Karst development of an evaporitic system and its hydrogeological implications inferred from GIS-based analysis and tracing techniques

The geomorphological characteristics and hydrogeological functioning of a geologically heterogeneous evaporitic karst plateau in Southern Spain were studied. Land surface information (LiDAR data) was used to analyze the shape and distribution of closed depressions. An artificial tracer test and monitoring of the natural responses of the main spring have allowed to infer the karstic development of the studied system. Three dyes were injected in selected swallow holes to trace the main groundwater flowpaths and to estimate the dimension of the conduit network. Discharge, electrical conductivity and temperature were monitored in the groundwater that drains the evaporitic plateau during an individual and intense recharge pulse. Tracing techniques were adapted to high salinity environments by using specific calibration standards (NaCl + dye). The hydrological connection detected between two of the swallow holes and the outlet, and the deduced orientation pattern for closed areas, would suggest that the karst evolution (internal and external) is related to fault orientation. The rapid tracer detection (16-20 h) and high estimated maximum flow velocities (125-192 m/h), together with the fast impulsional response of the controlled physical-chemical parameters in spring waters (~15-16 h) demonstrate the existence of quick flows under recharge conditions with well-defined system drainage, indicating a high degree of internal karstification (estimated master conduit diameter ~1.5 m). However, flooding of the depressions feeding swallow holes and analysis of the spring response times from natural and artificial tracers point to a restriction of the system´s drainage, most likely due to the constrained morphology of the karst conduits. This results in sustained recharge periods and delayed spring responses of some parameters, highlighting the relevant role of concentrated recharge in the hydrogeological behavior of the studied evaporitic karst