Freshwater-saltwater motion in a coastal karstic aquifer -

The case study of the brackish spring of "Almyros of Heraklio" in Crete (Greece) and its vast carbonate coastal aquifer is presented, showing the consequence of preferential flows of continental fresh water and saline sea water in karst galleries in a coastal area. Flow heterogeneity generates unexpected upconing in boreholes, and permits the spring of Almyros not to be directly connected with the surrounding water-table. This spring, with a seawater content inversely proportional to the discharge rate, is a typical karstic spring, which responds to rainfall events with impressive floods a few hours later. Water flows through deep karstic channel(s), where inflow of seawater occurs under specific pressure conditions within the drain, and then the mixed solution is rapidly transported away from the zone of saline intrusion up to the spring. Whereas the relation between the discharge and the spring water salinity is quite linear for high salinity values (Electric conductivity higher than 6000 μS.cm), the extrapolation for lower values remains uncertain. Moreover, an exceptional underground over-pressure is needed to make fresh groundwater reach the spring, with a loss of freshwater that is expelled toward the saline zone of the aquifer away from the drain. The functioning of the Almyros spring shows that, in this case, there is a dual micro-fractured and conduit flow, which should be integrated into a single groundwater flow model, to be used in studies of management plans.