Pollution by seawater intrusion into a karst system: new research in the case of the Almyros source (Heraklio, Crete, Greece)
Bruno Arfib, Ghislain de Marsily , Jacques Ganoulis - (29/1,2000)
Saline intrusion in karstic coastal aquifers is a common phenomenon which affects the quantity and quality of the freshwater resource. This paper examines the case of the Almyros system at Heraklio in Crete (Greece), characterized by a vast recharge area (300 km2) and a single brackish spring. Data from the Almyros spring and the surrounding wells are analyzed and a specific configuration of the karstic system is proposed. The evolution in time and space of the water temperature and chloride content is shown to be conditioned by the complex structure of this system and the heterogeneity of the karstic formations. These two parameters are analyzed and two storage zones are identified which generate different types of saline pollution. The water in the Almyros spring is not directly connected to the surrounding water-table aquifer. An inland reservoir far from the coast stores the cold, freshwater recharged in the mountains and supplies the Almyros spring. The pollution occurs during the transfer of the water toward the spring, through karstic conduits. Moreover, the local coastal aquifer is polluted by a generalized saline intrusion into the fractured matrix of the limestone, increased by withdrawals. Furthermore, the wells are contaminated by preferential saltwater flow through karstic channels reaching the seawater intrusion zone. The case of the Almyros system shows: (a) that a karstic coastal spring is not necessarily indicative of saline intrusion into the system, (b) that in optimal groundwater resource management, the whole hydrogeological system should be taken into account.