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22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHYDRAULIC HEAD EVOLUTION IN THE DISCHARGE ZONE OF THE MOTRIL-SALOBREÑA COASTAL AQUIFER (SE SPAIN): INFLUENCE OF THE RECHARGESánchez-Úbeda, J.P. 1 ; Calvache, M.L. 1 ; Duque, C. 2 ; López-Chicano, M. 1 and Crespo,F.J. 1jp353lm@correo.ugr.es1 - Department of Geodynamics, Av/ Fuentenueva s/n 18071. University of Granada. Spain.2 -Department of Geography and Geology. Øster Voldgade 10, DK-1350. University ofCopenhagen. Denmark.Abstract. Motril-Salobreña coastal aquifer (SE of Spain) presents different characteristicscompared with the surrounding coastal aquifers of the region because saltwater intrusion hasnever been detected. This situation is mainly related with a river recharge (Guadalfeo River) andthe infiltration of irrigation water. Nevertheless several recent changes are modifying these twofactors. The inputs to the aquifer are decreasing associated to anthropogenic modifications of asystem that was stable for a long time.The position of the interface has been located (the mixing zone is at 132-230 m depth) withelectrical conductivity logs of groundwater in a deep well (250 m depth), located at 300 m of thecoastline. Ghyben-Herzberg equation was applied to compare the direct measurements and thetheoretical calculations, but due to the vertical upward flow detected in the freshwater, theresults presented clear differences.The correlation of the heads in recharge and discharge sectors showed 2 flow paths in thedischarge area. Therefore the decrease of the recharge in the aquifer could lead to amodification of the current equilibrium of the salt water-freshwater contact, fast in the upper partof the aquifer and slower in the deeper sectors of it.Keywords: coastal aquifer, groundwater flow, fresh water-sea water contact, sea waterintrusion, hydraulic head.1. INTRODUCTIONThe Motril-Salobreña coastal aquifer is an exception of Mediterranean Spanish coast, due torepresents one of the 13 aquifer units of the 49 described units that are not affected by marineintrusion processes (López-Geta and Gómez-Gómez, 2007). In previous works, it was exposed itsgood situation, both quality and quantity of groundwater (Calvache et al., 2003; Duque et al.,2008; Calvache et al., 2009).However, this optimum situation is changing due to the construction of Rules dam on theGuadalfeo River, which would suppose an artificial barrier of the river recharge to aquifer, sinceit intercepts superficial and subterranean flow. In the other hand, another factor is the decrease ofthe recharge of the irrigation water because of the urbanization of agricultural land and change inthe systems of irrigation, especially dripping irrigation. Those changes would be able to cause analteration of the existing balance between saltwater and freshwater causing an advance of theinterface.235