Well hydrograph analysis for the characterisation of flow dynamics and conduit network geometry in a karst aquifer, Bükk Mountains, Hungary

Abstract

The present paper introduces new well hydrograph analytical tools for parameter estimation in karst aquifers. The analytical formulae provided in this study link aquifer properties with hydrograph recession coefficients, and provide quantitative characterisation of the spatial and temporal variations of the water table. Generally, spring hydrograph analytical techniques provide information on the characteristic hydraulic parameters and conduit spacing in a karstic catchment, while well hydrograph analysis provides information on local hydraulic and geometric properties of individual matrix blocks and in certain cases on the deep unkarstified aquifer zone. The combination of the spring and well hydrograph analytical methods represents a useful tool for understanding the structure and hydraulic behaviour of karst systems. A new well hydrograph analytical approach is presented, which makes the estimation of conduit spacing and catchment geometries possible. In most cases well hydrograph peaks can be decomposed into three exponential segments. Exponential segments in shallow systems do not correspond to different types of storage, but in most cases originate from the emptying of fissured matrix blocks. The proposed parameter estimation method is demonstrated through the application of field data. The test site is located in the Bükk Mountains, Hungary. Analytical methods were applied on two adjacent karstic catchments feeding the Szinva and Garadna springs. Hydrograph analysis of both springs and three well hydrographs were performed to investigate the hydraulic behaviour of the karst system and to estimate the spatial geometry of karst conduits. According to hydrograph analytical results, both spring and well hydrographs indicated similar matrix block geometries. Hydrograph analysis revealed the change of flow scale indicated by a significant drop of the value of recession coefficient. The investigation method introduced in this study provides important information for water resource assessment, contamination risk assessment, vulnerability assessment, flood prediction, geotechnical and speleological studies.