Sea water intrusion in coastal karst springs: Example of the Blaz spring (Croatia)

Brackish karst springs are common along every karstic sea shore consisting of limestone and dolomite. On the Croatian sea coast there are more than 300 permanent or temporary brackish karst springs. From the standpoint of water supply, the problem of karst spring water salinization is quite significant because large quantities of high quality fresh water are not available to be used either as drinking water or for industrial and agricultural purposes. The salinity of brackish karst springs situated along the Adriatic coast varies from 10 to more than 18 000 mg Cl 1(-1) with an unfavourable distribution during the year. In the wet winter period, when water quantities in the region are abundant, the salinity is exceedingly low. In the warm and dry summer period the chloride concentration is high. At that season, when a shortage of flesh water in the region occurs, especially due to tourism, karst spring water is so salty that it cannot be used at all. The mechanism of sea water intrusion is relatively well known but the problem of karst springs desalinization has not been solved in practice. The Ghyben-Herzberg relationship is formulated exclusively on the basis of hydrostatic equilibrium, and its use under dynamic conditions is limited. The dynamics of fresh water circulation towards karst spring exits are very specific for each individual spring. Using numerous hydrological, hydrometric, hydrogeological and speleological investigations of the brackish Blaz (Croatia) karst spring, this paper gives the plausible position and dimensions of the main karst conduits through which sea water penetrates into the spring exit.