems mainly with on conceptual models. Although these models are based on fundamental and well established physical and chemical principles that allow studying important processes from initial small scale fracture networks to the mature karst, systems for monitoring the evolution of karst phenomena are rare.

Considering that infrastructures in karst regions, particularly in gypsum, are prone to subsidence, severe problems can arise in urban areas. Data have been collected in the context of a highway upgrade located beside a river dam that was constructed on gypsum-containing rock. Surface water infiltrates upstream of the dam, circulates in the gravel deposits and in the weathered bedrock around and beneath the dam and exfiltrates downstream into the river. As a result an extended weathering zone within the bedrock and preferential flow paths within voids and conduits developed within a rapid evolving karst system. These processes enhance karstification processes in the soluble units of the gypsum-containing rock and resulted in subsidence of the dam and the highway.

The approach presented, comprises the combination of multiple data sources (lithostratigraphic information of boreholes, extensive groundwater monitoring, dye tracer tests, geophysics) with high-resolution numerical groundwater modeling and model simulations of karstification below a river dam. Steady state and transient groundwater models were set up to determine the individual characteristics of the present karst system and to consider the different flow processes (conduit and diffuse flow system) that could affect the evolution of the system. Thereby, particular focus was placed on the hydraulic behavior of the complex site specific conduit system. Subsequently, the groundwater model is merged with information of aquifer heterogeneity resulting from karstevolution models, which are developed in cooperation with the Institute of Geological Sciences, FU Berlin (Dr. Douchko Romanov, Prof. Dr Georg Kaufmann). The applied investigation methods are validated and the sensitivity of relevant parameters governing the processes determined. The approach should assist in optimizing investigation methods, including measurement and monitoring technologies with predictive character for similar subsidence problems within karst environments in urban areas.

3D geological and hydrogeological model

Visualization of hydraulic heads and particle tracks before (left) and after (right) the construction measures