Integrating field and numerical modeling methods for applied urban karst hydrogeology

摘要

Infrastructures constructed on unstable geologic formations are prone tosubsidence. Data have been collected in the context of an upgrading projectfor a highway located beside a river dam constructed on gypsum-bearingformations. Surface water infiltrates upstream of the dam, circulatesthrough the gravel deposits and into the weathered bedrock around andbeneath the dam, and exfiltrates downstream into the river. As a result, anextended weathering zone within the bedrock and preferential flow pathswithin voids and conduits developed as part of a rapidly evolving karstsystem. Enhanced karstification in the soluble units of the gypsum-bearingformations resulted in subsidence of the dam and the highway.Since 2006, changes in the groundwater flow regime have been investigated bydifferent methods that allowed the evaluation of the long-term performanceof the infrastructures. Geological (outcrops, lithostratigraphic informationfrom boreholes), hydrometrical (extensive groundwater monitoring, dye tracertests) and hydrogeophysical (Electrical Resistivity Tomography, ERT) datawere integrated into high-resolution 3-D hydrogeological and 2-D karstevolution models. The applied methods are validated and the sensitivity ofrelevant parameters governing the processes determined.It could be demonstrated that the applied methods for karst aquifercharacterization complement each other. Short-term impacts and long-termdevelopments on system-dynamics and the flow regime could be evaluated. Thisincludes the description of the transient character of the flow regimeduring and after episodic flood events (surface-groundwater interaction,conduit and diffuse model outflow) as well as the evaluation of time scalesfor karst evolution. Results allow the optimization of investigation methodsfor similar subsidence problems, ranging from general measurements andmonitoring technologies to tools with predictive utility.