Processes of infiltration to groundwater in a karstic area were studied by monitoring and sampling cave drips during 2004-2008 at two sites with different lithologies: dolomite of the Yagur Fm. and crystalline limestone of the Muhraqa Fm., in Mt. Carmel, Israel. Two tracer tests under different antecedent moisture conditions and "rainfall" intensities were performed.At both sites, 4 hydrological drip types were identified: Post-storm, Seasonal, Perennial, and Overflow, each exhibiting different patterns of discharge, chemistry, and travel time. Perennial drips represent the slow ("matrix") component; however, discharge and [Cl-] fluctuations after intense rainstorms indicate the relative contribution of by-pass flows (event-water). Based on [Cl-] during the natural season and electrical conductivity (EC) during the sprinkling experiment, seasonal and storm input of event-water versus old-water were calculated in the various drips using hydrograph separation. The fractions of calculated event-water in the perennial drips were always <30%. Overflow drips started late in the season, after drainage in the nearby drips exceeded their discharge capacity.Hydrograph recessions of drips have exponential drainage of few "reservoirs". Perennial and seasonal drips had at least two recession segments: (1) recession of quick-flow governed by a piston flow effect and small input of preferential flow, which lasted up to 10 days; (2) slow drainage of the vadose zone, which continued for a few months or until the next season. The recession constant(s) for post-storm and overflow drips were shorter than 10 days."Piston flow" effect indicators were the lag time of injected tracers after hydrographs onset, and the larger component of old-water in drips-hydrograph onset and rising limb. The different processes, associated lag times, and flow velocities have major impacts on groundwater vulnerability and aquifer recharge.
ASJC Scopus subject areas
- Earth and Planetary Sciences (all)