Spring Hydrograph Analysis: A Quantitative Approach

Quantitative methods for determining geometric and hydraulic parameters of karst aquifers from spring hydrograph analysis have been developed. Analytical formulae deduced from simple conceptual models quantitatively describe the connection between aquifer parameters and hydrograph recession coefficients. A significant difference between karst and fissured systems exists with regard to their hydraulic behavior during the recession process.

Analytical solutions suggest that different hydrograph components do not represent different classes of rock permeability. Hydrographs of individual homogeneous blocks can be decomposed into several exponential components. Increasing block asymmetry results in an increasing number of exponential components contributing significantly to total discharge.

When no infiltration is present into karst conduits, the entire recession process is controlled by the recession of individual blocks. Consequently, the hydraulic properties of a karst conduit system have no influence on spring discharge. In the case of both concentrated and diffuse recharges into an aquifer, the spring hydrograph can be reconstructed as a sum of individual block discharges and the discharge originating from the conduit network. The end of the influence of conduit flow on a hydrograph manifests as an inflection point on the recession limb. Beyond this point, a hydrograph can be decomposed in a similar manner to that of an individual homogeneous block.

The developed analytical formulae demonstrated the drawbacks of equivalent models. While equivalent discrete-continuum models of fissured systems may reflect their real hydraulic response, there is only one adequate parameter configuration for karst systems that yields appropriate recession coefficients. Consequently, equivalent discrete-continuum or equivalent porous medium models are inadequate for simulating the transient behavior of karst systems.