A quantitative method for the characterisation of karst aquifers based on spring hydrograph analysis
This paper presents a method for characterizing flow systems in karst aquifers by acquiring quantitative information about the geometric and hydraulic aquifer parameters from spring hydrograph analysis. Numerical sensitivity analyses identified two fundamentally different flow domains, depending on the overall configuration of aquifer parameters. These two domains have been quantitatively characterized by deducing analytical solutions for the global hydraulic response of simple two-dimensional model geometries. During the baseflow recession of mature karst systems, the hydraulic parameters of karst conduits do not influence the drainage of the low-permeability matrix. In this case the drainage process is influenced by the size and hydraulic parameters of the low-permeability blocks alone. This flow condition has been defined as matrix-restrained flow regime (MRFR). During the baseflow recession of early karst systems and fissured systems, as well as the flood recession of mature systems, the recession process depends on the hydraulic parameters and the size of the low-permeability blocks, conduit conductivity and the total extent of the aquifer. This flow condition has been defined as conduit-influenced flow regime (CIFR). Analytical formulae demonstrated the limitations of equivalent models. While equivalent discrete-continuum models of early karst systems may reflect their real hydraulic response, there is only one adequate parameter configuration for mature systems that yields appropriate recession coefficient. Consequently, equivalent discrete-continuum models are inadequate for simulating global response of mature karst systems. The recession coefficient of equivalent porous medium models corresponds to the transition between matrix-restrained and conduit-influenced flow. Consequently, equivalent porous medium models yield corrupted hydrographs both in mature and early systems, and this approach is basically inadequate for modelling global response of karst aquifers.