Derivation of effective hydraulic parameters of a karst aquifer from discharge hydrograph analysis

Abstract

In well-developed karst terrains, three or more distinct portions of the karst continuum can be identified from hydrographs of springs issuing from the karst aquifer. Hydrographs from two karst springs within the same drainage basin at the Crane Naval Surface Warfare Center, Indiana, have been analyzed, and ratios of transmissivity and specific yield (T/Sy) have been established for the conduit and diffuse flow systems. These ratios have been compared with values of T derived from aquifer tests, so that independent values of Sy can be calculated for the diffuse system. Similarly, if the value of Sy is assumed to be 1.0 for a pure conduit, then independent values of T can be calculated for this end-member of the karst continuum. The values of T and Sy derived from this study are similar to values obtained from a dye trace of the conduit-dominated flow system and of values derived from aquifer tests of the diffuse flow system. Values of T for the conduit system of these springs may need to be established at a local scale, while the values for the diffuse flow system may be applicable at a regional scale. A hydrograph separation using isotopic data suggests that the intermediate-flow system represents a mix of water from the conduit and diffuse flow systems. If this portion of the hydrograph is a truly mixing phenomena, ratios of T/Sy cannot be determined from the hydrograph analysis presented herein. However, if instead, the intermediate-flow system represents water released from a third reservoir (such as small fractures), ratios of T/Sy can be established for the intermediate-flow system.