Numerical modeling of a multilayer coastal aquifer in extreme drought with additional exploitation and impact on its associated ecosystems: Júcar river and La Albufera de Valencia (Plana de Valencia Sur, Spain)

Abstract

La Plana de Valencia Sur (MASub 080.142) constitutes a coastal hydrogeological system with high potential, which gives it great aptitude so that it can be considered as a strategic aquifer, understanding as such that it can be exploited in a short-term and intensive way during times of drought in order to compensate for the deficit created in demand systems. For this purpose, in the mid-90s and the first decade of this century, a large number of groundwaters catchments were built that were used during the extremely dry period from 2005 to 2008. This additional and scheduled exploitation required a meticulous piezometric and hydrochemical monitoring, as well as the volumes extracted, which was carried out by the Júcar Hydrographic Confederation (CHJ) and the Geological Survey of Spain (IGME). The data obtained allowed us to know the response of the system to a situation of exceptional water stress and to develop a detailed model of underground flow with the Visual MODFLOW software. The model domain, discretised in 4,357 cells of 359x359 m, covers an area of 56,15 km2 and consists of four layers equivalent to the four geological formations that comprise it. With its calibration and adjustment in steady state and transitory flow regimes, the aquifer balance has been determined, as well as its behaviour and evolution. One of the most relevant aspects is that it incorporates in a different way the main ecosystems dependent on groundwater: Júcar and Verde rivers, ullales or springs, drainage channels and La Albufera lake, in addition to direct outlets to the sea. The conclusions obtained include, at a general level, the suitability of the actions carried out and their environmental viability, confirming its good characteristics as a strategic aquifer, as well as its ability to be exploited intensively during times of extreme weather conditions. It also analyses, in a particularized way, the consequences that the intensive exploitation of the system has had on each of the different elements that make up its water balance, which has allowed us to know the conditions suffered by the two large ecosystems with which it is related, Júcar River and La Albufera de Valencia, throughout the period analysed.