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22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectiveswas performed by switching every second recharge drip to another color. Hence, it waspossible to investigate distinct freshwater flow paths, which were also revealed to remain incontact with the outflow zones at all times. Moreover, we were able to measure different flowvelocities of freshwater migrating from the surface through the lens to the outflow zones by acombination of the previously described spatial and temporal tracer color variations.Measuring the time and flow path length of a triple point to travel from the top of the island tothe outflow zone, we determined flow velocities that differed of at least a factor of ten,depending on the start location. It must be mentioned that observation accuracy in ourphysical model is the dominant limiting factor, which might be improved in future byincreasing the amount of recharge drips. Flow paths and travel times find their practicalapplication in the delineation of protection zones, e.g. the 50-day zone, which is intended toprevent fecal bacteria from entering a well.Fig. 2: Visualization of age stratification by temporal variation of different tracer colors(uranine, indigotine, eosine) in recharge waters.REFERENCESChesnaux, R., Allen, D.M., 2008. Groundwater travel times for unconfined island aquifersbounded by freshwater or seawater. Hydrogeology Journal, vol. 16, pp. 437–445.Diersch, H.-J.G., 2005. FEFLOW: Finite element subsurface flow and transport simulationsystem. WASY GmbH Institute for Water Resources Planning and Systems Research,Berlin, 292 p.Fetter, C.W., 1972. Position of the saline water interface beneath oceanic islands. WaterResources Research, vol. 8, pp. 1307-1314.222