Combining Quantitative Analysis Tools (Cross-Correlation Analysis and Dye Tracer Tests) to Assess Response Times in Karst Aquifers. The Ubrique Karst System (Southern Spain)

In this work, a preliminary conceptual model of the hydrogeological functioning of a binary karst aquifer located in southern Spain is presented, based on the natural responses of the springs and the dye tracer tests. Results derived from the long-term analysis of cross-correlation function (CCF) (global average time of recharge input) have been validated with those obtained from a dye tracer test, performed during a specific recharge event. The overall response times (CCF results) obtained for the three springs studied were 58 (SP-1), 72 (SP-3), and 81 h (SP-2). This pattern in response times was contrasted with the first detection times of the BTC-Tracer Breakthrough Curve—at the same three springs (30.9, 35.3, and 47 h) and their respective recovery rates (2.03, 21.9, and 78.4% for S1, S2, and S3, respectively). The distribution of response times, both those determined by long-term statistical analysis and the ones derived from the use of dye tracer test, is directly related to the karst network development in each of the drainage routes. Additionally, the rate of tracer recovery at each of the springs is linked to the hierarchy of flow paths from the selected injection point toward each spring, within the overall drainage network scheme. An accurate knowledge of all factors affecting the hydrogeological behavior as well as groundwater flow paths (from swallow holes to the springs) is crucial for suitable management of the resource and to mitigate the pollution risks derived from fast infiltration of surface water.